Traditionally in

geomorphology Geomorphology () is the scientific study of the origin and evolution of topographic and bathymetric features generated by physical, chemical or biological processes operating at or near Earth's surface. Geomorphologists seek to understand wh ...

, 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. Ollier, C.D. (1985) ''Glossary of Morphotectonics,'' 2nd ed. Bureau of Mineral Resources. Geology and Geophysics Record no. 1985/30. Dept. of Geology and Geophysics, Canberra, Australia. 55 pp. Fairbridge, R.W. (1968) ''Hogback and Flatiron.'' In R.W. Fairbridge, ed., pp. 524-525, ''The Encyclopedia of Geomorphology'' (Encyclopedia of Earth Sciences, Volume III), Reinhold, New York, 1296 pp. Huggett, JL (2011) ''Fundamentals of Geomorphology.'' Routledge. New York, New York. 516 pp. 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.Jackson, JA, J Mehl and K Neuendorf (2005) ''Glossary of Geology.'' American Geological Institute, Alexandria, Virginia. 800 pp.

Background

The Flatirons near Boulder, Colorado, is both an example of these landforms and the source of their name. Other well-developed flatirons are found in the eastern Uinta Mountains in northwestern Colorado,Hansen, WR (2005
''The Geologic Story of the Uinta Mountains.''
, United States Geological Survey, Reston, Virginia. the Waterpocket Fold in

Capitol Reef National Park Capitol Reef National Park is a List of national parks of the United States, national park of the United States in south-central Utah. The park is approximately long on its northsouth axis and just wide on average. The park was established in ...

, the

Superstition Mountains The Superstition Mountains () is a range of mountains in Arizona located to the east of the Phoenix metropolitan area. They are anchored by Superstition Mountain, a large mountain that is a popular recreation destination for residents of the ...

near

Phoenix, Arizona Phoenix ( ) is the List of capitals in the United States, capital and List of cities and towns in Arizona#List of cities and towns, most populous city of the U.S. state of Arizona. With over 1.6 million residents at the 2020 census, it is the ...

, and on the flanks of the Marathon Uplift in west Texas.MaCleod, B. (2009
''Southern Margin of the Marathon Basin.''Big Bend Photographs
Texas Geological Press. The term "flatiron" is also used for very small-scale landforms that are known as pediment flatirons and talus flatirons. These

landform A landform is a land feature on the solid surface of the Earth or other planetary body. They may be natural or may be anthropogenic (caused or influenced by human activity). Landforms together make up a given terrain, and their arrangement ...

s are small knolls with a triangular to

trapezoid In geometry, a trapezoid () in North American English, or trapezium () in British English, is a quadrilateral that has at least one pair of parallel sides. The parallel sides are called the ''bases'' of the trapezoid. The other two sides are ...

al-shaped sloping surface with the long side of this surface as their base and a point at their top. Both pediment flatirons and talus flatirons are associated with the scarps of a

cuesta A cuesta () 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 somew ...

, mesa, or

butte 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 table (landform), tablelands. The word ''butte'' comes from the French l ...

and with their tips directed towards the scarp. Both types of these flatirons are typically separated from the scarp by well-defined

ravine A ravine is a landform that is narrower than a canyon and is often the product of streambank erosion. Ravines are typically classified as larger in scale than gullies, although smaller than valleys. Ravines may also be called a cleuch, dell, ...

s and gullies. These flatirons consist of either talus, in the case of the talus flatirons, or pedisediment and

colluvium Colluvium (also colluvial material or colluvial soil) is a general name for loose, unconsolidated sediments that have been deposited at the base of hillslopes by either rainwash, Sheet erosion , sheetwash, slow continuous downslope creep, or a va ...

that cover

pediments Pediments are a form of gable in classical architecture, usually of a triangular shape. Pediments are placed above the horizontal structure of the cornice (an elaborated lintel), or entablature if supported by columns.Summerson, 130 In ancient ...

, in the case of pediment flatirons. Their surfaces are protected by a thin layer of caprock. The caprock commonly consists of caliche, which is about thick and rarely as much as thick, that has developed in either talus, pedisediment, or colluvium. Talus flatirons lie within the scarp slope – and pediment flatirons occur within the transition zone between scarp and foreland. Pediment flatirons can merge downward into a

fluvial terrace Fluvial terraces are elongated Terrace (geology), terraces that flank the sides of floodplains and fluvial valleys all over the world. They consist of a relatively level strip of land, called a "tread", separated from either an adjacent floodplai ...

. Both talus and pediment flatirons are the relict remnants of formerly active slope systems that were once part of the scarp's history.Schmidt, K-H (1989) ''Talus and pediment flatirons – erosional and depositional features on dryland cuesta scarps.'' Catena Supplement 14:107-118.Schmidt, K-H (2009) ''Hillslopes as Evidence of Climatic Change.'' In AJ Parsons and AD Abrahams, eds., pp. 675-694, Geomorphology of Desert Environments, 2nd ed., Springer Science+Business Media, New York, New York, 831 pp.

References

External links

*Ball, J. (2009
Flatirons ≠ pyramids, but they're still coolMagma Cum LaudeAmerican Geophysical Union Blogosphere
November 25, 2009. last accessed January 24, 2014. Mountain geomorphology Structural geology Slope landforms Erosion landforms Flatiron {{erosion-stub

Background

See also

References

External links