Week 5 – Jacob Fisher – Cascadia Subduction Zone

This week I visited the Cascadia subduction zone, a convergent plate boundary that spans from northern California up into British Columbia. The fault separates the Juan de Fuca and North American plates. The Juan de Fuca plate is being subducted beneath the North American plate to the east while being driven from the west by seafloor spreading at the Juan de Fuca Ridge. The fault is a thrust type due to the compression from the convergent plate boundary. (Pacific Northwest Seismic Network, n.d.)

Subduction of the Juan de Fuca Plate beneath the North American Plate [PHOTO: https://www.usgs.gov/media/images/subduction-juan-de-fuca-plate-beneath-north-american-pla]

The subducting slab causes the overlying mantle to partially melt, forming the magma that sustains the Cascade Range of volcanoes (black triangles in the above graphic). The rocks found throughout the Cascade Range are primarily andesite and dark basaltic rocks that contain very little silica. (Graham, 2005)

References

Cascadia Subduction Zone. (n.d.). Retrieved April 9, 2020, from https://pnsn.org/outreach/earthquakesources/csz

Graham, J. (2005). Mount Rainier National Park Geologic Resource Evaluation Report . National Park Service U.S. Department of the Interior. Retrieved from https://irma.nps.gov/Datastore/DownloadFile/425308