Escarpment

This is a steep or vertical cliff which usually extends over a considerable distance. The most common type of escarpment occurs where more resistant strata form a cap rock over easily eroded rocks. As EROSION takes place, the lower rock erodes more rapidly so that the cliff remains very steep. The NIAGARA ESCARPMENT continues from Tobermory, Ontario, into New York state. Its resistant cap rock, formed by the Lockport Dolomite, overlies several weaker shale and sandstone beds.

Some escarpments are formed by tectonic activity (ie, deformational movements of the Earth's crust or volcanism), particularly uplift along fault lines, and are distinguished as fault scarps. An excellent example is in the Aspy Valley of northern Cape Breton Island, NS. The angle of the fault scarp is controlled by the inclination of the fault plane and is often more gentle than that of the classic escarpment formed by strata of differing resistance. The latter can vary, however, from the flat, vertically sided feature, eg, the Niagara Escarpment, to a cuesta (with a steep scarp face and gentle dip face), or to a hogback ridge in which both faces are equally inclined.

See also PLATE TECTONICS.

Author R.B. BRYAN