Antecedent drainage stream

An antecedent stream is a stream that maintains its original course and pattern despite the changes in underlying rock topography. A stream with a dendritic 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-walled gorge. The stream thus keeps its dendritic pattern even though it flows over a landscape that will normally produce a trellis drainage pattern.[1]

A superposed stream is a stream that 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.[1]

Examples

  • Many Himalayan rivers are good examples of antecedent origin. These rivers originated well before the Himalayan region was uplifted. The rivers Indus, Brahmaputra, Sutlej, Kosi and Subansiri originated on the Tibetan side and now traverse the existing mountain ranges, cutting deep gorges.
  • The Colorado River cut the Grand Canyon as the Colorado Plateau rose between 5 and 2.5 million years ago. Paradox Valley is another good example in the Colorado Plateau.
  • Devil's Gate in 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.
  • The Meuse still flows south-north from France to Belgium through the Ardennes which were elevated after the river had assumed that course.

See also

References

  1. ^ a b Grotzinger, J. & Jordan, T.H. 2006. Understanding Earth, 5th ed., Freeman, New York ISBN 978-0716766827
Alexander Heron

Alexander Macmillan Heron, BSc DSc FGS FRGS, FRSE (31 July 1884 – 1971), was a Scottish geologist who became Director of the Geological Survey of India. He participated in the 1921 British Mount Everest reconnaissance expedition following which he produced a geological map of the Everest region of Tibet.

Canyon

A canyon (Spanish: cañón; archaic British English spelling: cañon) or gorge is a deep cleft between escarpments or cliffs resulting from weathering and the erosive activity of a river over geologic timescales. Rivers have a natural tendency to cut through underlying surfaces, eventually wearing away rock layers as sediments are removed downstream. A river bed will gradually reach a baseline elevation, which is the same elevation as the body of water into which the river drains. The processes of weathering and erosion will form canyons when the river's headwaters and estuary are at significantly different elevations, particularly through regions where softer rock layers are intermingled with harder layers more resistant to weathering.

A canyon may also refer to a rift between two mountain peaks, such as those in ranges including the Rocky Mountains, the Alps, the Himalayas or the Andes. Usually a river or stream and erosion carve out such splits between mountains. Examples of mountain-type canyons are Provo Canyon in Utah or Yosemite Valley in California's Sierra Nevada. Canyons within mountains, or gorges that have an opening on only one side, are called box canyons. Slot canyons are very narrow canyons that often have smooth walls.

Steep-sided valleys in the seabed of the continental slope are referred to as submarine canyons. Unlike canyons on land, submarine canyons are thought to be formed by turbidity currents and landslides.

Chalk stream

Chalk streams are streams that flow through chalk hills towards the sea. They are typically wide and shallow, and due to the filtering effect of the chalk their waters are alkaline and very clear. Chalk streams are popular with fly fishermen who fish for trout on these rivers.

Devil's Gate (Wyoming)

Devil's Gate or Devils Gate is a natural rock formation, a gorge on the Sweetwater River in Wyoming, 5 miles (8.0 km)miles southwest of Independence Rock. Although the actual route of travel did not pass through the narrow cleft, the site was a major landmark on the Oregon and Mormon trails, and is particularly significant in the history of the latter.

Once the Union Pacific Railroad was extended to Benton, six miles east of present-day Sinclair, Wyoming, the Mormon Trail was rerouted through Whiskey Gap in Carbon County to a point 10 miles west of Devil's Gate to rejoin the original trail.

Devil's Gate is a remarkable example of superposed or an antecedent drainage stream. The Sweetwater River cuts a narrow 100-meter deep slot through a granite ridge, yet had it flowed less than a kilometer to the south, it could have bypassed the ridge completely. The gorge was cut because the landscape was originally buried by valley fill sediments. The river eroded downward and when it hit granite, it kept on cutting.

The site is accessible via semi-improved hiking trails from the Mormon Handcart Historical Center at the Sun Ranch and from the old paved alignment of Wyoming Highway 220, approximately 60 miles from Casper and 12 miles northeast of Muddy Gap. It is on public land.

River ecosystem

River ecosystems are flowing waters that drain the landscape, and include the biotic (living) interactions amongst plants, animals and micro-organisms, as well as abiotic (nonliving) physical and chemical interactions of its many parts. River ecosystems are part of larger watershed networks or catchments, where smaller headwater streams drain into mid-size streams, which progressively drain into larger river networks.

River ecosystems are prime examples of lotic ecosystems. Lotic refers to flowing water, from the Latin lotus, meaning washed. Lotic waters range from springs only a few centimeters wide to major rivers kilometers in width. Much of this article applies to lotic ecosystems in general, including related lotic systems such as streams and springs. Lotic ecosystems can be contrasted with lentic ecosystems, which involve relatively still terrestrial waters such as lakes, ponds, and wetlands. Together, these two ecosystems form the more general study area of freshwater or aquatic ecology.

The following unifying characteristics make the ecology of running waters unique among aquatic habitats.

Flow is unidirectional.

There is a state of continuous physical change.

There is a high degree of spatial and temporal heterogeneity at all scales (microhabitats).

Variability between lotic systems is quite high.

The biota is specialized to live with flow conditions.

Water gap

A water gap is a gap that flowing water has carved through a mountain range or mountain ridge and that still carries water today. Such gaps that no longer carry water currents are called wind gaps. Water gaps and wind gaps often offer a practical route for road and rail transport to cross the mountain barrier.

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