1. Education

Water Gap, California

Erosional Landform Pictures

By

Water gaps are steep-sided river valleys that appear to have cut through a range of mountains. (more below)
Where rivers punch through mountains
Photo (c) 2003 Andrew Alden, licensed to About.com (fair use policy)
This water gap is in the hills on the west side of California's Central Valley, and the gorge was created by Corral Hollow Creek. In front of the water gap is a large, imperceptibly sloping alluvial fan.

Water gaps can be created in two ways. This water gap was made the first way: the stream was there before the hills began to rise, and it maintained its course, cutting down as fast as the land rose. Geologists call such a stream an antecedent stream. See three more examples: Del Puerto and Berryessa gaps in California and Wallula Gap in Washington.

The other way of forming a water gap is by stream erosion that uncovers an older structure, such as an anticline; in effect the stream is draped over the emerging structure and cuts a gorge across it. Geologists call such a stream a resequent stream. Many water gaps in the eastern U.S. mountains are of this type, as is the cut made by the Green River across the Uinta Mountains in Utah.

A water gap is not guaranteed. If the stream cannot cut fast enough, or if its course is abandoned because of stream capture or some other reason, a small gap might result without a stream in it, perched high on a ridge. That is called a wind gap.

  1. About.com
  2. Education
  3. Geology

©2014 About.com. All rights reserved.