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Stream capture by headward erosion, leaving a wind gap
Stream capture by headward erosion, leaving a wind gap

Stream capture, river capture, river piracy or stream piracy is a geomorphological phenomenon occurring when a stream or river drainage system or watershed is diverted from its own bed, and flows instead down the bed of a neighbouring stream. This can happen for several reasons, including:

The Maumee River basin. The Maumee, flowing north-east, has broken into part of the Wabash River basin, capturing west-flowing streams and reversing their flow direction on entering it.
The Maumee River basin. The Maumee, flowing north-east, has broken into part of the Wabash River basin, capturing west-flowing streams and reversing their flow direction on entering it.

The additional water flowing down the capturing stream may accelerate erosion and encourage the development of a canyon (gorge).

The now-dry valley of the original stream is known as a wind gap.

Capture mechanisms

Tectonic uplift

Glacial damming

The River Thames as it passes through the Goring Gap
The River Thames as it passes through the Goring Gap

Headward erosion

Karst

Glacier retreat

The Slims River was previously fed by meltwater from the Kaskawulsh Glacier in the St. Elias Mountains in the Yukon and its waters flowed into Kluane Lake and on to the Bering Sea. Because of climate change, the glacier has rapidly receded and the meltwater no longer feeds the Slims. The water instead now feeds the Kaskawulsh River which is a tributary to the Alsek River and drains into the Gulf of Alaska.[4][5]

Effect on freshwater life

River capture is a shaping force in the biogeography or distribution of many freshwater fish species.[6][7]

Australian freshwater fish

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The formerly massive Great Dividing Range runs the length of the eastern coastline of Australia and has isolated native freshwater fish populations east and west of the range for millions of years. In the last two million years erosion has reduced the Great Dividing Range to a critical point where west-to-east river capture events have been possible. A number of native fish species that originated in the Murray–Darling river system to the west are (or were) found naturally occurring in a number of coastal systems spanning almost the entire length of the range.

None of the river capture events that allowed native fish of the Murray-Darling system to cross into and colonise these East Coast river systems seem to have formed permanent linkages. The colonising Murray-Darling fish in these East Coast river systems have therefore become isolated from their parent species, and due to isolation, the founder effect, genetic drift and natural selection, have become separate species (see allopatric speciation).

Examples include:

Olive perchlet (Ambassis agassizii), western carp gudgeon (Hypseleotris klungzingeri), pygmy perch (Nannoperca australis) and Australian smelt (Retropinna semoni) also appear to have made crossings into coastal systems, the last two species seemingly many times as they are found in most or all coastal streams in south eastern Australia as well as the Murray-Darling system.

Unfortunately, with the exception of eastern freshwater cod and Mary River cod, it has not been widely recognised that these coastal populations of Murray–Darling native fish are separate species and their classifications have not been updated to reflect this. Many are threatened and two, the Richmond River cod and the Brisbane River cod, have become extinct.

See also

References

  1. ^ K.N. Dikshit, 2013, Origin of Early Harappan Cultures in the Sarasvati. Valley: Recent Archaeological Evidence and Radiometric Dates, Journal of Indian Ocean Archaeology, pp88-
  2. ^ Tom L. McKnight; Darrel Hess (2005). "16, "The Fluvial Processes"". Physical Geography: A Landscape Appreciation (8th ed.). Upper Saddle River, New Jersey: Pearson, Prentice Hall. p. 462. ISBN 0-13-145139-1.
  3. ^ Stokes, Maya; Goldberg, Samuel; Perron, J. Taylor (2018). "Ongoing River Capture in the Amazon". Geophysical Research Letters. 45 (11): 5545–5552. doi:10.1029/2018GL078129.
  4. ^ Retreating Yukon glacier makes river disappear, CBC News Posted: Jun 17, 2016
  5. ^ Shugar, Dan, H.; et al. "River piracy and drainage basin reorganization led by climate-driven glacier retreat". www.nature.com.
  6. ^ Albert, J. S., & Crampton, W. G. (2010). The geography and ecology of diversification in Neotropical freshwaters. Nature Education Knowledge, 1, 13–19
  7. ^ Albert, J. S., Schoolmaster, D. R., Tagliacollo, V., & Duke-Sylvester, S. M. (2016). Barrier displacement on a neutral landscape: Towards a theory of continental biogeography. Systematic Biology, syw080