Tuesday, 5 May 2015

Eruptive activity on Axial Seamount.

A seismic monitoring system beneath the northeast Pacific operated by the Ocean Observatories Initiative has detected a probable eruption on Axial Seamount, a submarine volcano roughly 480 km off the coast of Oregon. The network has detected around 8000 minor Earthquakes since Friday 1 May, accompanied by a drop in the sea-floor level of about 2.4 meters. Minor tremors around volcanoes are most commonly caused by magma moving through subterranean chambers beneath the vent of the volcano, and are therefore used as advances warning of eruptions. In this instance any eruption would be hard to directly observe due to its remote location, but presents little danger to any human settlement for the same reason.

A vent on Axial Seamount. Schmidt Ocean Institute.

Axial Seamount is a submarine volcano located on the Juan de Fuca Ridge, 480 km west of the Oregon Coast. It has been the subject of extensive study as it is extremely active and is of complex origins: it is on the intersection of the Cobb Hotspot Seamount Chain, and the Juan de Fuca extensional ridge; it is also close to the Blanco Fracture Zone. The seamount rises 700 m above the rest of the Juan de Fuca Ridge and about 1100 m above the surrounding sea floor; it is 1400 m bellow the sea surface. It is a biodiversity hotspot, hosting several 'black-smokers' - underwater hot springs producing super-heated mineral rich water, which support unique ecosystems.

The volcano appears to have a very regular eruptive cycle, enabling scientists to predict eruptions by the rate at which it inflates due to magma movements. It currently appears to be erupting roughly once every four years, having last erupted in 2011, and a 2015 eruption was predicted by Bill Chadwick of Oregon State University and Scott Nooner of the University of North Carolina Wilmington in September 2014.

The approximate location of Axial Seamount. Google Maps.

The Juan de Fuca ridge marks the extensional margin between the Juan de Fuca Plate and the Pacific Plate. The Juan de Fuca Plate is thought to be a remnant of an ancient plate known as the Farallon Plate, a once vast plate now largely subducted beneath the North American Plate. There are three remnants of this plate remaining off the west coast of the US; the Juan de Fuca Plate, the Gorda Plate to the south and the Explorer Plate to the north. The Juan de Fuca Ridge was once part of the longer Farallon Ridge, which ran along the eastern margin of the Farallon Ridge before it was fractured into three parts.

Spreading on the Juan de Fuca Ridge, and its relationship to the volcanoes of the North American west coast. Wikimedia Commons.

The Cobb Seamount Chain runs from the Aleutian Trench off the south coast of Alaska south to Axial Seamount. It is gets its name from the Cobb Seamount, which is 500 km west of the Washington coast, and was named after the research vessel MV John N Cobb; this can cause some confusion as other objects on the seafloor of the NE Pacific are also named after this vessel (Cobb) and are not necessarily related to the seamount chain.

See also...

Axial Seamount is a submarine volcano located on the Juan de Fuca Ridge, 480 km west of the Oregon Coast. It has been the subject of extensive study as it is extremely active and is of complex origins: it is on...


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