Heart Mountain is an

klippe 350px, Schematic overview of a thrust system. The shaded material is called a window_(geology).html"_;"title="nappe._The_erosional_hole_is_called_a__window_(geology)">window_or_fenster._The_klippe_is_the_isolated_block_of_the_nappe_overlying_aut ...

just north of

Cody Cody may refer to: People *Cody (given name) *Cody (surname) * Cody (wrestler), a ring name of Cody Runnels Places Canada * Cody, British Columbia United States * Cody, Florida * Cody (Duluth), Minnesota * Cody, Missouri * Cody, Nebraska *Cody, ...

in the

U.S. state In the United States, a state is a constituent political entity, of which there are 50. Bound together in a political union, each state holds governmental jurisdiction over a separate and defined geographic territory where it shares its sover ...

Wyoming Wyoming () is a U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the south ...

, rising from the floor of the

Bighorn Basin The Bighorn Basin is a plateau region and intermontane basin, approximately 100 miles (160 km) wide, in north-central Wyoming in the United States. It is bounded by the Absaroka Range on the west, the Pryor Mountains on the north, the Bighor ...

. The

mountain A mountain is an elevated portion of the Earth's crust, generally with steep sides that show significant exposed bedrock. Although definitions vary, a mountain may differ from a plateau in having a limited Summit (topography), summit area, and ...

is composed of

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

and

dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start ...

through Mississippian age (about 500 to 350 million years old), but it rests on the

Willwood Formation The Willwood Formation is a sedimentary sequence deposited during the late Paleocene to early Eocene, or Clarkforkian, Wasatchian and Bridgerian in the North American land mammal age, NALMA classification. For over one hundred years, geologists have tried to understand how these older rocks came to rest on much younger strata. The

carbonate A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate g ...

rocks that form Heart Mountain were deposited on a basement of ancient (more than 2.5 billion years old)

granite Granite () is a coarse-grained (phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies undergro ...

when the area was covered by a large shallow tropical sea. Up until 50 million years ago, these rocks lay about to the northwest, where the eastern

Absaroka Range The Absaroka Range ( or ) is a sub-range of the Rocky Mountains in the United States. The range stretches about across the Montana–Wyoming border, and at its widest, forming the eastern boundary of Yellowstone National Park along Paradise Va ...

now stands. BighornBasin Absaroka ETM 2000jul24

Between 75 and 50 million years ago, a period of mountain-building called the

Laramide Orogeny The Laramide orogeny was a time period of mountain building in western North America, which started in the Late Cretaceous, 70 to 80 million years ago, and ended 35 to 55 million years ago. The exact duration and ages of beginning and end of the o ...

caused uplift of the

Beartooth Range The Beartooth Mountains are located in south central Montana and northwest Wyoming, United States, U.S. and are part of the Absaroka-Beartooth Wilderness, within Custer National Forest, Custer, Gallatin National Forest, Gallatin and Shoshone Natio ...

and

subsidence Subsidence is a general term for downward vertical movement of the Earth's surface, which can be caused by both natural processes and human activities. Subsidence involves little or no horizontal movement, which distinguishes it from slope move ...

of the Bighorn and Absaroka Basins. Just south of the Beartooth Range, this

orogeny Orogeny is a mountain building process. An orogeny is an event that takes place at a convergent plate margin when plate motion compresses the margin. An ''orogenic belt'' or ''orogen'' develops as the compressed plate crumples and is uplifted t ...

uplifted an elongate, somewhat lower plateau which sloped gently to the southeast toward the Bighorn Basin and to the south toward the Absaroka Basin. Immediately following this period of mountain-building, volcanic eruptions began to form the now extinct

volcano A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates are ...

es of the Absaroka Range that lie to the south of the Beartooths and extend into

Yellowstone National Park Yellowstone National Park is an American national park located in the western United States, largely in the northwest corner of Wyoming and extending into Montana and Idaho. It was established by the 42nd U.S. Congress with the Yellowston ...

. Between 50 and 48 million years ago a sheet of rock about in area detached from the plateau south of the Beartooths and slid tens of kilometers to the southeast and south into the Bighorn and Absaroka Basins. This sheet, consisting of Ordovician through Mississippian carbonate rocks and overlying Absaroka volcanic rocks, was probably originally about thick. Although the slope was less than 2 degrees, the front of the landslide traveled at least and the slide mass ended up covering over . This is by far the largest

rockslide A rockslide is a type of landslide caused by rock failure in which part of the bedding plane of failure passes through compacted rock and material collapses ''en masse'' and not in individual blocks. Note that a rockslide is similar to an avalanc ...

known on land on the surface of the earth and is comparable in scale to some of the largest known submarine landslides. Many models have been proposed to explain what caused this huge slab of rocks to start sliding and what allowed it to slide so far on such a low slope, fragmenting, thinning and extending as it went. Most geologists who have worked in the area agree that Absaroka volcanism played a role in the sliding and many suggest that a major volcanic or steam explosion initiated movement. Another model involves injection of numerous igneous

dike Dyke (UK) or dike (US) may refer to: General uses * Dyke (slang), a slang word meaning "lesbian" * Dike (geology), a subvertical sheet-like intrusion of magma or sediment * Dike (mythology), ''Dikē'', the Greek goddess of moral justice * Dikes ...

s with the resulting heating of water within pores in rocks causing an increase in pressure which initiated sliding. Some geologists have suggested that hot pressurized water (hydrothermal fluids), derived from a volcano which sat north of

Cooke City, Montana Cooke City is an unincorporated community and census-designated place (CDP) in Park County, Montana, United States. As of the 2010 census, it had a population of 75. Prior to 2010, it was part of the Cooke City-Silver Gate CDP. The community si ...

, effectively lubricated the sliding surface. Another possibility is that once the slide was moving,

friction Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction: *Dry friction is a force that opposes the relative lateral motion of t ...

heated the limestone along the sliding surface, creating

pseudotachylite Pseudotachylyte (sometimes written as pseudotachylite) is an extremely fine-grained to glassy, dark, cohesive rock occurring as veinsTrouw, R.A.J., C.W. Passchier, and D.J. Wiersma (2010) ''Atlas of Mylonites- and related microstructures.'' Sprin ...

, which then further broke down to

calcium oxide Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, Caustic (substance), caustic, alkaline, crystalline solid at room temperature. The broadly used term "''lime (material), lime''" co ...

and

carbon dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...

gas (or

supercritical fluid A supercritical fluid (SCF) is any substance at a temperature and pressure above its critical point, where distinct liquid and gas phases do not exist, but below the pressure required to compress it into a solid. It can effuse through porous so ...

). The gas supported the slide in the way that

air pressure Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The Standard atmosphere (unit), standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equival ...

supports a

hovercraft A hovercraft, also known as an air-cushion vehicle or ACV, is an amphibious Craft (vehicle), craft capable of travelling over land, water, mud, ice, and other surfaces. Hovercraft use blowers to produce a large volume of air below the hull ...

, allowing the slide to move easily down the very low slope. When the rockslide stopped, the carbon dioxide cooled and recombined with calcium oxide to form the cement-like carbonate rock now found in the fault zone. The consensus favors catastrophic sliding and calculations suggest that the front of the sliding mass may have advanced at a speed of over , meaning that the mountain traveled to its present location in approximately 30 minutes. In the 48 million years since the slide occurred,

erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is distin ...

has removed most of the portion of the slide sheet which moved out into the Bighorn Basin, leaving just one big block of carbonate rocks—Heart Mountain. Farther south, a large block of carbonate rock forms Sheep Mountain, which lies just south of the road that goes from Cody into Yellowstone Park. Some of the best views of the sliding surface, called the Heart Mountain fault, can be found along the Chief Joseph Highway ( Wyoming Highway 296). The fault is particularly well exposed in Cathedral Cliffs, where it appears as a remarkably straight and nearly horizontal line just above a high cliff. The nearby

Heart Mountain War Relocation Center The Heart Mountain War Relocation Center, named after nearby Heart Mountain (Wyoming), Heart Mountain and located midway between the northwest Wyoming towns of Cody, Wyoming, Cody and Powell, Wyoming, Powell, was one of ten concentration camps ...

, where a number of

Japanese American are Americans of Japanese ancestry. Japanese Americans were among the three largest Asian American ethnic communities during the 20th century; but, according to the 2000 census, they have declined in number to constitute the sixth largest Asi ...

s were

interned Internment is the imprisonment of people, commonly in large groups, without charges or intent to file charges. The term is especially used for the confinement "of enemy citizens in wartime or of terrorism suspects". Thus, while it can simply ...

during World War II, was named after the peak.

References

{{Authority control Mountains of Wyoming Geography of Park County, Wyoming Mountains of Park County, Wyoming Landslides in the United States

See also

References