the process of subduction is responsible for forming the islands of japan.
the process of subduction is responsible for forming the islands of japan.
which process is responsible for forming the islands of japan?
subduction
the canadian portion of the pacific northwest began forming during the early jurassic period when a group of active volcanic islands collided against a pre-existing continental margin and coastline of western canada. these volcanic islands, known as the intermontane islands by geoscientists, were formed on a pre-existing tectonic plate called the intermontane plate about 245 million years ago by subduction of the former insular plate to its west during the triassic period. this subduction zone records another subduction zone called the intermontane trench under an ancient ocean between the intermontane islands and the former continental margin of western canada called the slide mountain ocean. this arrangement of two parallel subduction zones is unusual in that very few twin subduction zones exist on earth; the philippine mobile belt off the eastern coast of asia is an example of a modern twin subduction zone. as the intermontane plate drew closer to the pre-existing continental margin by ongoing subduction under the slide mountain ocean, the intermontane islands drew closer to the former continental margin and coastline of western canada, supporting a volcanic arc on the former continental margin of western canada. as the north american plate drifted west and the intermontane plate continued to drift east to the ancient continental margin of western canada, the slide mountain ocean began to close by ongoing subduction under the slide mountain ocean. this subduction zone eventually jammed and shut down completely about 180 million years ago, ending the arc volcanism on the ancient continental margin of western canada and the intermontane islands collided, forming a long chain of deformed volcanic and sedimentary rock called the intermontane belt, which consists of deeply cut valleys, high plateaus, and rolling uplands. this collision also crushed and folded sedimentary and igneous rocks, creating a mountain range called the kootenay fold belt which existed in far eastern british columbia.
volcanology of canada
following signing of the instrument of surrender, september 2, 1945, ryukyu islands were administered by department of the navy, september 21, 1945-june 30, 1946, with commanding officer, naval operating base, okinawa functioning as chief military government officer under authority of commander-in-chief u.s. pacific fleet. transfer of administration from department of the navy to war department authorized by joint chiefs of staff (jcs) approval, april 1, 1946, of jcs 819/11, march 5, 1946, with added proviso of jcs 819/12, march 22, 1946. pursuant to implementing instructions of general headquarters u.s. army forces in the pacific (ghq afpac), okinawa base command redesignated ryukyus command, effective july 1, 1946, by general order 162, headquarters u.s. army forces, western pacific, and made responsible for administration under a deputy commander for military government. ryukyu islands administered successively by ryukyus command, july 1-november 30, 1946; philippines-ryukyus command, december 1, 1946-july 31, 1948; and ryukyuan command, august 1, 1948-december 15, 1950. uscar established, effective december 15, 1950, by a directive of headquarters far east command (hq fec, formerly ghq afpac), ag 091.1 (5 dec 50) rca, december 5, 1950, implementing a jcs memorandum, sm 2474-50, october 11, 1950, directing commander-in-chief far east, gen. douglas macarthur, to organize a civil administration for the ryukyu islands in accordance with jcs 1231/14, october 4, 1950. uscar continued to function under department of the army (formerly war department), 1950-71. amami island group of ryukyu islands was returned to japan by the agreement between the united states of america and japan concerning the amami islands, signed december 24, 1953, and made effective december 25, 1953. uscar abolished following entrance into force, may 15, 1972, of the agreement between the united states of america and japan concerning the ryukyu islands and the daito islands, signed june 17, 1971, by which the remaining island groups of the ryukyu islands, including the okinawa island group, were returned to japan.
united states civil administration of the ryukyu islands