Antecedent drainage stream

Anantecedent streamis a stream that maintains its original course and pattern despite the changes in underlying rock topography. A stream with adendritic drainage pattern,for example, can be subject to slow tectonic uplift. However, as the uplift occurs, the stream erodes through the rising ridge to form a steep-walledgorge.The stream thus keeps its dendritic pattern even though it flows over a landscape that will normally produce atrellis drainage pattern.

Asuperimposed streamis astreamthat forms over horizontal beds that overlie folded and faulted rock with varying resistance. Having cut down through the horizontal beds, the stream retains its course and pattern as it proceeds to erode the underlying rocks despite their different character. The stream erodes a gorge in the resistant bed and continues its flow as before.

Examples

• ManyHimalayanrivers are good examples of antecedent origin. These rivers originated well before the Himalayan region was uplifted. The riversIndus,Brahmaputra,Sutlej,KosiandSubansirioriginated on the Tibetan side and now traverse the existing mountain ranges, cutting deepgorges.
• TheColorado Rivercut theGrand Canyonas theColorado Plateaurose between 5 and 2.5 million years ago.Paradox Valleyis another good example in the Colorado Plateau.
• Devil's Gatein Wyoming is a remarkable display of an antecedent stream. A 100-meter slot is cut through a granite ridge which would have missed the ridge completely had the river flowed just a kilometer to the south.
• TheMeusestill flows south-north from France to Belgium through theArdenneswhich were elevated after the river had assumed that course.

See also

• Canyon
• Water gap
• Wind gap