Geographical Features of the Earth

All of the wondrous features the earth can produce.

Mesa:

Mesas form in areas where horizontally layered rocks are 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 relative to their surroundings. This process is called differential erosion. The most resistant rock types include sandstone, conglomerate, quartzite, chert, limestone, lava flows and sills. 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. Mesas are erosional features.

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. 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. 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 head ward eroding streams, a section can be cut off from the main cliff, forming a mesa.

Inselbergs:

Inselbergs -isolated, steep-sided, erosional remnants of bedrock (characterized by greater resistance to weathering than surrounding mountains) that rise above flat desert plains. Inselberg is a German name for island mountain.

A monadnock or inselberg is an isolated hill, knob, ridge, or small mountain that rises abruptly from a gently sloping or virtually level surrounding plain.

The word inselberg is German for “island mountain”; the name was originally coined to describe the abundant such features found in southern Africa. The term monadnock is more usually used in the US.

Inselbergs are typically, though not only, formed in tropical areas. Volcanic or other processes may give rise to a body of rock resistant to erosion, inside a body of softer rock such as sandstone which is more susceptible to erosion. When the less resistant rock is eroded away to form a plain, the more resistant rock is left behind as an isolated mountain. If the inselberg is dome-shaped and formed from granite-gneiss, it can also be called a bornhardt.

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One Response to “Geographical Features of the Earth”
  1. bob Says...

    On August 11, 2011 at 10:44 pm

    this is a good website u got me through a project

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