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Welcome ! Geology 111 Volcanoes. Dr Ken Sprenke www.mines.uidaho.edu/~sprenke. Explosive eruptions are favored by high gas content and high viscosity (andesitic to rhyolitic magmas). Expansion of gas bubbles is resisted by high viscosity of magma - results in building of pressure

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welcome geology 111 volcanoes

Welcome !Geology 111Volcanoes

Dr Ken Sprenke

www.mines.uidaho.edu/~sprenke

slide4

Explosive eruptions are favored by high gas content and high viscosity (andesitic to rhyolitic magmas).

  • Expansion of gas bubbles is resisted by high viscosity of magma - results in building of pressure
  • High pressure in gas bubbles causes the bubbles to burst when reaching the low pressure at the Earth\'s surface.
slide6

Cloud of gas and tephra rises above volcano to produce an eruption column that can rise up to 45 km into the atmosphere.

slide8

If eruption column collapses a pyroclastic flow  may occur, wherein gas and tephra rush down the flanks of the volcano at high speed.  This is the most dangerous type of volcanic eruption. 

slide9

After the lateral blast on Mt St.Helens, pyroclastic flows of hot gas and ash raced down the mountain.

slide10

Pyroclastic flows from Mt Vesuvius instantly killed and entombed the citizens of Pompei and Herculaneum in 79 AD.

slide11

Lateral blasts and debris avalanches occur when gas is released suddenly by a large landslide taking out part of the volcano.

slide16

Fissure Eruptions - An eruption that occurs along a narrow crack or fissure in the Earth\'s surface.

slide18

Flow surfaces:

aa ---- rough

pahoehoe --smooth ropy texture

slide19

Hexagonal columns form as lava shrinks. The columns grow perpendicular to the cooling surface.

slide22

Spatter cone: small steep-sided cone formed from molten material thrown into air that falls back to surface and adheres together.

slide25

Stratovolcano (composite volcano) - a volcano built of interbedded lava flows and pyroclastic material.

slide29

Crater - a depression caused by explosive ejection of magma or gas

A typical summit crater on a cinder cone.

slide31

Formation of Crater Lake.

Is Crater Lake a crater?

No! Crater Lake occupies a caldera.

slide33

Some Volcanic Hazards

Nuee ardente--dense cloud of hot pyroclastic materials and gases.

Lahar: Mudflow composed

of volcanic materials

Volcanic gas emissions.

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