Transcript powerpoint_Volcanoes Lava and Types of Eruptions

Volcanoes &
Plate Tectonics
CH 6 Prentice Hall
p.178-181
Characteristics of Magma
• The force of an eruption depends partly on
the amount of gases dissolved in the magma.
• The temperature and the silica content are
also important factors.
– Temp- partially determines whether it is thick or
fluid. (Hotter- the more fluid it is.)
Characteristics of Magma
• Silica- a material found in magma composed
of the elements silica and oxygen. (The more
silica- the thicker the magma.)
• High Silica- light colored lava
– Rhyolite an extrusive igneous rock
– Pumice spaces left in the rock by gases bubbling out.
– Obsidian- cools very quickly giving a glassy texture.
• Low Silica- dark colored rocks
– Basalt dark colored extrusive igneous rock
Types of Volcanic Eruptions
• A volcano’s magma influences how the
volcano erupts.
• The silica content helps determine whether
the volcanic eruption is quiet or explosive.
Quiet Eruptions
• Magma flows easily.
• Dissolved gases in the
magma bubble out easily.
• Thin runny lava oozes from
the vent and flows.
• Examples
•
Iceland and Hawaii
aa
• Cooler, slow moving lava.
• Forms jagged chunks of lava.
Pahoehoe
• Fast moving, hot lava.
• Surface of lava looks like a solid
mass of wrinkles, billows and
ropelike coils.
Explosive Eruptions
• Magma is thick and sticky.
• Thick magma builds up in the
pipe, plugging it like a cork in a
bottle.
• Pressure builds up due to the
gases in the magma until the
volcano explodes.
• The gases push the magma out
with incredible force.
Explosive Eruptions
• Fragments:
• Volcanic Ash
– fine, rocky, grain of sand sized particles.
• Cinders– pebble sized particles
• Bombs– large pieces of rock (baseball to the size of a car)
• Pyroclastic Flow
• Occurs when an explosive eruption hurls out ash,
cinders and bombs as well as gases. (400mph,
1,800˚F)
Other types of Volcanic Activity
• Hot Spring- Forms when groundwater heated
by a nearby body of magma rises to the
surface and collects in a natural pool.
Other types of Volcanic Activity
• Geyser- A fountain of
water and steam that
erupts from the ground.
– Forms due to rising hot
water and steam that
become trapped
underground in a narrow
crack.
– Builds up pressure until it
sprays out of the ground.
Other types of Volcanic Activity
• Geothermal Energy- A
clean, reliable energy
source provided by
water heated by magma.
• Hot water can be piped
into homes.
• Used as a source of
electricity
– Steam is piped into a
turbine that spins and
generates electricity.
Monitoring Volcanoes
• Geologists are more successful with predicting
a volcanic eruption.
• Changes around a volcano shows signs of an
eruption and allow for a short warning time.
– Monitor a volcano with:
• Tiltmeters and Laser ranging devices to see ground
changes due to shifting magma.
• Monitor escaping gases and water level in a volcano's
crater lake.
Monitoring Volcanoes
– Monitor a volcano with:
• Check the temperature of the ground water to see if
the magma is heating it.
• Monitor the many small earthquakes triggered by
magma moving from the chamber to the pipe.
– Unable to predict the strength of the eruption
Volcano Hazards
• Time between eruptions can span hundreds of
years. (Dormant Volcano)
– People may be unaware of the danger.
– Mt. St Helens 123 years.
Volcano Hazards
• Quiet Eruptions:
– Lava flows- set fire and
bury everything in
their path.
• Explosive Eruptions:
– Hot clouds of volcanic
gases, cinders and
bombs
• Pyroclastic Flow
Volcano Hazards
• Volcanic Ash:
– Bury towns, damage crops, and clog car engines.
– Wet ash is heavy and can cause roofs to collapse.
• Plane engines can fail if pulled into the engine.
• Lahar:
– A mud flow of caused by melted snow.
• Carries ash, trees and rocks.
Volcano Hazards
• Pompeii