A Cascadian Connection

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Mount Shasta, California, USA - 4322 m (14,179 ft)

Did you toss and turn again last night wondering,  Where does all that tectonic plate material go?

If you have an earth science background you know about the connection between the Cascadia Subduction Zone and the Cascade Mountains.

Many more people have been hearing about the Cascadia Subduction Zone. The dramatic earthquake in Japan has reminded people in the western USA about our own earthquake risks.

The risk for the biggest earthquakes lies along the coast from far northern California up into southern British Columbia, Canada. Here tectonic plates (Gorda, Juan de Fuca, Explorer) under the Pacific Ocean are pushing eastward under the North American Plate.

(The famous San Andreas Fault that threatens San Francisco and Los Angeles is south of this region. It occurs along a different plate margin and moves in a different direction.)

As the Earth’s crustal material is pushed deep under the North American continent along the Cascadia Subduction Zone it eventually nears the Earth’s molten core. Over geologic time scales this crustal material is heated and becomes molten. It eventually escapes upward through the arc of volcanoes known as the Cascade Mountain Range.

The Cascade Mountains are inland but roughly parallel to the coastline where the Cascadia Subduction occurs. This north-south line of volcanoes roughly traces the leading edge of the subducting tectonic plates. The length of this zone is about 1,100 km (~685 miles). The Cascade’s include mountains such as Mt. Ranier, Mt. St. Helens, Mt. Hood and many others.

The southern edge of the Gorda Plate (the southern-most subducting plate) is roughly parallel with the southern edge of the Cascade Mountains, which is south of Mount Lassen in the state of California.

South of the Cascade Mountains another mountain range begins. The Sierra Nevada Mountains extend from there to the south through California and form the eastern edge of the fertile Central Valley. If you are familiar with California geography the separation between the Cascade Mountains and the Sierra Nevada Mountains is roughly along a west-to-east line from the town of Chico to Susanville.

The Cascadian Connection then is that the crustal material once under the Pacific Ocean, which pushed under North America long ago, now forms mountains such as Mount Shasta in this photograph. The scale of this system is enormous, both in time and space.

In this larger region the risk of earthquakes and volcanic eruptions is real. It is important to be prepared. Nobody can predict their occurrence precisely, at this time. The most prudent approach is to be prepared TODAY. Emergency supplies and shelter should be part of everyone’s routine.

If you have a refrigerator you should have an emergency supply kit.

How much energy do you think it took to push enough crustal material under North America to explosively build Mount Shasta, and all the other Cascade Volcanoes?

The answer is:  Enough energy to periodically and abruptly release violent earthquakes throughout the region. Are you ready?




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