Mesa 386596 222775734 2008-07-01T01:35:06Z Bobo192 97951 Reverted edits by [[Special:Contributions/141.158.44.5|141.158.44.5]] ([[User talk:141.158.44.5|talk]]) to last version by 76.235.50.25 {{otheruses}} [[Image:Gloss Mountains.jpg|thumb|right|Mesas in the [[Glass Mountains]] of western [[Oklahoma]].]] [[Image:Messa New Mexico.jpg|thumb|right|Several mesas near [[Los Alamos, New Mexico]].]] [[Image:TucMt.jpg|thumb|right|[[Tucumcari Mountain]] is a mesa outside of [[Tucumcari, New Mexico]].]] A '''mesa''' ([[Spanish language|Spanish]], [[Portuguese language|Portuguese]] and [[Arabic language|Arabic]] for "table") is an elevated area of land with a flat top and sides that are usually steep cliffs. It takes its name from its characteristic table-top shape. It is a characteristic [[landform]] of arid environments, particularly the southwestern [[United States]]. Many examples are also found in Spain, North and South Africa, Arabia, India, Australia, and the [[Badlands]] and Colorado regions of North America. The largest mesa in the world is considered to be the [[Grand Mesa]] in western [[Colorado]] in the United States. [[Urraca Mesa]] in northern [[New Mexico]] is particularly famous for being "haunted" in local tradition. ==Etymology== The term ''mesa'' is used in the southwestern [[United States]], in both English and Spanish, to describe a flat-topped mountain or hill. Elsewhere, in Spanish such a landform is more usually known as a ''meseta'' (see [[:es:Meseta|Spanish Wikipedia: Meseta]]). ==Formation== Mesas form usually in areas where horizontally layered rocks are uplifted by [[tectonics|tectonic]] activity, but may form also in its absence. Mesas are formed by [[weathering]] and [[erosion]]. 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 relative to their surroundings.<ref name="Easterbrook">{{cite book |last= Easterbrook |first= Don J. |title= Surface Processes and Landforms |year= 1999 |publisher= [[Prentice Hall]] |location= Upper Saddle River, NJ}}</ref> This process is called differential erosion. The most resistant rock types include [[sandstone]], [[conglomerate (geology)|conglomerate]], [[quartzite]], [[chert]], [[limestone]], [[lava|lava flows]] and [[sill (geology)|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 is what gives 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 (geology)|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 stair steps, 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 erosion|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 [[slump|slumping]] and flowage of the shale.<ref>{{cite book |last= Choreley |first= Richard J. |coauthors= Stanley A. Schumm, David E. Sugden |title= Geomorphology |year= 1985 |publisher= Methuen |location= New York }}</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 a little remains, it is known as a [[butte]]. ==See also== *[[Plateau]] *[[Dissected plateau]] *[[Butte]] *[[Potrero (landform)|Potrero]] *[[Tuya]] *[[Table Mountain (disambiguation)]] ==References== <references/> {{topography-stub}} [[Category:Landforms]] [[cs:Stolová hora]] [[da:Mesa]] [[de:Tafelberg (Geologie)]] [[fr:Mesa (géomorphologie)]] [[ko:메사]] [[it:Mesa]] [[he:הר שולחן]] [[lt:Stalkalnis]] [[nl:Tafelberg (geomorfologie)]] [[ja:メサ]] [[no:Mesa]] [[pl:Stoliwo]]