Volcanic Landforms: Extrusive Igneous

Mt.Drum Volcanic Crater Wrangell-St.Elias National Park
Mt.Drum Volcanic Crater in Wrangell-St.Elias National Park and Preserve

NPS Photo/ Betts and Hannan

Volcanic Landforms: Extrusive Igneous

Extrusive igneous landforms are the result of magma coming from deep within the earth to the surface, where it cools as lava. This can happen explosively or slowly, depending on the chemical composition of the lava and whether there is an easy path for it to take to the surface. If there is not a pathway, pressure builds up over time (like a shaken soda) until the magma forcibly explodes outward.
Formation of a Caldera
Diagram of the formation of a caldera

Trista L. Thornberry-Ehrlich, Colorado State University, after Stearns H.T. 1946 and Keating, B.H. 1992.

Volcanic processes are constantly changing the Earth. Eruptions can create new islands, build and destroy mountains, and alter landscapes. Active, dormant, and ancient remnants of eruptions are all contained within our National Parks. Volcanic processes create many features we see when visiting the National Parks such as:
  • Cinder cones- Short, steep volcanoes associated with limited eruptive events.
  • Shield volcanoes- Volcanoes ranging in size from small to truly massive, created by steady, non-violent outpouring of lava. Mauna Loa and Mauna Kea of Hawaii are shield volcanoes rising nearly 9 km (5.6 mi) fromt the seafloor.
  • Stratovolcanoes- Also known as composite volcanoes, stratovolcanoes erupt both as flows and violently. Mt. St. Helens and Mt. Rainier are stratovolcanoes.
  • Caldera- Collapse features that can fill in with water, creating a large lake. Crater Lake is an example of a caldera.

Hawaii is a chain of islands created by a hot spot, an unexplained source of concentrated heat deep within the earth. The hot spot remains in one place and the earth's crust moves over it, creating a chain of volcanoes.
Diagram of hot spot island chain formation
Diagram of Hawaii hot spot island chain formation.

Trista L. Thornberry-Ehrlich, Colorado State University.

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