A fin is a

geological formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

that is a narrow, residual wall of hard

sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

that remains standing after surrounding rock has been eroded away along parallel joints or fractures. Fins are formed when a narrow

butte __NOTOC__ In geomorphology, a butte () is an isolated hill with steep, often vertical sides and a small, relatively flat top; buttes are smaller landforms than mesas, plateaus, and tablelands. The word ''butte'' comes from a French word mea ...

plateau In geology and physical geography, a plateau (; ; ), also called a high plain or a tableland, is an area of a highland consisting of flat terrain that is raised sharply above the surrounding area on at least one side. Often one or more sides ha ...

develops many vertical, parallel cracks. There are two main modes of following

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 ...

. The first is when water flows along joints and fractures and opens them wider and wider, eventually causing erosion. The second is where the rock type (

stratum In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as ei ...

) is harder and more erosion resistant than neighboring rocks, causing the weaker rock to fall away. Fins are considered an intermediary stage of many other erosional geologic features like windows,

arches An arch is a vertical curved structure that spans an elevated space and may or may not support the weight above it, or in case of a horizontal arch like an arch dam, the hydrostatic pressure against it. Arches may be synonymous with vault ...

, and

hoodoos A hoodoo (also called a tent rock, fairy chimney, or earth pyramid) is a tall, thin spire of rock formed by erosion. Hoodoos typically consist of relatively soft rock topped by harder, less easily eroded stone that protects each column from the ...

. The formation of such features is a simplified four-step process. The first step is uplift that results in deep parallel, vertical fractures within the plateau. The second step is weathering and erosion that enlarges the fractures, producing fins. The third step is erosion attacking fins from below, causing windows and arches. The fourth step is continuing weathering that enlarges holes, causing arches and holes to collapse, creating spires or hoodoos.

Sandstones

Fins will form typically in sedimentary rocks, mainly

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...

. Sandstone is bedded, which provides zones of weakness, along which weathering and erosion takes place. Iron oxide and calcium carbonate cemented sandstones produce fins. These are typically seen as weak cements, compared to the erosion resistant silica cement, but in arid and semi-arid regions they are much more resistant. This is due to the lack of water in these regions that would otherwise chemically weather iron oxide cements and calcium carbonate cements. Because sandstones are bedded sedimentary rocks, they possess prominent joints and bedding planes which provides many channels for

drainage Drainage is the natural or artificial removal of a surface's water and sub-surface water from an area with excess of water. The internal drainage of most agricultural soils is good enough to prevent severe waterlogging (anaerobic conditio ...

. When drainage patterns follow these paths, it creates angular, dendritic patterns within topography. Lack of soil cover in these dry regions gives joints maximum control over drainage systems resulting in angular patterns, striking topography, and steep slopes.

Occurrence

Fins commonly occur in arid to semi-arid regions, like south western United States.

Arches National Park Arches National Park is a national park in eastern Utah, United States. The park is adjacent to the Colorado River, north of Moab, Utah. More than 2,000 natural sandstone arches are located in the park, including the well-known Delicate Arch, a ...

in Utah is home to

Navajo Sandstone The Navajo Sandstone is a geological formation in the Glen Canyon Group that is spread across the U.S. states of southern Nevada, northern Arizona, northwest Colorado, and Utah as part of the Colorado Plateau province of the United States.Anonymou ...

, an iron oxide cement sandstone, and displays all steps of the fin to spire erosion and formation process. The

Entrada Sandstone The Entrada Sandstone is a formation in the San Rafael Group found in the U.S. states of Wyoming, Colorado, northwest New Mexico, northeast Arizona, and southeast Utah. Part of the Colorado Plateau, this formation was deposited during the Jur ...

formation, a calcium carbonate cement sandstone, can also be found within this region, along with

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 ...

Colorado Colorado (, other variants) is a state in the Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the western edge of t ...

New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe , LargestCity = Albuquerque , LargestMetro = Tiguex , OfficialLang = None , Languages = English, Spanish ( New Mexican), Navajo, Ker ...

, and

Arizona Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a state in the Southwestern United States. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona is part of the Fou ...

Gallery

File:Garden of the Gods 01.jpg, A cluster of fins at

Garden of the Gods Garden of the Gods (Arapaho: ''Ho3o’uu Niitko’usi’i'') is a public park located in Colorado Springs, Colorado, United States. It was designated a National Natural Landmark in 1971. Name The area now known as Garden of the Gods was f ...

Colorado Springs Colorado Springs is a home rule municipality in, and the county seat of, El Paso County, Colorado, United States. It is the largest city in El Paso County, with a population of 478,961 at the 2020 United States Census, a 15.02% increase since ...

, US. File:Seneca Rocks by Asilverstein Oct 2013 High Dynamic Range Merge from 7 Exposures.jpg,

Seneca Rocks Seneca Rocks is a large crag and local landmark in Pendleton County in the Eastern Panhandle of West Virginia, United States. The south peak is one of a small number of peaks inaccessible except by technical rock climbing techniques on the East ...

, a prominent single fin in eastern

West Virginia West Virginia is a state in the Appalachian, Mid-Atlantic and Southeastern regions of the United States.The Census Bureau and the Association of American Geographers classify West Virginia as part of the Southern United States while the Bur ...

, US. File:Arches National Park aerial geology.jpg, Aerial view of innumerable rock fins at the Fiery Furnace area of

, Utah, US. File:More Devils Garden.jpg, Rock fins at

Devil's Garden In myrmecology and forest ecology, a devil's garden (Kichwa: ''Supay chakra''Frederickson, M. E., & Gordon, D. (2007). The devil to pay: the cost of mutualism with ''Myrmelachista schumanni'' ants in 'devil's gardens' is increased herbivory on ' ...

, Arches National Park. Image:Pia16128-640-MatijevicHill-EnduranceCrater-20120928.jpg, Fins are not restricted to the Earth:

Matijevic Hill Matijevic Hill, named after Americans, American NASA engineer Jacob Matijevic, Jacob "Jake" Matijevic (1947 - 2012), is a hill located on "Cape York (Mars), Cape York", itself on the western rim of Endeavour (crater), Endeavour Crater lying withi ...

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...

References

{{DEFAULTSORT:Fin (geology) Rock formations Erosion landforms