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
Dr Ken Sprenke
Explosive eruptions are favored by high gas content and high viscosity (andesitic to rhyolitic magmas).
Bursting of bubbles fragments the magma into pyroclastsandtephra (ash).
Cloud of gas and tephra rises above volcano to produce an eruption column that can rise up to 45 km into the atmosphere.
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.
After the lateral blast on Mt St.Helens, pyroclastic flows of hot gas and ash raced down the mountain.
Pyroclastic flows from Mt Vesuvius instantly killed and entombed the citizens of Pompei and Herculaneum in 79 AD.
Lateral blasts and debris avalanches occur when gas is released suddenly by a large landslide taking out part of the volcano.
Fissure Eruptions - An eruption that occurs along a narrow crack or fissure in the Earth's surface.
aa ---- rough
pahoehoe --smooth ropy texture
Hexagonal columns form as lava shrinks. The columns grow perpendicular to the cooling surface.
while the lava is cooling.
Lava tube: A tunnel below the solid surface of a flow where lava continued to flow.
Spatter cone: small steep-sided cone formed from molten material thrown into air that falls back to surface and adheres together.
Stratovolcano (composite volcano) - a volcano built of interbedded lava flows and pyroclastic material.
A typical summit crater on a cinder cone.
Caldera - a depression caused by collapse of a volcano into the cavity once occupied by magma
Is Crater Lake a crater?
No! Crater Lake occupies a caldera.
Nuee ardente--dense cloud of hot pyroclastic materials and gases.
Lahar: Mudflow composed
of volcanic materials
Volcanic gas emissions.
by mantle hot spots.