VOLCANOES

Magmatism

Magmatism is the formation of igneous rocks from magma.

Concept of Plate Tectonics is the idea that The earth’s crust and upper mantle are broken up into pieces into a series of rigid, mobile plates.

The plates move over a partly molten zone in the mantle tat is the source of most of the magma that accounts for volcanic activity.

Melting is caused by reduction of pressure as the magma goes up.

Magmas are typically generated in one of the three plate tectonic settings:

at Divergent Plate Boundaries Over Subduction Zones Hot Spots , Intraplate Volcanism

At Divergent Plate Boundaries- where plates split and move apart.

Most are seafloor ridges Magma produced are mafic

This is due to the ultramafic composition of the upper mantle beneath the seafloor.

Basaltic volcanism – dominant rock is basalt

There are also magmatism found in continental rifts but they are less common. They also produce mafic magma and they have basaltic volcanism like at the seafloor ridges.

At Subduction Zone – a type of plate boundary at which two plates converge and one plate is thrust beneath the other. Andesitic volcanism- dominant rock is

andesite. This is due to the assimilation or melting of

the overriding platee that is continental (mostly silicic) which is composed of granitic or granodioritic crustal material by mafic magma often produces an intermediate composition, andesitic melt.

Hot Spot, Intraplate Volcanism – isolated areas of volcanic activity that are not associated with plate boundaries.

Usually attributed to the presence of mantle plumes.

Mantle plumes are rising column of magma in the upper mantle. What causes plumes is not known for certain. Some geologists says that they formed over regions of locally high concentrations of (heat producing) radioactive element in the mantle. If the overlying plate of a plume is sufficiently weak, the magma breaks through to form a volcano

Expected to be basaltic volcanism. The composition of the material arupted

depends on the composition of the overlyinng plate.

When magma rises up through an oceanic plate, it is expected to be basaltic whether or not some seafloor is assimilated.

Hot spot volcanoes in the oceanic basins which are commonly built of many thin layers of fluid basaltic lavas, if the magma makes its way up through a crust, there is more potential for assimilation of ranitic material and production of a more silicic final magma.

Continental Rift

Divergent Plate Boundary

Subduction zone

Hot Spot volcano

Volcanoes and Fissure EruptionsWhen most people think of volcanic activity,

they think in terms: Volcanoes - individual mountains built

around discrete vents through which magma can erupt at the surface.

Lava – is simply magma that reaches to the surface Many volcanoes are built of layer

upon layer of lava. However, not a\ll volcanoes erupt only lava. Differences in the material that make up a volcano contribute to differences in both form and eruptive style.

Fissure Eruptionsthe eruption of a lava out of a long crack rather than from a single pipe or vent.

Shield VolcanoesVery flat and low in relation to its

diameter. Built by basaltic lavas (relatively low in

silica and high in iron and magnesium and comparatively fluid)

They form over mantle plumes from which the magma comes from.

Are very rare that makes 10% of the active volcanoes in the earth.

Volcanic Domesa compact, steep-sided volcanic structure from a very viscous lava. any steep-sided mound that is

formed when lava reaching the Earth’s surface is so viscous that it cannot flow away readily and accumulates around the vent.  

built by andesitic & rhylolitic composed silicic lavas. (tend to more viscous and flow less readily. They ooze out at the surface like thick toothpaste.)

Cinder Cones are volcanoes that are made

primarily of made of basaltic fragments.

are generally not very tall, generally not more than 500 m high.

are steep-sided, often symmetrical mountains that match the popular expectation of what a volcano should look like

Considered as monogenetic volcano because they only erupt once and then they become extinct.

Composite Volcanoes also known as stratovolcano. Are the most common mountain volcano

such as Mt. Pinatubo, Mt. Fuji and Mt. St. Helens.

Are polygenetic volcano for the capability of repeated eruptions and separated by dormancy periods over hundreds of thousand years.

Built mostly by andesitic lava. Are much more lager and taller than

cinder cones and they have more explosive eruptions.

Caldera A large, bowl-shaped summit depression

in a volcano. This is caused when much of the magma

has erupted or perhaps magma has drained back down to deeper levels leaving the volcano partially unsupported. The overlying rocks may collapse if they are very weak.

They can be bigger then the original crater from which the lava emerged.

This is the Crater Lake . This is actually a caldera collapse of the ancient volcano Mt. Mazama in southern Oregon. At 600 m depth, it is the deepest freshwater lake in the USA.

Volcanic Hazards Direct Hazards: Materials and

Eruptive StylePrimary volcanic hazards

include:LavaPyroclasticsAsh and dustGas

Lava Most people have regarded lavas are the

primary hazard during volcano eruption but actually, lava is not generally life-threatening . Most lava flows advance at speed of a few kilometer an hour at most, so one can evade the advancing lava readily even a foot.

The lava will of course, destroy or bury any property over it flows.

Lava temperatures are typically over 500°C over 950°F) and may be over 1400°C (2550°C). Combustible materials like houses and even forests are burn at such temperatures.

Other property are simply engulfed in lava, which then solidifies into solid rock.

Lavas, like all liquids, flow downhill, so one way to protect property is to simply iv away from a volcano. However, people still or build houses near at a volcano for some reasons:

They simply think that a volcano will not erupt again for a very long time.

Soil formed from the weathering of volcanic rock forms slowly but is often very fertile.

Sometimes, a volcano is the only land available. Some strategies do exist for reducing the

property damage from lava. In Iceland, in 1973, flow-quenching operations

saved a crucial harbor when the Edjell Volcano in Heimaey erupted.

Heimaey Island is surrounded with plentiful cooling water. Boats sprayed water on lava flows encroaching on the harbor thus, saving the harbor. As the lava cools, it becomes thicker, more viscous and flows more slower. They used water to fastened the cooling of the lava.

Some have tried diverting lava flow’s course away from the properties by carefully placing explosives t o the newly solidified lavas (only the crustal part of the lava have been solidified, the interior part is still molten and would take several days before it will fully solidify) which had been stopped flowing due to the lessen output of the volcano or upon encountering natural or artificial barrier.

In this way, the internal molten that have been exploded would take another path. Careful placing of the explosives would guide the flow to another course. This strategy was used in Italy in 1983, when Mt. Etna began another series of eruptions. Unfortunately, the strategy was only brief successful. Part of the flow deflected the course but after few days the lava left the planned alternate channel and resumed to its original path.

Lava flows may be hazardous, but they are at east predictable. Like other fluids, they flow downhill. Once they flowed on a relatively flat area, they tend to stop.

The Edjell Volcano in Heimaey, Iceland erupted.

Pyroclastics Pyroclastics are the bits of magma and

rocks that are wildly going out from a volcano during eruption. This is due to the sudden release and forcefully explosion of the built up gas pressure in a rising magma. There are also bock-sized, still molten lavas that are thrown out of e volcano called, volcanic bombs.

These are more dangerous than lava flows. They may erupt suddenly and explosively, and spread faster and farther. The larger the blocks the more danger it brings.

However, they usually fall quite close to the volcanic vent, so they affect small area.

Pyroclastic flow in Mt. St. Helens

Ash and Dust These are severe problems every volcanic

eruption. They can be carried over to a larger area by air. They cannot just be confined in a valley and low places but they can also blanket a countryside. As what happened on May 18, 1980 eruption of Mt. St. Helens was by no means the largest eruption recorded, but the ash blackened the midday skies more then 150 kilometers away, measurable ashfall was detected halfway across the USA.

Volcanic ash can be a problem in transportation. They will make the road slippery as they land on the ground causing accidents. Volcanic dust can choke car engines as they are in the air. Homes, cars and land were buried the hot ash.

Volcanic ash is also a health hazard that makes breathing both uncomfortable and difficult.

In the Philippines, when the 1991 eruption of Mt. Pinatubo, the combination of thick ashfall and soaking rains caused the widespread collapse of homes under the weight of the sodden debris.

Lahar is the result when hot falling ashes melts the snow on ice or even when falling ashes combined with heavy rain producing a mudflow. In the Philippines, the 1991 Mt. Pinatubo eruption caused lahar when rain-soaked ash on the mountain slopes suddenly slid downhill.

Nuée ardente- (French word for “glowing cloud”)

also known as pyroclastic flow is a special kind of deadly pyroclastic outburst . It is a denser-than-air mixture of hot gases and fine ash. Pyroclastic flow has a temperatures over 1000ºC in the interior and it can rush down the slopes of the volcano at more than 100 kilometers per hour, charring everything in its path , flattening trees and weak buildings. The most famous pyroclastic flow tragedy is the 1902 eruption of Mont Polée on the Caribbean in the Island of Martinique which caused fatal injury, burn to death and suffocation to approximately 25,000 to 40,000 people in the nearby town of St. Pierre and its harbor. The single reported survivor in the town was a convicted murder who was imprisoned underground in the town dungeon.

In the history, andesitic volcanoes have often histories of explosive eruptions so do many of them have a history of pyroclastic flow.

Volcano eruptions produce gases that could kill humans either through suffocation and poisoning. Some gases that are not considered poisonous but cause suffocations include water vapor and carbon dioxide. Gases like carbon monoxide, various sulfur gases and hydrochloric and hydrofluoric acids are all poisonous.

Mt. Pinatubo

Mt. St. Helens

Some volcanoes are deadly because of their location respectively. In case of an island volcano, the volcano may have a phreatic eruption, an eruption caused by large amount of water that have seeped into the rocks and went nearer to the hot magma below, turned into steam and blow up the volcano. This will produce an huge explosion and may cause for a high sea wave that could wash up its neighbor islands.

Phreatic eruption may also occur when

any water –groundwater, lake water, snowmelt and so on –seeps in to the crust to a hot magma body.

There are also instances that a viscous rhyolitic or andesitic lavas plug the vent, the pressure of gases associated with the magma may build until it rips the volcano apart. And such explosions are often unpredictable in the term.

Secondary Effects: Climate Intense explosive eruptions put large

quantities of volcanic dust high into the atmosphere and takes years to settle to the ground. Due to this, it will cause a partial blockage of incoming sunlight, thus causing measurable cooling. After the Krakatoa, Indonesia Eruption in

1883, worldwide temperatures dropped nearly half a degree centigrade, and the cooling effects persisted for almost ten years.

The larger eruption in Indonesia happened at Tambora on 1815, gave another cooling. 1816 was the known year in the Northern Hemisphere as “the years without a summer.”

Volcanic dusts are not all the cause of the climatic impacts of volcanic eruptions to the world. It is also caused by the gasses emitting from the volcano during eruptions. The 1982 eruption of the Mt. El Chichón

in Mexico did not produce large quantity of dust, but it did shoot volumes of unusually sulfur gases into the atmosphere. These gases produced clouds of sulfuric droplets that spread around the earth.

Acid droplets do not just block the incoming sunlight but they also become acid rain when they settle back to the ground.

The 1991 eruption of the Mt. Pinatubo in the Philippines became famous when it gave extensive output of both ash, dust and sulfur gases. The resultant sulfuric acid mist circled the globe.

The unusually cool summer of 1992 in the Northern Hemisphere was attributed to the eruption Mt. Pinatubo.

Prediction of Volcanic Eruptions Volcanoes are divided into 3

categories according to their activity although there are no precise rules for assigning volcano to a particular category: Active volcano Dormant or Sleeping volcano Extinct or Dead volcano

Active volcano Are those volcanoes that have erupted or shown signs

of activity in the past 600 years. Mt. Pinatubo, Mt. Mayon and Mt. Taal are the most famous active volcano in the country.

There are about 220 volcanoes in the Philippines, 25 of them are said to be active.

Dormant or Sleeping volcano The volcano has not erupted but is fresh looking and

not too eroded or worn down. Dormant volcanoes are inactive up to the present but

have the potentials to be come active again. Mt. Apo, Mt. Arayat and Mt. Makiling are the example of

this kind of volcano.

Extinct or Dead volcano A volcano that has not recent eruptive history but also

appears very much eroded.

As volcanologists learned, statistically, a typical volcano erupts once every 220 years, but 20% of all volcanoes erupt less than once every 1000 years, and 2% erupt less than once in 10,000 years.

As estimated, there are 300-500 volcanoes in the world (the uncertainty arises from not knowing whether some are truly active or dormant). Most are located over subduction zones. The Ring of Fire is the collection of

volcanoes

rimming around the Pacific Ocean, is a ring of subduction zones.

Monitoring all the volcano is a way of predicting the volcanic eruptions but it is a large task. Active volcanoes should be monitored for any sudden eruptions. Dormant volcanoes might become active at any time. Extinct volcanoes can be ignored but that’s assuming that they are long-term dormant volcanoes.

Volcanologists only uses information of the recent eruption of a volcano as their guide

for the future eruption.

Advance Warnings for Volcanic Eruption Seismic Activity

The rising magma and gas up through the crust beneath the volcano puts stress on the rocks, and the process may produce months of small (and occasionally large) earthquakes.

Bulging, tilt, or uplift of the volcano’s surface. It often indicates the presence of a rising

magma mass, the build up of gas pressure

or both. Uplift, tilt and seismic activity may indicate

that an eruption is approaching but geologists do not know yet the exact timing.

Changes in the mix of gas coming out of the volcano. Gas emissions may reflect the approach of

magma toward the surface as it rises associated with gas.

Surveys of ground-surface temperatures. Warm areas where magma is particularly

close to the surface and are about to breakthrough.

Animals There have been reports that animals

can anticipate volcanic eruptions because they sensitive to the earth’s changes.

PHIVOLCS (Philippine Institute of Volcanology and Seismology) is the agency that observes volcanic activities in the Philippines. They set the Volcanic Danger Zone,

the boundary around a volcano covering about 6 km wide.

There are observed simple cautionary action when a volcano shows signs of eruption. Before :

Store food, first aid kit, flashlights, water and other necessities in case of eruption.

Listen to radio, TV and other media for further informations and instructions regarding the volcano.

During : Evacuate immediately and do not wait for force

evacuation. After :

Do not go back to the houses without prior instructions from the government.

Major Volcanic Eruptions Since 1900

Major Volcanic Eruptions Since 1900

Volcano Location Year Deaths*

Santa María Guatemala 1902 1,500

Pelée Martinique 1902 29,000

Taal Philippines 1911 1,335

Kelut, Java Indonesia 1919 5,110

Merapi Indonesia 1930 1,369

Rabaul Caldera Papua New Guinea

1937 507

Lamington Papua New Guinea

1951 2,942

Hibok Hibok Philippines 1951 500

Volcano Location Year Deaths*

Agung Indonesia 1963 1,148

St. Helens United States 1980 57

El Chichón Mexico 1982 >2,000

Nevado del Ruiz Colombia 1985 23,000

Lake Nyos Cameroon 1986 1,700

Pinatubo Luzon, Philippines

1991- 1996 800

Unzen Japan 1991 39

Mayon Philippines 1993 70

*All death tolls are estimates.

Source: United States Geological Survey.

Active Volcanoes in the Philippines

Name of Volcano

Province Elevation(Km) 

No. of Historical Eruptions 

Latest Eruption/Activity

Babuyan Claro

Cagayan 0.843 4 1917

Banahaw Laguna, Quezon

2.169 3 1843

Biliran Biliran Island 1.340 1 1939 Sept. 26

Buddajo Sulu 0.62 2 1897

Bulusan Sorsogon 1.565 17 2010 Nov.-2011.Feb.

Cagua Cagayan 1.160 2 1907

Cabalian Southern Leyte

Camiguin de Babuyanes

Cagayan 0.712 1 1857

Didicas Cagayan (Babuyan group of Islands)

0.843 6 1978 Jan. 6-9

Name of Volcano

Province Elevation (Km)

No. of Historical Eruptions

Latest iEruption/ activity

Hibok-hibok Camiguin 1.332 5 1948 Sept. 31- 1953 July

Iraya Batanes 1.009 1 1454

Iriga Camarines Sur

1.143 2 1642 Jan. 4

Kanlaon Negros Oriental

2.435 26 2006 June

Leonard Kniaseff

Davao del Norte

0.200 NO DATA 1800 years ago

Makaturing Lanao del Sur

1.960 10 1882

Matumtum Cotabato 2.286 1 1911 March 7

Mayon Albay 2.460 49 2009 Dec.

Musuan Bukidnon 0.646 2 1867

Parker Cotabato 1.784 1 1640 Jan. 4

Pinatubo Boundaries of Pampanga, Tarlac and Zambales

1.445 3 1992 July 9-Augus 16

Ragang Cotabato 2.815 8 1916 July

Name of Volcano

Province Elevation (Km)

No of Historical Eruptions

Latest Eruption/ activity

Smith Cagayan (Babuyan Group of Islands)

0.688 5 1924

Taal Batangas 0.311 33 1977 Oct. 3