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USGS CMG InfoBank: Volcanoes Far From Plate Margins

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Comment: 11:51 - 13:20 (01:29)
Source: Annenberg/CPB Resources - Earth Revealed - 13. Volcanism
Keywords: "Richard Hazlett", "Robert Tilling", volcano, "convergent plate margin", "divergent plate margin", "oceanic hot spot", desert, California, subduction, "cinder cone", crust, tension, fracture, "plate tectonics", pressure, magma, eruption

Our transcription: Volcanoes are for the most part associated with convergent and divergent plate boundaries or well established hot spots, but there are some intriguing exceptions.
Volcanic activity has occasionally occurred far from these settings, such as here in the desert of southeastern California.
We're 700 kilometers from the nearest convergent plate boundary where subduction related volcano activity is occurring and 200 or 300 kilometers from the nearest divergent plate boundary.
And yet here we sit near the top of a young cinder cone volcano that has been active probably within the past few thousand years far from a plate boundary.
Well, that's certainly right, Rick.
Most of the volcanoes are no longer plate boundaries, but throughout the world there are lots of places where the crust is being stretched by tensional forces and fractures are opening up.
I think this still reflects plate tectonics in some sense because the crust is being thinned and pulled apart, and under that tension the crust actually fractures, and if you have that situation, the pressure is relieved on the system so the magma then can rise up.
So wherever in this region you have localized magma due to whatever heat sources that might exist, the magma will come through and erupt and form a cinder cone.

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