Английская Википедия:Espenberg volcanic field

Содержание

Текст

Текст

Текст

Текст

Текст

Текст

Текст

Текст

Текст

Espenberg is a volcanic field in Alaska that contains the largest maars on Earth. It was active during the Pleistocene until 17,500 years BP, when a large eruption formed the Шаблон:Convert wide Devil Mountain Maar and deposited tephra over Шаблон:Convert, burying vegetation and forming the largest maar on Earth. Other maars in the field are the North and South Killeak Maars and Whitefish Maar, and Devil Mountain is a shield volcano.

The large size of these maars has been attributed to the interaction between permafrost and ascending magma, which favoured intense explosive eruptions. Soils buried underneath the Devil Mountain Maar tephra have been used to reconstruct the regional climate during the last glacial maximum. The maars are part of the Bering Land Bridge National Preserve.

Toponyms

"Killeak" means "East" in the Inupiaq language.Шаблон:Sfn Devil Mountain Maar is also known as "Qitiqliik" or "Kitakhleek" ("Double Lakes") and Whitefish Maar as "Narvaaruaq" or "Navaruk" ("Big Lake").Шаблон:SfnШаблон:Sfn This volcanic field is also known as the Cape Espenberg-Devil Mountain volcanic field.Шаблон:Sfn

Geography and geomorphology

The Espenberg volcanoes lie on the northern Seward Peninsula in Alaska. They are the northernmost volcanoes of North America with late Pleistocene activity, lying just south of the Arctic Circle. Other volcanoes of the Seward Peninsula are found at Imuruk Lake.Шаблон:Sfn There are no roads in the area but the maars can be readily reached from the sea by following streamsШаблон:Sfn or by chartered bush aircraft.

Espenberg is located on a peninsula between the Chukchi Sea to the north and west and Goodhope Bay to the east. From east to west lie North and South Killeak Maar, Devil Mountain Maar and Whitefish Maar; additionally there are cinder cones, lava flowsШаблон:Sfn and five small shield-like volcanoesШаблон:Sfn such as Devil Mountain. Devil Mountain appears to be capped with an alignment of cinder cones with associated lava flows.Шаблон:Sfn Volcanologically, the field is situated in a back-arc region.Шаблон:Sfn Volcanic rocks from the field have basaltic compositions.Шаблон:Sfn

Файл:Devil Mountain Lakes from a Small Plane (4884042722).jpg

Devil Mountain Maar

Devil Mountain Maar is Шаблон:Convert wide and Шаблон:Convert deep, while North Killeak Maar, South Killeak Maar and Whitefish Maar are Шаблон:Convert, Шаблон:Convert and Шаблон:Convert wideШаблон:Sfn and the Killeak Maars reach depths of over Шаблон:Convert; Whitefish Maar is much shallowerШаблон:Sfn with a depth of Шаблон:Convert. Such dimensions make the Espenberg maars the largest known on Earth and the Espenberg maars comparable in size with calderas;Шаблон:Sfn other maars at lower latitudes are much smaller.Шаблон:Sfn The maars are mostly circular with the exception of Devil Mountain Maar which is partly separated by a small sand spit into the northern Шаблон:Convert wide North Devil Mountain Maar and the Шаблон:Convert wide South Devil Mountain Maar;Шаблон:Sfn formerly they were considered to be two separate maars.Шаблон:Sfn

The water surface of the maars lies between Шаблон:Convert below their rim.Шаблон:Sfn Eight Шаблон:Convert wide and Шаблон:Convert deep crater-like depressions lie underwater in Devil Mountain Maar and similar but partly filled depressions are also found at the Killeak Maars.Шаблон:Sfn Layered volcanic deposits crop out in Шаблон:Convert high cliffs around Devil Mountain MaarШаблон:Sfn and within gullies around the other maars.Шаблон:Sfn

The maars are emplaced in over Шаблон:Convert thick lavas and sediments of Pleistocene age.Шаблон:Sfn The Singeakpuk River, the Kalik River, the Kitluk River, the Espenberg River and the Kongachuk Creek flow through the volcanic field;Шаблон:Sfn the Kitluk River drains Devil Mountain Maar.Шаблон:Sfn Other than volcanic constructs, plateaus, thermokarst lakes, dry lakes and yedoma hills dot the landscape.Шаблон:Sfn

Climate, biota and human use

At Kotzebue, Шаблон:Convert northeast of the volcanic field, annual temperatures fluctuate between Шаблон:Convert in July and Шаблон:Convert in January. Annual precipitation there is about Шаблон:Convert, mostly falling during summer.Шаблон:Sfn The vegetation belongs to the Bering tundra ecoregionШаблон:Sfn and is not uniform over the area.Шаблон:Sfn Green alder thickets and willow grow on the maar benches;Шаблон:Sfn at Tempest Lake north of Devil Mountain Maar the vegetation is characterized by a tundra featuring forbs, mosses, sedges and shrubs and is quite dense.Шаблон:Sfn Caribou used to be frequent in the area, and there are numerous fish in the maars.Шаблон:Sfn

Native Americans used the maars as a source of fish and as hunting grounds, and remains of human activity have been identified at their shores. Devil Mountain was used as a lookout post, navigational landmark and as a source of rocks for sinkers and weights.Шаблон:Sfn In recent times, sediment cores were obtained from North Killeak Maar and Whitefish Maar;Шаблон:Sfn the former has been used to reconstruct the past climate of the region during the Holocene, including the occurrence of cold periods. The Espenberg volcanoes are part of the Bering Land Bridge National Preserve.Шаблон:Sfn

Eruption history

The non-maar vents at Espenberg appear to be over 500,000 years old, given that they are covered with vegetation and the lavas shattered by frost,Шаблон:Sfn and are probably older than the maars.Шаблон:Sfn The Espenberg maars were originally considered to be of Holocene age, but research has shown that the latest eruptions occurred during the Pleistocene. Various dating methods have been used to determine the ages of the Espenberg maars:Шаблон:Sfn

Файл:North & South Killeak Maar- 2991edit (16087886809).jpg

North and South Killeak Maar

• Whitefish Maar might be 100,000 – 200,000 years old,Шаблон:Sfn perhaps 160,000 years ago. Sedimentation since the eruption has partly filled in Whitefish MaarШаблон:Sfn and reduced its depth.Шаблон:Sfn
• North Killeak Maar is over 125,000 years old,Шаблон:Sfn older than South Killeak Maar.Шаблон:Sfn
• South Killeak Maar formed over 40,000 years ago.Шаблон:Sfn
• Devil Mountain Maar is the youngest vent, it formed 17,500 years BPШаблон:Sfn and is the most recent volcanic event of the area.Шаблон:Sfn Formerly it was believed that its northern half was 7,100 years old.Шаблон:Sfn

All maars formed in one complex eruption sequenceШаблон:Sfn which in the case of Devil Mountain Maar probably lasted only a few weeks to months.Шаблон:Sfn During the eruption, numerous individual explosions and surges took place and emplaced base surges and Strombolian deposits,Шаблон:Sfn while frozen blocks of sediment were ejected from the vents.Шаблон:Sfn Devil Mountain Maar appears to have formed from the coalescence of several vents during the course of the eruption. Individual explosive events formed the depressions on the floor of the maars.Шаблон:Sfn

Devil Mountain Maar deposited a tephra called the Devil Mountain Lake tephraШаблон:Sfn over an area of Шаблон:Convert.Шаблон:Sfn It reached thickness of more than Шаблон:Convert over an area of Шаблон:Convert, burying soil and vegetationШаблон:Sfn and falling into lakes. The soil found underneath the Devil Mountain Maar tephra is known as Kitluk paleosoil.Шаблон:Sfn Plant remains found buried underneath the tephra are well preserved and have been used to infer climatic and biotic conditions during the last glacial maximum in the region;Шаблон:Sfn vegetation at that time was apparently different from todayШаблон:Sfn and there was no widespread ice cover. The tephra is used as a tephrostratigraphic marker for the late Pleistocene. The eruption of the Killeak Maars also produced tephra deposits, which are also found in lakes and have similar compositions to the tephra of the Devil Mountain Maar.Шаблон:Sfn Their deposition disrupted local wetlands and altered the topography.Шаблон:Sfn

Mechanism of formation

Maars are after cinder cones the second-most common type of volcano. They form when magma interacts explosively with surrounding rocks, excavating broad but shallow craters on the surface. The Espenberg maars are the first known maars to have formed within permafrost;Шаблон:Sfn other large maars in permafrost have been found in the Pali-Aike volcanic field of Argentina.Шаблон:Sfn Interactions between magma and ice are different than these between lava and ice, as ice conducts heat only slowly and a large amount of energy is consumed during its sublimation; thus its melting and explosive evaporation occurs only slowly.Шаблон:Sfn

The maars lie in Шаблон:Circa Шаблон:Convert thick permafrost,Шаблон:Sfn which was probably thicker during the Pleistocene when the maars formed.Шаблон:Sfn The abundant ice would have produced a limited amount of water due to thermodynamic limitations of magma-induced ice melting, creating an ideal environment for highly explosive eruptions which may have been further intensified by the release of methane during the thawing of the permafrost. Landslides at the margins of the volcanic vents expanded the forming craters and supplied additional ice to the evaporation processes,Шаблон:Sfn ultimately yielding the large size of the Espenberg maars.Шаблон:Sfn The eruptions that formed the Espenberg maars occurred during fully glacial climate, while interglacial (including Holocene) eruptions on the Seward Peninsula have yielded lava flows; this implies that the glacial climate influenced the types of eruption that took place.

The Espenberg maars have been used as analogues for certain craters on Mars.

References

Sources

• Шаблон:Cite journal
• Шаблон:Cite journal
• Шаблон:Cite journal
• Шаблон:Cite journal
• Шаблон:Cite journal
• Шаблон:Cite journal
• Шаблон:Cite book

External links

• Environmental Histories from Whitefish and Imuruk Lakes, Seward Peninsula, Alaska