The Vance Seamounts are a group of seven

submarine volcano Submarine volcanoes are underwater vents or fissures in the Earth's surface from which magma can erupt. Many submarine volcanoes are located near areas of tectonic plate formation, known as mid-ocean ridges. The volcanoes at mid-ocean ridges ...

es located west of the

Juan de Fuca Ridge The Juan de Fuca Ridge is a mid-ocean spreading center and divergent plate boundary located off the coast of the Pacific Northwest region of North America. The ridge separates the Pacific Plate to the west and the Juan de Fuca Plate to the east ...

. Most of the seamounts contain a

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcano eruption. When large volumes of magma are erupted over a short time, structural support for the rock above the magma chamber is ...

. They are the southernmost of several near-ridge chains located on the

Pacific Plate The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At , it is the largest tectonic plate. The plate first came into existence 190 million years ago, at the triple junction between the Farallon, Phoenix, and Iza ...

, stemming from the

. The easternmost five of the seven were surveyed using SeaBeam

bathymetry Bathymetry (; ) is the study of underwater depth of ocean floors (''seabed topography''), lake floors, or river floors. In other words, bathymetry is the underwater equivalent to hypsometry or topography. The first recorded evidence of water de ...

. A chemical analysis of the lavas of the volcanoes indicated that the materials erupted from the volcanoes are relatively primitive. With the exception of one, the volcanoes form a nearly linear chain of circular volcanic cones. The second volcano from the northwest is not discretely shaped like the rest, rather it is a rough structure of lava cones and flows, which cover an area of at least . The six conical volcanoes (not including the odd one) range from in volume, averaging . Most of the volcanoes have gently sloping

plateau In geology and physical geography, a plateau (; ; ), also called a high plain or a tableland, is an area of a highland consisting of flat terrain that is raised sharply above the surrounding area on at least one side. Often one or more sides ha ...

s, in conformity with their low

shield volcano A shield volcano is a type of volcano named for its low profile, resembling a warrior's shield lying on the ground. It is formed by the eruption of highly fluid (low viscosity) lava, which travels farther and forms thinner flows than the more v ...

–like profiles, which have been heavily modified by multiple

s. These are generally very shallow, having been formed then filled almost completely by younger flows, leaving only parts of the rims untouched. Some also have landslide debris deposits near the base of the caldera rims, and several have since been breached (their sides have collapsed). Small cones lay along the seafloor surrounding the main formation. The southeastern volcanoes also have low-level parallel faults arranged linearly against the Juan de Fuca Ridge. The construction of the cones left a lot of debris scattered across the ocean surface, much of which is aligned parallel to the ridge axis. The largest of these cones are nearly across, whereas the smallest appear to be only a few hundred meters in diameter. In 2006, an expedition was conducted by the

Monterey Bay Aquarium Research Institute The Monterey Bay Aquarium Research Institute (MBARI) is a private, non-profit oceanographic research center in Moss Landing, California. MBARI was founded in 1987 by David Packard, and is primarily funded by the David and Lucile Packard Foundation ...

on the seamount formations.

References

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External links

2006 expedition
Submarine volcanoes Seamounts of the Pacific Ocean Seamount chains Ridge volcanoes

See also

References

External links