4/16/2023 0 Comments Stronghold 2 maps downloads![]() ![]() Eight eruptions produced about 1.3 cu mi (5.3 km 3) of basaltic lava during a time interval of a few hundred years about 10,500 years ago. During the past 11,000 years, eruptive activity at Medicine Lake Volcano has been episodic. Basalt is mostly absent at higher elevation, where andesite dominates and rhyolite and small volumes of dacite are present. The lower flanks consist of mostly basaltic and some andesitic lavas. Although mafic lavas predominate on the volcano's flanks, all lava compositions from basalt to rhyolite have erupted during Pleistocene time. Similar high-alumina basalt has continued to erupt around the volcano throughout its history. Medicine Lake Volcano began to grow about one million years ago in Pleistocene time, following the eruption of a large volume of tholeiitic high- alumina basalt. The small lake from which Medicine Lake volcano derives its name lies within the central caldera.Įruptive history Early history Late Holocene andesitic to rhyolitic lavas were derived by fractionation, assimilation, and mixing from high alumina basalt parental magma. Several small differentiated magma bodies may have been fed by and interspersed among a plexus of dikes and sills. ![]() Later conclusions were that Medicine Lake caldera formed by collapse in response to repeated extrusions of mostly mafic lava beginning early in the history of the volcano (perhaps in a manner similar to the formation of Kilauea caldera in Hawaii). The only eruption recognized to have produced ash flow tuff occurred in late Pleistocene time, and this eruption was too small to account for formation of the caldera. No single large eruption has been related to caldera formation. ![]() The distribution of late Pleistocene vents, mostly concentrated along the rim, suggests that ring faults already existed when most of the andesite erupted. The caldera may have formed by collapse after a large volume of andesite was erupted from vents along the caldera rim. Medicine Lake is in the caldera of the volcano, which measures 4.3 by 7.5 mi (7 by 12 km). It is believed that the Medicine Lake volcano is unique, having many small magma chambers rather than one large one. Medicine Lake is part of the old caldera, a bowl-shaped depression in the mountain. Helens, coating the volcano's sides with flow after flow of basaltic lava. The eruptions were gentle rather than explosive like Mount St. Medicine Lake Volcano has been active for 500,000 years. Lava Beds National Monument lies on the northeast flank of the volcano. Lavas from Medicine Lake Volcano are estimated to be at least 140 cu mi (600 km 3) in volume, making Medicine Lake the largest volcano by volume in the Cascade Range ( Newberry Volcano in Oregon has the second largest volume). The Medicine Lake shield rises about 3,900 ft (1,200 m) above the Modoc Plateau to an elevation of 7,795 ft (2,376 m). The volcano is primarily composed of basalt and basaltic andesite lava flows, and has a 4.3 by 7.5 mi (7 by 12 km) caldera at the center. The underlying rock has downwarped by 0.3 mi (0.5 km) under the center of the volcano. The 0.6 mi (1 km) thick shield is 22 mi (35 km) from east to west and 28 to 31 mi (45 to 50 km) from north to south, and covers more than 770 sq mi (2,000 km 2). ![]() The volcano is located in a zone of east-west crustal extension east of the main axis of the Cascade Volcanic Arc and the Cascade Range. Medicine Lake Volcano is a large shield volcano in northeastern California about 30 mi (50 km) northeast of Mount Shasta. Sentinel-2 true-color satellite image, scale 1:50,000. Medicine Lake Volcano, California, September 27, 2017. ![]()
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