My Blogs (olelog) are mainly based on my daily reading of earth science news.
Here on whatonearth.olehnielsen.dk I try to weave some of the pieces together to a greater whole with added background info.
The Pacific Ocean is the world's largest geographic feature, the Pacific Ocean covers more than 166 million square kilometers,which is about one-third of the earth's surface. The area of the Pacific is greater than that of all of the continents combined, and it makes up nearly half of the area covered by the earth's oceans.
Volcanic arcs and oceanic trenches partly encircling the Pacific Basin form the so-called Ring of Fire, a zone of frequent earthquakes and volcanic eruptions. The trenches are shown in blue-green. The volcanic island arcs, although not labelled, are parallel to, and always landward of, the trenches. For example, the island arc associated with the Aleutian Trench is represented by the long chain of volcanoes that make up the Aleutian Islands.
There are (at least) 18 trenches in the Pacific Ocean
The Kuril Islands are a volcanic arc made of about 45 volcanoes on 20 islands. The Pacific plate moves northwest with respect to the Okhotsk plate with a velocity of about 90 mm/year. The Pacific plate subducts beneath the Okhotsk plate at the Kuril Trench and becomes progressively deeper to the northwest, remaining seismically active to a depth of 680 km.
Heated up by the subduction melting magma rises through the Okhotsk plate to feed the volcanoes of the Kuril Islands.
The formation of the Kuril Archipelago began in the late Cretaceous (approximately 90 million years before present).
Proposed Plate boundaries
The Okhotsk Plate is a continental tectonic plate covering the Sea of Okhotsk, the Kamchatka Peninsula, and Eastern Japan. It was considered a part of the North American Plate, but recent studies show that it is an independent plate. It is bounded on the north by the North American Plate, on the east by the Pacific Plate at the Kuril-Kamchatka Trench and the Japan Trench, on the south by the Philippine Plate at the Nankai Trough, on the west by the Eurasian Plate, and possibly on the southwest by the Amurian Plate. (See The Russian peninsula Kamchatka is not American). The location of the Okhotsk-Eurasia boundary is poorly constrained. The Okhotsk plate is being compressed and extruded from between North America and Eurasia.
The Amurian Plate (or Amur Plate) is a proposed continental tectonic plate covering Manchuria, the Korean Peninsula, Western Japan, and Primorsky Krai. It is not clear yet whether it is an independent plate or a part of the Eurasian Plate. It is bounded on the north and west by the Eurasian Plate, on the northeast by the Okhotsk Plate, and on the south by the Philippine Plate. Lake Baikal is considered a boundary between the Amurian Plate and the Eurasian Plate.
(The existence of the Amurian plate (AM), which covers the region from the Baikal rift to the Nankai trench, including the Korean Peninsula, was proposed first by Zonenshain and Savostin (1981) [Zonenshain, L. P., and L. S. Savostin, ''Geodynamics of the Baikal rift zone and plate tectonics of Asia,'' Tectonophysics, 76, 1-45, 1981]).
The deepest known point on Earth is at the bottom of the Mariana Trench, a depression in the floor of the western Pacific Ocean, just east of the Mariana Islands. The Mariana Trench is 2 500 km long and averages 70 km wide. Within it, about 210 miles southwest of Guam, lies the deepest known point on Earth. Named the “Challenger Deep” for the British survey ship Challenger II that located it in 1951, this underwater gorge plunges to a depth of ca.11,000 meters! It is deeper than Mt. Everest is tall. The trench is the boundary where two tectonic plates meet, a subduction zone where the Pacific Plate is being subducted under the Philippine Plate.
The mud volcanoes of the Mariana Trench region provide a unique look at rocks and fluids from a subduction zone.
The water depth ofthe trench increases westward as a result of less sediment
input from smaller volcanic islands.
The trench is almost filled, and extensively over-ridden by Alaskan accretionary prism in the east
The Aleutian arc extends about 3,000 km from the Gulf of Alaska to Kamchatka. It marks the region where the Pacific plate subducts into the mantle beneath the North American plate. This subduction is responsible for the generation of the Aleutian Islands and the deep offshore Aleutian Trench. Relative to a fixed North American plate, the Pacific plate is moving north-west at a rate that increases from 6.6 cm per year in the arc's eastern region to 8.6 cm per year near its western edge. In the east, the convergence of the plates is nearly perpendicular to the plate boundary. However, because of the boundary's curvature, as one travels westward along the arc, the subduction becomes more and more oblique to the boundary until the relative plate motion becomes almost parallel to the boundary at its western edge.
is a subduction trench of the Pacific plate under the North American plate and it extends from offshore central Kamchatka to Hokkaido
is a deep basin in the southern Sea of Okhotsk northwest of the Kuril arc
is a volcanic peninsula in eastern Siberia and the northward extension of the Kuril Islands.
is an extension of the Kuril Trench, and sometimes the whole Trench is referred to as the Kuril-Kamchatka Trench.
See A Hawaiian Hotspot Puzzle Solved
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