Cuesta

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Cuesta in Italy Monte Baldo, Blick zum Monte Brione.JPG
Cuesta in Italy
Schematic cross section of three cuestas, dip slopes facing left, and harder rock layers in darker colors than softer ones Cuesta schematic1.PNG
Schematic cross section of three cuestas, dip slopes facing left, and harder rock layers in darker colors than softer ones
Cuesta in Crimea Crimea Cuesta.jpg
Cuesta in Crimea
Magaliesberg Range, Transvaal, South Africa Magaliesberg08.jpg
Magaliesberg Range, Transvaal, South Africa

A cuesta (from Spanish cuesta "slope") is a hill or ridge with a gentle slope on one side, and a steep slope on the other. In geology the term is more specifically applied to a ridge where a harder sedimentary rock overlies a softer layer, the whole being tilted somewhat from the horizontal. This results in a long and gentle backslope called a dip slope that conforms with the dip of resistant strata, called caprock. Where erosion has exposed the frontslope of this, a steep slope or escarpment occurs. The resulting terrain may be called scarpland.

Contents

Definition

In general usage, a cuesta is a hill or ridge with a gentle slope (backslope) on one side, and a steep slope (frontslope) on the other. The word is from Spanish: "flank or slope of a hill; hill, mount, sloping ground". In geology and geomorphology, cuesta refers specifically to an asymmetric ridge with a long and gentle backslope called a dip slope that conforms with the dip of a resistant stratum or strata, called caprock. The outcrop of the caprock forms a steeper or even cliff-like frontslope (escarpment), cutting through the dipping strata that comprise the cuesta. [1] [2] [3]

Formation

Cuestas are the expression of extensive outcrops of gently dipping strata, typically sedimentary strata, that consist of alternating beds of weak or loosely cemented strata, i.e. shale, mudstone, and marl and hard, well-lithified strata, i.e. sandstone and limestone. The surfaces of the hard, erosion-resistant rock strata form the caprock of the backslope (dip-slope) of the cuesta, where erosion has preferentially removed the weaker strata. The frontslope of the cuesta consists of an escarpment that cuts across the bedding of the strata comprising it. Because of the gently dipping nature of the strata that forms a cuesta, a significant shift in horizontal location will take place as the landscape is lowered by erosion. [1] [2] [4] [5] Because the slope of a cuesta dips in the same direction as the sedimentary strata, the dip angle of this bedding (θ) can be calculated by (v / h) = tan(θ) where v is equal to the vertical distance and h is equal to the horizontal distance perpendicular to the strike of the beds. [6]

Cuestas, homoclinal ridges, and hogbacks comprise a sequence of landforms that form a gradational continuum. These landforms differ only on the steepness of their backslopes and the relative differences in the inclination of their backslopes and frontslopes. These differences depend upon whether the dip of the strata from which they have been eroded are either nearly vertical, moderately dipping, or gently dipping. Because of their gradational nature, the exact angle of the backslope that separates these landforms is arbitrary and some differences in the specific angles used to define these landforms occur in the scientific literature. It also can be difficult to sharply distinguish immediately adjacent members of this series of landforms because of their gradational nature. [2] [4] [5] [7]

Examples

Two well-known cuestas in western New York and southern Ontario are the Onondaga escarpment and the Niagara Escarpment, respectively. The dip of the Onondaga is about 40 feet per mile (about 7.6 m/km) to the south. The escarpment edge faces north, and in its most populated section, runs roughly parallel to the southern Lake Ontario shoreline.

The Gulf Coastal Plain in Texas is punctuated by a series of cuestas that parallel the coast, as are most coastal plains. [8] The Reynosa Plateau is the most coast-ward cuesta, which has surface expression with the Bordes-Oakville escarpment, on the northwest side and a low ridge on the eastern boundary, called the Reynosa Cuesta, where the deposits dip below later Pliocene-Pleistocene deposits of the Willis and Lissie Formations.

Cuestas have less dramatic expression in the United Kingdom, with two notable examples being the northwest-facing escarpment of the Cretaceous chalk White Horse Hills and the similarly aligned escarpment of the Jurassic limestones in the Cotswolds, sometimes called the Cotswold Edge. Other examples include the Brecon Beacons, Wenlock Edge, the Chilterns, the North and South Downs and the Greensand Ridge of Kent and Surrey

In continental Europe, the Swabian Alb offers particularly good views of cuestas in Jurassic rock. In France, the term for a cuesta is the same as for a coastline: côte.[ citation needed ] Notable French cuestas are the wine-growing regions of Côte d'Or.

The Machinchang Formation outcrops in the Langkawi islands off the coast of northwestern Malaysia. The formation is one of the oldest exposed rock units in Southeast Asia and has an extensive eroded anticline cuesta topography—dating back to Cambrian.[ citation needed ]

See also

Related Research Articles

<span class="mw-page-title-main">Niagara Escarpment</span> Escarpment in Canada and the United States

The Niagara Escarpment is a long escarpment, or cuesta, in Canada and the United States that starts from the south shore of Lake Ontario westward, circumscribes the top of the Great Lakes Basin running from New York through Ontario, Michigan, and Wisconsin. The escarpment is the cliff over which the Niagara River plunges at Niagara Falls, for which it is named.

<span class="mw-page-title-main">Escarpment</span> Steep slope or cliff separating two relatively level regions

An escarpment is a steep slope or long cliff that forms as a result of faulting or erosion and separates two relatively level areas having different elevations.

<span class="mw-page-title-main">Peneplain</span> Low-relief plain formed by protracted erosion

In geomorphology and geology, a peneplain is a low-relief plain formed by protracted erosion. This is the definition in the broadest of terms, albeit with frequency the usage of peneplain is meant to imply the representation of a near-final stage of fluvial erosion during times of extended tectonic stability. Peneplains are sometimes associated with the cycle of erosion theory of William Morris Davis, but Davis and other workers have also used the term in a purely descriptive manner without any theory or particular genesis attached.

<span class="mw-page-title-main">Inselberg</span> Isolated, steep rock hill on relatively flat terrain

An inselberg or monadnock is an isolated rock hill, knob, ridge, or small mountain that rises abruptly from a gently sloping or virtually level surrounding plain. In Southern Africa a similar formation of granite is known as a koppie, an Afrikaans word from the Dutch diminutive word kopje. If the inselberg is dome-shaped and formed from granite or gneiss, it can also be called a bornhardt, though not all bornhardts are inselbergs. An inselberg results when a body of rock resistant to erosion, such as granite, occurring within a body of softer rocks, is exposed by differential erosion and lowering of the surrounding landscape.

<span class="mw-page-title-main">Landform</span> Feature of the solid surface of a planetary body

A landform is a natural or anthropogenic land feature on the solid surface of the Earth or other planetary body. Landforms together make up a given terrain, and their arrangement in the landscape is known as topography. Landforms include hills, mountains, canyons, and valleys, as well as shoreline features such as bays, peninsulas, and seas, including submerged features such as mid-ocean ridges, volcanoes, and the great ocean basins.

Landforms are categorized by characteristic physical attributes such as their creating process, shape, elevation, slope, orientation, rock exposure, and soil type.

<span class="mw-page-title-main">Butte</span> Isolated hill with steep, often vertical sides and a small, relatively flat top

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 the French word butte, meaning knoll ; its use is prevalent in the Western United States, including the southwest where mesa is used for the larger landform. Due to their distinctive shapes, buttes are frequently landmarks in plains and mountainous areas. To differentiate the two landforms, geographers use the rule of thumb that a mesa has a top that is wider than its height, while a butte has a top that is narrower than its height.

<span class="mw-page-title-main">Mesa</span> Elevated area of land with a flat top and sides

A mesa is an isolated, flat-topped elevation, ridge or hill, which is bounded from all sides by steep escarpments and stands distinctly above a surrounding plain. Mesas characteristically consist of flat-lying soft sedimentary rocks capped by a more resistant layer or layers of harder rock, e.g. shales overlain by sandstones. The resistant layer acts as a caprock that forms the flat summit of a mesa. The caprock can consist of either sedimentary rocks such as sandstone and limestone; dissected lava flows; or a deeply eroded duricrust. Unlike plateau, whose usage does not imply horizontal layers of bedrock, e.g. Tibetan Plateau, the term mesa applies exclusively to the landforms built of flat-lying strata. Instead, flat-topped plateaus are specifically known as tablelands.

<span class="mw-page-title-main">Ridge</span> Long, narrow, elevated landform

A ridge is a long, narrow, elevated geomorphologic landform, structural feature, or a combination of both separated from the surrounding terrain by steep sides. The sides of a ridge slope away from a narrow top, the crest or ridgecrest, with the terrain dropping down on either side. The crest, if narrow, is also called a ridgeline. Limitations on the dimensions of a ridge are lacking. Its height above the surrounding terrain can vary from less than a meter to hundreds of meters. A ridge can be either depositional, erosional, tectonic, or a combination of these in origin and can consist of either bedrock, loose sediment, lava, or ice depending on its origin. A ridge can occur as either an isolated, independent feature or part of a larger geomorphological and/or structural feature. Frequently, a ridge can be further subdivided into smaller geomorphic or structural elements.

<span class="mw-page-title-main">Allegheny Front</span> Major escarpment in the Allegheny Mountains

The Allegheny Front is the major southeast- or east-facing escarpment in the Allegheny Mountains in southern Pennsylvania, western Maryland, eastern West Virginia, and western Virginia, USA. The Allegheny Front forms the boundary between the Ridge-and-Valley Appalachians to its east and the Appalachian Plateau to its west. The Front is closely associated with the Appalachian Mountains' Eastern Continental Divide, which in this area divides the waters of the Ohio/Mississippi river system, flowing to the Gulf of Mexico, from rivers flowing into Chesapeake Bay and from there into the Atlantic Ocean.

<span class="mw-page-title-main">Dip slope</span>

A dip slope is a topographic (geomorphic) surface which slopes in the same direction, and often by the same amount, as the true dip or apparent dip of the underlying strata. A dip slope consists of the upper surface of a resistant layer of rock, often called caprock, that is commonly only slightly lowered and reduced in steepness by erosion. Dip slopes form the backslopes of cuestas, homoclinal ridges, hogbacks, and flatirons. The frontslopes of such ridges consist of either an escarpment, a steep slope, or perhaps even a line of cliffs. Generally, cuestas and homoclinal ridges are asymmetrical in that their dip slopes are less steep than their escarpments. In the case of hogbacks and flatirons, the dip of the rocks is so steep that their dip slope approaches the escarpment in their steepness.

<span class="mw-page-title-main">Terrace (geology)</span> A step-like landform

In geology, a terrace is a step-like landform. A terrace consists of a flat or gently sloping geomorphic surface, called a tread, that is typically bounded on one side by a steeper ascending slope, which is called a "riser" or "scarp". The tread and the steeper descending slope together constitute the terrace. Terraces can also consist of a tread bounded on all sides by a descending riser or scarp. A narrow terrace is often called a bench.

<span class="mw-page-title-main">Pediplain</span> Extensive plain formed by the coalescence of pediments

In geology and geomorphology a pediplain is an extensive plain formed by the coalescence of pediments. The processes through which pediplains forms is known as pediplanation. The concepts of pediplain and pediplanation were first developed by geologist Lester Charles King in his 1942 book South African Scenery. The concept gained notoriety as it was juxtaposed to peneplanation.

<span class="mw-page-title-main">Hogback (geology)</span> Long, narrow ridge

In geology and geomorphology, a hogback or hog's back is a long, narrow ridge or a series of hills with a narrow crest and steep slopes of nearly equal inclination on both flanks. Typically, the term is restricted to a ridge created by the differential erosion of outcropping, steeply dipping, homoclinal, and typically sedimentary strata. One side of a hogback consists of the surface of a steeply dipping rock stratum called a dip slope. The other side is an erosion face that cuts through the dipping strata that comprises the hogback. The name "hogback" comes from the Hog's Back of the North Downs in Surrey, England, which refers to the landform's resemblance in outline to the back of a hog. The term is also sometimes applied to drumlins and, in Maine, to both eskers and ridges known as "horsebacks".

<span class="mw-page-title-main">Geology of Kansas</span>

The geology of Kansas encompasses the geologic history and the presently exposed rock and soil. Rock that crops out in the US state of Kansas was formed during the Phanerozoic eon, which consists of three geologic eras: the Paleozoic, Mesozoic and Cenozoic. Paleozoic rocks at the surface in Kansas are primarily from the Mississippian, Pennsylvanian, and Permian periods.

<span class="mw-page-title-main">Homocline</span> Geological structure in which rock strata dip uniformly in a single direction

In structural geology, a homocline or homoclinal structure, is a geological structure in which the layers of a sequence of rock strata, either sedimentary or igneous, dip uniformly in a single direction having the same general inclination in terms of direction and angle. A homocline can be associated with either one limb of a fold, the edges of a dome, the coast-ward tilted strata underlying a coastal plain, slice of thrust fault, or a tilted fault block. When the homoclinal strata consists of alternating layers of rock that vary hardness and resistance to erosion, their erosion produces either cuestas, homoclinal ridges, or hogbacks depending on the angle of dip of the strata. On a topographic map, the landfroms associated with homoclines exhibit nearly parallel elevation contour lines that show a steady change in elevation in a given direction. In the subsurface, they characterize by parallel structural contour lines.

<span class="mw-page-title-main">Homoclinal ridge</span> Ridge with a moderate sloping backslope and steeper frontslope

A homoclinal ridge or strike ridge is a hill or ridge with a moderate, generally between 10° and 30°, sloping backslope. Its backslope is a dip slope, that conforms with the dip of a resistant stratum or strata, called caprock. On the other side of the other slope, which is its frontslope, of a homoclinal ridge is a steeper or even cliff-like frontslope (escarpment) that is formed by the outcrop of the caprock. The escarpment cuts through the dipping strata that comprises the homoclinal ridge.

<span class="mw-page-title-main">South German Scarplands</span> Landscape in Switzerland, Bavaria and Baden-Württemberg

The South German Scarplands is a geological and geomorphological natural region or landscape in Switzerland and the south German states of Bavaria and Baden-Württemberg. The landscape is characterised by escarpments.

<span class="mw-page-title-main">Flatiron (geomorphology)</span> Steeply sloping triangular landform

Traditionally in geomorphology, a flatiron is a steeply sloping triangular landform created by the differential erosion of a steeply dipping, erosion-resistant layer of rock overlying softer strata. Flatirons have wide bases that form the base of a steep, triangular facet that narrows upward into a point at its summit. The dissection of a hogback by regularly spaced streams often results in the formation of a series of flatirons along the strike of the rock layer that formed the hogback. As noted in some, but not all definitions, a number of flatirons are perched upon the slope of a larger mountain with the rock layer forming the flatiron inclined in the same direction as, but often at a steeper angle than the associated mountain slope. The name flatiron refers to their resemblance to an upended, household flatiron.

<span class="mw-page-title-main">Scarp retreat</span>

Scarp retreat is a geological process through which the location of an escarpment changes over time. Typically the cliff is undermined, rocks fall and form a talus slope, the talus is chemically or mechanically weathered and then removed through water or wind erosion, and the process of undermining resumes. Scarps may retreat for tens of kilometers in this way over relatively short geological time spans, even in arid locations.

References

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  2. 1 2 3 Simonett, SD (1968) Cuesta. In RW Fairbridge, ed., pp. 233, The Encyclopedia of Geomorphology (Encyclopedia of Earth Sciences, Volume III), Reinhold, New York, 1296 pp. ISBN   978-0879331795
  3. Jackson, JA, J Mehl and K Neuendorf (2005) Glossary of Geology. American Geological Institute, Alexandria, Virginia. 800 pp. ISBN   0-922152-76-4
  4. 1 2 Thornbury, W. D. (1954). Principles of Geomorphology . New York: John Wiley & Sons.
  5. 1 2 Twidale, C. R.; Campbell, E. M. (1993). Australian Landforms: Structure, Process and Time. Adelaide, South Australia: Gleneagles Publishing. ISBN   1-875553-02-9.
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