more about volcanoes
TRANSCRIPT
-
8/13/2019 More About Volcanoes
1/34
More about Volcanoes
Liang-Fang Chao
-
8/13/2019 More About Volcanoes
2/34
Making Magma
Mantle is not hot
enough to melt rock.
Decrease the pressure
=> Rock melting
Add water =>Melting at lower
temperature.
-
8/13/2019 More About Volcanoes
3/34
Mid-ocean lavareduced pressure
Divergent Plate Boundaries
-
8/13/2019 More About Volcanoes
4/34
Subduction ZoneWater
Rocks Melt due to extra water content.
Divergent Plate Boundaries
-
8/13/2019 More About Volcanoes
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.
-
8/13/2019 More About Volcanoes
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 -
8/13/2019 More About Volcanoes
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.
-
8/13/2019 More About Volcanoes
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.
-
8/13/2019 More About Volcanoes
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.
-
8/13/2019 More About Volcanoes
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
-
8/13/2019 More About Volcanoes
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.
-
8/13/2019 More About Volcanoes
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 -
8/13/2019 More About Volcanoes
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 -
8/13/2019 More About Volcanoes
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 -
8/13/2019 More About Volcanoes
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 -
8/13/2019 More About Volcanoes
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 -
8/13/2019 More About Volcanoes
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
-
8/13/2019 More About Volcanoes
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.
-
8/13/2019 More About Volcanoes
19/34
-
8/13/2019 More About Volcanoes
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
-
8/13/2019 More About Volcanoes
21/34
The True Killers are
pyroclastic flows
and lahars
Merapi, Indonesian, 2006 (volcanoes.usgs.gov)
-
8/13/2019 More About Volcanoes
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.
-
8/13/2019 More About Volcanoes
23/34
-
8/13/2019 More About Volcanoes
24/34
-
8/13/2019 More About Volcanoes
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.
-
8/13/2019 More About Volcanoes
26/34
Geysers
Geysers and hot
springs are the result
of water in the ground
coming in contactwith magma-heated
rock below the
surface.
-
8/13/2019 More About Volcanoes
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.
-
8/13/2019 More About Volcanoes
28/34
-
8/13/2019 More About Volcanoes
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.
-
8/13/2019 More About Volcanoes
30/34
-
8/13/2019 More About Volcanoes
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
-
8/13/2019 More About Volcanoes
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
-
8/13/2019 More About Volcanoes
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 -
8/13/2019 More About Volcanoes
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