. The Cascade Range is a long series of volcanoes that extends from Mount Lassen

Question

. The Cascade Range is a long series of volcanoes that extends from Mount Lassen and Mount Shasta in northern California through the states of Oregon and Washington. These are considered to be active volcanoes, although none are erupting at the moment. Use plate tectonics theory to briefly explain why there are active volcanoes in this region of North America. Include in your answer the specific names of lithosphere plates involved at this location. (There is no need to explain particular magma forming processes or the difference between shield volcanoes and strato-volcanoes

Explanation / Answer

Ans:

West coast of North American plate (it is a continental plate), comprising of northern California, Oregon and Washington, is bordered by the Juan de Fuca plate (it is an oceanic plate; Figs. 1 and 2). The convective motion of partially molten rocks in the asthenosphere, pushes away the Juan de Fuca plate towards the North American plate away from the Pacific plate (Figs. 1 and 2). Owing to the high density Juan de Fuca plate is submerged below the continental plate of North America. The submerged portion of the oceanic plate melts because of high pressure and temperature at deeper levels. Thus, the molten rocks or magma ejects out when it finds a way through the cracks and fissures in the upper continental plate of North America. This is the mechanism in which Cascade Range of volcanoes were formed. The presence of active volcano in the Cascade Range indicates that the Juan de Fuca plate is still moving towards the North American plate. Following figures explains the above statements.

Reference:

http://www.google.co.in/imgres?imgurl=http://www.earthscope.org/images/remote/https_s-media-cache-ak0.pinimg.com/originals/2a/39/11/2a39114e379be45b1320826f63ef93ff.jpg&imgrefurl=http://www.earthscope.org/science/geo-events/m4.5-oregon&h=720&w=763&tbnid=kXflkUJa-0fM-M:&zoom=1&docid=wPuOQcfS5MxspM&ei=bR46VZb5JMe7mgXWwIGYAQ&tbm=isch&ved=0CCsQMygRMBE

http://en.wikipedia.org/wiki/List_of_Cascade_Range_topics

http://en.wikipedia.org/wiki/Cascade_Range

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