Volcanoes are grouped into four types: cinder cones, composite volcanoes, shield volcanoes and lava volcanoes.
Cinder cones are circular or oval cones made up of small fragments of lava from a single vent that have been blown into the air, cooled and fallen around the vent.
Composite volcanoes are steep-sided volcanoes composed of many layers of volcanic rocks, usually made from high-viscosity lava, ash and rock debris.
Mt. Rainier and Mount St. Helens are examples of this type of volcano.
Shield volcanoes are volcanoes shaped like a bowl or shield in the middle with long gentle slopes made by basaltic lava flows.
Basalt lava flows from these volcanoes are called flood basalts.
The volcanoes that formed the basalt of the Columbia Plateau were shield volcanoes.
Lava domes are formed when erupting lava is too thick to flow and makes a steep-sided mound as the lava piles up near the volcanic vent.
The eruption of Mount St. Helens in 1980 was caused in part by a lava dome shifting to allow explosive gas and steam to escape from inside the mountain.
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