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Langara College
GEOL 2207

Magma  What is magma and how and where does it form? o Magma: melted rock in the earth – below the earth’s surface; melt + crystals + bubbles o Lava: melted rock exposed at the earth’s surface; melt + crystals + bubbles o Magma is created by the melting of pre-existing rock in earth’s interior (mantle and crust) o Reaches the surface through fractures and erupts as lava or pyroclastic material (tephra)  List the different categories of volcanic rocks and explain the differences between the magmas they came from. o Dark colour – Light colour o Mafic (less silica)  intermediate  intermediate  Felsic (more silica) o Hot (1200-1400)  Cool (600-1000) o Low viscosity  High viscosity o Non-explosive (lava)  Explosive (pyroclastic) o Basalt  Andesite  Dacite  Rhyolite  Glass is a non-crystalline or amorphous, metastable solid formed by quenching a melt. o Cools so fast that a regular crystal lattice cannot form  As magma rise, they: crystallize, exsolve volatiles o Volatiles (gases) dissolved  exsolved  Explain what lava flows, fire fountains, lava bombs and volcanic ash are and how they form. o Magma is generated by melting of existing rock o Primary Processes o Effusive:  Lava flows (mafic-intermediate) Downslope, ponds in topographic lows Outer crust cools and solidifies insulating the molten interior  Lava domes (felsic intermediate)  Gravitational collapse of lava flows/domes (block and ash flows) o Explosive:  Buoyant eruption column of ash  Pyroclastic fall: widespread distribution of ash, 10’s of kms  Pyroclastic fl
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