Snake River Plain
The Snake River Plain ( German : Ebene des Snake River) is a geographic region in the south of the US state of Idaho . It is characterized by volcanic manifestations and the Snake River , which gives it its name, flows in it . The plain is the economic center of the state, in it are eight of the ten largest cities of Idaho, including the capital Boise , and the most important agricultural areas. The basis of the economic importance is the artificial irrigation of arable land by water from the Snake River, its reservoirs and an important aquifer below the plain.
Geographically, the level of the Snake River is an elongated depression around 600 km long and 50 to 100 km wide at an average of 1437 m above sea level. It runs in an arc from the Yellowstone Plateau and the Teton Range in the Rocky Mountains in the east to the state border with Oregon in the west and covers about the southern third of Idaho. In doing so, it cuts the outermost northern foothills of the Basin and Range region , whose horst structures limit it to the north and south. The United States Geological Survey assigns them to the geological province of the Columbia Plateau .
geology
Geographically, the Snake River Plain is a unit, the surface shape is essentially constant apart from the most recent volcanic manifestations. In the subsurface, however, significant differences can be seen between the western third and the eastern majority of the plain, as well as a small transition zone.
The west of the plain is a rift valley . Flood basalts with an age of 16 to 14 million years and, on a smaller scale, up to 6 million years ago, which originate from crevice volcanoes and are counted as Columbia plateau basalt, extend into it from the west . Essentially, the bottom of the trench is covered with several thousand meters of sediment deposited by rivers and lakes in which rhyolithic layers of tuff and volcanic ash , typically between 15 and 11 million years old, are embedded. To the west of Twin Falls there are even younger basaltic lava fields, less than 700,000 years old. In much of the Pliocene , the west of the plain was covered by prehistoric Lake Idaho , which contributed significantly to sedimentation.
The character of the eastern part of the Snake River Plains is less easy to determine. Previous assumptions have suggested that the discharge of volcanic material created cavities that collapsed under the weight of the surface rocks associated with volcanic deposits; other authors suggested a stretch fracture.
Yellowstone hotspot
The subsoil of the central and eastern plains are rhyolithic tuff and rocks from compacted volcanic ash . The established explanation takes a volcanic hotspot in which by a plume of magma from the mantle was fed. The North American Plate , one of the tectonic plates of the earth's crust , shifts over this plume , so that volcanic activity appears to be moving from southwest to northeast. The hotspot is now under the Yellowstone National Park and is responsible for the volcanic activity of the Yellowstone super volcano , its caldera , the geysers and the other volcanic manifestations of the national park.
The first eruptions that can be safely assigned to this hotspot occurred in today's Nevada in the Neogene , around 17 million years ago . About 12 million years ago it reached what is now the Snake River Plain. The magma rising from the earth's mantle melted granite rocks in the earth's crust . The surface of the earth bulged. A further increase in energy resulted in a catastrophic eruption and the melted granite was ejected in the form of rhyolite . A caldera and large layers of tuff and ash were created. With the apparent migration, the location of the next eruption shifted. Until about 6–4 million years ago, largely overlapping calderas with a diameter of 15–70 km each formed. One study counted 142 large eruptions, with medium and small eruptions being added. The Island Park Caldera was formed by the last eruption associated with the plain. Since then, the hotspot has moved on to its current location in northwest Wyoming under the Yellowstone area. Rhyolitic tuff and rocks from volcanic ash originate from the activity of the hotspot, they form the deep subsoil of the eastern Snake River Plain. In the earth's crust, at a depth of at least 10 km, the melting processes of the hotspot left a layer of basaltic slag around 10–15 km thick , which to this day is largely in a molten state. Since then, it has provided the energy for volcanic activity in the region. After cooling, the surface subsided, resulting in a subsidence that marks the migration route of the hotspot: the lowlands of the Snake River Plain.
Basalt eruptions
The rhyolitic rocks are covered on around 95% of the area by quaternary basaltic lava , in which smaller amounts of sedimentary rock are embedded. Around six million years ago, a tectonic process began in western North America that led to the expansion of the earth's crust, which resulted in a large number of largely parallel rift fractures running roughly in a north-south direction . At that time the Basin and Range region was created, which extends from Mexico in the south to Idaho in the north and is characterized by parallel structures of eyrie and ditch . Where the forces hit the volcanic rocks left behind by the hotspot that had passed through a few million years earlier, the stretching of the crust led to a large number of elongation fractures in a northwest-southeast orientation. Through them, molten basalt emerged from the pocket left by the hotspot as lava to the surface. Both shield and crevice volcanoes formed at the expansion fractures and their surroundings , from which large basaltic lava flows emerged in the period from around 6 million years ago to around 15,000 years ago. They form several layers up to 1200 m thick in the center of the Snake River Plain, in which individual layers of sedimentary rock are embedded.
Around 300,000 years ago, five lava domes formed in the eastern Snake River Plain when rhyolite magma rose rapidly through vents . The highest of them is the Big Southern Butte with a height of 2273 m above sea level, it rises around 760 m above the surrounding plain.
The last phase of volcanism in the plain so far took place in the period from around 15,000 years ago to around 2000 years ago. The largest of the parallel elongation fractures has a length of around 80 km and is known as the Great Rift (of Idaho) . In its vicinity, three more lava flows from crevice and small shield volcanoes , accompanied by cinder cones , arose in the rest of the eastern plain . The most prominent lava field is the Craters of the Moon area on the Great Rift , which has been a protected area as the Craters of the Moon National Monument since 1924. This is where the region's youngest volcanic activity is located, the 2000 year old North Crater Flow .
In the transition area between the rift valley in the west and the volcanic plain in the center and east, the volcanic subsoil and sediment layers overlap. Significant fossil sites are located here , particularly the Hagerman Fossil Beds National Monument .
A special event occurred at the end of the last Ice Age (known as Wisconsin glaciation in North America ) around 14,000 years ago, when prehistoric Lake Bonneville in what is now Utah , which was filled by ice-age meltwater, rose above the height of Red Rock Pass , the lowest Place its bank, and the soft rock broke through within a very short time. The water masses of this approximately 52,000 km² large and up to 300 m deep lake flowed in a catastrophic flood event , the Bonneville Flood , first to the north and then in the Snake River Plain to the west. They tore away the vegetation, the humus cover and parts of the sedimentary rock and partially exposed the volcanic layers. Boulders carried into the plains by the tide can be seen in Massacre Rocks State Park .
Settlement history
Away from the river and outside of the artificially irrigated area, the landscape is characterized by the original dry steppe. The landscape is determined by sagebrush and various grasses. The most common is the blue tuft wheatgrass ( Agropyron spicatum - also: Pseudoroegnaria spicata ), which grows in dense tufts. Purshia tridentata and Sarcobatus are common shrubs. The roof brim appears as a neophyte . Without irrigation, the land is hardly fertile and uninviting.
The Snake River Plain was therefore only sparsely populated by prehistoric Indians. Traces of the Clovis culture were found sporadically. In historical times it was inhabited by Shoshone and Bannock Indians, who now live together in the Fort Hall reservation near Pocatello. The Lewis and Clark expedition of 1805/6 brought the first whites to what is now Idaho, but they passed the area north of the Snake River. In the 1830s, the Snake River area was frequented by trappers and fur traders from the British Hudson's Bay Company . In 1833, US officer Benjamin Bonneville explored the Snake River and parts of the plain. The Oregon Trail ran along the river in the 1840s, as pioneers and settlers moved west.
Volcanic soil contains many minerals in easily soluble form and is therefore far above average fertile. However, it is also permeable to water and arable farming is mostly dependent on artificial irrigation. Early settlers used the Snake River as a source of water to irrigate their fields. From the 1920s, the Bureau of Reclamation created several large and many small reservoirs on the Snake River and its tributaries. The largest is the American Falls Reservoir west of Pocatello. Canals led from the reservoirs through the plain and transported the water to more distant cultivation areas.
The remoteness in the center of the Snake River Plain was used during World War II when locations for internment camps were sought as part of the internment of Americans of Japanese descent. In 1942, the Minidoka War Relocation Center was set up in the hinterland of the Snake River, north of Twin Falls , where nearly 10,000 Japanese and Japanese Americans were interned by 1945.
When in 1947 the Argonne National Laboratory in Illinois was looking for a large test site for nuclear research , it turned to remote Idaho again. The National Reactor Testing Station was set up west of Idaho Falls , from what is now the Idaho National Laboratory . In the course of time, 52 research reactors were built there, three of which are still running today (as of early 2010).
The Snake River Plain today
Eight of Idaho's ten largest cities, including the capital Boise , and most of Idaho's arable land are now on the Snake River Plain . The plain is accessed in its full length in the south by the Interstate Highway I-86 , I-84 and the US Highway US-30, which is largely bundled with it . The US-20 runs north of the plain . To the east, Interstate 15 crosses the area from north to south.
As early as the 1920s, geologists from the United States Geological Survey explored the groundwater conditions in the Snake River Plain. Only the development of drilling technology after the Second World War made it possible to use the groundwater in a meaningful way by drilling wells . Under the eastern Snake River Plain lies a huge aquifer with an area of around 28,000 km² and a thickness of up to 1500 m, even if the relevant groundwater movements only take place in the uppermost 90–150 m. In this layer alone there are around 250-370 million cubic kilometers of water, which is not quite the same as Lake Erie or five to seven times that of Lake Constance . Under the western Snake River Plain, there are larger groundwater resources in the so-called Treasure Valley with the two largest cities of Idaho, Boise and Nampa, and Caldwell, another one of the ten largest cities in the state. Here lies a complex system of aquifers close to the surface, those in medium depths and deep layers.
Around 2/3 of the irrigation water on the Snake River Plain comes from surface water and 1/3 from groundwater. The irrigation technology allowed the boom in agricultural production and, as a result, population growth and the development of modern industry. Boise's population doubled in the 1960s, and it doubled again by around 1995. Today the region has a strong base in both agriculture and industrial enterprises.
Web links
- Digital Atlas of Idaho: Snake River Plain . Idaho State University
- United States Geological Survey: America's Volcanic Past - Idaho
Individual evidence
- ^ Snake River Plain in the Geographic Names Information System of the United States Geological Survey
- ↑ a b c d e Douglass E. Owen: Geology of Crater of the Moon. ( Memento of October 30, 2011 in the Internet Archive ) (PDF; 3.3 MB, copy in the Internet Archive) National Park Service, 2008, pages 5–7
- ↑ USGS: Geologic Provinces of the United States: Columbia Plateau Province
- ↑ USGS: America's Volcanic Past - Idaho ( Memento of the original from November 19, 2009 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ a b c d e State University of Idaho: Idaho Geology Web Course - Module: Neogene Snake River Plain-Yellowstone Volcanic Province
- ^ Digital Atlas of Idaho: Snake River Plain . Idaho State University
- ↑ John W. Shervais, Scott K. Vetter, Barry B. Hanan: Layered Mafic Sill Complex Beneath the Eastern Snake River Plain: Evidence from Cyclic Geochemical Variations in Basalt . In: Geology, May 2006, pp. 365-368
- ^ National Park Service: Craters of the Moon - Geologic Activity
- ↑ http://www.nature.com/ngeo/journal/v6/n5/pdf/ngeo1774.pdf
- ^ Robert Baer Smith, Lee J. Siegel: Windows into the earth: the geologic story of Yellowstone and Grand Teton. Oxford University Press, 2000. ISBN 0195105974 , page 45 in Google Book Search
- ↑ United States Geologic Survey: America's Volcanic Past - Craters of the Moon National Monument ( Memento of the original from May 17, 2008 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Big Southern Butte in the Geographic Names Information System of the United States Geological Survey
- ↑ Lake Bonneville and the Bonneville Flood. USGS / Cascades Volcano Observatory, Vancouver, Washington, accessed February 2, 2010 .
- ^ Robert C. Bright, H. Thomas Ore: Evidence for the spillover of Lake Bonneville, southeastern Idaho . In: Geological Society of America, Centennial Field Guide - Rocky Mountain Section , Volume 2. Boulder, Colorado, Geological Society of America, 1987, ISBN 0-8137-5406-2 , pages 143-146
- ↑ Environmental Protection Agency: Ecoregions of Idaho - Front and Ecoregions of Idaho - Back .
- ^ State University of Idaho: Idaho Geology Web Course - Module: Snake River Plain Aquifer
Coordinates: 42 ° 52 ′ 33.5 " N , 113 ° 41 ′ 11.5" W.