Volcanism

VOLCANISMIts Features

Glenn Kenneth A. CalugasBSED General Science-4

CENTRAL MINDANAO UNIVERSITY

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Albert Garcia’s award-winning photo taken on June 15, 1991 was chosen by Time as one of the “Greatest Images of the 20th Century” and also by the National Geographic Magazine as one of “100 Best Pictures” of the 20th Century. Garcia is currently the photo editor of Manila Bulletin.

Catastrophically Award-Winning!

http://www.balita.com/mt-pinatubo20-photo-exhibit-more-than-just-pictures-it-was-a-reunion-of-survivors-2/

2VOLCANISM: Its Features

VOLCANISM? Sounds familiar!

Volcanism is the eruption of molten rock (magma) onto the surface of a planet. A volcano is the vent through which magma and gases are discharged. Magma that reaches the surface is called lava. Volcanos are named for Vulcan the Roman god of fire!


LET’S PUSH THESE!

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How do volcanoes form?What causes volcanoes to erupt?Where do most volcanoes occur?

What are the different types of volcanoes?

What determines the degree of violence associatedwith volcanic activity?

VOLCANISM: Its Features

Ah! Yes, let’s define the terms…A volcano is a vent or opening on planet’s surface which allows molten rock called magma, volcanic ash and gas to escape out onto its surface. A volcano gives a look like a mountain from which lava erupts. The hot magma erupting from a volcano is called lava.

KNOWLEDGE ERUPTION!Definition of Terms

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Most volcanoes are formed by the movement of tectonic plates on the surface of the earth. These plates are basically huge pieces of rock that ‘float’ on the mantle (a layer of the earth that is sort-of liquid rock).

KNOWLEDGE ERUPTION!How Volcanoes Form

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TECTONIC PLATES


KNOWLEDGE ERUPTION!Origin of Volcanoes

1. Magma rises2. As the magma rises it melts gaps in the surrounding rock

3. As more magma rises a large reservoir 4. Pressure from the surrounding rock causes the magma to blast

5. The magma, now called lava, builds up at the vent forming a volcano.6. Often the volcano sides will be higher than the vent forming a depression called a crater


KNOWLEDGE ERUPTION!What Causes Volcanoes to Erupt?

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TECTONIC PLATES AND SETTINGS

Subducting Plate Margins

Spreading Plate MarginsIntraplate (Hotspot)


Again, it’s in the edge of TECTONIC PLATES.

KNOWLEDGE ERUPTION!Areas Where Most Volcanoes Occur

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The Pacific Ring of Fire

KNOWLEDGE ERUPTION!Areas Where Most Volcanoes Occur

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-It is a string of volcanoes and sites of seismic activity around the edges of the Pacific Ocean. -It isn’t quite a circular ring. It is shaped more like a 40,000-kilometer (25,000-mile) horseshoe.-A string of 452 volcanoes.


KNOWLEDGE ERUPTION!What determines the degree of violence

associatedwith volcanic activity?Magma – molten rock or liquid that is mostly silica

Lava – solidified magmaPyroclasts – from the Greek pyro, “fire”, and clast “broken”

– rock fragments (pyroclastic debris is also called tephra)Lava flows – fissures in the groundExtrusive rock - surface rock resulting from volcanic activity (rock formed by solidification of lava)



associatedwith volcanic activity?

Crater – funnel shaped pit at the top of a volcano. formed

when material is blown out of the volcano by explosions

Caldera – when the volcano collapses due to an empty magma chamber

CRATER

CALDERA 14



associatedwith volcanic activity?DEVELOPMEN

T OF A CRATER LAKE

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Whether eruptions are very explosive or relatively "quiet" is largely determined by two factors: (1)the amount of gas in the lava or

magma(2) the ease or difficulty with which the gas can escape to the atmosphereViscosity – resistance to flow

PHYSICALCHARACTERISTIC

S OF LAVA




FelsicContains more

than 65% Silica

TYPES OF LAVA

MaficSilica (Poor) (45-52%)

RholiteBasaltAndesiteIntermedia

teSilica

Composition (53-65%) 17


The two most important factors that influence viscosity are the (1)temperature of

the lava relative to the cooler temperature which it solidifies

(2)the silica (Si content of the lava)




KNOWLEDGE ERUPTION!

Composite volcanoes often form the largest and tallest volcanoes. They are the most explosive and dangerous of the types of volcanoes.

Types of Volcano

Composite Volcanoes

Mt. Saint Helens in Washington state.

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KNOWLEDGE ERUPTION!

Usually smaller in size than composite volcanoes, and the eruptions are smaller also. They form into steep cone shaped hills.

Types of Volcano

Cinder Cone Volcanoes

Paricutin in Mexico

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KNOWLEDGE ERUPTION!

Shield volcanoes do not erupt or explode like composite or cinder cone volcanoes. Shield volcanoes have much smaller eruptions producing less ash.

Types of Volcano

ShieldVolcanoes

Muana Loa in Hawaii.

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KNOWLEDGE ERUPTION!Pyroclastic flow descending Mayon volcano, Philippines.

-Most of the gas released during eruption is water vapor-Carbon dioxide, sulfur dioxide, hydrogen sulfide, and hydrochloric acid, are given off in lesser amounts -Surface water introduced into a volcanic system can greatly increase the explositivity of an eruption.-At high altitudes, the pyroclastics often spread out into a dark, mushroom

cloud. The fine particles are transported downwind by high atmosphere winds. Eventually debris settles back to earth under gravity's influence as ashfall (or sometimes pumicefili) deposits.A pyroclastic flow is a mixture of gas and pyroclastic debris that is so dense that it hugs the ground as it flows rapidly into low areas.

Gases and Pyroclastics


KNOWLEDGE ERUPTION!Types of Volcanic Eruptions

In a Hawaiian eruption, fluid lava is ejected from a vent as fire fountains or lava flows. The 1969 eruption at Mauna Ulu, a vent of Kilauea Volcano in Hawaii, was a spectacular example of fire fountaining. Photo by D.A. Swanson, USGS, August 22, 1969.

Hawaiian Eruption



Short bursts of glowing lava, created from the

bursting of large gas bubbles at the summit

vent of a volcano typify a Strombolian eruption. This

photo, taken from the summit of Stromboli, a volcano in the Aeolian Islands, Italy, shows a

classic example of this activity. Photo by Andrew Hague, Istockphoto.com.

Strombolian Eruption



Relatively small but violent explosions of viscous lava create columns of ash and gas and occasional pyroclastic flows, as seen at this eruption of the Santiaguito volcanic dome complex in Guatemala. Photo by Jessica Ball, March 15, 2009.

Vulcanian Eruption



The largest and most violent of all explosive eruptions, Plinian eruptions send columns of pulverized rock, ash, and gases that rise miles into the atmosphere in a matter of minutes. Mount St. Helens in Washington State experienced a Plinian eruption following a major flank collapse in 1980. Photo by Austin Post, USGS, May 18, 1980.

Plinian Eruption



Lava domes, such as this example in the crater of Mount St. Helens, are piles of viscous

lava that are too cool and sticky to flow far. Domes grow and collapse in cycles, and often form at volcanoes that also

experience Plinian eruptions. Photo by Lyn Topinka, USGS,

August 12, 1985.

Lava Dome



Lava erupting through water creates the dramatic plumes of scoria and billowing ash-and-gas clouds of a Surtseyan eruption. The type example of this eruption occurred at Surtsey, a volcanic island off the coast of Iceland. NOAA image of the 1963 eruption. Surtseyan Eruption 26


KNOWLEDGE ERUPTION!Types of Lava Flow

A smooth and continuous lava crust. Pahoehoe forms when the effusion rate is low and consequently the velocity of lava flow is slow. Pahoehoe lava flow is usually at least 10 times slower than typical aa lava flow. Pahoehoe



Aa lava is a rough rubbly crust of a lava flow. It is a major lava flow type.

Aa28



A distinctive lava flow morphology that has been appearing in our dredges is pillow lava. Pillow lavas form when hot lava flows into water and cools rapidly, creating long tubes and bulbous pillow-shaped mounds of rock. Pillow lavas are found not only in the ocean but also under glaciers that overlie volcanoes.Pillow Lava



Blocky flows are common if the silica content of lavas is higher (composition of basaltic andesite to rhyolite).Blocky


KNOWLEDGE ERUPTION!Three Definitions of Volcanoes

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Volcanism

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Transcript of Volcanism