Cobb hotspot

The Cobb hotspot is a marine volcanic hotspot at (46˚ N, 130˚ W),[1] which is 460 km (290 mi) west of Oregon and Washington, North America, in the Pacific Ocean. Over geologic time, the Earth's surface has migrated with respect to the hotspot through plate tectonics, creating the Cobb-Eicklberg seamount chain. The hotspot is currently collocated with the Juan de Fuca Ridge.

Cobb Hotspot Map
Labeled Map indicating the Cobb Hotspot and surrounding features
Hotspots
The Cobb hotspot is shown as 5 on map.

Cobb Seamount chain

The Cobb hotspot has created an underwater mountain range that extends 1,800 km (1,100 mi) to the northwest and ends at the Aleutian Trench. The oldest mount in the chain is the Marchland Seamount, at 30 to 43 Ma (million years old). The old, northwestern end of the chain collides with a subduction zone; therefore, the true age of the hotspot is difficult to determine as the oceanic crust is being consumed.[2] Axial Seamount is the hotspot's most recent eruptive center, which last erupted in 2015, 2011 and 1998.[3][4] The central ridge of the hotspot is thicker than the surrounding crust by a few kilometers and may be accumulated buildup from the magma released at the hotspot, which is essentially a submarine volcano with a root twenty to forty kilometres (12 to 25 mi) in diameter, reaching a depth of 11 kilometres (6.8 mi) beneath the volcano. The magma flows at a rate of 0.3 to 0.8 m3/s (11 to 28 cu ft/s). The caldera is 1,450 metres (4,760 ft) below sea level.[5][6]

Geochemistry

Hotspots are formed when magma from the lower mantle upwells to the crust of Earth and breaks through the surface crust, whether that be oceanic crust or continental. This movement of magma breaks through the upper mantle, or the lithosphere, and creates a volcanic spot. This does not mean that all volcanoes are hotspots; some are created through interactions at plate boundaries. Tectonic plates move over hotspots creating a chain of volcanically-formed mountains over time. This is supported by the theory of plate tectonics. The peaks and mountains left behind are no longer active volcanoes. Hotspots do not necessarily occur on a plate boundary, though the Cobb Hotspot does.[7]

Comparisons with mid-ocean ridge basalts

The magmas from the spreading ridge and the hotspot have differences. For one, they contain dissimilar concentrations of elements like Na2O, CaO and Sr at a given mafic level. This difference highlights that the magmas were formed at different depths in the mantle. It is theorized that the hotspot magma was melted deeper than that of the ridge. For these two masses of magma to exist, the temperature of the magma at the Cobb Hotspot must be of a particularly high temperature.[8][9] It is undetermined whether the hotspot was created from mantle-core boundary convection, as the end of the chain is subducting under another. The initial plume of magma would leave behind geologic evidence at the surface, but due to the consumption of the older end of the chain this evidence isn't visible.

Variations along the chain

Trace elements were used to discover that older mounts created by the Cobb Hotspot contained more minerals like olivine and augite; both mafic minerals. Younger mounts created by the hotspot contain more minerals like calcic plagioclase, augite and pigeonite; they contain little to no olivine. These characteristics found at the younger mounts are like those found in basalts recovered from the Juan de Fuca Ridge.[10] It is inferred that much of the difference in basalt composition along the chain is due to the time-dependent distance between hotspot and ridge. Oceanic crust thickens with distance from the mid-ocean ridge at which it originated. Therefore, as the Pacific plate migrated, the magma from the Cobb hotspot interacted with different thicknesses of crust. A thicker ocean crust would result in more differentiated basalt, while thinner crusts, like those at the current hotspot location, create less differentiated magma.[11]

Interaction of the Cobb hotspot and the Juan de Fuca Ridge

The magma supply to the Cobb hotspot is more primitive than that of the Juan de Fuca Ridge magma. As the archaic magma flows beneath the magma chamber of the ridge, it causes further melting and rapid cooling, which allows for fractional crystallization.[6][9]

See also

References

  1. ^ Latitude.to. "GPS coordinates of Cobb hotspot, United States. Latitude: 46.0000 Longitude: -130.0000". Latitude.to, maps, geolocated articles, latitude longitude coordinate conversion. Retrieved 2017-05-05.
  2. ^ Keller, R.; Fisk, M.; Duncan, R.; Rowe, M.; Russo, C.; Dziak, R. (2003-12-01). "Cobb Hotspot Volcanism Prior to 7 Million Years ago". AGU Fall Meeting Abstracts. 32: V32A–1002. Bibcode:2003AGUFM.V32A1002K.
  3. ^ Chadwick, J.; Perfit, M.; Embley, B.; Ridley, I.; Jonasson, I.; Merle, S. (2001-12-01). "Geochemical and Tectonic Effects of the Interaction of the Cobb Hotspot and the Juan de Fuca Ridge". AGU Fall Meeting Abstracts. 31: T31D–02. Bibcode:2001AGUFM.T31D..02C.
  4. ^ "Axial Seamount - Hydrothermal vents". www.pmel.noaa.gov. Retrieved 2017-06-04.
  5. ^ Michael West; William Menke; Maya Tolstoy (February 2003). "Focused magma supply at the intersection of the Cobb hotspot and Juan de Fuca ridge" (PDF). Retrieved 2008-11-19.
  6. ^ a b Michael West; William Menke; Maya Tolstoy. Focused Melt supply at the Cobb Hotspot/ Juan de Fuca Plate (PDF).
  7. ^ "What is a Hot Spot? | Volcano World | Oregon State University". volcano.oregonstate.edu. Retrieved 2017-05-05.
  8. ^ Rhodes, J. M.; Morgan, C.; Liias, R. A. (1990-08-10). "Geochemistry of axial seamount lavas: Magmatic relationship between the Cobb Hotspot and the Juan de Fuca Ridge". Journal of Geophysical Research: Solid Earth. 95 (B8): 12713–12733. Bibcode:1990JGR....9512713R. doi:10.1029/JB095iB08p12713. ISSN 2156-2202.
  9. ^ a b Chadwick, J (2005). "Magmatic effects of the Cobb hot spot on the Juan de Fuca Ridge". Journal of Geophysical Research: Solid Earth. 110: 1–16. doi:10.1029/2003jb002767.
  10. ^ "Geochemical evolution of the Cobb hotspot". gsa.confex.com. Retrieved 2017-04-22.
  11. ^ "Abstract: Progressive changes in the composition of Cobb hotspot lavas due to thinning lithosphere (2012 GSA Annual Meeting in Charlotte)". gsa.confex.com. 2012-11-07. Retrieved 2017-06-04.

Coordinates: 46°00′N 130°00′W / 46.0°N 130.0°W

Axial Seamount

Axial Seamount (also Coaxial Seamount or Axial Volcano) is a seamount and submarine volcano located on the Juan de Fuca Ridge, approximately 480 km (298 mi) west of Cannon Beach, Oregon. Standing 1,100 m (3,609 ft) high, Axial Seamount is the youngest volcano and current eruptive center of the Cobb–Eickelberg Seamount chain. Located at the center of both a geological hotspot and a mid-ocean ridge, the seamount is geologically complex, and its origins are still poorly understood. Axial Seamount is set on a long, low-lying plateau, with two large rift zones trending 50 km (31 mi) to the northeast and southwest of its center. The volcano features an unusual rectangular caldera, and its flanks are pockmarked by fissures, vents, sheet flows, and pit craters up to 100 m (328 ft) deep; its geology is further complicated by its intersection with several smaller seamounts surrounding it.

Axial Seamount was first detected in the 1970s by satellite altimetry, and mapped and explored by Pisces IV, DSV Alvin, and others through the 1980s. A large package of sensors was dropped on the seamount through 1992, and the New Millennium Observatory was established on its flanks in 1996. Axial Seamount received significant scientific attention following the seismic detection of a submarine eruption at the volcano in January 1998, the first time a submarine eruption had been detected and followed in situ. Subsequent cruises and analysis showed that the volcano had generated lava flows up to 13 m (43 ft) thick, and the total eruptive volume was found to be 18,000–76,000 km3 (4,300–18,200 cu mi). Axial Seamount erupted again in April 2011, producing a mile-wide lava flow. There was another eruption in 2015.

Bowie hotspot

The Bowie hotspot is a volcanic hotspot, located 180 kilometres (110 mi) west of the Queen Charlotte Islands in the Pacific Ocean.

Almost all magma created by the hotspot has the composition of basalt, and so the volcanoes are constructed almost entirely of this igneous rock. The eruptions from the Bowie hotspot are effusive eruptions because basaltic magma is relatively fluid compared with magmas typically involved in more explosive eruptions, such as the andesitic magmas that produce some of the spectacular and dangerous eruptions around the margins of the Pacific Ocean.

Bowie hotspot is believed to be perhaps 100 to 150 km (60 to 90 mi) wide and underlain by a mantle plume that is relatively deep. It is also considerably weak.Eruptions from the Bowie hotspot have left a trail of underwater mountains across the Pacific, called the Kodiak-Bowie Seamount chain, which is an underwater mountain region of seamounts along a line beneath the northern Pacific Ocean. The oldest volcano in the chain is Kodiak Seamount with an estimated age of 24 million years and the youngest called Bowie Seamount.

Geological studies show that the base of Bowie Seamount formed less than a million years ago. The summit of Bowie Seamount is even younger and shows signs of having been active as recently as 18,000 years ago. Because of its shallow depth, some geologists believe Bowie Seamount was an active volcanic island throughout last ice age.

Brown Bear Seamount

Not to be confused with Bear Seamount.Brown Bear Seamount is a seamount (underwater volcano) approximately 300 mi (483 km) west of the coast of Oregon. It is connected to the larger Axial Seamount by a small ridge. Brown Bear Seamount was created by the Cobb hotspot, and is located on the near west of the Juan de Fuca Ridge. It has not been affected by ocean spreading as much as its neighbor, and is therefore not quite as geologically complex. Brown Bear is the second youngest volcano in the chain, after Axial. No eruptions are known.

Cobb Seamount

Cobb Seamount is a seamount (underwater volcano) and guyot located 500 km (310 mi) west of Grays 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 lies just west of the Cascadia subduction zone, and was discovered in August 1950 by the U.S. Fish and Wildlife Service fisheries research vessel R/V John N. Cobb (FWS 1601). 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, and 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.

Cobb–Eickelberg Seamount chain

The Cobb-Eickelberg seamount chain is a range of undersea mountains formed by volcanic activity of the Cobb hotspot located in the Pacific Ocean. The seamount chain extends to the southeast on the Pacific Plate, beginning at the Aleutian Trench and terminating at Axial Seamount, located on the Juan de Fuca Ridge.The seamount chain is spread over a vast length of approximately 1800 km. The location of the Cobb hotspot that gives rise to these seamounts is 46° N -130° W. The Pacific plate is moving to the northwest over the hotspot, causing the seamounts in the chain to decrease in age to the southeast. Axial is the youngest seamount and is located approximately 480 km west of Cannon Beach, Oregon. The most studied seamounts that make up this chain are Axial, Brown Bear, Cobb, and Patton seamounts. There are many other seamounts in this chain which have not been explored.

Geology of the Pacific Ocean

The Pacific Ocean evolved in the Mesozoic from the Panthalassic Ocean, which had formed when Rodinia rifted apart around 750 Ma. The first ocean floor which is part of the current Pacific Plate began 160 Ma to the west of the central Pacific and subsequently developed into the largest oceanic plate on Earth.The tectonic plates continue to move today. The slowest spreading ridge is the Gakkel Ridge on the Arctic Ocean floor, which spreads at less than 2.5 cm/year (1 in/year), while the fastest, the East Pacific Rise near Easter Island, has a spreading rate of over 15 cm/year (6 in/year).

Hotspot (geology)

In geology, the places known as hotspots or hot spots are volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the surrounding mantle. Their position on the Earth's surface is independent of tectonic plate boundaries. There are two hypotheses that attempt to explain their origins. One suggests that hotspots are due to mantle plumes that rise as thermal diapirs from the core–mantle boundary. The other hypothesis is that lithospheric extension permits the passive rising of melt from shallow depths. This hypothesis considers the term "hotspot" to be a misnomer, asserting that the mantle source beneath them is, in fact, not anomalously hot at all. Well-known examples include the Hawaii, Iceland and Yellowstone hotspots.

Musicians Seamounts

Musicians Seamounts are a chain of seamounts in the Pacific Ocean, north of the Hawaiian Ridge. There are about 65 seamounts, some of which are named after musicians. These seamounts exist in two chains, one of which has been attributed to a probably now-extinct hotspot called the Euterpe hotspot. Others may have formed in response to plate tectonics associated with the boundary between the Pacific Plate and the former Farallon Plate.

The seamounts were constructed on young oceanic crust during the Cretaceous, but a second phase of volcanic activity took place during the Eocene. Deep sea coral reefs occur on the seamounts.

Outline of oceanography

The following outline is provided as an overview of and introduction to Oceanography.

Patton Seamount

Patton Seamount is a prominent seamount (underwater volcano) in the Cobb–Eickelberg Seamount chain in the Gulf of Alaska. Located 166 nmi (307 km; 191 mi) east of Kodiak Island and reaching to within 160 m (520 ft) of the ocean surface, Patton is one of the largest seamounts in the Cobb–Eickelberg Seamount chain. It was originally created near the coast of Oregon by the Cobb hotspot 33 million years ago, and was moved to its present location by tectonic plate movement. Patton is one of the most well-understood seamounts, as a major expedition using DSV Alvin in 1999 and another in 2002 helped define the scope of the seamount's biological community. Like other large seamounts, Patton acts as an ecological hub for sea life. Dives have revealed that the volcano is heavily encrusted in sea life of various forms, including sea stars, corals, king crabs, demersal rockfish, and other species.

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