Causes of Avulsion: An Overview

  1. N. D. Smith4 and
  2. J. Rogers5
  1. L. S. Jones1,† and
  2. S. A. Schumm2

Published Online: 17 MAR 2009

DOI: 10.1002/9781444304213.ch13

Fluvial Sedimentology VI

Fluvial Sedimentology VI

How to Cite

Jones, L. S. and Schumm, S. A. (1999) Causes of Avulsion: An Overview, in Fluvial Sedimentology VI (eds N. D. Smith and J. Rogers), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304213.ch13

Editor Information

  1. 4

    Department of Geosciences, 214 Bessey Hall, University of Nebraska, Lincoln, NE 68588-0340, USA

  2. 5

    Cape Town, South Africa

Author Information

  1. 1

    Department of Geology and Geophysics, University of Wyoming, Laramie, WY 82071, USA

  2. 2

    Colorado State University, Department of Earth Resources, Fort Collins, CO 80523, USA

  1. 1967 South Van Gordon Street, Lakewood, CO 80228, USA

Publication History

  1. Published Online: 17 MAR 2009
  2. Published Print: 7 OCT 1999

ISBN Information

Print ISBN: 9780632053544

Online ISBN: 9781444304213

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Keywords:

  • Avulsion: Modern and Ancient;
  • causes of avulsion;
  • avulsion - relatively rapid shift of river to a new channel on lower part of a floodplain, alluvial plain;
  • increased lateral slope away from existing channel;
  • in-channel deposition;
  • lateral shift of channel intersecting adjacent - leading to capture and avulsion of main channel

Summary

Avulsion, i.e. the relatively sudden displacement of a river channel, has an important effect on sediment distribution and on architecture of fluvial deposits because avulsion is a primary control on channel location on a floodplain. Most avulsions occur when a triggering event, commonly a flood, forces a river across a stability threshold. The closer the river is to the threshold, the smaller is the flood discharge needed to initiate an avulsion.

Avulsions can be categorized by the processes or events that decrease stability and move the river toward the avulsion threshold, and/or serve as avulsion triggers. These processes or events produce one or more of the following:

1 an increase in the ratio of avulsion course slope to existing channel slope caused by a decrease in gradient of the existing channel;

2 an increase in the ratio of avulsion course slope to existing channel slope caused by an increase in gradient away from the existing channel;

3 a non-slope-related reduction in the capacity of the existing channel to carry all the water and sediment delivered to it.

In most cases several of these causes will combine to bring a river close to a threshold, after which the next triggering event of sufficient magnitude will push the system across the threshold and avulsion will occur.

Avulsion frequency is controlled by the interaction between the rate at which various processes combine to move a river toward the avulsion threshold (instability) and the frequency of triggering events. If the combined processes that lead to instability proceed rapidly relative to triggering events, then the frequency of the triggering events will control avulsion frequency. In such settings, avulsion frequency may be a predictable function of flood frequency. If triggering events occur frequently relative to the rate at which the river becomes unstable, however, then the rate at which a combination of processes leads to instability will control avulsion frequency.