Cobb Seamount
Encyclopedia
Cobb Seamount is a seamount
(underwater volcano) and guyot
located 500 km (310.7 mi) west of Gray's Harbor, Washington, United States
. Cobb Seamount is one of the seamounts in the Cobb-Eickelberg Seamount chain
, a chain of underwater volcanoes created by the Cobb hotspot
that terminates near the coast of Alaska. It is aligned along the Cascadia subduction zone
, and was discovered in 1950 by MV John N. Cobb. By 1967, over 927 km (576 mi) of soundings and dozens of samples from the seamount had been collected.
Cobb Seamount is geologically interesting for its terraced, pinnacle structure; however, most of the attention it has received has been to its biological community. Like many other seamounts, Cobb Seamount acts as a biological center of diversity, and supports a dense oceanic ecosystem. Relatively convenient access and an interesting biological setting have made the seamount an object of several scientific cruises and dives.
of basalts retrieved from the volcano show that it is 27 ± 6 million years in age. Cobb Seamount's slopes average 12° in grade, and are indented by four prominent terraces at various depths; this unique morphology suggests that it was formed in the Oligocene
period, and was then terraced over time by wave erosion. Cobb Seamount's summit itself sits atop a 100 m (328 ft) deep terrace. The volcano's pinnacle is generally flat, and is defined by a pocketed area approximately 880 m (2,887 ft) by 577 m (1,893 ft) in size.
and functions as an "island of stability" for local organisms. It supports an extensive fish population, mostly Sebastes
species and especially Sebastes miniatus
. Bird life has been noted in the area of its summit, indicating that it is a prime fishing ground.
The summit of the volcano is dominated by a carpet of Hinnites multirugosus, which forms the base of a dense ecosystem of sponges and other small, sessile organisms. The species is otherwise scarce in its distribution in the Pacific; its abundance is accommodated by the scarcity of its chief predator, the Sea Star
Orthasterias koehleri. The reason for the sea star's disparity is unknown, as it is extremely common on nearby seamounts.
The steeper flanks of the volcanoes are carpeted by coralline algae
of the Lithothamnion
and Lithophyllum
geneses. In some areas, Borgiola pustulosa is more common. Red-colored colonies of demosponge
and related species predominant the ecosystem, which includes sea urchin
s, sponges, algae
, anemone
s, and gastropods. While overall the species diversity on the seamount is lower than a comparable area on the surface, the species present have grown in greater numbers and have formed larger colonies, to the point that there was little to no bare rock surface on the seamount, and none has been found in expeditionary dives. Some endemism to the seamount has also been noted.
The seamount's abundant sea life has made it a target for heavy fishing since the 1960s. However, the fishing is very difficult to monitor, since Cobb lies outside of the U.S. Exclusive Economic Zone
and therefore fishing vessels are not regulated. It is known that it has been the site of trawling, gill net, and longline fishing for some time, mostly by the Japanese
and Oregon
ian fleets. In 1993, the National Oceanic and Atmospheric Administration
sponsored a study on the seamount, which concluded that concerns as to overfishing at the seamount have some merit. The study also notes that fishermen there have different fishing patterns, because of different physical conditions at the seamount.
There was tentative expert interest in installing an experimentation platform on Cobb Seamount. The seamount is an accessible distance away from the shore, and would give scientists the ability to work with Cobb Seamount's unique, isolated, and scientifically significant seamount biology. The idea was proposed by P. L. Peterson et al. in a presentation to the Offshore Technology Conference
in 1969.
Seamount
A seamount is a mountain rising from the ocean seafloor that does not reach to the water's surface , and thus is not an island. These are typically formed from extinct volcanoes, that rise abruptly and are usually found rising from a seafloor of depth. They are defined by oceanographers as...
(underwater volcano) and guyot
Guyot
A guyot , also known as a tablemount, is an isolated underwater volcanic mountain , with a flat top over 200 meters below the surface of the sea. The diameters of these flat summits can exceed ....
located 500 km (310.7 mi) west of Gray's Harbor, Washington, United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. Cobb Seamount is one of the seamounts in the Cobb-Eickelberg Seamount chain
Cobb-Eickelberg Seamount chain
The Cobb-Eickelberg Seamount chain is a seamount chain stretching from the Aleutian Trench in the north to Axial Seamount, the youngest volcano in the chain, which lies approximately 300 miles west of Cannon Beach, Oregon. The chain was created by the Cobb hotspot as the Pacific Plate drifted in a...
, a chain of underwater volcanoes created by the Cobb hotspot
Cobb hotspot
The Cobb hotspot is a volcanic hotspot located off the Oregon/Washington coast of the United States. The hotspot is at the Juan de Fuca Ridge, and has made the Cobb-Eickelberg Seamount chain...
that terminates near the coast of Alaska. It is aligned along the Cascadia subduction zone
Cascadia subduction zone
The Cascadia subduction zone is a subduction zone, a type of convergent plate boundary that stretches from northern Vancouver Island to northern California. It is a very long sloping fault that separates the Juan de Fuca and North America plates.New ocean floor is being created offshore of...
, and was discovered in 1950 by MV John N. Cobb. By 1967, over 927 km (576 mi) of soundings and dozens of samples from the seamount had been collected.
Cobb Seamount is geologically interesting for its terraced, pinnacle structure; however, most of the attention it has received has been to its biological community. Like many other seamounts, Cobb Seamount acts as a biological center of diversity, and supports a dense oceanic ecosystem. Relatively convenient access and an interesting biological setting have made the seamount an object of several scientific cruises and dives.
Geology
Cobb Seamount lies 270 mi (434.5 km) off the coast of Washington, in the 8500 ft (2,590.8 m)-deep Cascadia Basin. Potassium-argon datingPotassium-argon dating
Potassium–argon dating or K–Ar dating is a radiometric dating method used in geochronology and archeology. It is based on measurement of the product of the radioactive decay of an isotope of potassium into argon . Potassium is a common element found in many materials, such as micas, clay minerals,...
of basalts retrieved from the volcano show that it is 27 ± 6 million years in age. Cobb Seamount's slopes average 12° in grade, and are indented by four prominent terraces at various depths; this unique morphology suggests that it was formed in the Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
period, and was then terraced over time by wave erosion. Cobb Seamount's summit itself sits atop a 100 m (328 ft) deep terrace. The volcano's pinnacle is generally flat, and is defined by a pocketed area approximately 880 m (2,887 ft) by 577 m (1,893 ft) in size.
Biology
Although it is one of over 100 underwater features in the region, Cobb Seamount is the only one known to extend well upwards into the region of the ocean penetrated by light. Like many other seamounts, Cobb Seamount is a local biological hotspotBiodiversity hotspot
A biodiversity hotspot is a biogeographic region with a significant reservoir of biodiversity that is under threat from humans.The concept of biodiversity hotspots was originated by Norman Myers in two articles in “The Environmentalist” , revised after thorough analysis by Myers and others in...
and functions as an "island of stability" for local organisms. It supports an extensive fish population, mostly Sebastes
Sebastes
Sebastes is a genus of fish in the family Sebastidae , most of which have the common name of rockfish. Most of the world's almost 110 Sebastes species live in the north Pacific, although two live in the south Pacific/Atlantic and four Sebastes is a genus of fish in the family Sebastidae (though...
species and especially Sebastes miniatus
Sebastes miniatus
Sebastes miniatus is a species of rockfish known by the common names vermilion rockfish, red snapper, and red rock cod. It is native to the waters of the Pacific Ocean off western North America from Baja California to Vancouver Island....
. Bird life has been noted in the area of its summit, indicating that it is a prime fishing ground.
The summit of the volcano is dominated by a carpet of Hinnites multirugosus, which forms the base of a dense ecosystem of sponges and other small, sessile organisms. The species is otherwise scarce in its distribution in the Pacific; its abundance is accommodated by the scarcity of its chief predator, the Sea Star
Sea star
Starfish or sea stars are echinoderms belonging to the class Asteroidea. The names "starfish" and "sea star" essentially refer to members of the class Asteroidea...
Orthasterias koehleri. The reason for the sea star's disparity is unknown, as it is extremely common on nearby seamounts.
The steeper flanks of the volcanoes are carpeted by coralline algae
Coralline algae
Coralline algae are red algae in the order Corallinales. They are characterized by a thallus that is hard because of calcareous deposits contained within the cell walls...
of the Lithothamnion
Lithothamnion
Lithothamnion is a genus of thalloid red alga comprising 103 species. Its members are known by a number of common names.Recorded common names are griuán, maërl, punalevä-suku, stenhinna and maerl. The monomerous, crustose thalli are composed of a single system of filaments which grow close to the...
and Lithophyllum
Lithophyllum
Lithophyllum is a genus of thalloid alga comprising 120 species. The monomerous, crustose thalli are composed of a single system of filaments which grow close to the underlying surface. Lithophyllum reproduces by means of conceptacles...
geneses. In some areas, Borgiola pustulosa is more common. Red-colored colonies of demosponge
Demosponge
The Demospongiae are the largest class in the phylum Porifera. Their "skeletons" are made of spicules consisting of fibers of the protein spongin, the mineral silica, or both. Where spicules of silica are present, they have a different shape from those in the otherwise similar glass sponges...
and related species predominant the ecosystem, which includes sea urchin
Sea urchin
Sea urchins or urchins are small, spiny, globular animals which, with their close kin, such as sand dollars, constitute the class Echinoidea of the echinoderm phylum. They inhabit all oceans. Their shell, or "test", is round and spiny, typically from across. Common colors include black and dull...
s, sponges, algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
, anemone
Anemone
Anemone , is a genus of about 120 species of flowering plants in the buttercup family Ranunculaceae in the north and south temperate zones...
s, and gastropods. While overall the species diversity on the seamount is lower than a comparable area on the surface, the species present have grown in greater numbers and have formed larger colonies, to the point that there was little to no bare rock surface on the seamount, and none has been found in expeditionary dives. Some endemism to the seamount has also been noted.
The seamount's abundant sea life has made it a target for heavy fishing since the 1960s. However, the fishing is very difficult to monitor, since Cobb lies outside of the U.S. Exclusive Economic Zone
Exclusive Economic Zone
Under the law of the sea, an exclusive economic zone is a seazone over which a state has special rights over the exploration and use of marine resources, including production of energy from water and wind. It stretches from the seaward edge of the state's territorial sea out to 200 nautical...
and therefore fishing vessels are not regulated. It is known that it has been the site of trawling, gill net, and longline fishing for some time, mostly by the Japanese
Fishing industry in Japan
The fishing industry in Japan constitutes both a major industry and export.-Fisheries:Fishing in Japan has long been a vital resource. While much Japanese fishing is done far from Japan, the fishing near Eastern Japan and Northeast is in question due to radiation and grocery shoppers may want to...
and Oregon
Oregon
Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...
ian fleets. In 1993, the National Oceanic and Atmospheric Administration
National Oceanic and Atmospheric Administration
The National Oceanic and Atmospheric Administration , pronounced , like "noah", is a scientific agency within the United States Department of Commerce focused on the conditions of the oceans and the atmosphere...
sponsored a study on the seamount, which concluded that concerns as to overfishing at the seamount have some merit. The study also notes that fishermen there have different fishing patterns, because of different physical conditions at the seamount.
Expeditions
Since its discovery in 1950 by the MV John N. Cobb, Cobb Seamount has been the target of passing cruises and sampling missions, totaling to over 927 km (576 mi) of soundings and dozens of samples by 1967. In 1968, Project Sea Use, a multi-party expedition using the RV Oceanographer, visited the seamount, and much of what was initially known about it stems from the expedition. This was followed in 1970, two expeditions in the late 1970s, and 1992, however all have been fairly limited in scope.There was tentative expert interest in installing an experimentation platform on Cobb Seamount. The seamount is an accessible distance away from the shore, and would give scientists the ability to work with Cobb Seamount's unique, isolated, and scientifically significant seamount biology. The idea was proposed by P. L. Peterson et al. in a presentation to the Offshore Technology Conference
Offshore Technology Conference
Offshore Technology Conference is an important conference and exhibition focused on the development of offshore energy resources, primarily oil and natural gas. It was started in 1969 and is held annually during the first week of May at Reliant Park in Houston, Texas, USA.OTC is the largest oil...
in 1969.