mass wasting events

Natural disasters in the Cordillera Blanca, Peru

Why human sacrificies in mountains?

• Archaeological sites and mummies have been found in the Andes at altitudes up to 6,700m

• Incas constructed the sites in the 15th century to appease the mountain gods

The town of Huaraz flattened

Natural disasters in the Cordillera Blanca, Peru

• Major tectonic faults that are active• Marked glacierization• Geologically young, steep mountains• Pro-glacial lakes• Immediate vicinity of human settlements

ALPAMAYO

HU

AN

DO

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ARTESONRAJU

Mt HUASCARAN, PERU

1962 HUASCARAN AVY

• Large snow year• 50 degree F increase in temp over a few

minutes• Caused avalanche• 4,000 fatalities• Yungay protected by ridge

1970 Avalanche

• Triggered by 7.7 magnitude earthquake• Rock face failure• Incorporated 30 meters of snow and ice!• Moraines confined flow initially• Accelerated over a distance of 2.4 km• Became airborne at change of slope

Church before 1970 avalanche. Note palm trees in foreground.

Many years after the avalanche. Note palm trees survived.

Yungay is now completely abandoned. Cemetery has a monument to the dead.

Guiness book of records as the most deaths ever from an avalanche

1970 HUASCARAN AVY

• Trigger was a large earthquake; 7.7• Caused avalanche with rock slide• 20,000 fatalities• Yungay destroyed

1941 Huaraz Disaster

• Moraine damming the proglacial Lake Palca (cocha = lake: Palcacocha) broke

• Resulting flood killed 6,000 people in Huaraz

HUARAZ, circa 1970

1970 Earthquake that caused the Huascaran disaster killed about 40,000 people in Huaraz.

Streets of Huaraz after the1970 Earthquake.

Adobe houses collapsed, killing people inside.

A potential disaster in the icy Andes: a regrettable blunder

May 3, 2003: “NASA feels the heat as glacier pictures cause unrest in Peru”, according to Nature

HUARAZ CASE STUDIES

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are needed to see this picture.

NASA press release

• A chunk of glacier was threatening to fall into an Andean lake and cause major flooding in a Peruvian city of 60,000. A fissure has appeared in the glacier that feeds the Lake Palcacocha near the city of Huaraz, 270 km north of Lima.

NASA press release

• If the piece breaks off, ensuing floods would take 15 minutes to reach the city. In 1941, the lake overflowed and caused massive destruction, killing 7,000 people.

NASA press release

• The city can be seen in the left-center part of the image. Lake Palcacocha is in the upper right corner of the image at the head of a valley, below the snow and glacier cap. The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument, aboard NASA’s Terra satellite, is being tasked to obtain current images of the glacier to help monitor the situation.

ASTER image,2001

Fissure

NASA interprets as huge crevasse

ASTER image,2003

Fissure

NASA believes glacial release into the lake is imminent

Palcacocha, historical photograph

Palcacocha

Rock band from glacial retreat, not crevasse.

LAGO PARON

Located above YungayPotential Pro-glacier flood

1940’s flood from glacier failure

Huge rock glacier dammed lake.Could collapse at any time.

Installed drainage tunnelLowered lake level

Summary: disaster

• 1962 Huascaran avalanche killed 4,000• 1970 Huascaran avalanche killed 20,000• 1941 proglacial lake outburst from

Palcacocha killed 6,000 in Huaraz• Lago Paron could have an outburst at any

time from (a) collapse of rock glacier damn; (b) glacial ice fall into lake; c) combination of both

Summary: causes

• Major tectonic faults that are active• Marked glacierization• Geologically young, steep mountains• Pro-glacial lakes• Immediate vicinity of human settlements