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Geolens

Case study US

Cascadia subduction zone

Pacific Northwest

Cascadia links an offshore subduction zone with earthquakes, tsunamis and the Cascade volcanoes. The shared plate setting produces these hazards through different processes.

Snow-covered Mount Adams viewed from the Naches Loop Trail in Washington.
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Mount Adams, Washington. This Cascade arc volcano is part of the volcanic chain above the Cascadia subduction zone.
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Location: 46.20°, -124.00°

Oceanic lithosphere descends beneath North America at the Cascadia subduction zone. Water released from the descending plate promotes partial melting in the mantle above, helping supply the Cascade volcanic arc over geological time.

A large earthquake on the offshore plate boundary can displace the seabed and generate a tsunami. Use the plate-boundaries and tsunami models to separate gradual subduction, sudden fault slip and the movement of water that follows.

Open this state in the lab

Exam-style question

Explain how the Cascadia subduction system forms a volcanic arc over geological time, and how a megathrust earthquake can generate a tsunami in minutes.

Teacher hint: Distinguish magma generation above the descending slab from the rapid seafloor displacement that can produce a tsunami.

Process labs

Plate boundariesEarthquakesTsunamiVolcanoes

Sources

  • USGS Cascadia
  • NOAA / NWS tsunami