A cuesta (from
Spanish ''cuesta'' "slope") is a
hill or
ridge
A ridge or a mountain ridge is a geographical feature consisting of a chain of mountains or hills that form a continuous elevated crest for an extended distance. The sides of the ridge slope away from the narrow top on either side. The line ...
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
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 ...
, called
caprock. Where erosion has exposed the frontslope of this, a steep slope or
escarpment occurs. The resulting terrain may be called scarpland.
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.
[Cotton, CA (1952) ''Geomorphology An Introduction to the Study of Landforms.'' John Wiley and Sons, New York. 505 pp.][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. ][Jackson, JA, J Mehl and K Neuendorf (2005) ''Glossary of Geology.'' American Geological Institute, Alexandria, Virginia. 800 pp. ]
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
Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...
,
mudstone
Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...
, and
marl
Marl is an earthy material rich in carbonate minerals, clays, and silt. When hardened into rock, this becomes marlstone. It is formed in marine or freshwater environments, often through the activities of algae.
Marl makes up the lower part o ...
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.
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.
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.
Examples
Two well-known cuestas in western
New York
New York most commonly refers to:
* New York City, the most populous city in the United States, located in the state of New York
* New York (state), a state in the northeastern United States
New York may also refer to:
Film and television
* '' ...
and southern
Ontario are the
Onondaga escarpment and the
Niagara Escarpment
The Niagara Escarpment is a long escarpment, or cuesta, in Canada and the United States that runs predominantly east–west from New York through Ontario, Michigan, Wisconsin, and into Illinois. The escarpment is most famous as the cliff over ...
, 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.
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
The Cotswolds (, ) is a region in central-southwest England, along a range of rolling hills that rise from the meadows of the upper Thames to an escarpment above the Severn Valley and Evesham Vale.
The area is defined by the bedrock of Jur ...
, sometimes called the Cotswold Edge.
In continental Europe, the
Swabian Alb
The Swabian Jura (german: Schwäbische Alb , more rarely ), sometimes also named Swabian Alps in English, is a mountain range in Baden-Württemberg, Germany, extending from southwest to northeast and in width. It is named after the region of ...
offers particularly good views of cuestas in
Jurassic rock. In
France, the term for a cuesta is the same as for a coastline: "côte". Notable French cuestas are the wine-growing regions of
Côte d'Or
Côte is a British cafe chain founded by Richard Caring, Andy Bassadone, Chris Benians and Nick Fiddler in Wimbledon, London
Wimbledon () is a district and town of Southwest London, England, southwest of the centre of London at Charing Cross ...
.
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.
See also
*
References
External links
{{Commons category, Cuestas
Escarpment geology
Geomorphology
Structural geology
Slope landforms
Erosion landforms
Ridges