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Mesa

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File:Mount Conner - panoramio.jpg
Mount Conner, a mesa located in Northern Territory, Australia
File:Over Monument Valley, Navajo Nation.jpg
Aerial view of mesas in Monument Valley, on the Colorado Plateau
File:Cockburn Range.jpg
Cockburn Range, Kimberley, Western Australia, Australia
File:HarQatum.jpg
Har Qatum, a mesa located on the southern edge of Makhtesh Ramon, Israel
File:Amadiya - panorama.jpg
Amadiya, Iraq, a city in its entirety built on a mesa
File:Ingleborough from Little Ingleborough - geograph.org.uk - 548604.jpg
Ingleborough in North Yorkshire, England
File:Mesa in Colorado.jpg
Mount Garfield, a mesa in Colorado
File:PIA21585 - A Mesa in Noctis Labyrinthus.jpg
A mesa in Noctis Labyrinthus on Mars, viewed by HiRISE

A mesa is an isolated, flat-topped elevation, ridge, or hill, bounded from all sides by steep escarpments and standing distinctly above a surrounding plain. Mesas consist of flat-lying soft sedimentary rocks, such as shales, capped by a resistant layer of harder rock, like sandstone or limestone, forming a caprock that protects the flat summit. The caprock may also include dissected lava flows or eroded duricrust.

Unlike a plateau, which is a broader, elevated region that may not have horizontal bedrock (e.g., Tibetan Plateau), a mesa is defined by flat-lying strata and steep-sided isolation. Large, flat-topped plateaus with horizontal strata, less isolated and often part of extensive plateau systems, are called tablelands. A butte is a smaller, eroded mesa with a limited summit, while a cuesta has a gentle dip slope and one steep escarpment due to tilted strata.<ref name="DuszyńskiOthers2019a2">Duszyński, F., Migoń, P. and Strzelecki, M.C., 2019. Escarpment retreat in sedimentary tablelands and cuesta landscapes–Landforms, mechanisms and patterns. Earth-Science Reviews,' no. 102890. doi.org/10.1016/j.earscirev.2019.102890</ref><ref name="Migoń2004a2">Migoń, P., 2004a. Mesa. In: Goudie, A.S. (Ed.), Encyclopedia of Geomorphology. Routledge, London, pp. 668. Template:ISBN</ref><ref name="NeuendorfOthers2011a2">Neuendorf, Klaus K.E. Mehl, James P., Jr. Jackson, Julia A.. (2011). Glossary of Geology (5th Edition). American Geosciences Institute. Template:ISBN</ref>

Names, definition and etymologyEdit

As noted by geologist Kirk Bryan in 1922, mesas "...stand distinctly above the surrounding country, as a table stands above the floor upon which it rests".<ref name="Bryan1992a">Template:Cite journal</ref> It is from this appearance that the term mesa was adopted from the Spanish word mesa, meaning "table".<ref name="Migoń2004a">Migoń, P., 2004a. Mesa. In: Goudie, A.S. (Ed.), Encyclopedia of Geomorphology. Routledge, London, pp. 668. Template:ISBN</ref>

A mesa is similar to, but has a more extensive summit area than, a butte. There is no agreed size limit that separates mesas from either buttes or plateaus. For example, the flat-topped mountains which are known as mesas in the Cockburn Range of North Western Australia have areas as large as Template:Convert. In contrast, flat topped hills with areas as small as Template:Convert in the Elbe Sandstone Mountains, Germany, are described as mesas.<ref name="DuszyńskiOthers2019a">Duszyński, F., Migoń, P. and Strzelecki, M.C., 2019. Escarpment retreat in sedimentary tablelands and cuesta landscapes–Landforms, mechanisms and patterns. Earth-Science Reviews,' no. 102890. doi.org/10.1016/j.earscirev.2019.102890</ref><ref name="Migoń2004a"/><ref name="NeuendorfOthers2011a">Neuendorf, Klaus K.E. Mehl, James P., Jr. Jackson, Julia A.. (2011). Glossary of Geology (5th Edition). American Geosciences Institute. Template:ISBN</ref>

Less strictly, a very broad, flat-topped, usually isolated hill or mountain of moderate height bounded on at least one side by a steep cliff or slope and representing an erosion remnant also have been called mesas.<ref name="NeuendorfOthers2011a"/>

In the English-language geomorphic and geologic literature, other terms for mesa have also been used.<ref name="DuszyńskiOthers2019a"/> For example, in the Roraima region of Venezuela, the traditional name, tepui, from the local Pomón language, and the term table mountains have been used to describe local flat-topped mountains.<ref name="BriceñoOthers1990a">Briceño, H.O. and Schubert, C., 1990. Geomorphology of the Gran Sabana, Guayana Shield, southeastern Venezuela. Geomorphology, 3(2), pp.125-141.</ref><ref name="Doerr1999a"> Doerr, S.H., 1999. Karst-like landforms and hydrology in quartzites of the Venezuelan Guyana shield: Pseudokarst or" real" karst?. Zeitschrift fur Geomorphologie, 43(1), pp.1-17.</ref> Similar landforms in Australia are known as tablehills, table-top hills, tent hills, or jump ups (jump-ups).<ref name="Jack1915a">Jack, R.L., 1915. The Geology and prospects of the Region to the South of the Musgrave Ranges, and the Geology of the Western Portion of the Great Australian Artesian Basin. Geol. Survey South Australia Bulletin 5, pp. 72.</ref><ref>Template:Citation</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The German term Tafelberg has also been used in the English scientific literature in the past.<ref name="King1942a">King, L.C., 1942. South African Scenery. A Textbook of Geomorphology. Oliver and Boyd, Edinburgh, London (340 pp.).</ref>

FormationEdit

Mesas form by weathering and erosion of horizontally layered rocks that have been uplifted by tectonic activity. Variations in the ability of different types of rock to resist weathering and erosion cause the weaker types of rocks to be eroded away, leaving the more resistant types of rocks topographically higher than their surroundings.<ref name="Easterbrook">Template:Cite book</ref> This process is called differential erosion. The most resistant rock types include sandstone, conglomerate, quartzite, basalt, chert, limestone, lava flows and sills.<ref name="Easterbrook"/> Lava flows and sills, in particular, are very resistant to weathering and erosion, and often form the flat top, or caprock, of a mesa. The less resistant rock layers are mainly made up of shale, a softer rock that weathers and erodes more easily.<ref name="Easterbrook"/>

The differences in strength of various rock layers are what give mesas their distinctive shape. Less resistant rocks are eroded away on the surface into valleys, where they collect water drainage from the surrounding area, while the more resistant layers are left standing out.<ref name="Easterbrook"/> A large area of very resistant rock, such as a sill, may shield the layers below it from erosion while the softer rock surrounding it is eroded into valleys, thus forming a caprock.

Differences in rock type also reflect on the sides of a mesa, as instead of smooth slopes, the sides are broken into a staircase pattern called "cliff-and-bench topography".<ref name="Easterbrook"/> The more resistant layers form the cliffs, or stairsteps, while the less resistant layers form gentle slopes, or benches, between the cliffs. Cliffs retreat and are eventually cut off from the main cliff, or plateau, by basal sapping. When the cliff edge does not retreat uniformly but instead is indented by headward eroding streams, a section can be cut off from the main cliff, forming a mesa.<ref name="Easterbrook"/>

Basal sapping occurs as water flowing around the rock layers of the mesa erodes the underlying soft shale layers, either as surface runoff from the mesa top or from groundwater moving through permeable overlying layers, which leads to slumping and flowage of the shale.<ref>Template:Cite book</ref> As the underlying shale erodes away, it can no longer support the overlying cliff layers, which collapse and retreat. When the caprock has caved away to the point where only little remains, it is known as a butte.

Examples and locationsEdit

AustraliaEdit

CzechiaEdit

FranceEdit

GermanyEdit

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  • Quirl, Saxony<ref name="morph" />

IndiaEdit

IraqEdit

IrelandEdit

  • Kings Mountain, County Sligo<ref name="rds80">Journal of Earth Sciences Royal Dublin Society. (1980). Ireland: The Society.</ref>
  • Knocknarea, County Sligo<ref name="rds80" />
  • Knocknashee, County Sligo<ref name="rds80" />

IsraelEdit

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  • Har Qatum

ItalyEdit

PolandEdit

United KingdomEdit

EnglandEdit

Durham University. Available at Durham E-Theses Online: http://etheses.dur.ac.uk/9349/ </ref>

ScotlandEdit

United StatesEdit

Many but not all American mesas lie within the Basin and Range Province.

ArizonaEdit

ArkansasEdit

CaliforniaEdit

ColoradoEdit

NevadaEdit

OklahomaEdit

TexasEdit

  • Floating Mesa<ref name="obscurafmt">{{#invoke:citation/CS1|citation

|CitationClass=web }}</ref>

UtahEdit

WisconsinEdit

On MarsEdit

A transitional zone on Mars, known as fretted terrain, lies between highly cratered highlands and less cratered lowlands. The younger lowland exhibits steep walled mesas and knobs. The mesa and knobs are separated by flat lying lowlands. They are thought to form from ice-facilitated mass wasting processes from ground or atmospheric sources. The mesas and knobs decrease in size with increasing distance from the highland escarpment. The relief of the mesas range from nearly Template:Convert to Template:Convert depending on the distance they are from the escarpment.<ref>Baker, David M. Morphological Analyses of Mesas and Knobs in the Northwest Fretted Terrain of Mars; Constraints on the Presence and Distribution of Ice-Facilitated Mass-Wasting. Ed. Alexander K. Stewart and James W. Head. Vol. 40. Issue 2. pp. 72. United States: Geological Society of America (GSA) : Boulder, CO, United States, 2008.</ref>

See alsoEdit

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ReferencesEdit

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