Water Erosion
Splash erosion: Raindrops may have sufficient kinetic energy when they fall on soil that the
impact can produce detachment and airborne movement of small soil particles.
Sheet erosion is produced by heavy rain on bare soil where water flows as a sheet down gently
sloping land, removing soil particles in thin layers more or less evenly.
Runoff occurs where precipitation exceeds soil infiltration rates. Surface runoff turbulence can
often cause more erosion than the initial raindrop impact.
Heavy rainfall or the melting of snow create running water which removes soil by sheet, rill, or
gully erosion.
Development of gully erosion
Image Credit: MBG
Erosive activity at different stream gradient
Examples of intense gully erosion. Concepcion
Image Credit: MBG
Examples of intense gully erosion. Concepcion
Erosive activity at different stream gradient
Image Credit: MBG
Erosive activity at different stream gradient
Image Credit: MBG
Erosive activity at different stream gradient
Rill erosion occurs in discrete streamlets carved into the soil. When rills become too deep to be
removed by plowing, gullies form.
Gully erosion results where water flows along a linear depression eroding a trench.
Valley or stream erosion is produced when water continuously flows along a linear feature,
eroding downward, deepening the valley, and extending the valley headward towards the hillside.
In all stages, the most intensive erosion occurs during times of flood, as more and faster-moving
water can act more erosively because it can carry a larger sediment load (clay and silt as
suspended particles, sand-siozed grains as saltation load, and pebbles and boulders as
rolling/sliding bedload).
In early stages of stream erosion, the erosive activity is dominantly vertical with stream gradient
relatively steep forming valleys with typical V cross section.
When some base level is reached, the erosive activity switches too lateral erosion, which widens
the valley floor and creates a narrow floodplain.
When stream gradient becomes nearly flat, meanders form, and lateral deposition of sediments
becomes important.
In all stages the most intensive erosion occurs during times of flood, as more and faster-moving
water act more erosively as it carry a larger sediment load (suspended abrasive particles,
pebbles and boulders).
Mountains, climates and erosion processes
All mountains chains serve to a greater or lesser extent, depending on their size, shape,
orientation, and relative location, as barriers for air and moisture that may have a direct influence
on regional climates.
The rise of new mountain chains will directly influence the climate at a regional scale, therefore
leading to erosive processes in the changing area. Chemical weathering and water erosion will
dominate the humid side, while wind and physical erosion will be more important on the dry
areas.
Climatic barrier effect exerted by mountains. Rainfall and humid conditions dominate on the seaside of the
mountain chain, while dry conditions dominate the continental side
Image Credit: MBG
Uspalalta valley, Argentina, east of the Andes and dominated by dry conditions
Image Credit: MBG
Erosive activity at different stream gradient