technical report safety measures for dangerous glacial lakes in
TRANSCRIPT
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Technical Report SAFETY MEASURES FOR DANGEROUS GLACIAL LAKES IN THE
CORDILLERA BLANCA, PERU
WORKING DRAFT: JUNE 2013
César A. Portocarrero Rodríguez [email protected]
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SAFETY MEASURES FOR DANGEROUS GLACIAL LAKES IN THE CORDILLERA BLANCA, PERU
Table of Contents
1. Background: The Cordillera Blanca and the Callejón de Huaylas ...................................... 2. History of Glaciological Research in Peru and the Cordillera Blanca.................................
3. Basic Concepts of Glacial Morphology ...................................................................................
4. Primary Natural Disasters in Peru and Possible Explanations for Their Cause ............
5. Glacial Lakes in the Cordillera Blanca ................................................................................... 6. Factors that Influence Risk Assessment of Dangerous Glacial Lakes..................................
6.1 Characteristics of the glacier............................................................................................................ 6.2 The slope of the bedrock ................................................................................................................... 6.3 The geometry and structure of the glacier ...................................................................................... 6.4 Length of the valley ........................................................................................................................... 6.5 Presence of hanging glaciers............................................................................................................. 6.6 Glacier tongues underminded by the glacial lake .......................................................................... 6.7 Volume of the lake............................................................................................................................. 6.8 Seismic and tectonic factors.............................................................................................................. 6.9 Discharge rate .................................................................................................................................... 6.10 About the trigger .............................................................................................................................
7. Procedures for Reducing the Risk from Dangerous Glacial Lakes...................................... 7.1 Cutting “V-shaped” moraines.......................................................................................................... 7.2 Construction of drainage tunnels..................................................................................................... 7.3 Filtration.............................................................................................................................................
8. Methodology for Implementing Safety Measures .................................................................. 8.1 Initaial assessment............................................................................................................................. 8.2 In-depth study.................................................................................................................................... 8.3 Watershed hydrological analysis ..................................................................................................... 8.4 Implementation of safety measures based on information from in-depth studies ......................
9. Case Studies from Peru: Cordillera Blanca Lakes Featuring Safety Works ...................... 9.1 Safuna Alta Lake ............................................................................................................................... 9.2 Jancarurish Lake............................................................................................................................... 9.3 Hatuncocha Lake............................................................................................................................... 9.4 Parón Lake......................................................................................................................................... 9.5 Llanganuco Lake ............................................................................................................................... 9.6 Lake 69 ............................................................................................................................................... 9.7 Huallacocha Lake .............................................................................................................................. 9.8 Lake 513 ............................................................................................................................................. 9.9 Paccharruri Lake .............................................................................................................................. 9.10 Llaca Lake........................................................................................................................................ 9.11 Palcacocha Lake .............................................................................................................................. 9.12 Cuchillacocha Lake ......................................................................................................................... 9.13 Tullparraju Lake............................................................................................................................. 9.14 Shallap Lake .................................................................................................................................... 9.15 Allicocha Lake ................................................................................................................................. 9.16 Lazo Huntay Lake (Cordillera Huaytapallana) ........................................................................... 9.17 Chuspicocha Lake (Cordillera Huaytapallana)............................................................................ 9.18 Riticocha Lake: A recent 2010 case study.....................................................................................
10. Discussion and Conclusions....................................................................................................
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1. BACKGROUND: THE CORDILLERA BLANCA AND THE CALLEJÓN DE HUAYLAS
The Cordillera Blanca (White Range), in the department of Ancash, forms the landscape of the Río Santa (Santa River) valley from its source at Aguascocha Lake to its northern limit at Nevado (snowcapped) Champará Mountain.
Figure 2. The location of the Cordillera Blanca with respect to the Pacific Ocean (left), and the landscape of Arhuaycocha Lake and the Pucahirca Nevados (right). http://www.rlc.fao.org/es/tecnica/parques/revista/pdf/art23.pdf
The Cordillera Blanca has attracted local and foreign visitors for many years, including mountain climbers from around the world attempting to summit its challenging peaks.
Building safety measures for this famous range’s glacial lakes requires studying how those lakes originated. Presumably they were formed at different times in the earth's climate history. Thousands of years ago major alluvial phenomena occurred and left clear traces in different watersheds but we do not know precisely when that happened. However, people are still afraid of such events happening again, as in the Peruvian city of Caraz, in Ancash department (state), where the subsoil of much of the town is made up of boulders of different sizes and materials that were transported during a landslide. Although the avalanche may have happened very long ago, the memories linger in people’s minds.
Many highly destructive and deadly alluvial processes have taken place in Peru. The two most well known are, first, the event of December 13, 1941, in the city of Huaraz that destroyed a third of the city and killed about 4,000 people. The second event was the well-known catastrophic flood originating on snowcapped Mount Huascaran on May 31, 1970. The avalanche occurred a few minutes after a 7.9 magnitude earthquake buried the town of Ranrahirca for the second time, and obliterated the town of Yungay, where it likely killed some 10,000 people (some estimates are as high as 25,000 killed).
Many other similar events have destroyed towns and infrastructure and taken human lives. Several of these events have taken place in the area located between the two watersheds of the Cordillera Blanca, where the greatest number (about 35%) of Peru’s Andean glaciers are situated.
The valley called Callejón de Huaylas is located on the western slopes of the Cordillera Blanca,
where many major towns of Ancash department are located. A smaller number of towns are located on the eastern watershed. The inhabitants of these towns have always lived under the threat of glacial lake outburst floods, which are part of the painful history of this region.
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The examples shown below are derived mostly from towns in Callejón de Huaylas, which is part of the Santa River Basin that runs a total length of about 320 km. The batholith or rock base of the Cordillera Blanca consists of granodioritic rock in association with slates.
Figure 1. Location of the Cordillera Blanca, department of Ancash, Peru (above). Location of the Cordillera Blanca in the Peruvian Andes (below).
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Table 1. Main peaks in the Cordillera Blanca and Huayhuash
Mountain Ranges Mountain Height Mountain Height Alpamayo 5,947 Quitaraju 6,040 Artesonraju 6,025 Ranrapalca 6,162 Caraz 6,025 Tocllaraju 6,032 Chopicalqui 6,354 Urus 5,450 Huandoy 6,395 Vallunaraju 5,686 Huandoy Sur 6,160 Yerupaja 6,634 Huantsan 6,395 Yerupaja Chico 6,089 Huascaran 6,768 Pisco 5,752 Ishinca 5,530 Quitaraju 6,040 Maparaju 5,326 Ranrapalca 6,162 Pisco 5,752
2. HISTORY OF GLACIOLOGICAL RESEARCH IN PERU AND THE CORDILLERA BLANCA
This document does not detail the experiences of societies living in glacial watersheds, but
rather intends to demonstrate how the survival instinct of Andean communities has taught them the methods and procedures needed to counter those and other natural events. At the same time, this author hopes to encourage further research and management of dangerous glacial lakes currently forming due to glacial retreat in all mountainous regions of the world.
Although this phenomenon has occurred repeatedly in many places around the world, we have
yet to develop an appropriate technology to prevent it. Nevertheless, this document describes the procedures and technologies implemented in many glacial lakes in Peru. It is a compendium of the knowledge acquired through the strong effort and dedication of many generations of technicians and researchers, made available to the global community for its potential application according to the characteristics, possibilities, and context of each place, glacial lake, and country. There is no single formula for its implementation since each case requires action based on the best locally available knowledge and engineering to reduce the risk posed by these water bodies.
Peru, along with other developing countries, has not sufficiently supported research across a
range of disciplines, including geography, climatology, animal science, and botany. Any pioneering work in development and natural resource conservation has often been circumstantial, and often a result of personal initiatives and contacts, or for political convenience.
Unfortunately, we lack a joint effort for development planning that would allow sufficient time
and understanding resulting in a meticulous, systematic, and inter-institutional processing of information from various disciplines. Each institution works on its own, for its own interest if it has one, based on plans that sometimes duplicate efforts and misuse resources that are difficult to obtain in a country like ours. Development planning is thus lacking a positive inter-institutional integration.
There are some instances of what could be described as “heroic” efforts to work for the common
good. One example is the installation of the hydrometeorological network in the Río Santa watershed in the 1950s, conceptualized, planned, and implemented by the renowned engineer Luis Ghilino at his own personal expense, due to a misunderstanding with the directors of the Peruvian Santa Corporation. This network was maintained by the institutions managing the Cañón del Pato hydroelectric plant while it belonged to the government, but abandoned when the plant was privatized. This caused immeasurable damage to all users of the Río Santa throughout the departments of Ancash and La Libertad. The
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Government of Peru should once again take charge of the situation and sanction the owner of Cañón del Pato for the damages caused.
Social dynamics have also brought old concerns about falling ice and potential outburst floods
back to the forefront of discussion for urgent glacial lake management. In addition, climate change is affecting the planet’s water resources and water supply.
The catastrophes resulting from devastating outburst floods containing ice, rock, and mud in the
Cordillera Blanca and other ranges of Peru have highlighted the need for detailed risk assessments that would lead to a broader and more methodical understanding of natural conditions in mountain environments. The goal is to prevent these natural disasters to safeguard local communities and the livelihoods of society at large.
Based on this objective, an office was established to assess the conditions contributing to glacial
lake stability, first in the Cordillera Blanca and later in other ranges. The central task was to prepare an inventory of glacial lakes to identify those that posed a risk and adopt adequate prevention measures.
Figure 3. An outburst flood in the city of Huaraz in December 1941.
Source: Servicio Aerofotográfico del Perú.
Figure 4. Lake Palcacocha before (left) and after (right) an outburst flood and landslide (Kinzl, 1932 and
1941).
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Figure 5. A recent photograph of Lake Palcacocha.
It was believed that only a technical and organized entity could lead such an important task.
Since the 1930s, the Cordillera Blanca and its glaciers have been the subject of many national and international studies. All have focused on observing and evaluating the distribution and stability of the numerous glacial lakes in the range; however, efforts were scattered and the studies lacked the unity and shared criteria needed as the basis for methodical research.
Glaciology studies today should focus on a wide range of objectives, although all should
maintain some relation to disaster risk management. For the Cordillera Blanca, research on the risks associated with glacial lakes has led to studies on the physical properties of glaciers, and more recently, due to the implications of climate change, on glacial dynamics and variations in volume and mass. The current needs of a growing population and increased demand for natural resources require more detailed studies on the hydrological effects of changing glacial masses and their implications for future water supplies. Glaciology studies, therefore, must be oriented toward mitigating the risk of landslides and outburst floods while simultaneously analyzing water supplies at the watershed, sub-watershed, and micro-watershed scale.
This document focuses primarily on studies, projects, and safety measures in glacial lakes in the
Cordillera Blanca and other mountain ranges in the country with technology developed in Peru. These collective efforts have successfully reduced the risk posed by the high volumes of water contained in many glacial lakes, with safety measures implemented specifically in 35 lakes in the Cordillera Blanca. Lake 513 in the Nevado Hualcán demonstrated the effectiveness of these measures, where lowering the lake 20 meters (66 feet) prevented a catastrophic peak surge discharge toward the Chucchún River watershed and the downstream communities of Acopampa and Carhuaz on April 11, 2010.
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3. BASIC CONCEPTS OF GLACIAL MORPHOLOGY IN THE CORDILLERA
BLANCA The Cordillera Blanca and Callejón de Huaylas (Huaylas Valley) are oriented from south-southeast
to north-northwest. The Callejón de Huaylas is flanked by the Cordillera Blanca (or White Range, the highest snow-covered range and the one with the most glaciers in the tropics) to the east and the Cordillera Negra (Black Range) to the west. The Cordillera Blanca, named for the masses of ice on its peaks, is a large mass of plutonic rock composed mainly of granodioritic rock, slate, sandstone, and shale. The Cordillera Negra is constituted mostly by volcanic rock.
The Callejón de Huaylas valley is partially covered with glaciofluvial, glacial, or alluvial material, separated by outcrops of volcanic rock.
Local geological formations in the Cordillera Blanca consist of the four types listed here:
• Rocks formed by shales and fine sandstones of considerable thickness with a good degree of settling in the so called Chicama Formation. This formation is found mostly in some glacial cirques and fluvioglacial deposits.
• Quartzitic rocks, sandstones, and shales with coal seams, in the so called Chimu Formation. Boulders of detrital material from this formation are found in some gorges.
• Sandstones and shales with thin layers of brown quartzite interleaved with limestone and gypsum. This type of formation is called Carhuaz, because it is mostly found in the Carhuaz province of Callejón de Huaylas.
• Granodiorite is the base rock of the Cordillera Blanca. It is very hard and strong. Prior to the intrusion of the granodioritic batholith from the Cordillera Blanca, the morphology of
the valley is believed to correspond to the end of the tertiary and more so the quaternary period, placing the formation of the low-sloping and low elevation valley at approximately 7 million years ago. The intrusion of the granodioritic batholith from the Cordillera Blanca raised the elevation of the valley over 2,000 meters, shearing the western flank where multiple transverse faults are present.
The increased erosion resulting from the raising event led to the formation of side canyons and
gorges. The successive glaciations later played an important role in the geomorphology of the region. Current research indicates that seven glaciations have occurred over the last 650,000 years, with the last major cooling event peaking 18,000 years ago. A minor cooling event, known as the Little Ice Age, occurred between the years 1450 and 1850. Evidence of the Little Ice Age is easily found in the small moraines near the glaciers in the Cordillera Blanca. Examples of glacial activity are abundant on the higher slopes of the range, including glacial cirques, U-shaped valleys, morainic arcs, and naturally, glacial lakes.
Lower elevations display a high degree of heterogeneity of detrital rock deposits and irregular
shapes from the underlying volcanic processes. These have created a unique morphology for the banks of the Río Santa, characterized by soft undulations abruptly cut by areas of sheet erosion, which oftentimes are confused for landslides.
The glaciers on the Cordillera Blanca were formed as a consequence of changes in climate over
the past 700,000 years. Glaciological research indicates that seven cooling events have occurred on earth over the last 650,000 to 680,000 years. Glacial masses in mountainous areas and in other continental regions of the planet extended and receded intermittently during this time. The last cooling event is estimated to have peaked 18,000 years ago, leading to an interglacial period that lasted for approximately 6,000 years. It is from this point forward that higher temperatures and decreased snowfall have resulted in gradual ice melt and glacial recession.
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A discussion of the formation of glacial lakes begins with a review of glacial movement. Due to gravity, the masses of ice accumulated over thousands of years overcome friction and move down the mountain slope, carrying with them any material in their path and essentially acting as natural bulldozers. This downward movement leads to the formation of moraines, or accumulations of residual material resulting from glacial erosion. Since glaciers will transport anything in their path, moraines have a heterogeneous structure.
A typical moraine will include fine sediment such as clay, silt, and sand, coarse sediment such as gravel and coarse sand, and much larger material such as rocks of varying dimensions. Moraines located along the edges of glaciers are called lateral moraines, while those at the front of the ice mass are called terminal or frontal moraines.
This morainal material forms a natural dam around the glacial lake basins found throughout the Andean range. In cases where the sediment is tightly compacted and cohesive, the basin becomes an excellent container for water storage. These natural dams are weaker where the moraine is composed of non-cohesive sandy sediment or sandy silt mixed with non-cohesive fine sediment. In these cases, erosional water processes can lead to violent overflows and discharges that can have catastrophic consequences. These events are so prolific and widespread that they form part of the history of communities living along the mouths of rivers whose flow originates from glacial melt in the mountains.
As glaciers melt and recede, the area and space they once occupied is often replaced by glacial
lakes of varied dimensions. The diverse morphologies of this terrain, in terms of shape and gradient, are one of the risk factors associated with glacial lake evolution. Risk increases with growth of water volume in the lakes, retreat of glacier termini, moraine erosion, potential piping or pothole erosion, and the potential for glacial lake outburst floods (GLOFs) that occur when the lake’s natural dam ruptures.
Below are some common terms and themes from the Cordillera Blanca’s glacial history:
• Quaternary and modern materials largely constitute the foundation or subsoil of the cities,
surrounding hills, and moraine dams supporting the glacial lakes. Glaciers and rivers have strongly influenced erosion through the following processes: Moraine formation from glacial sediment transfer and compaction Violent discharge of moraine and rocky material, mixed with water and ice, due to moraine
ruptures and consequent outburst floods Transport over short distances by rivers and currents in steep gradients, leading to the formation
of glaciofluvial material Transport of eroded and deposited sediment over long distances by more gently sloping rivers,
leading to the formation of fluvial material of varying granulometry
• Moraines, or sediment from glacial erosion, are formed by a heterogeneous mix of large rocks, angular rocks, gravel, and sands with varying proportions of clay, silt, etc. In many cases this sediment is highly compacted, with a high mechanical resistance and sealing properties. Moraines often have steep gradients.
• Floods are common phenomena in the Andes due to steep gradients, the occurrence of glacial lakes with non-cohesive moraine dams, and high overhanging ice. Many flood events in the Peruvian Andes have resulted from the impact of falling ice onto the glacial lake, creating the necessary hydrodynamic thrust for lake overflow.
• Glaciofluvial material is composed of angular boulders and gravels, clay, and sand in a mix of
varying proportions. Each layer can exhibit a certain degree of local homogeneity, but the composition changes greatly between layers, as do physical characteristics such as resistance to erosion, cohesion, and angle of internal friction.
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• Fluvial and torrential material is deposited over the terrain, composed primarily of well-sedimented pebbles and gravel with sandy or silty top layers and little clay. Alluvial fans also form along river banks and mouths, constituted by material similar to torrential lava but without the larger sediment. The sedimentation is sometimes visible and in some cases located along steep gradients. Floods resulting from a breached dam can lead to sedimentation and damming downstream, where deposition of silt or other fine sediment in horizontal layers can form temporary reservoirs or lakes along the main river channel.
• Glaciers are a clear indication that the morphology of the area has been strongly influenced by glacial activity. These large masses of ice are responsible for most natural disasters in the Cordillera Blanca. Glacial responses to a number a factors have been the subject of earlier studies. Aerial inspections of the Cordillera Blanca after the earthquake of 1970, for example, revealed that with the exception of the events in the Nevado Huascarán, the earthquake did not cause any hanging glaciers to fall or any glacial tongues to slide along the rock.
Other specialized literature describes, for example, how the 1964 earthquake in Alaska did not cause any hanging glaciers to fall but did result in small avalanches. In other cases, strong earthquakes have resulted in larger avalanches like those in northern Tibet, east of KunlunShan, after a magnitude 8 earthquake (GSA Bulletin, March/April 2004). Nevertheless, there are known cases where glaciers were dragged by avalanches of unstable rock, such as occurred in the Nevado Huascarán in 1970. These events highlight the need to study the conditions that bind the glacier to the underlying rock, in addition to the stability of the terrain itself.
• Outburst floods and avalanches have caused the majority of natural disasters in the Cordillera
Blanca (see Table 2 in the next section), making research and assessments of these events extremely important. Knowledge of the conditions that cause these events and their characteristics can provide insights for initial preventive measures. The planet’s climatic conditions can affect the conditions leading to landslides, outburst floods, and overall glacial movement, creating a truly fascinating opportunity and motivation for research. A GLOF can occur for various reasons or causes called triggers, including an earthquake, the sliding of the inner morainic wall of a lake, and even a rock avalanche on a lake. But not only GLOFs can produce mass flow movements. These may also result from prolonged periods of heavy rain that cause solifluction phenomena. Violent lake outbursts may occur also as a consequence of human intervention to build safety works, as happened once in the Cordillera Blanca. Construction of an open pit canal can cause a violent outburst of lake water if an ice avalanche on the lake or any of the other trigger events occurs. At present, the likelihood of avalanches is increasing due primarily to the effect of global warming on glaciers, which are losing their adherence to the rock base.
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4. PRIMARY NATURAL DISASTERS IN PERU Peru has a long and fairly well documented history of natural disasters (Table 1). However, it is possible that significant glacial retreats during the medieval warming period (800 to 1200 A.D.) also produced avalanches whose traces are visible on many slopes around the Cordillera Blanca, in areas such as Caraz, Marcará, and Callejón de Huaylas
Table 2. Natural disasters in the Cordillera Blanca Year Event 1725 Outburst flood buries town of Ancash 1725 Avalanches and outburst floods in Huaraz 1883 Outburst flood in Macashca, close to Huaraz 1869 Outburst flood in Monterrey - Huaraz 1917 Outburst flood from Nevado Huascarán over Ranrahirca 1938 Outburst flood in the Ulta - Carhuaz ravine 1941 Outburst flood in Pativilca watershed 1941 Outburst flood in Huaraz (4,000 – 5,000 dead) 1945 Outburst flood over the Chavín de Huantar ruins 1950 Outburst flood in Jancarurish reservoir. Hydropower plant destroyed 1951 First outburst flood in Artesoncocha Lake – Parón Lake 1951 Second outburst flood in the Artesoncocha Lake – Parón Lake 1952 Outburst flood in Millhuacocha Lake – Quebrada Ishinca 1953, 1959 Outburst flood in Tullparaju Lake – Huaraz 1962 Outburst flood in Ranrahirca, in Nevado Huascarán (4,000 dead) 1965 Outburst flood in the Tumarina Lagoon – Carhuascancha 1989 Outburst flood in Huancayo, from an outburst of Chuspicocha Lake 1970 Outburst flood in Yungay and Ranrahirca (15,000 dead) 1998 Outburst flood in Machupicchu. Hydropower plant destroyed
As we review the conclusions reached from the study of these disaster events from the 1960s to
more recent times, we realize that the science needs to be updated. In the 1960s, glacial studies focused more on physical characteristics and transformation processes. Current research is more oriented toward changes in mass and the impacts of climate change. Temporal analysis of glacial volumetric variance currently includes methods using satellite imagery, topographic measurements, photographic comparisons, and other techniques. These are especially helpful in determining how decreasing glaciers affect water availability for a variety of activities.
According to Dr. Louis Liboutry, in the case of cold-based glaciers, where base temperatures
are below the pressure melting point and the glacier is well adhered to the bedrock, ruptures occur in the ice prior to any ruptures due to contact with the ground.
Base temperatures in warm-based glaciers are more or less equal to the pressure melting point.
In these cases, friction plays an important role as the ice slides over the bedrock surface. The slope of the bedrock surface is similar to the slope of the glacier when it is relatively thin (approximately 30 meters or 98 feet).
The tangential force of an earthquake may theoretically overcome resistance or contact friction.
In reality, as the velocity of the slippage increases, the following can occur: a) A cavitation appears where the forces of friction diminish and the velocity of the slippage increases.
This phenomenon can accelerate until it produces an avalanche. b) There is no cavitation as the forces of friction increase and equal velocity, leading to a dynamic
equilibrium. The scale and duration of earthquakes generally do not result in a cavitation.
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The presence of melt water between the ice and bedrock also decreases the contact resistance between the two surfaces, and can also be the cause of slippage. Melt water and seismic activity create favorable conditions for calving and slippage for glaciers already in a state of disequilibrium, for the following reasons: a) The change in thermal conditions. Changes in temperature affect glacial movements. Sharp surges,
reaching speeds of 35 meters (115 feet) per day, are the result of increased temperatures at the interface between glaciers and the underlying bedrock surface. In valley glaciers, this often leads to a violent downhill acceleration, while in hanging glaciers the result is calving.
b) Glacier surges. Equilibrium in a glacier depends, among other things, on accumulation and ablation. An excess of accumulation can lead to a glacier surge that would change the glacier’s geometric (thickness, slope, etc.) and physical characteristics. A rapid increase in thickness can break equilibrium and cause a significant downhill surge.
Installing a monitoring system was recommended to anticipate these events, with the following
objectives:
a) Determining the temperatures of the ice at different elevations and monitor changes over time. b) Monitoring glacial regimes to quickly identify glacier surges.
Unfortunately, high costs and safety concerns have deterred implementation of these
recommendations. Although it is not possible to foresee a natural disaster, prevention is still possible by eliminating dangerous glaciers with explosives or induced melting. The simplest solution remains to relocate communities in safe areas, away from the risk of avalanches.
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5. GLACIAL LAKES IN THE CORDILLERA BLANCA
An updated glacier and glacial lake inventory indicates that there are 830 glacial lakes in the Cordillera Blanca, with 514 draining into the Río Santa watershed and the larger Pacific watershed. All 514 have areas greater than 5,000 m2 and volumes between 100,000 m3 and 79 million m3.
Many of these glacial lakes have caused natural disasters in the past while others currently pose significant threats. On the snow-covered slopes moraine dam failures have been more periodic than erratic. Over the last three decades, increased climate variability has modified glacier stability and created conditions different from those studied prior to the 1970s. Prevention measures need to include new criteria and disaster risk analyses.
The analysis of glacier stability or risk assessment for glacial lakes has, from a pragmatic perspective, directed us toward a safety measure implemented over the last 60 years. Reducing the volume of the glacial lake is a less radical and more analytical solution than the complete lake drainage originally proposed.
Naturally, the process of reducing lake volume has been gradually improved over the years due to the increasing availability of financial resources and new technology such as mechanical equipment. In the present context of climate change and its impact on water resources, the treatment given to dangerous lakes must also take into account the management of water resources. 6. FACTORS THAT INFLUENCE RISK ASSESSMENTS FOR GLACIAL LAKES
Many factors need to be addressed when assessing the danger of glacial lakes, but it is also very important to determine which events may trigger the occurrence of a GLOF phenomenon, i.e. a great outflow caused by the rupture of a glacial lake. A lake’s large volume is not always a source of danger or high risk, because the water body may be contained by a strong dock or bucket that mitigates the involved risk. Similarly, we must think of solutions that fit the economies of and available technologies in developing countries, though always ensuring there is no significant risk to inhabitants, infrastructure, and overall production processes downstream of the lakes.
Theoretically, the best though very expensive solution in many cases is to completely empty the
lake. Otherwise, we must look for intermediate solutions that eliminate most of the threat and allow for an acceptable or manageable risk.
The Glaciology Unit, until 1996, in its study, design, and building of safety works in dangerous lakes, understood its responsibility to society, knowing that a lake’s overflow may slow down or indefinitely hamper regional development. For this reason, teams who are responsible for the study and treatment of dangerous lakes should be dedicated to these tasks on an exclusive basis, which will provide continuity to their work and allow for continuously improving prevention procedures,.
An entity must be accountable to official authorities and society regarding changes in glaciers
and the emergence of dangerous lakes so the risk they might pose can be timely addressed through basic prevention measures.
Prevention requires utilizing high resolution satellite monitoring, field equipment for on-site
verification, and enough logistical equipment to take immediate action in critical cases. Conducting only occasional monitoring of glaciers as dangerous lakes develop could result in failure to detect critical changes that can cause GLOFs, resulting in fatal losses in many cases.
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The following factors need to be considered when assessing glacial lakes risk: 6.1 Glacier characteristics: These include slope, the magnitude of crevassing, the magnitude of
fragmentation, and estimated thickness. Thickness measurements become more and more important when developing an adequate model of approximate flows that could result from an outburst flood. Technology is available to measure, with a high degree of precision, the ice thickness and other glacier characteristics through aerial photography or land-based measurement techniques using the same criteria.
6.2 The slope of the bedrock: This is an important factor in determining the potential for avalanches
that fall into glacial lakes. The slope is used to calculate glacier stability and the probability of failure from edge effects or ramp type. The University of Zurich has developed empirical relationships based on glacier studies in the Alps (Figure 8), which help to determine the slope at which slippage would occur based on ambient temperatures. This relationship provides a criterion for determining the potential of a flood event, based on slope measurements from satellite imagery and digital elevation models. For example, a 25 degree gradient could cause sliding in warm glaciers like those found in Peru. Naturally, adhesion of the ice to underlying rock is highly dependent on ambient air temperature.
6.3 The geometry and structure of the moraines forming the lake basin: Considering that many
GLOFs result from moraine material and rock sliding into the lake, the composition and slope of the interior lake boundaries determine the stability of the basin. In principle, the geometry or cross section of a moraine may be trapezoidal or triangular in shape. The latter shows greater signs of instability, and rain and wind erosion can gradually create a triangular form on a steep slope. With a trapezoidal section, in contrast, the moraine is much more compacted, stable, and not easily eroded by rain, wind, or other natural processes.
6.4 Length of the valley: When a glacial lake outburst flood occurs, the destruction it will cause
downstream strongly depends on its volume and kinetic energy.
The flood’s kinetic energy will depend on the physical characteristics of the path of the downstream flow. A long path with a shallow slope will dissipate some of the energy, as experienced in the valleys downstream of the Quelccaya glacier. In 2006, a new glacial lake at the terminus of the QoriKalis Glacier tongue overflowed. Due to the extensive length and shallow gradient of the valley, the flood lost speed and other than increased discharge in the Salcca River, communities downstream were unaware of the events in the upper watershed.
In contrast, in October 2010 a small GLOF caused by falling ice at the foot of the Nevado Chicón, in the Cordillera Urubamba, caused significant destruction. The flood velocity increased on the steep slopes downstream, with the energy only dissipating when the floodwaters reached the Occoruruyoc plain.
6.5 Presence of hanging glaciers. Masses of ice on very steep slopes are termed hanging glaciers. The
combined effects of their large volume and gravity can cause large avalanches and waves that may result in dangerous surges. This was the case in Lake 513 and possibly in many other glacial lakes where moraine dams were subjected to strong hydrodynamic events.
In the Lake 513 example, a sheet of ice with an approximate volume of 380,000 m3 (13,419,573 cubic feet) slid toward the lake, carrying with it one million cubic meters (35,314,666 cubic feet) of rock. Its impact produced a wave over 20 meters (66 feet) high in a lake of 8 million cubic meters volume (282.5 million cubic feet) and 85 meters (279 feet) deep.
The decreasing adherence between the ice and the basal rock due to warmer temperatures, especially in tropical glaciers, creates unstable conditions for glaciers on steep, rocky slopes.
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Figure 7 provides a simple diagram of hanging glaciers and their location on the uphill side of a glacial lake. Several factors can cause the hanging glaciers to slide and fall directly into the lake, causing a strong hydrodynamic surge in the form of waves. The waves may flow directly over the moraine dam or erode the dam to the point where a complete outburst flood can occur, with well-known serious consequences downstream.
Figure 7. Types of glacial avalanches. Ramp type (a), edge type (b), ramp including rock failure type.
(Huascarán 1970).
Source: Institute of Geography of the University of Zurich Figure 8. Critical slopes for different types of tropical and high latitude glaciers. Legend: Slippage surface gradient. Cold glaciers, Polythermal transition zone. Temperate glaciers. Average annual air temperature.
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Figure 9. Hanging glaciers over Lake 513 in Carhuaz, Ancash.
Figure 10. Hanging glacier over Lazo Huntay Lake in the Cordillera Huaytapallana, in central Peru.
6.6 Glacier tongues undermined by glacial lakes (calving): As glaciers retreat, they leave behind empty spaces that gradually are filled with melt water and eventually form lakes. As these lakes are still in direct contact with the glacier tongue (Figure 11), the temperature difference between the water and the glacier produces an eroding effect that practically cuts off the glacial tongue from the rest of the glacier, causing it to eventually break off and fall into the lake. This can create
17
a potentially dangerous wave, depending on the mass of the ice and volume of the lake. This phenomenon has caused natural disasters in many places. Examples include the event in Huaraz from Palcacocha Lake, in Huancayo from Lazo Huntay Lake, and, more recently, an unnamed lake at the foot of the Nevado Chicón.
Figure 11. Glacier in contact with a lake in the Nevado Pastoruri, Cordillera Blanca, showing the calving
process. 6.7 Volume of the lake: Various trigger events may have an impact on the glacial lake, where the
destructive processes truly begin (exceptions include the avalanche in the Nevado Huascarán in 1970 and the snow avalanches in the Alps). The magnitude of the outburst will depend on the volume of the lake. A seismic trigger event (if it truly destabilizes the glacier), an avalanche, the collapse of a glacier, a slide of the lake basin itself, or other factors create downstream motion in the lake. From the more than 60 years of preventive work in Peru, the simplest and most effective preventive measure has been to reduce the volume of lakes categorized as dangerous.
6.8 Seismic and tectonic factors: Although the relationship between seismic activity and glacier
stability is questionable, the case of the Lazo Huntay and Chuspicocha lakes in the Shullcas River watershed, where the city of Huancayo is located in central Peru, is worth mentioning. In 1969, seismic activity along the Huaytapallana fault caused large fragments of ice to fall into Lazo Huntay Lake, breaking the stone and mortar dam used for water storage.
6.9 Discharge rate: It is necessary to know the magnitude and variation of discharge rates from the
glacial lake to properly design pipelines and overflow sluices to prevent water from rising to undesirable levels. This measurement should determine a value where water can be transported easily through the pipeline even during periods of heavy rainfall and inflows into the lake.
Another significant case in Peru was the large avalanche in the Nevado Huascarán (Figure12), estimated between 50 and 100 million m3, after a magnitude 7.9 earthquake. The trigger of the avalanche was likely falling basal rock from the northern summit of the Nevado Huascarán that dragged the overlying glacier with it.
18
Figure 12 The Nevado Huascarán in May 1970 after a 7.9 magnitude earthquake. Approximately 15,000
people are believed to have died during the avalanche.
6.10 Determining the trigger: This is one of the important aspects for evaluating a lake and determining the degree of danger. A GLOF can have several causes. However, it is important to determine which of the triggers is most likely to occur from the historical, statistical, or even modeling viewpoints. Possible triggers could be an earthquake, a flood caused by a glacier, a landslide in the lake’s basin, or a piping process. It is important to identify the possible trigger to assess the risk; once the threat and vulnerability are known, the feasibility of a risk mitigation process can be determined.
2 km
BURIED CITY OF YUNGAY
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7. PROCEDURES FOR REDUCING THE RISK FROM DANGEROUS
GLACIAL LAKES Safety measures adopted for glacial lakes in the Cordillera Blanca have two primary objectives:
a) Decrease the volume of the lake, build structures to maintain the volume at desirable levels, and contain potential GLOFs resulting from falling ice.
b) Utilize the structures to regulate the lake as a reservoir, in light of potential future water shortages.
The following procedures will reduce risk from dangerous glacial lakes:
7.1 Cutting the open face of the moraine into a V shape (Figures 13 and 14). This process will gradually lower the water level parallel to the face. This measure has been widely implemented in glacial lakes with moraine dams, but it is a daring procedure that has been successful most of the time only because no avalanches occurred during construction. In Los Cedros in 1951, an avalanche of ice fell into Lake Jancarurish during the building of drainage works, resulting in an uncontrollable surge and the Jancarurish outburst flood. It is therefore recommended to lower the level of the lake by pumping or siphoning prior to the process of cutting the moraine edge, essentially creating an edge that can buffer potential surges.
Figure 13. Diagram of the excavation process to lower the water level of glacial lakes held by moraine dams or other loose sediments.
Section A – A
Figure 14. Cross-section showing the characteristics of the spillway (left) and a lateral view of the canal
showing the restored security dam that will contain surges resulting from falling ice (right).
20
7.2 Construction of drainage tunnels. Drainage tunnels can be cut in glacial lakes with natural
rock dams and, in some cases, also in lakes with loose moraine dams. Several procedures have been used to construct these tunnels, and the connection to the lake has varied from case to case. The most important example is in Lake Parón, where a 1,300 meter (4,265 feet) tunnel was connected to the lake with two 60 centimeter (35 inch) diameter holes. The lake was drained through the tunnel and subsequent geotechnical studies evaluated its use and suitability as a reservoir.
7.3 Filtration. This has also been used with moraine dams, such as the procedure in Lake
Yanarraju in the eastern region of the Cordillera Blanca. Use the safety measures to build the necessary structures to prevent increases in volume and
contain potential surges produced by falling ice. The climatic conditions that currently affect water resources necessitate analysis of other goals related to activities with dangerous glacial lakes. On the one hand, the lake’s volume must be reduced, while on the other, some of the water must be conserved to satisfy the needs of the valleys downstream for agriculture, drinking, and other purposes.
Regulation systems have been built in two lakes in Peru: Lake Parón, to regulate 45 million (1.59 billion feet), and Lake Cullicocha, to regulate 12 million m3 (4.23 billion feet3). Two other reservoirs have also been created but for the sole purpose of regulation, without adequate consideration of the risk of keeping high water levels near glaciers that could cause outburst floods with disastrous consequences.
21
8. METHODOLOGY FOR IMPLEMENTING SAFETY MEASURES
The traditional methodology that has been systematically followed has included the following steps: 8.1 Carry out an initial assessment of the characteristics of the lake and surrounding glacier.
In this phase, preliminary studies are carried out to include the study area in the inventory of glacial lakes.
8.2 Carry out a more in-depth study. If the initial assessment finds characteristics that indicate there is a risk downstream, further study is warranted. This includes cartographic and bathymetric studies of the glacial lake and surrounding terrain, glaciological studies of the glacier, geological studies, and analyses of the soil mechanics of the terrain. These studies should already begin to address the potential implementation of safety measures.
8.3 Analyze the hydrology of the watershed. This is equally important to determine safe
discharge levels for the design of overflow canals, allowing for safe removal of excess lake volume.
8.4 Implement the safety measures based on information collected from the in-depth studies. Safety measures include volume reductions, hydraulic infrastructure such as open canals, and the drainage tunnel or channel that will be covered by the rebuilt dam to contain potential surges caused by falling ice.
Figure 15. Construction of the spillway in a glacial lake in the Cordillera Blanca in the 1950s.
22
9. CASE STUDIES FROM PERU
We describe below some of the lakes where prevention or safety features have been added.
Figure 16. Other measures implemented in the Cordillera Blanca.
23
Table 3. Cordillera Blanca Lakes with Safety Features.
COORDINATES PRESENT CHARACTERISTICS DATE Nº NAME WGS84 - UTM BAT.
EAST NORTH ALTITUDE AREA VOLUME DEPTH
1 SAFUNA ALTA
211812
9021933 4,359.8
334,358.76
15'524.434.96
84.30
2010 2 PUCACOCH
A 210484
9019995 4,494.0
277,201.00
8,463,000.00
78.50
2006 3 LLULLACOC
HA 209379
9020071 4 CULLICOCH
A 196513
9018963 5 YURACCOC
HA 199098
9016830 4,618.0
287,269.00
8,177,746.00
55.40
2011 6 TAULLICOC
HA 215396
9014575 4,426.0
133,766.00
2,448,917.81
63.50
2007 7 JATUN
COCHA 207040
9011874 3,886.0
486,550.80
9,233,206.06
34.40
2007 8 ARHUAYCO
CHA 211054
9016670 4,400.0
398,823.70
19,550,795.00
97.70
2011 9 PARON 20481
7 9004082 4,174.
0 1,480,488.70
39,888,952.61
43.20
2007 10 HUANDOY 20555
1 9002687 4,740.
0 7,718.40 16,722.22 4.90
2007 11 LLANGANUCO ALTA
270756
8997252 3,833.0
684,199.20
2,018,263.75
9.80 2007 12 LLANGANUC
O BAJA 208810
8995916 3,820.0
579,950.20
11,747,149.88
28.70
2007 13 LAG. 69 21310
9 9002790 4,604.
0 97,800.03 2'763,008.5
7 58.40
2009 14 ARTESA 22345
6 8991580 4,286.
0 22,796.50 124,743.00 12.2
0 2005
15 HUALLCACOCHA
219979
8986361 4,355.0
163,066.50
4,664,723.80
75.90
2005 16 COCHCA 22053
5 8980233 4,538.
0 69,204.60 1,001,230.1
0 27.20
2007 17 RAJUPAQUI
NAN 219341
8979461 4,150.0
35,438.20 462,407.40 27.40
2007 18 513 21961
0 8980533 4,431.
0 207,585.10
9,250,937.50
83.00
2011 19 LEJIACOCH
A 224493
8974312 4,618.2
183,907.00
1,356,126.00
19.90
2005 20 PACCHARU
RI 230643
8972602 4,462.3
278,053.00
7,134,636.00
50.00
2005 21 PUCARANR
ACOCHA 242454
8967368 4,390.0
234,622.00
4,398,307.79
46.10
2007 22 AKILLPO 23398
1 8966754 4,704.
0 412,463.04
3,896,312.00
31.80
2004 23 PACLIASH
COCHA 240238
8967073 4,564.0
218,679.23
2'451,103.86
25.90
2010 24 ISHINCA 23438
4 8961439 4,960.
0 87,901.69 785,872.00 24.7
0 2004 25 PACLIASH 23528
8 8963197 4,577.
4 188,873.3 3'985,344.1 42.2
0 2011 26 MULLACA 22795
1 8956287 4,596.
0 110,695.0 2,043,738.0
0 38.00
2006 27 LLACA 23152
2 8955886 4,474.
0 43,987.6 274,304.58 16.8
0 2004 28 PALCACOC
HA 238513
8960238 4,562.0
518,425.9 17,325,206.57
73.10
2009 29 CUCHILLAC
OCHA 241514
8958875 4,620.0
145,732.0 2,138,936.00
27.30
2005 30 TULLPARRA
JU 242681
8957684 4,282.9
463,757.2 12,474,811.86
63.50
2011 31 CAYESH 24393
1 8953451
32 SHALLAP 241239
8949775 4,260.0
165,251.1 3,467,585.29
36.60
2004 33 RAJUCOLTA 24277
5 8946411 4,272.
7 512,722.93
17,546,151.00
72.70
2004 34 YANARAJU 22702
8 8989463 4,142.
0 229,707.00
7,642,096.00
61.40
2005 35 ALLICOCHA 23016
8 8977001 4,543.
0 357,517.68
5,698,018.56
33.00
2006
HAYTAPALLANA CORDILLERA 36 LAZO HUNTAY 37 CHUSPICOCHA HUAYHUASH CORDILLERA 38 JURAO 39 SARAPOCOCHA URUBAMBA CORDILLERA 40 RITICOCHA
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9.1 SAFUNA ALTA LAKE
Safuna Alta Lake was at 4360 masl in Quitaracza River basin, in the Pomabamba province of
Ancash. Due to the conditions of the surrounding glaciers, the moraines’ structure was highly unstable. A recommendation was made therefore in the early 1960s to build a 47-meter tunnel to prevent the lake’s water level from rising.
A month before the earthquake of May 1970, a tunnel was completed that reduced the water level by 38 meters (Ames and Francou). The tunnel was above the lake’s water level. The tunnel was severely damaged by the earthquake. A new tunnel had to be built 159 meters long that, like the previous tunnel, would be excavated entirely through morainic material. (Report of the Glaciology and Lake Control Office of the Corporation Peruana del Santa, 1972).
Figure 17. View of High and Low Safuna Lakes.
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Figure 18. Two tunnels built to prevent water level from rising in Safuna Alta Lakes.
But reality proved otherwise and the lake’s water level continued to decrease so that in 1974
when the author visited the lake, the level of water was down just over 10 meters and continued to decline further in subsequent years. It should be mentioned that the depth of the lake has changed markedly since 1967, when it reached a depth of 154 meters. In 1973 the depth was 98 meters; in 2001, 119 meters; in 2002, 81.5 meters, and in 2010, 84 meters.
In 2002, a rock slide caused a wave of at least 80 meters (Reynolds Geo Sciences Ltd., 2003) that damaged both tunnels. Figure 19 shows the area where the rockslide occurred that caused the big waves.
Figure 19. Rock slide area (Photo: Reynolds Geosciences Ltd.).
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9.2 JANCARURISH LAKE
Jancarurish Lake is located in the western part of Alpamayo and, like many other lakes in the Cordillera Blanca, is a dangerous lake because of the Alpamayo glaciers. As mentioned above, in most cases the criteria and procedure to mitigate the hazard has been to reduce the volume of lake water. Likewise, in Jancarurish, because of its loose and poorly consolidated morainic material, the same procedure was adopted.
To drain Jancarurish Lake, an open pit cut was made to lower the water level. The water was contained using sandbags that stemmed the flow of water and allow digging on dry ground. Depending on the amount of water reaching the lake, the water level may rise from 20 to 50 cm per day. At the end of the day in the afternoon the dam is opened to let the water flow and carry the fine material downstream. Opening of the sluice can pose a risk because if a hanging glacier causes an avalanche, the path to a violent flow of water is open and, under certain random circumstances, a GLOF or avalanche may occur.
Figure 20. The majestic Nevado Alpamayo (top) and the opening left by the 1950 avalanche after the violent
outburst of Jancarurish Lake (Photos from 1990).
At that time, staff reported that the head of the work team at Jancarurish Lake decided to dam up the lake for four consecutive days. The height of the dammed water might have exceeded one meter and when the sandbags dam was removed, a large flow ensued that eroded the moraine dam and emptied the lake (Figure 20).
This GLOF or rupture of the natural moraine dam of Jancarurish Lake seriously damaged the Jancarurish small hydroelectric plant in Los Cedros that was built during the construction of the Cañón
27
del Pato hydroelectric power plant, and also caused damage to farmland, roads, and other public and private infrastructure in that area. It is even mentioned that the impacts were felt as far as the port of Chimbote, located more than 150 km away.
Most safety measures executed in the Cordillera Blanca have failed to take preventive measures such as installing early warning systems. When safety works are undertaken in lakes, especially when making open pit cuts, at least temporary early warning systems should be installed as a measure against the contingency of an extreme event such as an ice avalanche falling on a lake. This precaution is necessary because global warming is reducing the adherence of glacier masses to the base rock, which in turn may initiate the sliding of these masses downhill. 9.3 HATUN COCHA (BIG) LAKE
Hatuncocha Lake is located in Santa Cruz ravine, in the northern Cordillera Blanca, in the province of Huaylas. It is one of the most popular local tourist spots because of its variety and diversity of landscapes. Several paths to climb the Alpamayo, Santa Cruz, Pucahirca, and other snowcapped mountains begin near the lake.
Safety works in Hatuncocha Lake were built in the early 1960s and included the installation of two steel pipes 1.20 meters in diameter, each arranged in parallel as shown in Figure 21. A safety dike was then built to contain waves.
After about 50 years, these prevention works further demonstrated their effectiveness when in February 2012, the Low Artizon Lake, located north of Nevado Artesonraju, overflowed. The works built in Hatuncocha Lake decades ago successfully contained the surge (Figure 21).
Figure 21. Views of the path carved by the overflow of Low Artizon Lake (top left). Works in Hatuncocha
Lake executed in 1960s (top right) and the impact of the overflow (bottom left). The last photograph (bottom right) shows how the waters were contained, preventing a catastrophe downstream.
(Photos: Alejo Cochachin)
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Figure 22. Damage downstream from Santa Cruz Ravine.
Although Hatuncocha dam contained the raging flow torrent of flood, the flow through the two
pipes from, one to two cubic meters per second down a steep ravine slope, caused enormous erosion and destruction, as shown in Figure 22. As happened in Lake 513, described earlier, prevention initiatives have demonstrated their effectiveness many years after they were adopted. 9.4 PARON LAKE
Paron Lake is the most emblematic case of glacial lake management in the Cordillera Blanca and at the national level. Located on the western slope of the Cordillera Blanca, Paron Lake is the headwater source for the Río Parón-Llullán River watershed, one of the principal basins draining into the Santa River. The watershed has an area of 42 km2 (16 square miles) at the edge of the lake, and a total area of 146 km2 (56 square miles). The coordinates at the center of the lake are 8° 59’ 40” south, and 77° 40’ 19” west. At outburst level, the elevation at the surface of the lake is 4,200 meters (13,779 feet). It is 3,600 meters (11,811 feet) long at its maximum length and 750 meters (2,461 feet) wide at its maximum width, with an average depth of 69.5 meters (228 feet) and an outburst volume of 79 million m3 (2.79 billion cubic feet). It is the largest lake in the Río Santa watershed (Figure 23).
Figure 23. Paron Lake is surrounded by eight snow-covered peaks: Huandoy, Pisco, Chacraraju,
Pirámide, Paria, Artesonraju, Nevados de Caraz, and Aguja Nevada.
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Paron Lake has received attention for many years not just because of its size and volume, but
also because it presents the ideal conditions for regulation as a reservoir. It is also considered a dangerous glacial lake due to the proximity of glacial ice and the steep gradient of its banks. Recent disputes over water rights and access have resulted in ongoing inter-institutional efforts to improve management of the sub-watershed for the benefit of agriculture, potable water systems, aquaculture, hydroelectric power, and other water uses.
The natural dam on Paron Lake is distinguished by two elements visible on the surface: a) the
left flank, formed by the lateral moraine that extends from the tongue of the Hatunraju Glacier on the slope of the Nevado Huandoy, and b) the right flank, formed by an alluvial cone from the glacial lake at the foot of the Aguja Nevada Glacier.
A very important social consideration related to Paron is how people perceive the Rio Llullán Parón watershed that starts at the lake. Recently, because the 7.9 scale earthquake did not significantly alter the lake, it is thought that the lake does not pose a threat to water and tourist activities. The following arguments, however, should be put forward to the population of the city of Caraz, which is the largest town in the subbasin.
First, the sub floor of Caraz is made up of alluvial materials, mostly boulders and transported
material of unknown chronological origin, dating probably hundreds or even thousands of years. As mentioned by Mark Carey in In the Shadow of Melting Glaciers (Carey, 2010), generation after generation of Caraz residents have asked the government to act to provide security to the city of Caraz.
Various studies on Paron Lake have focused on preventing the natural disasters that would
result from GLOFs. These include:
• In 1950, Dr. Ali Szpessy Schaurek measured the displacement velocity of the Hatunraju Glacier, registered as Glacier 506A. These measurements continued throughout the following decade as reference data for this glacier covered by moraine detritus.
• In 1951, Luis Ghilino Antúnez wrote detailed notes and observations on Paron Lake after the two outburst floods from Artesoncocha Lake, located above Paron Lake (Figure 24).
• Also in 1951, Dr. Hans Span determined that the GLOFs from Artesoncocha Lake did not have any major effects on Paron Lake due to low water levels, allowing it to receive the discharge from Artesoncocha without consequence.
• In 1952, Dr. Trask concluded that reducing the volume and level of Paron Lake was a necessity after reviewing several glacial lakes in the Cordillera Blanca.
• That same year, Dr. Torres Vargas recommended carrying out reconnaissance surveys in the natural drainage channel and the lake’s natural dam.
• Finally, in 1964, Jorge Matellini recommended focusing on Paron Lake as a priority over other dangerous lakes in the Cordillera Blanca.
30
Figure 24. Location of Artesoncocha Lake with respect to Paron Lake.
Figure 25. Sand bag dam in 1951. Figure 26. Land surveyors in 1951.
After the outburst flood from Lake Artesoncocha, some safety measures (e.g. placing sand bags over the natural dam) were implemented and topographical studies began to examine the characteristics of the lake for future drainage projects. These activities are show in Figures 27 and 28.
The Peruvian Santa Corporation, as the entity that led the development of the Ancash department through 1967, contracted the services of several recognized experts to analyze glaciers and glacial lakes in the Cordillera Blanca. They included Dr. Louis Lliboutry (glaciology), André Pautre (geology), and Georges Post (soil mechanics). They reached several important conclusions about potential events that could lead to GLOFs:
• Seismic activity, which can affect the Hatunraju moraine or alluvial cone along the right side of
the lake, through a process of liquefaction.
LAGUNA ARTESONCOCHA
LAKE PARÓN
31
• A karst network in the ice of the Hatunraju Glacier, causing ice below the Lake Paron water level to melt. The hollows left by the melting ice could then lead to a violent discharge from the lake.
• An excessively rapid discharge from the lake. • An outburst flood resulting from blocked infiltration networks, calving from the glacier, or
increased volumes from outburst floods from secondary glacial lakes above.
The potential for GLOFs from many different events and the high level of risk associated with Lake Paron led to the radical recommendation of draining the lake. The experts concluded that “taking into account the unknown and dreadful consequences that a rupture of the Lake Paron dam would have, the most sensible course of action is to drain the lake as much as possible.”
The corporation analyzed the followed alternatives:
• An open face cut in the moraine. This alternative was rejected on the grounds that it would
destabilize the slopes of both the lateral moraine on the left side of the lake and the alluvial cone on the right side.
• Pump water out of the lake. This would be a temporary and expensive solution. • Bore a tunnel or sluice along the rocky right side of the lake, digging through the bottom of the
lake in the thinnest stratum of detritus. This was accepted as the safest technical alternative.
Although the experts recommended draining the lake to the maximum extent possible or to completely dry it out, the possibility of regulating the lake as a reservoir for the summer months was already being explored at the time (second page of the letter from Coyne et Bellier from Paris to the general manager of the Peruvian Santa Corporation, November 28, 1966).
Although Dr. Louis Lliboutry recommended a possible drying out of the lake, later studies by Peruvian technicians showed that methods that would both ensure safety and use of the water from the lake were feasible. Obviously this implies multiple uses of the water that would first flow through farming areas and catchments for urban consumption and other uses, and ultimately the water would be used for energy generation. It is not clear if all the security studies and works in the lakes undertaken by the Peruvian government have adopted energy generation as the main purpose for using the lakes’ waters. Even now, when climate change is having a significant impact on water resources, studies and works must adopt both points of view and include recommendations about multiple uses of water resources.
The author wishes to thank the technical advisor of SIDERPERU, at that time the state-owned steel
maker, who encouraged the company’s president and general manager to provide funds to complete the water regulation works at Paron Lake, since the steel company indirectly benefited from electricity derived from Lake Paron for its steel production. This led Electroperu to react and provide the necessary funds to finish the project, revealing the fact that the government agency’s senior management did not plan on using water resources from the lakes for electricity production.
Following the recommendation by the experts, excavation for the spillway commenced in 1970.
After advancing 1,063 meters (3,487 feet), the construction was stopped in 1972 due to a dispute between the project supervisors and the contractors. It was subsequently abandoned for ten years, leaving the construction unfinished and the goals of enhanced safety and regulation unmet.
In August 1982 construction of the spillway commenced again under the guidance of the lead
entity in the Peruvian energy sector, ELECTROPERU, and the national Glaciology Unit. The final length of the tunnel reached 1,245 meters (4,084 feet). Drainage of the lake began in February 1982 through two holes with a diameter of 60 cm (35 inches) each (Figures 27, 28, and 29).
32
Figure 27. Location of the sluice for Paron Lake.
Figure 28. Diagram of the sluice for Paron Lake.
Figure 29. Diagram of the final section of the sluice and its connection to the lake at a depth of 54 meters
(177 feet).
Location of the sluice
33
The drainage process was carried out cautiously, heeding to the many studies dating back to early explorations of the lake predicting that an excessively rapid discharge could result in dam failure and landslides. The water level was only lowered between 15 and 20 cm (5.9 and 7.8 inches) per day. This was accompanied by measurements of water table variation and infiltration rates in the natural dam. Upon completion, this information was compiled in a report detailing dam responses to the drainage process, helping to establish the parameters for the third phase of the project to regulate the lake as a reservoir. Figure 30 shows the potential trajectory a GLOF would follow from Paron Lake down to the city of Caraz.
Figure 30. Potential trajectory of a GLOF from Lake Parón down to the city of Caraz, Ancash.
It is appropriate to mention an incident that occurred when connecting the first hole. While
drillers vented their joy over the success of the first hole, when we actually proceeded to measure the lake’s outflow, we found it was only half of what was projected. So despite a load 54 meters high and a 60 cm diameter hole, only about a half of the calculated 4 m3/second was not reached.
This was because the level of the tunnel and hence of the holes was rather low and we were practically adjacent to the deposits of material from the bottom of the lake. These connections through holes were drilled at 4146 meters of altitude, while the Coyne and Belier project required them to be 9 meters above, i.e. at 4155 meters.
Clearly, the drilling aimed at the bottom of the sediment layer and the two holes effectively hit the bottom debris cone. The drillers proposed to introduce a blade into the hole to "beat" the material
34
and allow it to flow out. This was done but almost at the cost of the lives of two of the drillers. Fortunately, this was only a scare. These works were the beginning of a gradual solution to the problem.
It is a well-known saying that success belongs to everyone but errors look for culprits and so the design company blamed the Works Supervisor for allowing material from the digs to be thrown to the foot of the talus, thus obstructing the orifices. Later when we designed the final tunnel connection for the regulation works, the company was careful to build the mouth at the 4155 m level.
Drainage began midway through 1983 and continued into 1984, but was interrupted by a
landslide into the spillway at the union between the loose material at the entrance to the canal and the rocky massif. Repairs took several months in 1984, delaying completion of the drainage process until 1985.
The Dam Characteristics Report, prepared at the completion of the drainage process to establish parameters for regulating the lake, included the following conclusions and recommendations:
• No fossil ice is present under the surface of the lake that could produce a karstic phenomenon. • Both types of materials forming the natural dam are fairly uniform and are covered by a thick
impermeable layer. • The slopes of the dam upstream and downstream ensure high slope stability even during strong
seismic events. • The drainage rate for the lake level should not exceed 20 cm per day. • A water level of 4,190 meters above sea level (13,747 feet) should be set as the maximum level
of the lake as a reservoir. • For protection against surges and seismic events, the lake level should remain 15 meters (49
feet) below the top of the natural dam. A 10 meter height difference (33 feet), with water levels at 4,190 meters (13,747 feet) above sea level, would necessitate updating risk assessments and raising the level of the natural dam.
• Movement of glacial ice into the lake is more likely to occur as the result of slope failure in the rock base than of calving. However, 20 years after this report, calving risk should not be discarded.
• Strong earthquakes can generate considerable wave surges due to the regular shape of the basin, the steep surrounding slopes, and the funneled shape of the lake.
• The near-vertical cliffs on either side of the lake have not been studied, and little is known about their characteristics.
• The installed drainage system is effective only for lowering the volume of water in the lake. For regulation as a reservoir, an additional gallery would need to be built and a system with floodgates rather than valves installed.
• For installation of the regulation system, a definitive connection should be made between the spillway and the lake. This requires that the water level be lowered to 4,155 meters (13,632 feet) above sea level, or 45 meters (147 feet) below the outburst level at 4,200 meters above sea level.
• The water supply into the lake is sufficient for the water needs of agricultural activities, potable water supplies, electric power generation, and other activities downstream.
The third phase of the project was completed in 1992, following the recommendations of the
report. Since then, other challenges have arisen that require continued efforts on Lake Parón nearly 20 years after completion of the construction.
Contexts have changed over time. When the project began in the early 1970s, glacial studies did
not consider the effects of global warming, climate change, and glacial retreat, and their implications on water resources management.
35
Figure 31 shows a diagram of the two channels connected to Paron Lake. The first blue line shows the first sluice built, installed with control valves. After completion of the drainage process and following geotechnical studies, a more reliable regulation system was installed instead of the valves, as these have a limited lifespan.
Figure 31. A bird’s eye view of the two channels connected to Paron Lake. The lower blue line shows the
second channel built as part of the reservoir regulation system.
Figure 32 shows the floodgate control room for the regulation system, located at a depth of 60 meters (197 feet). Figure 33 shows the valves used for the drainage process and Figure 34 shows the hydraulic system of the electronic regulating system of the lake.
Figure 32. Lateral view of the regulation channel and the vertical tunnel for access to the floodgate control
room. (The missing contents of this illustration will be supplied later.)
LAKE
LAKE
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Figure 33. Valves with a diameter of 60 cm installed for drainage of Paron Lake.
Figure 34. Floodgate chamber and control room for the regulation of Paron Lake.
Upon completing all construction in 1992, the ELECTROPERU Electrical Company transferred
control of the facilities to Cañón del Pato Hydropower Plant. This proved an ineffective way of integrated water resources management, as the hydroelectric company managed the reservoir solely for electric power generation without considering the effects on other activities such as agriculture or the impact of variable flows on downstream ecosystems.
In 1995, Cañón del Pato Central Hydroelectric was privatized and Duke Energy took control of
Paron Lake and Cullicocha Lake. The new owners managed the water supply without consideration of downstream users, who eventually expelled Duke Energy personnel in 2008 and have managed Paron Lake ever since.
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Again, it should be noted that conflicts that occur in the different extraction and production industries, despite voluminous environmental and natural resources regulations, are due to the absence of the state. The population of the Parón Llullán River subbasin has endured 15 years of biased mismanagement of Paron Lake because the organization responsible for the management of water resources never challenged or punished the company that owns the Cañón de Pato Hydropower Plant for misusing stored water without coordinating with other users for agricultural, domestic, and other uses. It is understandable that an affected population should react as did the community of the Llullán Paron subbasin in the case of Paron Lake.
But the inefficiency persists. From 2008 to date (mid-2012), almost four years after the control
facilities of the lake were seized by the community, no solution is on the horizon. A serious condition was identified in 2011, when the flood regulation system started failing. The importance of such failure is not fully appreciated. In fact, a system failure could cause the floodgates to open completely out of control, and thus significantly damage the river channel.
Ongoing conversations are attempting to resolve the conflicts regarding the management of the
lake and the sub-watershed, with the hope of establishing a more integrated management model in the Llullan Paron sub-watershed for a more participatory and rational use of the Llullan Paron River.
The story of Paron Lake does not end here. Two outburst floods from upstream Lake
Artesoncocha into Paron Lake led the community of Caraz to request assistance from the Peruvian Santa Corporation. While lowering the volume of Paron Lake addressed this risk, the permanent state of glacial retreat is leading to the formation of a new upstream lake by the Artesonraju and Paria glacier tongues (see Figure 35 a, b, and c,).
(a)
(a) (b)
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(c)
Figure 35. A new lake being formed by retreating glaciers upstream from Paron Lake (a, b, c).
9.5 LLANGANUCO LAKE
The High and Low Llanganuco lakes are at a height of 3863 meters above sea level. Their geographical coordinates are 9° 04 'S and 77º 39' W. They are in Yungay province of Ancash. As a result of the 1970 earthquake, several ice avalanches from the Huandoy and Huascaran mountains created an impoundment that raised the level of the High Llanganuco Lake.
Figure 36. High Llanganuco Lake.
The volume of the lake water grew fivefold and the lake’s length grew by more than two
kilometers, flooding all the roads in that area (Figure 36).
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Work to drain the lake started immediately after the earthquake, considering the serious
implications of a violent outburst of the lake if the dam formed by the avalanches should collapse. The safety works were directed primarily at lowering the water level and to allow safe passage of travelers to the area east of the Cordillera Blanca. A 540 meter long cut was opened and castled walls were built to protect the road, and the Low Llanganuco Lake’s small safety dam was raised. 9.5 LAKE 69
This lake lies at an altitude of 4620 meters above sea level, at the head of the Llanganuco ravine, at the base of the Chacraraju snowcapped mountain, on the western slope of the Cordillera Blanca, to the east of the town of Yungay in the province of the same name in Ancash department.
Studies of this lake demonstrate the hazard it poses to the populations and activities downstream. This danger results mainly from the presence of a hanging glacier tongue that is part of the Chacraraju snowcapped mountain’s cirque glaciers. The tongue is heavily fractured and continuously drops ice into the lake.
Originally, the lake was 60 meters deep and could store 3.1 million cubic meters of water. The activities to be considered in the treatment plan for this lake included:
a) Cleaning the bridle path to the lake. b) Installing a temporary camp.
c) Building a drainage channel 190 meters long by cutting open the pit along the natural drainage channel.
d) Lowering the level of the water surface of the lake by 10 meters from 4620 masl to 4610 masl, and evacuating 965,000 cubic meters of water.
e) Reinforcing the drainage channel by placing stones along 150 meters with a width of 5.80 meters.
(a)
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(b)
Figure 37 a and b. Views of spectacular Lake 69 at the foot of Chacraraju mountain. 9.6 HUALLCACOCHA LAKE
Huallcacocha Lake is located at 4300 meters above sea level on the eastern flank of Chequiaraju
Nevado at the head of the glacial valley called Paccha, located at the foothills of the Tullparaju and Chekiaraju snowcapped mountains. The road from Chacas to Carhuaz runs along this tributary valley leading to the left side of the Ulta gorge (or Buin gorge in Shilla district).. Because of the lake’s position at the top of the gorge, the steep slopes surrounding the lake, and the condition of the glaciers hanging above the lake, it seemed advisable to build more safety works, in addition to those executed in past decades. The new works required completely removing previous constructions from 20 years earlier and lowering the level of the lake surface by 14 meters, and then constructing a reinforced concrete sluice covered by an impermeable earthen dam to contain possible wave surges created by ice masses falling into the lake. Indeed this assumption was confirmed during execution of works of the open pit cut when a glacier mass fell into the lake. Fortunately it was not large enough to create waves that would damage the cut underway.
It is worth mentioning here that the works were contracted out. The operating company had the
excellent idea of opening a very simple road to move essential mechanical equipment and supplies for the construction. After more than three decades, the alterations to the landscape due to the opening of the dirt road have virtually disappeared. This demonstrates that when works in a nature preserve are executed properly, the beauty of the landscape and the environment will not be altered.
The following is an example of a safety measure implemented in the late 1970s and early 1980s.
Figure 38 (a) shows the location of Huallcacocha Lake at the bottom of Tullparaju and Chekiaraju Nevados. Chekiacocha and Auquiscocha lakes are to the west. The size of the lake and finished safety measures are shown in Figures 15 (e) and (f). Figures 38 (a), (b) and (c) show the characteristic steep slopes around Lake Huallcacocha, confirming the need for safety measures.
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(a)
(b) (c)(b(
(b) (c) Figure 38. Location of safety works and characteristics of Huallcacocha Lake.
42
17 (e) 17 (f)
(Left photo is missing and will be added later.) Figure 39. Various views of Huallcacocha Lake and site works.
Figure 40. The left image shows the open canal that will drain the lake. The center image shows the
construction of the sluice that will be covered by the artificial dam. The image on the right shows the built sluice, with two bars to prevent ice from entering the channel and blocking the flow from the lake.
This lake has been treated twice. The first time, the former Control Bureau of Cordillera Blanca
Lakes lowered water levels by 10 meters, then built a stone masonry covered sluice, 1m x 1m square cross section and 102 meters long.
An artificial dam 10 meters high, stabilized by riprap, was built on top of the structure. After the
earthquake of May 31, 1970, the geological, glaciological, and topographic studies were updated. They determined that due to the volume stored, the slope of the inner slope of the lake surface had suffered and that due to settlements within the structure, additional security works were needed.
Given the dangerous conditions of this lake, mainly due to the hanging glaciers, the Studies Division of the Glaciology Unit recommended the implementation of safety works that were carried out in two stages.
The first stage consisted basically of lowering the level of the water surface of the lake by 10 meters by evacuating the water through an open pit on the terminal or front moraine of the lake. In the second phase of the work, a reinforced concrete pipe was built of 1.80 m diameter and 77 m length. Inflow and outflow canals of stone masonry and a fast exit waterway in reinforced concrete, as well as an energy sink, were also built to prevent soil erosion by water exiting at high velocity through the covered conduit.
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Finally, to contain potential surges due to falling ice masses (avalanches) on the lake, a dirt 20
meter platform with a waterproof screen in the center or core of the dam was built. The outside walls were finished by stone masonry sealed with cement mortar.
Figure 41. These four figures show different stages of the work, including open pit excavation and construction of the canal later covered by the safety dam.
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(a)
(b)
Figure 42. (a) and (b) show the start of construction of the safety dam and the finished work. 9.8 LAKE 513
Lake 513 is another example of safety works built at the end of the 1980s and into the 1990s. The lake is named for its proximity to Glacier 513 in the National Glacier Inventory (Figure 43). The lake started forming in the early 1970s. At that time, engineers from the Basic Studies and Glaciology
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Studies divisions of the Glaciology Unit started visiting the site regularly to determine the actions to take in this case.
This lake finished forming in the late 1980s and was subject to several outburst floods due to the
hanging glaciers near its uphill edge. The communities in the valley below were constantly concerned by the damage to households, the riverbed, the access road, agricultural fields, and some infrastructure, as well as the thermal baths in Hualcán in the province of Carhuaz.
Previously the Lake Control Bureau did some work in the early 1950s to partially empty the Cochca and Yanahuanca lakes in the same area.
In the mid-1980s the initial signs of glacier action were noticed when small overflows occurred and the moraine deposited on the rock embankment of this lake was permanently washed away. The material of this moraine was about 6 meters thick but it was gradually removed, finally leaving only naked rock, as can now be seen at the lake site.
These small overflows when the glacier was in contact with the lake raised the concern of the population downstream in Hualcán district and nearby towns of Pariacaca and Obrajes. Even the hot springs of La Merced were affected by these overflows.
Due to the remoteness of the area and the lack of resources to undertake a major project, the temporary and provisional siphoning of water was proposed using plastic pipes 10" and 12" in diameter, to lower the water level by about 6 meters (Figure 46). But as mentioned above, this was an interim mitigation measure, so the drilling of a tunnel to lower the water surface of the lake by 20 meters started in 1992 with financing from the Citizen Protection Agency (Instituto de Defensa Civil).
It was suggested that the tunnel should come into contact with the lake at a depth of 20 meters, using underwater blasting to then place devices inside the tunnel to regulate the outflow. However, during construction this type of connection was discarded. Instead, a sloping shaft was built from which connections would gradually be built at 5, 10, 15m, and 20 meters depth (Figure 47).
In this way it was possible to ensure successful blasting and activate the outflow of Chucchún River water to its mouth on Santa River. A free 20 meter high edge or rock wall was left to contain potential wave surges created by ice masses falling into the lake.
Figure 43. Glacier 513 prior to the formation of Lake 513. The outline shows the approximate location of
the lake.
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Figure 44. Glacier 513 and small lakes being formed in the early 1970s.
These are the precursors to Lake 513.
In the aerial photograph from 1962 shown in Figure 43, the glacier tongue is still visible for Glacier 513, prior to the formation of Lake 513. Lake Cochca, still existing today, is visible to the right. In Figures 44 and 45, the glacier tongue is already in recession, leaving behind small glacial lakes.
Figure 45. The image on the left shows Glacier 513 melting in the 1970s. On the right, Lake 513 is almost completely formed in the late 1980s due to the rapid rate of melting of Glacier 513. Small outburst floods
resulted from glacial movement within the lake.
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Figure 46. The image on the left shows the initial siphoning process to lower the water level of Lake 513. This was an interim measure until the required funding was received for construction of the spillway.
Figure 47. Diagram of the design for Lake 513.
(a) (b) (Photo b will be supplied later.)
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(c) Figure 48. Entrance to the sluice at a depth of 20 meters (66 feet). (a) Downstream end of the sluice, already with a consistent flow. (b) Three connections constructed in response to the glacier calving into the lake on
April 11, 2010. (c) The drainage system effectively prevented an outburst flood.
About 18 years had elapsed since this work was completed, fulfilling its mission to regulate the flow produced by moderate snow avalanches from Hualcán mountain, when in April 2010, an avalanche of considerable magnitude, presumably about 300–400,000 m3, caused a hydrodynamic thrust and a wave higher than 20 meters that in two spates caused an avalanche from Chucchun mountain and destroyed some bridges, crop fields, and some houses located near the river course.
Figure 49, Three views show the origin and pathway of the avalanche.
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The avalanche obviously increased the water level, causing the tunnel to work under pressure of a
large load of water, and the Chucchun River flow rose for approximately 30 hours. International experts confirmed the success of the safety works built into Lake 513, which prevented the larger water flow from damaging the Chucchun river course. However, eventually evidence showed that some risk continued to exist.
These circumstances have led to a proposal to install an early warning system in the Chucchun River watershed as a complement to the work carried out in Lake 513.
This example reveals that the increasing magnitude and frequency of glacier avalanches requires
reviewing the design concepts and principles from previous projects.
9.9 PACCHARRURI LAKE Paccharruri Lake is located on the western slope of the Cordillera Blanca at the base of Nevado
Paccharaju, to the east of the town of Marcara, in Carhuaz province of Ancash department at an altitude of 4445 meters. Access is from the city of Huaraz , two hours by car via Huaraz-Marcara-Quebrada Honda and from there two hours along a hiking trail to the lake. Between 1964 and 1965 the former Control Bureau of the Cordillera Blanca Lakes had built a stone masonry-covered duct and an 8 meter high artificial dirt dam.
When the proposed consolidation of this lake was executed in 1977, and due to the conditions resulting from the 1970 earthquake, i.e. the morphology of the glacier tongue that was still in contact with the lake and had left only a short free edge of the earth dam, it became imperative to build a new structure that would provide the required safety.
Therefore, the work to lower the level of the water surface by 10 meters was planned and executed. A covered sluice 71 meters long and 1.80 meters in diameter was built, over which an 18 meter tall safety dam was built. As in other works of the same type, covered access and exit conduits were built to and from the duct to better direct water flows and prevent erosion of the moraine material and thus safely deliver water to the waterway further downstream (Figures 50 and 51).
Figure 50. Paccharruri Glacier and lake, and sluice to lower water level.
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Figure 51. Completed works in Paccharruri Lake showing safety dam and outflow canal beyond the
covered sluice. 9.10 LLACA LAKE
Llaca Lake is at 4409 meters above sea level at the head of the creek of the same name, northeast of
the city of Huaraz. After the 1970 earthquake, the works there settled and the vent pipe was damaged, raising the urgent need to reassess the safety of the lake and build further protection works in two stages.
The first step was to build preliminary works like in all other lake safety works, i.e. improve dirt roads and camp sites, and then proceed to partially dry out the lake to lower the level of the water surface by 10 meters through an open pit cut. Then, a steel pipe vent of ARMCO type, 48" in diameter, was installed. After the work, the lake’s maximum depth was 19 meters. This first phase was built between 1973 and 1974.
Then from 1976 to 1977 the second stage of the project involved building a 10 meter high earth dam with an impermeable core and castled walls finishing with cement mortar sealed joints.
Figure 52 shows how the lake has been rising due to the accelerated melting of the glacier tongue in contact with the lake, and the safety dam completed in 1977. The prevention dam is still in good operative condition. The completed project is also shown in Figure 52.
51
Figure 52. Evolution of Llaca Lake and finished works circa 1976.
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9.11 PALCACOCHA LAKE
Palcacocha Lake (formerly known as Cojup Lake) has a special meaning from different points of view for both the beginning and for the future treatment of dangerous glacial lakes in the Cordillera Blanca and other mountains of Peru. This special connotation is because of the following reasons:
a) An avalanche in 1941 that destroyed the city of Huaraz and killed many people. b) Construction of security works after the flood of 1941. c) Reconstruction and improvement of the works. d) Small overflow of the lake in March 2003. e) Growth in the volume of the lake by 34 times from 1970 to 2010.
Early in the morning of December 13, 1941, this lake caused the avalanche that destroyed at
least a third of the city of Huaraz, and took the lives of 4,000 people. In the decade of the 1930s, during surveying work in the Cordillera Blanca, Hans Kinzl took pictures of Palcacocha Lake, noting that because of its volume and characteristics, it could cause highly destructive flash flooding. Figure 54 shows Kinzl’s photo of the silted lake, with a very close glacier tongue. Figure 55 shows the lake after the catastrophe. An estimated 10 to 12 million cubic meters of water traveled about 20 miles down the river from Paria Lake to its confluence with Santa River (Figures 56 and 57).
Figure 53. Glacier front and size of Palcacocha Lake.
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Figure 54. Photo by Hans Kinzl (1930s). Figure 55. View of Palcacocha after the avalanche.
Figure 56. Glacier gorge path of Palcacocha avalanche. Figure 57. Huaraz after the flood.
Figure 58. Campsite for beginning of excavation at Palcacocha, 1971.
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The lake in 1974 and 2009
Figure 59. Safety dam under construction and finished works in 1974.
Several factors contributed to the catastrophe, including:
a) The lack of roads from Huaraz to remote Palcacocha Lake. b) The lack of knowledge about glacial phenomena among government officials and the
scientific, technological, and possibly academic communities of Peru. c) Absence of glaciers and glacial lakes monitoring. d) Lack of precautions by the people, possibly due to a temporary absence of such phenomena in
the decades preceding 1940. When the event occurred it caused much confusion. Some people thought it was an air attack and others simply surrendered to the destructive force of the flood.
Palcacocha Lake is designated as 110 in the lakes inventory. It is located northeast of the city of
Huaraz, at the head of the Quebrada Cojup at an altitude of 4567 meters above sea level and discharges its waters into the Paria River ,which after converging with Auqui River forms the Quilcay River that runs through the city of Huaraz, to then flow into the Santa River.
After the catastrophe that devastated Huaraz specifically but also affected Ancash department and the country at large, the Peruvian government created an agency to study mitigation alternatives to the problems caused by glaciers and dangerous glacial lakes.
Subsequently, a system of two 36" ARMCO type steel pipes was installed at the mouth of Palcacocha Lake and an 8 meter high rammed earth dam was built. These works remained operational
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until the May 31, 1970 earthquake destroyed them. Specifically, the earthquake destroyed the foundations of the safety dam and broke the exhaust pipes installed there.
The Lakes Safety and Glaciology Unit, from its beginnings in the early1970s, had planned improvements to the existing works while preserving their original features. The level of the lake’s water was lowered by one meter only, given the characteristics of the lake, especially its volume of only 500,000 m3, and then an ARMCO steel pipe of 1.20 m diameter was installed and a new tightly compacted dirt dam 8 meters in height was built on top (Figures 58 and 59).
Simultaneously the right hand side of the terminal or front lake moraine was strengthened to avoid rapid erosion caused by lake outbursts. In 1974, the above works were completed with their present features.
In March 2003, a first and very serious warning came when the left moraine of the lake slipped and caused a violent diagonal wave that rippled longitudinally to the lake and destroyed or heavily eroded the right portion of the reinforced dam, literally obliterating the reinforcement’s top layer.
The photograph shown in Figure 60 was taken five days after the event. It shows chunks of ice still sitting on the 8 meter dam and water levels still four 4 meters above their normal level. Obviously this new event brought a lot of concern to the community and authorities of the city of Huaraz. In 2003, the regional government of Ancash quickly repaired the damaged structures so they could serve the purpose for which they were designed and built.
Figure 60. The dike after the March 9th, 2003 event.
As in Paron Lake, more work took place in Palcacocha. After the March 2003 event, a
bathymetry of the lake determined a volume of 3.8 million cubic meters, a figure that remained reliable until April 2009, when a more detailed bathymetry found the volume was 17 million cubic meters, which not surprisingly raised many doubts about the bathymetry of 2003.
From this moment on, because of the changing conditions of the hanging glacier on the lake and the steep slopes of the lake’s interior walls, additional and urgent safety works were advised,, specifically because the lake’s volume which had increased from half a million cubic meters in 1974 to 17 million, while the population of the city of Huaraz now at risk had increased from some 25 thousand people in 1941 to 160,000 at the time of the study.
Following the methodology proposed and implemented in many other dangerous glacial lakes, the Glaciology and Water Resources unit (the new name for Glaciology and Security Gaps, changed in 1989) given the present importance of study, evaluation, and treatment of water resources) prepared a project to lower the water level of Palcacocha Lake by 15 meters given the lake’s new characteristics, shown in Table 4:
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Table 4. Palcacocha Lake characteristics.
Total Volume at 4562.44 17,325,206.57 m3 Drained volume (-15m) 6,580,182.23 m3 Dead volume at 4547.44 10,745,024.34 m3 Length of open pit canal 676.37 m. Total earth movement 158,322.46 m3
The cost of these works was estimated at US$4 million, but officials at the regional government
of Ancash felt that they could not authorize that cost so quickly and looked for an interim and cheaper way to decrease the risk. They planned to siphon off the water using six 10" diameter pipes about 700 meters long and evacuate about 7 million cubic meters of water. Unfortunately the National Water Authority (ANA), had decided to suspend the Glaciology and Water Resources Unit’s role of conducting the evaluation, study, and safety assessments of dangerous lakes in Peru’s snowcapped mountain ranges. The water agency decided that the detailed study, design, and construction of works in dangerous lakes should be carried out by the regional government of Ancash. As a result, nobody in particular takes responsibility.
About two years after the need to carry out the safety works was identified and after many bureaucratic snarls, the water was finally siphoned off, though at a slower rate than planned due to design defects. (As of July 4, the level of the water surface had dropped only 2.7 meters) (Figures 61 and 62).
Figure 61. Siphoning pipes. Figure 62. Operation with only one pipe.
It is important to mention that once the water level is lowered, work should start immediately to
cut a drainage ditch about 15 feet deep, build the concrete covered pipe and restore the safety levee to at least 15 meters high. Moreover, now that glaciers are not as stable as previously, an early warning system is also needed to prevent eventual incidents.
More needs to be done to secure Palcacocha Lake against possible glacier mass landslides. Results from the siphoning process are not yet known, nor what the final project will look like, what alternatives are available to face an unforeseen situation, or how a true early warning system would operate. (Despite the very high risk involved, at present a radio is the only contact with the regional government.)
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9.12 CUCHILLACOCHA LAKE
Cuchillacocha lies to the east of the city of Huaraz at an altitude of 4500 m, at the foot of the
Pucaranra Nevado. It is also known as Bayococha and registered under number 115. In 1942 a cut in its terminal moraine lowered the level of water by 14 meters, leaving an open canal (Figure 63 (a)).
In 1956 the Lake Control Bureau installed a 106 cm diameter pipe over which a 4 foot high rammed earth dam was built. In 1971, after the earthquake that devastated this region, the Santa River Corporation decided to prepare the studies and project to consolidate the lake, which at that time spanned over 170,437 m2, and had a volume of 3,014,000 m3 and a depth of 33 meters.
(a) (b)
(Left photo is missing and will be added later.) Figure 63. Cuchillacocha Lake and works.
When the lake’s stability was evaluated, as in other cases, the glacial hanging front with an
estimated thickness of 50 meters was thought to be a hazard as it could trigger a large avalanche on the lake. Given the low dam (4 m) it seemed advisable to build additional safety works on the lake.
It was decided to lower the level of the water surface of the lake by 10 meters, evacuate about 1.6 million cubic meters of water, build a covered conduit, and erect a 16 meter earth dam over it to contain possible glacier avalanches and consequent potential wave surges(Figure 63 (b)).
Additionally, in and outflow canals were built for the covered duct and ancillary works such as bridle roads and camps for field workers were also built.
9.13 TULLPARRAJU LAKE
Located east of the city of Huaraz, at 4100 meters, and at the foot of the Tullparaju Nevado, this
lake was mitigated in 1942 to lower its water level by 18 meters. In 1950 the lake was 700 meters long by 250 meters wide, 18 meters deep, and had a volume of 1.6 million cubic meters. This lake showed
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favorable features like small landslides of ice on gentle surfaces and clayish natural levee resistant to erosion. Unfavorable features were the steep lateral moraines with slopes greater than 45 degrees likely to produce landslides, and numerous leaks along the tunnel.
For these reasons it was considered necessary to strengthen the drainage tunnel with reinforced concrete structures, and build an additional 10 meter high earthen dam to counteract possible glacier wave surges caused by avalanches or landslides over the lagoon (Figure 64).
Figure 64. Entry and exit of the vent tunnel at Tullparaju Lake. 9.14 SHALLAP LAKE
Located at the head of the creek by the same name, about 20 km directly east of the city of
Huaraz at a height of 4200 meters and west of San Juan Nevado, Shallap Lake’s water level was lowered eight meters in 1948. In 1951 two ARMCO type, 42" pipes were placed for the exhaust of the lagoon; in 1952 a 4 meter earth dam was added.
After the 1970 earthquake more detailed studies of the lake determined it was 720 meters long, 320 meters wide, and could hold 4.7 million cubic meters. The natural dam consists of two rather high lateral moraines and a lower front or terminal moraine where the 4 meter high dam was built (Figures 65 and 66).
The volume of the lake, the small diameter of the pipes that could become easily clogged, and the low height of the safety dam were deemed a threat to the stability of the dam when combined with the conditions of the adjacent San Juan Glacier, which is almost in direct contact with the lake.
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For these reasons it was recommended to lower the level of the water surface of the lake by 10
meters, and build an 80 meter long covered passage. As in other cases, the artificial dam should have a waterproof core and castled covered walls.
Figure 65. Changes in the glacier front at San Juan mountain near Shallap Lake.
Figure 66. Progress of works at Shallap Lake.
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Figure 67 show the facilities built by Cañón del Pato Hydropower Plant to create a lake they used as a regulation reservoir. However, the project did not take into account the need to manage the risks created by the glacier over the lake. In the end, officials decided to leave the safety works as had been initially conceived and did not use the lake as a regulating reservoir.
Figure 67. Safety works and discarded changes to turn Shallap into a flow regulation impoundment.
Figure 68. Panoramic view of Shallap Lake and completed works.
9.15 ALLICOCHA LAKE Allicocha is located on the eastern flank of the Cordillera Blanca in Chacas District of the
province of Asunción in the department of Ancash, at an altitude of 4500 m. Its original volume was 13.8 million cubic meters and its depth, 53 meters.
61
In 1966 the Cordillera Blanca Lake Control Bureau ordered building safety work in this lake because of the volume stored, a moraine dam with steep slopes to the lake, and a glacier tongue directly in contact with the lake. Therefore it was determined that there was a high probability of flooding of the lake due mainly to the occurrence of ice avalanches that produce dangerous waves and cause the regressive erosion of the moraine dam (Figure 69).
Fig. 69 Allicocha Lake and the town of Chacas.
The work consisted of lowering the level of the water surface by 20 meters, construction of a 53
meters long covered passage and inflow and outflow conduits, and raising the dam up to its original height of 18 meters. The dam has an impervious core and both upstream and downstream castled walls with cement sealed joints. 9.16 LAZO HUNTAY LAKE, HUAYTAPALLANA MOUNTAIN RANGE, JUNIN
Cordillera Huaytapallana is in the department of Junín in the central Andes of Peru. It is
comprised of a small set of glaciers that are rapidly retreating. Two alluvial events took place in recent decades, one in Huntay Lazo Lake in 1969, and the other in Chuspicocha Lake, in December 1989.
In the first case, the violent overflow of Huntay Lazo Lake resulted from the fall of a mass of hanging glacier on the lake that produced a hydrodynamic thrust and destroyed the stone masonry and concrete dam. This led to a large outflow of water that destroyed everything along the lake’s shores.
Figures 70 and 71 show the location of Huntay Lazo Lake and the Huaytapallana Mountain glaciers hanging over it.
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Figure 70. Location of Lazo Huntay and Chuspicocha lakes in the Huaytapallana mountain range.
Figure 71. Huaytapallana mountain range glaciers hanging over Lazo Huntay Lake in 1977.
Figure 72. Masonry dam destroyed in 1969 by Lazo Huntay Lake overflow.
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A factor that triggered the landslide was the earthquake that took place in the vicinity of Mount Huaytapallana, where an active fault line is present. After 1977 safety works were executed to partially dewater the lake. Then in early 1990 work was completed that lowered the water level and built an exhaust duct on which a dam was rebuilt, as shown in Figure 73.
Figure 73. Safety dam in Lazo Huantay Lake after partial dewatering and building of the concrete sluice to
prevent the water level from rising.
The people and authorities of Huancayo had repeatedly objected to this work because the Shullcas River basin, where Hyatapallana mountain drains its waters, suffer from continued water shortages. This strongly negative water balance is obviously a source of much discontent.
A safety versus water supply controversy has ensued. This debate should be taken into account in future projects for disaster risk management in mountain glacier areas. Given the consequences of climate change on hydrological regimes, water management issues necessarily must be taken into account when managing disaster risk.
The importance of water resources is so great that people will focus on this concern rather than discuss disaster risk management issues. This is of course understandable given the importance of water resources for life, the environment, and the people’s own development.
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9.17 CHUSPICOCHA LAKE, HUAYTAPALLANA MOUNTAIN RANGE, JUNIN In December 1989, a rock mass that fell on Chuspicocha Lake that caused the Shullcas River to
flood the city of Huancayo and caused considerable damage along the river banks and to several bridges crossing the river.
Figure 74 shows Chuspicocha Lake after the GLOF event and the safety works, which in this case amounted merely to the partial drain of the lake and the construction of a lined canal to prevent erosion of the lake’s moraine dam.
Figure 74. Chuspicocha Lake after completion of the safety works. The rock mass fell from the red circled
area.
9.18 RITICOCHA LAKE, A RECENT 2010 CASE
The site under study is at the foot of Mount Riticocha Chicon, in the Upper Rio Chicon River.
Its area of influence comprises the district and province of Urubamba, in Cusco department. Its geographical coordinates are 13° 12' 50.1" South and 72º 04' 24.9" West. It is located at 4756 meters of altitude and local communities in the catchment area include San Isidro de Chicon, Yanaconas Chichubamba in the Chicon River basin, and the city of Urubamba (Figure 75).
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The town of Urubamba is located 78 kilometers from Cusco via Pisaq, Calca, and 57 kilometers
away along the Poroy, Cachimayo, and the Chinchero road. The community of San Isidro de Chicón can be reached by a dirt road starting in Urubamba, and then continuing on foot from this point to the foot of Nevado Chicon, in approximately five hours.
Figure 75. Study and influence areas.
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Figure 76. Sector of Urubamba city damaged on October 17, 2010, at the mouth of Chicon ravine. The
waterway of the Tullumayo (or Chicon) river narrows at this point, adding to the danger.
Urubamba is located in a fertile valley with a very mild climate. Corn, potatoes, and fruit are grown. Humidity is 42%, the average temperature is 18 °C, and average northward winds reach 14 km/h. It is also known as the "Sacred Valley," the "Pearl of the Vilcanota," and the "Archaeological Capital of Peru" because of its many archaeological sites. In the upper Chicon basin the glaciers make the weather cold and windy.
The valley is located at 2,871 meters above sea level, on an alluvial fan of moderate to light slopes and alluvial terraces on both banks of the Vilcanota River. Chicon is a long, narrow valley of sloping flanks bordered by very steep to moderate slopes. In its upper reaches the topography is steep and abrupt with scattered lakes at different levels. Chicon at 5,530 meters of altitude is the main snowcapped mountain in the upper reaches of the Chicon River basin of the Urubamba Mountain Range.
Urubamba Valley soils are alluvial and originate in cyclical floods. The soils at the floor of the Chicón Valley are alluvial and colluvial-alluvial while the hillsides are fluvial-colluvial to alluvial, comprised in the lithological units of the Cretaceous to the Tertiary periods (Mitu Group, Huancané Formation, and plutonic rocks), which emerge mostly in the upper basin.
The distance between the area where the glacial lakes are located to the nearest rural town is approximately 8 km. The approximate distance from the glacial lakes to Urubamba Valley is 11 km. All distances above are as the crow flies. Naturally, bridle trails are longer. A light vehicle ride from Urubamba to San Isidro, the last town, takes about 20 minutes. Another 5.5 to 6 hours are needed to reach the study area at a reasonable speed given the poor condition of the road. According to National Statistics figures, in 2007 the local population reached 56,685. Altitudes: Urubamba Valley is located at 2,871 masl. Chicon valley is located between 3,950 and 3,500 masl. Chicon Mountain rises from 4,800 masl at the foot and 5,530 masl at the summit. The lakes are between 4,600 masl and 4,800 masl.
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Populations at risk: San Isidro de Chicón: rural, 300 Yanaconas: rural, 150 Chichubamba: rural, 450 Urubamba: urban, 18,000
According to the inventory that was published in 1989 by Hidrandina SA, the Urubamba Cordillera spanned an area of 41.5 km2, with 90 glaciers classified according to the regulations of the World Glacier Inventory. However, the rapid retreat of glaciers both in our country and globally since the early 1970s and currently exacerbated by global warming the glacier area of the Cordillera Urubamba may have shrunk the glaciers by least 30%, leaving a present area of approximately 29 km2.
Glacier retreat has two main implications or consequences. One is the dwindling of water reserves represented by mountain ice; the other implication from the point of view of disaster risk management is the formation of new ponds whose stability depends heavily on the glaciers located in the surrounding areas.
Generally glaciers collapse over lakes, producing waves and sometimes floods. Because of temperature differentials, lake waters cavitate and pierce the base of the glaciers and erode their foundations, leading to their collapse over the lake’s waters, as described above.After this process, glaciers continue to retreat (melt) and end up hanging over occasionally very steep rocky slopes or embankments, increasing the likelihood of avalanches (landslides) over the lakes. These avalanches transform potential energy into kinetic energy that create a hydrodynamic thrust on the waters and then cause even more violent overflows.
The morphology of the study area shows that in the upper basin of Chicon River alluvial phenomena have occurred previously. Possibly the flood that devastated Urubamba in 1942 originated in an avalanche from a glacier hanging over a lake and which caused its rupture and the ensuing flood. Clear traces of this phenomenon can be found at the end of the Occoruruyoc plain where presumably there was a glacial cirque (an amphitheater-shaped bedrock feature at the head of a glacial valley) where the terminal moraine shows traces of a rupture and possibly a violent outburst.
Figure 77 schematically shows a longitudinal profile of the location of glaciers, the lakes on gentle slopes, the large difference in level and almost vertical slopes before the Occoruruyoc plain where flows gather speed and becomes a strong erosive force, with the plain receiving all the transported material. Flow speed falls and finally arrives at Chicon Creek and, after passing through the rural villages, the flow reached the town of Urubamba with the consequences shown in the following figures.
Figure 77. Glaciers, glacial lakes, Occoruruyoc plain, Chichon gorge, and Urubamba city.
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Figure 78. Turbulent waters flowing down a street in Urubamba at the mouth of Chicon Gorge.
Figure 79. Damaged house in rural Chicon Gorge.
Figure 80. Chicon River flowing down a street on October 17, 2010.
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Within the town of Urubamba there has always been some concern about the glaciological activity specifically related to Nevado Chicon. In the 1980s the author was invited to visit this area, and found no reason to execute safety or prevention jobs. Unfortunately, old habits die hard and despite past catastrophic events people have rebuilt in areas that may become alluvial channels. Mark Carey clearly described this behavior in his book, In the Shadow of Melting Glaciers (Carey, 2010), where he explains how people show concern at the time of the event but rapidly forget the consequences of these disasters. This is especially evident in the Callejón de Huaylas at the foot of the Cordillera Blanca (which contains the largest glacier mass in Peru).
To explain how an avalanche occurs we must start by mentioning that glacier melt water flowing between the ice and the rock base acts as a lubricant, which enhances the possibility of the glacier sliding (decreasing its adherence). Higher ambient temperatures also weaken the adherence of glaciers to the base rock.
Increasingly frequent glacier and snow slides (avalanches) in the Cordillera Blanca have caused serious damage, as in Santa Cruz (Caraz), and fatalities, as in Punta Olimpica, along the road from Chacas to Carhuaz in recent months, in addition to avalanches in the Huascaran, Huandoy, and other mountains. Most alluvial processes have been a combination of slippage and fall of ice masses on lakes located at the foot of the mountains. However, an exceptional event occurred on Huascaran Mountain in 1970 when only a mixture of ice, rock, detritus, soil, sand, and other materials produced a major flood of an estimated volume of between 50 and 100 million cubic meters.
The difference in altitude between the summit of Huascaran Mountain and the city of Yungay is 4,500 meters. This altitude differential created the great potential and kinetic energy carried by the destructive mass. The event that occurred in Riticocha Lake belongs to the first type, because the glacier is still in contact with the emerging lake. Only destabilized masses fall into the lake. Once the glacier further separates from the lake and starts to retreat up the bedrock, then the conditions will obviously be more difficult, exacerbating the risk to the valleys downhill.
Our visit to the area and this document, with its conclusions, recommendations, and mitigation alternatives are aimed at preventing an increased danger or threat. We must act immediately to reduce the risk to the greater possible extent so people can live and work safely. Moreover, while the required works are prepared and financing for the early warning system is obtained, it is vital to preserve the life of the people.
Figure 81 shows the changes in the glaciers in the Nevado Chicon area. Despite the cloud cover, these images from Google Earth and NASA are a good visual tool to gain a better knowledge of the Upper Chicon River glaciers and lakes area.
1969 2005
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2007 Zoom-in view. 2007
Figure 81. Changes of the Chicon Glacier.
Near midnight on October 17, 2010, an extraordinary flash flood caused by the Chicon River created panic in the city of Urubamba and the towns upstream. The flash flood was the result of an overflow of a new pond that appeared at the foot of the Chicon Glacier tongues.
Figure 82 shows the area where the phenomenon occurred. The Google Earth and NASA satellite image is a contribution of the Department of Geography, at the University of Zurich, in Switzerland. This phenomenon likely occurred at least half an hour before the flood reached the town of Urubamba, given the clearly glacial features or triggers of the event.
Figure 82. Location of Riticocha Lake and the Chicon River’s downstream path.
A new lake that has formed at the foot of Nevado Chicon was suddenly filled by a falling glacier
mass that pushed or propelled the lake’s water downstream where it reached smaller Pucacocha (“red water” in the Quechua language) Lake, so called because of the color of the surrounding clay sediments.
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The original mass of water may have caused the second lake to be partially drained, as shown in the photos (Figures 83 and 84) and videos taken at that time.
Figures 83 and 84 were captured by Urubamba staff from a video recording made a few days after the event. These photos show detached pieces of ice floating on the "frozen pond," as the videographers called it. It should be noted that when a glacier mass falls, fragments are transported by water and left on the surface. That explains the presence of chunks of ice next to the rocky walls of the glacier front immediately after the occurrence of the phenomenon. All this material melts in just a few days after the event.
Figure 83. Glacier ice fragments floating on the lake and across the rock wall that acted as a
containment wall or natural dam.
Figure 84. View of the rock wall across the glacier and ice fragments after the avalanche and waves that
deposited these fragments. This photograph was taken at the time of the event.
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Presumably, the volume of the lake overflow was larger than the present lake volume, to create such mass destruction and the transport of a significant amount of solid material, as shown in Figure 85.
This assumption is based on the following reasons:
• The magnitude and size of rock material, debris, and boulders transported to the town of Urubamba.
• Despite the damping or dissipation of kinetic energy that occurred in the Pampa Occoruruyoc, the flow into Chicon Creek was substantial, as shown by the level reached by the flood, as shown in Figures 86 and 87.
• It is assumed that the back portion of the lake was dammed up by the glacier itself and then the existing canal opened. This is how the lake’s waters drain. This opening was probably made by the same hydrostatic pressure created when the water level rose.
• The large number and size of the chunks of ice that were deposited in front of the glacier’s rocky walls could only have been caused by the same waves stemming from the glacier avalanche. This is clearly seen in Figure 85.
Also worth mentioning is that at the time of the event, two aggravating elements led the water to
overflow the Chicon River channel or riverbed. First, construction of a road through the area had loosened the earth, and secondly it seems that due to those works the Chicon riverbed was full of weeds and broken tree trunks.
Figure 85. Material carried by the extraordinary flow of Chicon River.
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Figure 86. Material carried and flooding of local homes.
Figure 87. Level reached by flood in local dwellings.
The present (April, 2012) condition of the glacier and the lake at the foot of the glacier should be
considered. A comparison of the photos taken at the time of our visit on April 23, 2012, and those taken in October 2010, and accounts by the Urubamba Fire Company Chief reveal significant changes in the structure of the glacier, basically a significant retreat over the two year period. The most striking changes have occurred in the drainage canal or vent in close proximity to the glacier, to a side of the lake.
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When the October 2010 event occurred, this depression in the ground did not exist. In fact it was opened by the hydrostatic pressure exerted by the lake when its level rose as a consequence of the glacier falling in it.
The most important and worrying feature within the structure of the glacier is that it has formed an arch over the lake as a result of the cavitation or erosion by the lake itself on the ice due to the temperature gradient. Probably this "bridge" may break suddenly due to the effect of the force of gravity and collapse into the lake, presumably creating again a temporary dam though which the water will eventually pour into the Chicon River with predictable impacts.
The lake’s volume is estimated at around 80,000 m3. We estimated a maximum length between 150 and 200 m, a width greater than 100 m and a depth of 10 m. Our estimates are based on measurements by municipal inspectors from Urubamba.
The above is a coarse estimate that must be corrected with sound bathymetry, which will be executed shortly. It suggests the volume of the overflow from the lake must have been very significant to account for the large volume of solids that were transported, as shown in Figures 85, 86, and 87.
Figure 88. October 2010. Figure 89. April 23, 2012.
Figure 90. View of the glacier arc formed over the lake and which may collapse at any time. The yellow arrows show the arc and the direction in which the glacier may collapse. The red arrows in both views show
the direction the lake drains at present.
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Figure 91. Lake drainage canal. Arrow point to the surface of the lake.
Figures 88 and 89 show the changes in the glacier due to accelerated melting under current conditions. As a result of this phenomenon, the fracturing of the terminal part of the glacier has become a normal condition in almost all glaciers.
Image processing techniques and GIS software could be useful to help determine the slope of the glacier to evaluate the possibility of future avalanches when the glacier moves away from the lake and avalanches begin to travel down the bedrock’s slope. After the field visit and taking into account that:
a) The material of the Riticocha Lake basin is very strong intrusive rock, ensuring the lake will not likely break and burst out suddenly, and
b) The volume of the lake, around 80 to 100 thousand cubic meters, is kept under control, we considered the risk of ice avalanches on the lake to be very high and events can happen at any time. Therefore those authorities responsible for managing the risk of local and regional disasters should consider introducing mitigation to avoid or prevent panic and anxiety, as occurred October 2010.
The variables involved in the determination or quantification of danger or threat are:
a) The glacier mass, its volume, its structure, and its slope with respect to the lagoon. b) The characteristics of Riticocha Lake, in particular its volume, which naturally is very
important. c) The characteristics of the lake’s basin, including its geology, structure, and geometry. d) The characteristics of the channel downstream of the lake, i.e. its slope and its length to the
town of Urubamba.
Figures 92 and 93 compare the head of the Pampa Occoruruyoc after the October 2010 event to its condition in April, 2012. Note that vegetation has invaded the area covered by the flow.
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Figure 92. October 2010. Figure 93. April 2012.
Similarly Figures 94 and 95 show plant regrowth at the bottom of the Pampa Occoruruyoc close to what was the mouth of a glacial lake long ago. Moraines are obvious and their rupture caused the emptying of the ancient lake.
Figure 94. October, 2010. Figure 95. April 2012. (Missing photo will be added later.)
The glaciers of the Cordillera Urubamba show the same dynamics and variations as other glaciers that are in the 19 snowcapped mountain ranges of Peru. This activity is reflected in the rapid retreat of glacier fronts that reduced their mass and therefore affect very valuable reserves of water. Meanwhile this glacial retreat also creates new lakes that can overflow for these main reasons: due to cavitation the water causes in the adjacent glacier, triggering the collapse of large ice blocks that in turn "push" the water of the lakes and create extraordinary flows of water that can result in highly destructive floods and even producing catastrophes as in Urubamba in 1942 and in Huaraz in 1941.
The event from October 2010 at Riticocha Lake, in Urubamba Mountain Range at the foot of the Chicon Nevado, was the result of a typical phenomenon that is occurring in all snowcapped mountain ranges.
At present the volume of Riticocha Lake fluctuates possibly between 80 and 100 thousand cubic meters. However, at the time of the October 2010 event the volume was larger, given the impact it created and as shown graphically. Because of conditions observed in the glacier, this event may repeat. The conditions for such recurrence are building again in the glacier area and the lake. The glacier is becoming gradually less stable and eventually will fall again into the lake. To understand the magnitude of the outpour we urgently need to know the volume of the lake, something that can only be determined through a fairly accurate bathymetric survey with both longitudinal and transverse sectioning. At the
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same time it is our duty to recommend that the staff conducting the bathymetry must take the necessary safety precautions, given the critical conditions in the glacier.
The terminal portion of the glacier or glacier tongue in contact with the lake can collapse at any time so the early warning system covering the town of Urubamba and human settlements located along the river should be permanently active while the engineering designs to reduce the risk that the lake poses are carried out, and also while seeking funding for the execution of the works.
After the glacier front has collapsed and melted, the glacier tongue as it retreats will become a hanging glacier, thereby exponentially increasing the risk if precautions are not taken now.
The variables to be considered in risk mitigation or prevention are the volume of the lake, the condition of the glacier, the characteristics of the lake’s basin, the characteristics of the lake’s natural dam, which include obviously its geology, morphology, and the free edge of the glacier slope, the location and characteristics of the drainage channel, and present drainage or venting. Other important variables are the channel’s slope downstream of the lake, the distance to towns or production areas, and downstream valley slopes, especially those made of unconsolidated or loose material. Within these variables the one factor that has been managed to address major problems of this type has been the modifying of volume of the lakes to reduce the flow of potential violent outbursts.
The theory of disaster risk management requires giving consideration to hazard identification, vulnerability analysis, and risk assessment. In this case the threat is created by nature as an external factor. However, the vulnerability is the internal risk factor as set by humans, i.e. the population including their authorities and leaders. Therefore the quantification of risk will depend on how much vulnerability can be mitigated and whether the population in rural areas in Urubamba and along the Chicon River can be organized and trained to understand the hazards through education in the schools and other institutions.
The new lakes forming at the foot of the glaciers of the Cordillera Urubamba and the glaciers themselves should be monitored on an ongoing and continuous basis. For this reason a recommendation was made to set up a Glaciology Unit in Cusco. For permanent monitoring good roads are needed that are also clearly marked for safer and faster access. The bridle path (which in some places is not easily seen by the naked eye) to Riticocha Lake is in very poor condition and will need to be repaired and rebuilt in its entirety, with appropriate signs to allow field visits at any time. Similarly, cheaper and safer bridges are needed to cross rivers and streams, to ensure the safety of the personnel involved in monitoring or technical activities. In areas where the slope of the bridle path is very steep, weatherproof ropes must be provided to help people travel.
The construction of a safe bridle path should be the first emergency mitigation effort for the lake, as walking inspection tours are the only way to get an accurate idea of high mountain conditions.
a) Prioritize the following mitigation measures for Riticocha Lake: 1) Establish adequate access to the lake. 2) Investigate in some detail the characteristics of the lake’s basin, including its
dimensions, area, and volume at different depths. 3) Based on the data, reduce the lake’s volume by lowering the level of water by 6 meters
and then proceed to further lower the water level according to the characteristics of the drainage channel.
4) Build a drainage channel to prevent the water level from rising again. 5) For prevention and to reduce the risk even more thoroughly, analyze the technical and
economic possibility of building additional works in the outlet mouth of the Occoruruyoc basin, which was possibly a lake that overflowed in times past.
6) Maintain the early warning system, improving its functionality and reliability.
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b) Build a proper bridle path from San Isidro town to Riticocha Lake, including safe pedestrian bridges and drains in areas of high humidity.
c) To carry out engineering designs leading to the implementation of alternative mitigation or
prevention measures, urgently investigate the volume of the lake. This can only be determined through an accurate and detailed bathymetric survey for both longitudinal and cross sections. The staff conducting the bathymetry should take the necessary precautions to safeguard their lives, given the critical contact between the glacier and the lake. Along with this, it is necessary to conduct a detailed bathymetric survey including meter by meter contour lines of the lake basin from the surface level of water to the summit of the rocky lake basin so various levels can be compared.
d) Similarly, create a longitudinal profile of the bed of the drainage channel bed for a distance of at least 500 meters downstream from the lake.
e) Gauge incoming flows to the lake from melting and outflows to determine the design and volume of siphoning.
f) With respect to mitigation or prevention measures, adopt the same procedures as in other dangerous lakes around the country, i.e decrease the volume of the lake or drain. Since the depth of the lake is about 10 to 11 meters, it is advisable to study the possibility of completely emptying the lake, provided technical and economic conditions are met and excessively costly options are avoided.
As explained above, the purpose of this study is to prevent a new alluvial process in the Chicon
River subbasin and thus protect the population and productive activities downstream, including farming and tourism that are so important in this area of the country.
We analyzed several possibilities to regulate the extraordinary flow that could be ejected from the lake by glacier activity, both in the upper rocky valley in the vicinity of Riticocha, around other neighboring lakes, and in the low sections, especially in Pampa de Occoruruyoc. But these may be costly solutions that may be only partially effective for safety purposes.
a) For this reason it is suggested that the solution to be adopted for Riticocha is to drain the lake and so eliminate the manageable risk variable.
b) The purpose is not only to drain the lake but also to ensure it will not be replenished with water from the melting glacier.
c) To permanently drain the lake a canal in the bottom of the lake must be built. This involves digging very strong rock as shown in the pictures, and using explosives, which also may further destabilize nearby and fractured glaciers.
d) For this reason it is proposed to execute the task by reverse siphoning using light drain pipes. To this effect the following factors must be taken into account: outflow of the lake and longitudinal profile of the channel to determine pipe lengths.
e) After siphoning, the final drainage channel must be built through careful excavation. The dimension of the channel must be calculated for proper flow evacuation while ensuring that the lake water does not rise again.
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10. DISCUSSION AND CONCLUSIONS Disaster risk management needs to go alongside development planning to ensure that efforts are
sustainable in the long run. It is within this context that we must develop our initial technologies for glacial lake management.
Disaster risk management for glacial lakes must go hand in hand with water management. Water
resources are seriously impacted by global warming and climate change. Contrary to what happened four decades ago, when the only concern was the safety of areas adjacent to glaciers and dangerous lakes, now special interest must be paid also to preserving water resources.
Nationwide, watersheds with glaciers in their headwaters have been subject to natural disasters, as
in the Cordillera Blanca over many centuries, in the Cordillera Huaytapallana in 1969 and 1989, and in the Cordillera Urubamba in 1941. In each of these cases the result has been widespread destruction, death, and desolation, often paralyzing the development of each area. These events began to occur when the glaciers began their retreat approximately 11,000 years ago, at the end of the last glacial period.
The subsoil in all glacial watersheds shows clear evidence of this through the presence of large
moraines, such as those seen in the Rio Santa watershed and in the residues of flood events where communities have developed. There are no written or anecdotal records of floods prior to the 18th century, although the author considers their occurrence likely during the medieval warming period (from 800 and 1200 A.D.), as many communities in the foothills show clear evidence of fluvial material in their subsoils. Caraz is a clear example, as the subsoil in this area contains large rocks and boulders, helping to explain the effect of the 1970 earthquake on the community.
Outburst floods can still occur today although their impacts are expected to be weaker, given that
the magnitude of the avalanches and calving into glacial lakes is smaller due to reduced volumes of glacial ice. Warming temperatures, however, lead to higher frequencies of these events and therefore increase the overall risk of natural disasters. Rates of glacier retreat have increased since the mid-1970s. The growing number of hanging glaciers on steep slopes is evident, increasing the risk of avalanches and GLOFs.
Global warming is also causing permanent changes in glacial structures, resulting in settlement,
landslides, and avalanches, depending on the characteristics of the bedrock. Many such events have been registered over the last three centuries, although geomorphological
evidence and subsoil structures in many watersheds indicate that some occurred even before this period. Unfortunately, these earlier events have been forgotten and communities have rebuilt in almost the exact same locations, mostly due to socioeconomic conditions that have made relocation to a safer area difficult.
It was in response to the devastating outburst flood in Huaraz in December 1941, that government
action attempted to mitigate, reduce, and prevent the consequences and negative impacts of floods. Glaciological research commenced at the same time, with mass balance studies showing a permanent loss in glacial mass. Terminus measurements for many representative glaciers found an increasing rate of retreat. Unfortunately, over the past decades resource cuts have greatly reduced the Glaciology Unit’s ability to conduct research and implement safety measures. Glaciological studies and inventories since the 1970s indicate that there have been negative mass balances and permanent losses in glacial mass continue. Furthermore, rates of retreat have increased considerably over the last four decades, coinciding with other climate phenomena such as the Pacific Decadal Oscillation (PDO).
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In response to the many natural disasters in Peru, Peruvian technical staffs have developed a methodology to mitigate and prevent these events. The methodology can be summarized in the following steps:
• Preliminary studies of the general characteristics of glacial lakes (topography, basic geology,
basic glaciology, profile analysis in case where glacier masses are in contact with or inside the moraines).
• Basic studies to determine risk factors associated with each lake (detailed topography and bathymetry, detailed geology, and moraine geotechnology).
• Define the trigger that can produce an avalanche in each particular case. In some cases it can be an avalanche of glacier mass (e.g. Lagoon 513), in other cases a shift of one of the walls of the moraines (e.g. Palcacocha Safuna, 2002-2003), or the fall of a rock mass into the lake (e.g. Chuspicocha in Junin). Also to be considered as a trigger is a possible tubificación phenomenon.
• Logistics are an important consideration in the planning of safety work in dangerous lakes. The distance that tools, materials for construction, food, and other materials must travel is an important element in cost analysis and time planning.
• More detailed studies to determine the basic parameters for the implementation of safety measures.
• Design of the safety measures with detailed implementation procedures. • Implementation of the safety measures in compliance with sound engineering standards and
parameters. • Given the current conditions created by increasing global warming, it is very important today to
take the necessary preventive measures during the execution of the works since avalanches have been occurring more frequently. The occurrence of one of these phenomena during the execution of the works would be very serious so it is recommended that early warning systems be installed in the basins and towns that are under the influence of a lake where work is underway.
• Examine the possibility of combining safety projects with water development projects for lakes, within the constraints posed by these cases.
• Several decades of efforts have demonstrated the effectiveness of safety works to prevent catastrophic events.
Literature Cited Ames and Francou Carey, Mark. 2010. In the Shadow of Melting Glaciers: Climate Change and Andean Society. 2010. NY:
Oxford University Press Coyne et Bellier from Paris to the general manager of the Peruvian Santa Corporation, November 28, 1966 GSA Bulletin, March/April 2004 Huascarán 1970 Institute of Geography of the University of Zurich Kinzl 1932 and 1941 Report of the Glaciology and Lake Control Office of the Corporation Peruana del Santa, 1972 Reynolds Geo Sciences Ltd., 2003