Week 5: Converging Plates - Jon Morris

Week 5:  Converging Plates - Jon Morris

As my interest in Geology grows, I decided to take my family on a trip to observe a convergent-plate margin, specifically convergent boundaries between oceanic and continental plates.  We decided as a family to go and visit the Cascade volcanoes along the Washington-Oregon coast of North America, as it was accessible for us since going to the next nearest example of convergent boundaries between oceanic and continental plates is in the Andes Mountain Range in South America.

The Cascade Volcanoes are a number of volcanoes in a volcanic arc in western North America, that extend from British Columbia, through Washington and Oregon, and down to Northern California.  The distance of this range of volcanoes is well over 700 miles.  While we were there, we learned that this arc of volcanoes formed due to subduction along the Cascadia subduction zone.  I had to remind my daughter that a subduction zone is a zone in which a tectonic plate of the Earth’s crust moves downward into the mantle beneath another tectonic plate.

The cities that are near the aforementioned arc are Portland, Seattle, and Vancouver.  Because these cities exist in the greater subduction zone, they are subject to earthquakes and volcanic activity.  I have learned that due to the high population of these areas, it makes the cities that exist in this subduction zone extremely dangerous.  The Cascade Volcanic Arc has an eruptive history that is complete with the possibility of more eruptions in the future.  The Cascade Volcanic Arc volcanoes are not extinct and have, and are expected to, erupt in the future.

There are nearly 20 major volcanoes in the Cascade Arc, and I was both dismayed and excited to learn that the area has been active with volcanic activity for the last 37 million years.  To be honest, I am glad that my family does not live anywhere near the area of the Cascade Volcanic Arc.

The deformation of the Cascade Volcanic Arc has been low as recently measured, but have been known to include landslides, pyroclastic flows, lava flows, and huge mudflows of volcanic ash and debris known as lahars.  The types of stresses involved actually include both tensionial and compressional stresses at the same time.  Because the Cascade Volcanic Arc covers almost 700 miles, we can observe different types of structures being produced in different specific locations along the Cascade Volcanic Arc.

One interesting picture we saw of the Cascade Volcanic Arc is a picture of some of the Cascades Volcanoes in Oregon.  You’ll notice that the picture shows several of the peaks of the Cascade Range in Oregon forming an almost straight line:

("Cascades Volcanoes in Oregon - EPOD - a service of USRA", 2012)

This picture looks northward from near McKenzie Pass, Oregon, and shows the variability of the Oregon Cascades.

Cascades Volcanoes in Oregon - EPOD - a service of USRA. (2012). Retrieved from https://epod.usra.edu/blog/2012/04/cascades-volcanoes-in-oregon.html