• Magma is a mixture of melted rock and hot gasses.

• Magma is a mixture of melted rock and hot gasses.

• Not all magma is the same:1. the kind of melted rock; and2. the amount of gas in the magma; make different types of magma.

• The amount of silica (quartz crystals) in the rock from which magma is made effects the viscosity or thickness.

• The amount of silica (quartz crystals) in the rock from which magma is made effects the viscosity or thickness.

• More silica (quartz) in the magma makes it thicker or higher viscosity.

• BASALTIC – made from oceanic crust and mantle material, so it has low silica content.

• BASALTIC – made from oceanic crust and mantle material, so it has low silica content.

• Low silica content means low viscosity, thinner magma.

• BASALTIC – made from oceanic crust and mantle material, so it has low silica content.

• Low silica content means low viscosity, thinner magma.

• Makes quiet volcanoes, like Hawaiian Islands, Iceland, Africa.

• GRANITIC – made from continental crust, so it has high silica content.

• GRANITIC – made from continental crust, so it has high silica content.

• High silica content means high viscosity, thicker magma.

• GRANITIC – made from continental crust, so it has high silica content.

• High silica content means high viscosity, thicker magma.

• Makes explosive volcanoes, like Mt. St. Helens, Vesuvius, Krakatau.

• The amount of water in the rock also determines whether a volcano is quiet or explosive.

• The amount of water in the rock also determines whether a volcano is quiet or explosive.

• More water in the rock makes it easier to melt.

• The amount of water in the rock also determines whether a volcano is quiet or explosive.

• More water in the rock makes it easier to melt.

• The water also turns to water vapor, which builds up as gas bubbles.

• MORE WATER, MORE GAS, BIGGER BLAST!

• MORE WATER, MORE GAS, BIGGER BLAST!

• How would you get more water in the rock?

• MORE WATER, MORE GAS, BIGGER BLAST!

• How would you get more water in the rock?

• In subduction zones, ocean water is also pulled down into the mantle with the plates.

• Most volcanoes are found at convergent plate boundaries.

• WHY?

• Most volcanoes are found at convergent plate boundaries.

• WHY?• Subduction pushes oceanic crust into

the mantle.

• Most volcanoes are found at convergent plate boundaries.

• WHY?• Subduction pushes oceanic crust into

the mantle.• The crust melts and rises back up to

make volcanoes.

• Volcanoes can also be found at divergent boundaries.

• Plates spread apart and lava oozes out.

• HOT SPOTS – extra hot plume of hot mantle material rises up from the core and melts the crust.

• Examples: Hawaii, Yellowstone

• MAGMA CHAMBER – pocket where magma collects.

• MAGMA CHAMBER – pocket where magma collects.

• VENT - opening in Earth’s crust where magma comes out.

• MAGMA CHAMBER – pocket where magma collects.

• VENT - opening in Earth’s crust where magma comes out.

• CRATER – bowl shaped pit around the main vent.

• MAGMA CHAMBER – pocket where magma collects.

• VENT - opening in Earth’s crust where magma comes out.

• CRATER – bowl shaped pit around the main vent.

• CALDERA – huge depression created when the magma chamber collapses.

• SHIELD VOLCANO: volcano with broad, gently sloping sides.

• SHIELD VOLCANO: volcano with broad, gently sloping sides.

• Quiet eruptions, basaltic lava, little gas.

• SHIELD VOLCANO: volcano with broad, gently sloping sides.

• Quiet eruptions, basaltic lava, little gas.• Largest volcanoes – found at hotspots

(Hawaii, Galapagos) and divergent boundaries (Iceland, East Africa).

• COMPOSITE VOLCANO: A volcano with steep sides formed by layers of thick lava, tephra (hot rocks), and ash.

• COMPOSITE VOLCANO: A volcano with steep sides formed by layers of thick lava, tephra (hot rocks), and ash.

• Usually have explosive eruptions, lots of gas, pyroclastic flows.

• COMPOSITE VOLCANO: A volcano with steep sides formed by layers of thick lava, tephra (hot rocks), and ash.

• Usually have explosive eruptions, lots of gas, pyroclastic flows.

• Found at convergent boundaries with subduction zones – Mt. St. Helens, Krakatoa, Mt. Fuji, Mt. Rainier, Vesuvius.

• CINDER CONE: small volcano with steep sides formed by tephra (hot rocks).

• CINDER CONE: small volcano with steep sides formed by tephra (hot rocks).

• Large volcanoes usually have small cinder cones on them, like pimples.

• A supervolcano is a volcano which is a thousand times bigger than any we have seen during recorded human history.

• A supervolcano is a volcano which is a thousand times bigger than any we have seen during recorded human history.

• Geologic evidence shows that many such eruptions have happened in Earth’s past, and will likely happen again.

• A supervolcano is a volcano which is a thousand times bigger than any we have seen during recorded human history.

• Geologic evidence shows that many such eruptions have happened in Earth’s past, and will likely happen again.

• These large eruptions can alter weather and climate and lead to extinction of species.

• At least two supervolcanoes are suspected of creating or causing mass extinctions:

• At least two supervolcanoes are suspected of creating or causing mass extinctions:

• SIBERIAN TRAPS – 250 million years ago. May have caused Permian extinction.

• At least two supervolcanoes are suspected of creating or causing mass extinctions:

• SIBERIAN TRAPS – 250 million years ago. May have caused Permian extinction.

• DECCAN TRAPS – 65 million years ago. Now suspected of killing off the dinosaurs.

• Last erupted about 74,000 years ago.

• Last erupted about 74,000 years ago.• 1,000 times bigger than Mt. St. Helens.

• Last erupted about 74,000 years ago.• 1,000 times bigger than Mt. St. Helens.• Caldera is 100 kilometers long and 30

kilometers wide.

• Last erupted about 74,000 years ago.• 1,000 times bigger than Mt. St. Helens.• Caldera is 100 kilometers long and 30

kilometers wide.• Eruption created “volcanic winter” – ash

and dust blown into the atmosphere blocks out the Sun.

• “Volcanic winter” kills plants, makes the Earth colder.

• 60% of the human population may have died as a result of this eruption.

• “Volcanic winter” kills plants, makes the Earth colder.

• 60% of the human population may have died as a result of this eruption.

• Last erupted 640,000 years ago.

• Last erupted 640,000 years ago.• Smaller than Lake Toba, caldera is 72 km

long and 55 km wide.

• Last erupted 640,000 years ago.• Smaller than Lake Toba, caldera is 72 km

long and 55 km wide.• Caused by North American plate moving

across a “hot spot” in Earth’s mantle.

• Last erupted 640,000 years ago.• Smaller than Lake Toba, caldera is 72 km

long and 55 km wide.• Caused by North American plate moving

across a “hot spot” in Earth’s mantle.• Supereruptions on this hot spot have

regularly occurred every 600,000 to 800,000 years.

• In recent years, Yellowstone has seen increases in earthquakes around the caldera.

• In recent years, Yellowstone has seen increases in earthquakes around the caldera.

• Ground has begun rising an average of 3 inches per year.

• In recent years, Yellowstone has seen increases in earthquakes around the caldera.

• Ground has begun rising an average of 3 inches per year.

• Is it getting ready to erupt?

• Supereruption would send 1000 cubic kilometers of ash into the air.

• Supereruption would send 1000 cubic kilometers of ash into the air.

• Ash would cover most the United States.

• Supereruption would send 1000 cubic kilometers of ash into the air.

• Ash would cover most the United States.

• Ash could be as much as 6 inches deep in the Salt Lake Valley.

• Supereruption would send 1000 cubic kilometers of ash into the air.

• Ash would cover most the United States.

• Ash could be as much as 6 inches deep in the Salt Lake Valley.

• Volcanic winter would effect climate in Utah and around the world.