The Pacific Northwest’s non-Cascade volcano

Lying about 300 miles west of Cannon Beach, Oregon is Axial Seamount. This undersea volcano, which was discovered right around the time Mount St. Helens had its infamous eruption, was the first seamount to be observed in an eruptive state in real-time by instruments on its slopes. That event occurred in 1998, with other eruptions observed in 2011 and 2015. The 2011 eruption even produced a mile wide lava flow. It is 3,700 feet tall at the summit, which lies 4,600 feet below the ocean’s surface.

Axial Seamount sits atop the Juan de Fuca Ridge, which is a spreading center where the Pacific Plate and the Juan de Fuca Plate are being actively created. From here, the new basaltic seafloor of the Pacific Plate moves to the northwest before being subducted below the North American Plate, creating the geologic setting for most of Alaska’s volcanoes. The Juan de Fuca Plate moves to the east from this spreading center to subduct below the Pacific Northwest, creating the Cascade volcanoes that we know and love.

Axial Seamount isn’t the only volcano on the Juan de Fuca Ridge. What sets it apart is that it is at the location where the ridge meets a geologic hotspot. On top of existing magmatic activity from the ridge, the hotspot brings an added source of heat rising from deep within the mantle.

This can be thought of as being similar to Iceland. That island nation also sits atop a divergent tectonic plate boundary, but the presence of the hotspot there gives the volcanism that extra boost to reach above the Atlantic Ocean’s surface. While Axial does not make it above the surface like Iceland does, it is the largest seamount in its area. Other examples of volcanic hotspots include Hawaii and Yellowstone, but as far as we know Axial does not experience supervolcanic eruptions like the latter.

Aside from this, Axial’s geology is complex and poorly understood. Part of this stems from its two different sources for activity within an existing, but geologically different, volcanic region. More than that, though, is its inaccessibility. Our maps of the surface of both Mars and the Moon are more accurate and detailed than those of the seafloor (see: NASA), and Axial Seamount is a good example of this. It is an over 3,000 foot tall very active volcano that wasn’t discovered until around 1980.

While very interesting, based on our current understanding, Axial’s eruptions are not a threat to land or to people who pass over it while transiting the Pacific Ocean.