Many streams develop curves in their channels called meanders Figure below. This causes these meanders to migrate laterally over time. As the river moves onto flatter ground, the stream erodes the outer edges of its banks to carve a floodplain , which is a flat level area surrounding the stream channel Figure below. Base level is where a stream meets a large body of standing water, usually the ocean, but sometimes a lake or pond.
Streams work to down cut in their stream beds until they reach base level. The higher the elevation, the farther the stream is from where it will reach base level and the more cutting it has to do. As a stream gets closer to base level, its gradient lowers and it deposits more material than it erodes.
On flatter ground, streams deposit material on the inside of meanders. When a stream flows onto its floodplain, its velocity slows and it deposits much of its load. These sediments are rich in nutrients and make excellent farmland Figure below.
The Mississippi floodplain is heavily farmed. Flooding can wipe out farms and towns, but the stream also deposits nutrient-rich sediments that enrich the floodplain. A stream at flood stage carries lots of sediments. When its gradient decreases, the stream overflows its banks and broadens its channel. The decrease in gradient causes the stream to deposit its sediments, the largest first. These large sediments build a higher area around the edges of the stream channel, creating natural levees Figure below.
When a river enters standing water, its velocity slows to a stop. The stream moves back and forth across the region and drops its sediments in a wide triangular-shaped deposit called a delta Figure below. The main stream channel splits into many smaller distributaries. If a stream falls down a steep slope onto a broad flat valley, an alluvial fan develops Figure below.
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Warm temperature s can cause ice-rich permafrost to break off coastlines in huge chunks, often carrying valuable topsoil and vegetation with them.
Mass wasting describes the downward movement of rocks, soil, and vegetation. Mass wasting incidents include landslides, rockslides, and avalanche s. Mass wasting can erode and transport millions of tons of earth, reshaping hills and mountains and, often, devastating communities in its path. Some of the natural factors impacting erosion in a landscape include climate, topography, vegetation, and tectonic activity. Climate is perhaps the most influential force impacting the effect of erosion on a landscape.
Climate includes precipitation and wind. Climate also includes seasonal variability, which influences the likelihood of weathered sediments being transported during a weather event such as a snowmelt, breeze, or hurricane. Topography , the shape of surface features of an area, can contribute to how erosion impacts that area. The earthen floodplains of river valleys are much more prone to erosion than rocky flood channels, which may take centuries to erode. Soft rock like chalk will erode more quickly than hard rocks like granite.
Vegetation can slow the impact of erosion. Plant roots adhere to soil and rock particles, preventing their transport during rainfall or wind events. Trees, shrub s, and other plants can even limit the impact of mass wasting events such as landslides and other natural hazards such as hurricanes. Deserts, which generally lack thick vegetation, are often the most eroded landscapes on the planet. Finally, tectonic activity shapes the landscape itself, and thus influences the way erosion impacts an area.
Tectonic uplift , for example, causes one part of the landscape to rise higher than others. In a span of about 5 million years, tectonic uplift caused the Colorado River to cut deeper and deeper into the Colorado Plateau, land in what is now the U.
It eventually formed the Grand Canyon, which is more than 1, meters 1 mile deep and as much as 29 kilometers 18 miles wide in some places. Eroded sediments have profoundly influenced the development of civilization s around the world.
Agricultural development is often reliant on the nutrient -rich soils created by the accumulation of eroded earth. When the velocity of wind or water slows, eroded sediment is deposited in a new location. The sediment builds up in a process called sedimentation and creates fertile land.
River delta s are made almost entirely of sediment that has eroded from the banks and bed of a river. The rich delta soils of the San Joaquin and Sacramento rivers in northern California, for example, have created one of the most agriculturally productive areas in the world. Loess is an agriculturally rich sediment made almost entirely of wind-blown, eroded sediment. The Yellow River in central China gets its name from the yellow loess blown into and suspended in its water.
Human activity altering the vegetation of an area is perhaps the biggest human factor contributing to erosion. Trees and plants hold soil in place. When people cut down forests or plow up grasses for agriculture and development, the soil is more vulnerable to washing or blowing away.
Landslides become more common. Water rushes over exposed soil rather than soaking into it, causing flooding. Global warming , the current period of climate change , is speeding erosion.
The change in climate has been linked to more frequent and severe storms. Storm surge s following hurricanes and typhoon s can erode kilometers of coastline and coastal habitat. These coastal areas are home to residences, businesses, and economically important industries, such as fisheries. The rise in temperature is also quickly melting glaciers.
The slower, more massive form of glacial erosion is being supplanted by the cumulative impact of rill, gully, and valley erosion. In areas downstream from glacial snouts, rapidly melting glaciers are contributing to sea level rise.
The rising sea erodes beaches more quickly. Erosion control is the process of reducing erosion by wind and water. Farmer s and engineer s must regularly practice erosion control. Sometimes, engineers simply install structures to physically prevent soil from being transported.
Gabion s are huge wireframes that hold boulders in place, for instance. Gabions are often placed near cliffs. These cliffs, often near the coast, have homes, businesses, and highways near them. When erosion by water or wind threatens to tumble the boulders toward buildings and cars, gabions protect landowners and drivers by holding the rocks in place.
Erosion control also includes physically changing the landscape. Communities often invest in windbreak s and riparian buffer s to protect valuable agricultural land. Windbreaks, also called hedgerow s or shelterbelt s, are lines of trees and shrubs planted to protect cropland from wind erosion.
Riparian buffers describe plants such as trees, shrubs, grasses, and sedges that line the banks of a river. Riparian buffers help contain the river in times of increased stream flow and flooding. Living shoreline s are another form of erosion control in wetland areas. Living shorelines are constructed by placing native plants, stone, sand, and even living organisms such as oysters along wetland coasts.
These plants help anchor the soil to the area, preventing erosion. By securing the land, living shorelines establish a natural habitat. They protect coastlines from powerful storm surges as well as erosion. Eroding Animals. Cave entrances can be on land or in water. Also called limestone and calcium carbonate. Dust Bowl. Also known as an ice age. Northern Hemisphere.
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