Geology Cafe

Stream Erosion: Processes That Wear Down the Land

Stream flow is constantly changing the landscape. Material that is uplifted along fault systems, mountain ranges, and in volcanic regions are being removed by erosion, dominantly by stream action. Runoff from storms carry sediments into streams which then gradually transport these materials downstream until they are deposited at sea, on floodplains, or in enclosed sedimentary basins.
Water and relief in California
Click on thumbnail images for a larger view.
Stream erosion processes encompass all parts of a landscape. Precipitation falls relatively evenly over large areas, but once on the ground, the water either soaks into the ground, or, if conditions are right, moves across the surface to merge into increasingly larger channels moving downslope. As flow volume increases, the amount of material that can be loosened and transported increases. The result is that stream cut into a landscape, often keeping pace with the rate that the landscape rises. This valley is on the east flank of Loma Prieta in the Santa Cruz Mountains.
Between wet periods, stream flow diminishes, even dry up except in areas where spring water provides a source of surface flow. During wet periods (storms), steams typically change from clearwater flow to sediment filled flood water. This is Uvas Creek in the Santa Cruz Mountains near San Jose.
High elevations typically receive more precipitation, and mountain streams tend to be perennial sources of water, and are typically clear due to spring-fed water supplies. This creek is in Castle Rock State Park in the Santa Cruz Mountains.

This stream gravel bar is along Waddell Creek, draining from Big Basin in the Santa Cruz Mountains. Gravel Bars are exposed along streams that experience episodic, often intense flooding, keeping them clear of vegetation. Note that the bridge shown in the distance was destroyed by floodwaters shortly after this picture was taken. This view shows a meandering stream channel along the Salinas River. Rivers constantly change their courses through the process of stream meandering. Fast moving water on the outside of a river bend is a location of erosion, whereas, calmer water conditions on the inside of a bend allows sediments to accumulate. Over time, stream bends (meanders) typically migrate downstream. Cutoff bends can become oxbow lakes.
Stream meanders on the Cuyuma River in central California. View of a typical California gravel bar. Gravel is easily transported downstream during flood condition. The gravel stops moving as floodwaters recede. This view is along Coyote Creek in Morgan Hill, CA.
A mountain stream in the heart (and heat) of summer is a valuable resource! This view is of Arroyo Seco Canyon in the Santa Lucia Range of central California. Sediment carried by streams are powerful agents of erosion. This fluted stream channel is in Mosaic Canyon in Death Valley. The stream in this canyon only flows after episodic storms.
View of a talus block hanging over a stream bed in Pinnacles National Monument. Flash floods from episodic storms are powerful forces of erosion. This slot canyon shows how flashflood erosion can carve deep narrow canyons. This view is in Painted Canyon in southern California.
This huge granite boulder was transported by flashflood waters many miles from its source before becoming wedged in a narrow section of a canyon. This view is in Marble Canyon in Death Valley. Painted Canyon in near Mecca, CA. Episodic storms cause flashfloods that carve deep, narrow canyons along mountain fronts.
Flashfloods caused by episodic storms in arid environments in areas with poorly consolidated sediments in produce "badlands"topography. This view is of Gower Wash with Manly Beacon in the distance, located in Death Valley. Golden Canyon is an scenic area with badlands topography in Death Valley.
Badlands topography in Death Valley. This view is from Zabrisky Point Overlook near Furnace Creek. Badlands topography in the Mecca Hills in southern California.
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8/28/2012