Soil Erosion
Erosion The first five pictures of this presentation are of the same rock, just in different time periods. Pay attention to the dates on the side of the pictures and see what the water did to this rock. 1890
Erosion Still the same rock. 1910
Erosion Still the same rock. 1920
Erosion Still the same rock. 1970
Erosion Still the same rock, but where did it go? 1990
Water is the leading cause of soil erosion! Rain drops strike with a surprisingly powerful force Particles fly off of the surface every time a rain drop hits Those dislodged particles are then carried away by thin sheets of flowing water Called “sheet” erosion
These are tiny streams that form after the sheets of flowing water Water forms rills These are tiny streams that form after the sheets of flowing water Create trenches or “gullies”
Water Erosion The four types of water erosion are as follows: the movement of soil by rain splash and its transport by this surface flow. Rill erosion by concentrated flow in small rivulets. Gully erosion by runoff scouring large channels (deeper than 1 foot). Stream bank erosion by rivers or streams cutting into banks.
Stream Erosion Streams generally erode their channels, lifting loose particles by abrasion, grinding, and by dissolving soluble material. A stream’s bedload is solid material too large to carry in suspension. Deposition occurs as stream flow slows down Larger, heavier particles are deposited first
Glacier Erosion Glaciers mainly erode in two ways: Plucking is when the bottom layer of a glacier melts and the water seeps into the surrounding rock. This water then refreezes and cracks and splits the rock. These rocks are then incorporated into the glacier. Abrasion occurs when a glacier made of ice and rock moves over a bedrock surface which is then scraped and smoothed by the glacier. Glacial drift applies to all sediments deposited by glaciers. There are two types of glacial drift: till and stratified drift.
Glacier Erosion Glacial drift applies to all sediments deposited by glaciers. Till is deposited as the glacier melts and drops its load of rock debris. Ice cannot sort the sediment it carries, therefore till deposits are usually unsorted mixtures made up of many particle sizes. Stratified drift is sediment laid down by glacial meltwater. It contains particles that are sorted according to size and weight of the debris.
Glacial Till
Wind Erosion In general, most erosion results from running water, although in deserts, wind erosion is more significant than elsewhere because deserts soils are dry. Wind erodes much slower With extremely dry conditions, however, wind can move mass quantities of soil Wind erodes in the desert in two ways: deflation and abrasion.
Wind Erosion In general, most erosion results from running water, although in deserts, wind erosion is more significant than elsewhere because deserts soils are dry. Wind erodes in the desert in two ways: deflation and abrasion.
Deflation Deflation is the lifting and removal of loose particles such as clay and silt. Deflation can lower elevation of land by a meter or more. Deflation also results in shallow depressions called blowouts. Deflation creates a stony surface layer called desert pavement when it removes all the sand and silt and leaves only coarser particles.
Abrasion Abrasion happens when wind-blown sand cuts and polishes exposed rock surfaces. Blowing sand can grind away at boulders and smaller rocks, sometimes sandblasting them into odd shapes.
How do humans affect erosion? Erosion is strongly influenced by human activity: Removal of natural vegetation, such as farming, logging, & construction greatly increase erosion. Plant roots bind the soil together Over-steepened slopes due to construction can lead to instability of soil and mass movements.