Biogeomorphology - Braiding vs. Meandering Rivers
Thursday, 8. October 2009, 15:23:26
Biogeomorphology is the study of interactions between living organisms (ecology/biology) and the development of landforms (geomorphology). Organisms affect geomorphic processes in a variety of ways. For example, trees can reduce landslide potential where their roots penetrate to underlying rock, plants and their litter inhibit soil erosion, biochemicals produced by plants accelerate the chemical weathering of bedrock, and marine animals cause the bioerosion of coral.
A braided river consists of a network of small channels separated by small and often temporary islands called braid bars or aits or eyots. Braided rivers are relatively rare today. I only remember to have seen them in barren (glacial) environments.
At the beginning practically all rivers were braided. A literature compilation and fieldwork on fluvial deposits show that, prior to effective plant colonisation, Cambrian to Early Silurian fluvial deposits were largely braided-river sand-sheets passing into sandy coastal and offshore deposits.
After trees and deep roots developed late in the Early Devonian, meandering rivers became more common, and today they are the norm.
Sedimentologists have generally dismissed or underestimated the importance of vegetation on riverine landscapes, although the few pristine modern rivers illustrate the intense effects of vegetation.
Late Palaeozoic plants fundamentally and irrevocably changed environments on land.
Reference:
Gibling and Davies
Rivers and Plants: Evolving Fluvial Systems through the Paleozoic
IAS 2009 27th Meeting, Book of Abstracts, p, 183
PS:
The trick to create meandering channels in the lab is indeed to plant alfalfa seedlings to give the banks some cohesion. See
http://scienceblogs.com/highlyallochthonous/2009/10/how_to_build_a_meandering_rive.php
An experiment that stresses the importance of living organisms in river morphology.
A braided river consists of a network of small channels separated by small and often temporary islands called braid bars or aits or eyots. Braided rivers are relatively rare today. I only remember to have seen them in barren (glacial) environments.
At the beginning practically all rivers were braided. A literature compilation and fieldwork on fluvial deposits show that, prior to effective plant colonisation, Cambrian to Early Silurian fluvial deposits were largely braided-river sand-sheets passing into sandy coastal and offshore deposits.
After trees and deep roots developed late in the Early Devonian, meandering rivers became more common, and today they are the norm.
Sedimentologists have generally dismissed or underestimated the importance of vegetation on riverine landscapes, although the few pristine modern rivers illustrate the intense effects of vegetation.
Late Palaeozoic plants fundamentally and irrevocably changed environments on land.
Reference:
Gibling and Davies
Rivers and Plants: Evolving Fluvial Systems through the Paleozoic
IAS 2009 27th Meeting, Book of Abstracts, p, 183
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http://water.usgs.gov/osw/techniques/workshop/osterkamp.html
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http://www.pnas.org/content/early/2009/09/28/0909417106
PS:
The trick to create meandering channels in the lab is indeed to plant alfalfa seedlings to give the banks some cohesion. See
http://scienceblogs.com/highlyallochthonous/2009/10/how_to_build_a_meandering_rive.php
An experiment that stresses the importance of living organisms in river morphology.
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