more about volcanoes

8/13/2019 More About Volcanoes

1/34

More about Volcanoes

Liang-Fang Chao


2/34

Making Magma

Mantle is not hot

enough to melt rock.

Decrease the pressure

=> Rock melting

Add water =>Melting at lower

temperature.


3/34

Mid-ocean lavareduced pressure

Divergent Plate Boundaries


4/34

Subduction ZoneWater

Rocks Melt due to extra water content.

Divergent Plate Boundaries


5/34

Subduction Zone

A subducting plate bends and passes under a

more buoyant less dense plate.

As the subducting plate sinks into the mantle,

mud and water are carried along into the mantle.

Water combines with the hot mantle rock. That

allows the rock to melt at a lower temperature.

The magma is less dense so it rises and forms avolcano.


6/34

Basalt and Silica

Silicamakes magma thick andsticky.

Quartzis mineral made of

silica. Basaltmagma is runny

because of its low silica

content. What kind of rock is found

near Kilauea?

Basalt
http://mail.ab.mec.edu/~mdoiron/010B7EF2-000F6E99.2/basalt.jpg


7/34

Basalt

Basalt is a dark-colored rock that

is not silica rich.

Formed from thin and runny

magma.

Mostly coming out of gentle

volcanoes near divergent plates.

Ocean floor is mostly covered in

Basalt.


8/34

Silica Rich Rock

Silica rich rock is light in color, thick, sticky andless dense than basalt magma.

When cooled, the silican-rich magma forms

granite and other closely-related rocks. The famous granite domes of Yosemite were

formed as silica-rich magma rose through the

edge of the subduction zone that no longerexists.

The surrounding land later eroded away.


9/34

Silica is not dense

Continents are made of granite (and

andesite).

Silica-rich granite is not as dense as the basalt

of the ocean floor.

This is why continental plates float high on the

lower mantle.


10/34

Silica versus Gas

Shield Volcano

Composite Volcano

Cinder Cone Volcano

obsidian rockgranite, andesite,

pumice, scoria rocks,

ash

basalt and gabbro rocks basalt and gabbro rocks


11/34

Three Types of Volcanoes

Low silica magma produces a

shield volcano.

A tall cone, or composite

volcanoforms from thick, stickymagma because it is silica-rich.

A cinder coneis formed by lava

cinders around the vent whenmagma has high levels of

dissolved gas.


12/34

Shield Volcanoes

Low silica and low gasmagma produces a shieldvolcano.

Because low silica magma isrunny, it cant build up a tall

volcano. The types of eruptions that

occur at shield volcanoeshave been named Hawaiianeruptions.

Types of Rock: basalt (coolsslowly), gabbro (coolsquickly)

Kilauea in Hawaii
http://en.wikipedia.org/wiki/File:Mauna_Kea_from_Mauna_Loa_Observatory,_Hawaii_-_20100913.jpg


13/34

Shield Volcanoes

Example: Kilauea in Hawaii(3km in diameter).Fernandin in the Galpagosislands, Ecuador. Iceland.

East Africa.

Shield volcanoes andvolcanic vents have been

found on Mars, Venus, andsubsurface hotspots onEuropa.

http://en.wikipedia.org/wiki/Shield_volcano

Three enormous

volcanoes on Mars

(300km in diameter)
http://en.wikipedia.org/wiki/File:Tharsis_mons_Viking.jpg


14/34

Cinder Cone

When magma has high levels ofdissolved gas, gas bubbles outas it reaches the volcano vent.

The lava cinders form a conearound the vent called a cindercone.

It could be rich in silica or low insilica.

Formed in the caldera (areaaround the vent).

Simply a pile of rock bits.

Capulin Volcano, Mexico

Fire Fountain
http://en.wikipedia.org/wiki/File:Capulin_1980_tde00005.jpg


15/34

Piracutin Cinder Cone

The most famous cinder cone, Paricutin, grew outof a corn field in Mexico in 1943 from a new vent.Eruptions continued for 9 years, built the cone toa height of 424 meters.

Like most cinder cones, Parcutin is believed to bea monogenetic volcano, which means that once ithas finished erupting, it will never erupt again.

http://en.wikipedia.org/wiki/Cinder_cone During 1943 eruption
http://en.wikipedia.org/wiki/Cinder_conehttp://i107.photobucket.com/albums/m313/elisson1/Miscellaneous/Paricutin.jpghttp://www.mastersoftrivia.com/blog/wp-content/uploads/2011/07/21073469.jpghttp://en.wikipedia.org/wiki/Cinder_cone


16/34

Composite Volcanoes

Layers of lava and ash.

Also called stratovolcano(strato-= layers). Most common.

Forms from thick, sticky magmabecause it is silica-rich.

Violent eruptions.

Rock Types: as in granite (cools

slowly), rhyolite (cools quickly) ,andesite, pumice (high gascontent) or obsidian (low gascontent).

Mount Fuju in Japan
http://en.wikipedia.org/wiki/File:FujiSunriseKawaguchiko2025WP.jpg


17/34

Composite Volcanoes

Common at subduction zones,forming chains along platetectonic boundaries where

oceanic crust is drawn undercontinental crust. (Convergentplate boundaries)

Example: Krakatoa, Indonesia.

Vesuvius, Italy. like Mount St.Helens, USA. Mount Pinatubo,Philippine.

Krakatoa, Indonesia


18/34

Lava with high gas

The cone may explode near the vent, throwinga column of gas and lava bits high into theatmosphere.

The lava bits puff up and rip apart as thedissolved gas expands inside each bit.


19/34


20/34

Lava flow is not deadly, but

Flowing lava or even splatter thrown out oferupting craters kill relatively few people.

It is usually possible to run, or even walk away

from most lava flows! The real killers are much more frightening.

travel at over 100 miles per hour,

move across land and sea,

flow uphill as well as down,

rip trees up by their roots,

flatten buildings and kill people and animals instantly.

http://www.geography-site.co.uk/pages/physical/earth/volcanoes/pyroclastic%20flows.html


21/34

The True Killers are

pyroclastic flows

and lahars

Merapi, Indonesian, 2006 (volcanoes.usgs.gov)


22/34

Pyroclastic Flow Pyroclastic flows are clouds of hot volcanic gases, ash and

volcanic bombs that race down a composite volcano's sidesat speeds over 100 miles per hour.

Pyroclastsare loose clumps of particles of lava.

The speed force, and heat of the flow make it extremelydestructive.

poisonous gasses at temperatures hot enough to burn yourlungs away.

Examples: Vesuvius, Italy, 29AD. Krakatoa, Indonesia. StHelens.


23/34


24/34


25/34

Lahar by Casita volcano

In 1998 at the Casita volcano in Nicaragua a lahar

claimed over 2,500 lives. As it swept over the towns ofEl Porvenir and Rolando Rodriguez the only warning wasa noise like helicopters or thunder, and ground tremorsthat some thought were earthquakes. The towns were

totally covered by the mud in less than 3 minutes, killingalmost everybody.

A large boulder carried

by the lahar. A plaque

is placed on it to honor

those who were killed.


26/34

Geysers

Geysers and hot

springs are the result

of water in the ground

coming in contactwith magma-heated

rock below the

surface.


27/34

Old Faithful Old Faithful in Yellowstone shoots

water 100 to 200 feet high every35 to 120 minutes.

Old Faithful, near Calistoga,

California shoots water 60

to 100 feet every 30

minutes.


28/34


29/34

Igneous Rocks

Igneous rocks are formed as melted rock cools

and crystalizes.

Their crystals are tightly locked together.

Melted rock that cools quicklyproduces small

crystalsformed on Earths surface.

Slowcooling process produces larger crystals

rocks formed from undergroundmagma.


30/34


31/34

Silicon-Rich

Granite, rhyolite, and obsidianall come from the same silica-rich magma.

Granite cools underground andhas large crystals.

Rhyolite cools on the surfaceand has fine crystals.

Obsidian cools so fast that ithas no crystals and is oftencalled volcanic glass.

granite

rhyolite

obsidian


32/34

Granite

Granitemakes upcontinental plates.

Formed from thick,

sticky magma, high-silica. Less dense;thus, float.

It has large crystals. Mount Rushmore is a

famous granitesculptured mountain.

Half Dome, Yosemite


33/34

Basalt

Basalt makes up oceanic plates.Ocean floor is mostly coveredin Basalt.

Formed from thin, runnymagma, low silica. More dense;thus, sink.

It has fine crystals.

Mostly coming out of gentlevolcanoes near divergent plateboundaries.
http://mail.ab.mec.edu/~mdoiron/010B7EF2-000F6E99.2/basalt.jpg


34/34

Pumice

High-Silica magma with

dissolved gas.

When the gas in themagma puffs up before the

magma cools to a solid, it

produces pumice. Pumice is so light that it

floats.

Owens River Valley California

more about volcanoes

Documents