At this national lakeshore, tiny bluffs give way to larger dunes, and the ecosystem eventually creates the ideal conditions for an oak forest through the process of plant succession. The Indiana Dunes, for example, are extensions of beach ridges formed by the waters of Lake Michigan. Beach ridges run parallel to the shoreline and are often associated with sand dunes. Beach ridges are formed entirely by waves lapping onshore, pushing sand and sediment up and away from the body of water. The constant erosion of feeder bluffs supplies (feeds) sediment to the beaches and seashore downstream below.Īnother sort of coastal bluff is the beach ridge. state of Washington, are sometimes called feeder bluffs. Coastal bluffs, especially those in the Puget Sound region of the U.S. These bluffs are often more rugged than their inland counterparts, and are more vulnerable to major erosion. A floodplain’s bluff lines may be steep and narrow, or they may be wide and gentle.Ĭoastal bluffs are formed through a combination of erosion from wind, sea spray, and crashing waves. In fact, a “ bluff line” defines the outer limits of a river’s floodplain, and is often another name for valley wall. Where the meanders, or loops, of the river reach valley walls, the water may carve bluffs. Over thousands of years, a meandering river gradually shifts from side to side across its floodplain. state of Minnesota, for example, were carved by the meanderings of the mighty Mississippi River.Įrosion also produces bluffs along the wider floodplain of a river. The 150-meter (500-foot) Great River Bluffs in the U.S. No longer supported, the upper part of the bank breaks off, leaving the high wall of a bluff. River currents on the outside of the curve erode, or wear away, the lower part of a river bank. Most bluffs border a river, beach, or other coastal area.īluffs may form along a river where it meanders, or curves from side to side. Therefore, in addition to growing laterally, the bends also gradually migrate down the valley.A bluff is a type of broad, rounded cliff. Due to the slope of the channel, erosion is more effective on the downstream side of a meander. Thus by eroding its outer bank and depositing material along its inner bank, a stream moves sideways without changing its channel size. At the same time the reduced current at the inside of the meander results in the deposition of coarse sediment, especially sand. The sideways movement occurs because the maximum velocity of the stream shifts toward the outside of the bend, causing erosion of the outer bank. Meanders change position by eroding sideways and slightly downstream. Where the bends of two meanders meet, they bypass the curve of river, creating an oxbow lake which may then be infilled with overwash sediment. This creates an erosional surface on the outer edge (a cut bank) and a depostional surface on the inner edge (a point bar). Phil Reiker, NPS Geologic Resources DivisionĪ meandering stream has a single channel that winds snakelike through its valley, so that the distance 'as the stream flows' is greater than 'as the crow flies.' As water flows around these curves, the outer edge of water is moving faster than the inner. Oxbow lake formation in a meandering stream
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