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.[1]

Eruptions from the Bowie hotspot have left a trail of underwater mountains across the Pacific, called the Kodiak-Bowie Seamount chain,[2] 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.

Hotspots
The Bowie hotspot is marked 3 on map.
Kodiak-Bowie Seamounts
Over millions of years, the Pacific Plate has moved over the Bowie hotspot, creating the Kodiak-Bowie Seamount chain in the Gulf of Alaska

See also

References

  1. ^ Nataf, Henri-Claude (2000). "Seismic Imaging of Mantle Plumes". Annual Review of Earth and Planetary Sciences. 28 (1): 391–417. Bibcode:2000AREPS..28..391N. doi:10.1146/annurev.earth.28.1.391.
  2. ^ "NOAA Ocean Explorer: Gulf of Alaska 2004". Retrieved 2007-09-02.
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).

Hodgkins Seamount

Hodgkins Seamount is a seamount in the Kodiak-Bowie Seamount chain, located south of Pierce Seamount and north of Bowie Seamount. It has apparently experienced two generically different episodes of volcanism, separated by about 12 million years. Like the rest of the Kodiak-Bowie seamounts, it was formed by the Bowie hotspot.

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.

Kodiak Seamount

Kodiak Seamount is the oldest seamount in the Kodiak-Bowie Seamount chain, with an estimated age of 24 million years. It lies at the northernmost end of the chain and its flat-topped summit is strewn with fault lines. Like the rest of the Kodiak-Bowie seamounts, it was formed by the Bowie hotspot.

Kodiak Seamount will eventually be destroyed by subduction by the Aleutian Trench once it is carried into the trench by the ongoing plate motion, although this will not fully occur for several million more years if the current rate of motion is maintained. Because of Kodiak Seamount's approach into the Aleutian Trench, it is literally cracking up under the stress. Although Kodiak is the oldest extant seamount in the Kodiak-Bowie chain, the adjacent lower slope contains transverse scars indicating earlier subduction of seamounts.

Kodiak–Bowie Seamount chain

The Kodiak–Bowie Seamount chain, also called the Pratt–Welker Seamount chain and the Kodiak Seamounts, is a seamount chain in southeastern Gulf of Alaska stretching from the Aleutian Trench in the north to Bowie Seamount, the youngest volcano in the chain, which lies 180 km (112 mi) west of the Queen Charlotte Islands, British Columbia, Canada. The oldest volcano in the chain is the Kodiak Seamount. Although the Kodiak Seamount is the oldest extant seamount in the Kodiak-Bowie chain, the adjacent lower slope contains transverse scars indicating earlier subduction of seamounts.

The Kodiak–Bowie Seamount chain are mostly extinct volcanoes that formed above the Bowie hotspot. This is a 100-to-150-km-wide morphological swell presumably of thickened hotspot generated crust, although there are no seismic refraction data across the swell to define crustal thickness. The crest of one such peak, Patton Seamount originally formed off Washington state as a submerged volcano 33 million years ago. Over time, as the Pacific Plate moved steadily northwest, Patton Seamount was carried off the Bowie hotspot and into the Gulf of Alaska. New volcanoes were formed one after another over the hotspot, creating the Kodiak–Bowie Seamount chain.

Explorations of the Kodiak–Bowie Seamount chain have shown that despite the fact that most of the seamounts were created by the Bowie hotspot, all are unique in their size, shape, and volcanic features. The seamounts teem with deep-sea corals, sponges, and fish. Recent expeditions to these seamounts using manned submersibles and ROVs have discovered many marine species and have greatly expanded the knowledge of the range of deep sea corals in this region. For example, the Bowie Seamount is a biologically rich area with a dynamic and productive ecosystem. Because of this unique biological rich area, Bowie Seamount was declared a Pilot Marine Protected Area on December 8, 1998.The Kodiak–Bowie seamount chain is at the northern triple junction between the Pacific, North American, and Juan de Fuca plates. Available age determinations on Kodiak and Giacomini Seamounts give an approximate average rate of movement along the chain of 6.5 cm (3 in) per year.

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