Volcanoes Key Terms Vent lava erupting through crack

Volcanoes

Key Terms � Vent- lava erupting through crack/ hole in the crust � Crater- bowl shaped depression at the top of the volcano � Caldera- up to 50 km forms when part of volcano collapses � Tephra- rock fragments thrown into the air � Pyroclastic flow- the flow of material down the side of the volcano � Lahar- mudflow with volcanic debris

Formation of a volcano � 1. lava erupts through a vent � 2. lava cools and hardens around vent � 3. slowly builds up walls of volcano

Volcanic material �Sizes vary • Dust <2 mm • Ash > dust, but < 2 mm in diameter • Lapilli 2 -64 mm (little stones in Italian) • Tephra up to size of a small building �May be blown up to 10 km into the air �Pyroclastic may move down the volcano up to 200 km p/h �Creates lahar when mixed with mud �May exceed 700 C

�Forms Types of volcanoes Shield Volcano out of non explosion eruptions. �Has broad slight slopes �Build layer by flowing lava �Straight sides �Quiet eruptions Mauna Loa in Hawaii

Cinder cone volcano �Formed out of explosions and material falling around vent �Steep sides �<1000 m high �Contains large amounts of silica, water, and gas § Small in comparison Lava Butte in Newberry National Volcanic Monument, Oregon

Stratovolcano �Formed layer upon layer of mostly viscous magma �Relative steep sides �A volcano composed of both lava flows and pyroclastic material. �Very large �Highly explosive

Convergent volcanisn �Occur due to plates moving into each other �Magma forced upward due to additional material being subducted �Ex. Pacific ring of fire

Divergent volcanism � Mostly occur along ocean ridges � Caused by plate separation forming new ocean floor (through the process of seafloor spreading) � Ex. Mid Atlantic ridge

�Unusually Hot Spots hot regions of the mantle near the crust �Will dissolve into the crust (lithosphere) �May be formed by plumes of heat close to the core