Soil Erosion

Soil Erosion1890

ErosionThe 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.ErosionStill the same rock.1910

ErosionStill the same rock.1920

ErosionStill the same rock.1970

ErosionStill the same rock, but where did it go?1990

Water is the leading cause of soil erosion!Rain drops strike with a surprisingly powerful forceParticles fly off of the surface every time a rain drop hitsThose dislodged particles are then carried away by thin sheets of flowing waterCalled sheet erosion

Water forms rillsThese are tiny streams that form after the sheets of flowing waterCreate trenches or gullies

Water ErosionThe 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 ErosionStreams generally erode their channels, lifting loose particles by abrasion, grinding, and by dissolving soluble material.A streams bedload is solid material too large to carry in suspension.Deposition occurs as stream flow slows downLarger, heavier particles are deposited first

Glacier ErosionGlaciers 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 ErosionGlacial 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 TillWind ErosionIn 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 slowerWith extremely dry conditions, however, wind can move mass quantities of soilWind erodes in the desert in two ways: deflation and abrasion.Wind ErosionIn 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.DeflationDeflation 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.

AbrasionAbrasion 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.