WEATHERING VS.
EROSION
1. Weathering — the disintegration and
decomposition of rock at or near the Earth surface
2. Erosion — the incorporation and
transportation of material by a mobile agent such
as water, wind, or ice.
AGENTS OF EROSION
Running water
• Styles of erosion: Vertical erosion (downcutting),
lateral erosion, headward erosion.
• Streams transport their sediment load in three ways: in
solution (dissolved load), in suspension (suspended
load), sliding and rolling along the bottom (bed load)
• Deposition occurs when a river loses its capacity to
transport sediments. With decrease in velocity and
competence, sediments start to settle out. River
deposits are sorted by particle size.
Erosional landforms:
River valleys, waterfalls, potholes, terraces, gulley/
rills, meanders (exhibit both erosional and
depositional features), oxbow lake, peneplane
• Depositional landforms:
Alluvial fans/cones, natural levees, deltas
2. Ocean or sea waves
how waves erode and move sediment along the shore.
• Shoreline erosion processes: Hydraulic action, abrasion,
corrosion.
• Transport by waves and currents: Longshore current, beach
drift.
3. Glaciers -moving body of ice on land that
moves downslope or outward from an area of
accumulation (Monroe et. al., 2007
• Valley (alpine) glaciers — bounded by valleys and tend to be long and
narrow.
• Ice sheets (continental glaciers) — cover large areas of the land
surface; unconfined by topography. Modern ice sheets cover
Antarctica and Greenland.
• Ice shelves — sheets of ice floating on water and attached to the land.
4. Wind
• Wind erodes by: deflation (removal of loose, fine particles from the
surface), and abrasion (grinding action and sandblasting)
• Deflation results in features such as blowout and desert pavement.
Abrasion yields ventifacts and yardangs.
• Wind, just like flowing water, can carry sediments such as: (1) bed
load (consists of sand hopping and bouncing through the process of
saltation), and (2) suspended load (clay and silt-sized particles held
aloft).
5. Groundwater
• The main erosional process associated with groundwater is solution.
Slow-moving groundwater cannot erode rocks by mechanical
processes, as a stream does, but it can dissolve rocks and carry these
off in solution. This process is particularly effective in areas underlain
by soluble rocks, such as limestone, which readily undergoes solution
in the presence of acidic water.
• Rainwater reacts with carbon dioxide from atmosphere and soil to
form a solution of dilute carbonic acid. This acidic water then
percolates through fractures and bedding planes, and slowly dissolves
the limestone by forming soluble calcium bicarbonate which is carried
away in solution.
• Karst topography —a distinctive type of landscape which develops as
a consequence of subsurface solution. It consists of an assemblage of
landforms that is most common in carbonate rocks, but also
associated with soluble evaporate deposits.
• (1) Cave/Cavern – forms when circulating groundwater at or below
the water table dissolvescarbonate rock along interconnected
fractures and bedding planes. A common feature found in caverns is
dripstone, which is deposited by the dripping of water containing
calcium carbonate. Dripstone features are collectively called
speleothems, and include stalactites, stalagmites, and columns
• (2) Sinkholes (Dolines) – circular depressions which form through
dissolution of underlying soluble rocks or the collapse of a cave’s roof.
• (3) Tower karst – tall, steep-sided hills created in highly eroded karst
regions.
6. Gravity
• Mass wasting — the downslope movement of soil,
rock, and regolith under the direct influence of gravity
• Factors that control mass wasting processes include:
• As the slope angle increases, the tendency to slide down
the slope becomes greater.
• Role of water: adds weight to the slope, has the ability to
change angle of repose, reduces friction on a sliding
surface , and water pore pressure reduces shear strength
of materials
• Discuss the events that trigger mass wasting processes.
• a. Shocks and vibrations – earthquakes and minor shocks such as those produced
by heavy trucks on the road, man-made explosions
• b. Slope modification – creating artificially steep slope so it is no longer at the
angle of repose
• c. Undercutting – due to streams eroding banks or surf action undercutting a
slope
• d. Changes in hydrologic characteristics – heavy rains lead to water-saturated
regolith increasing its weight, reducing grain to grain contact and angle of repose;
• e. Changes in slope strength – weathering weakens the rock and leads to slope
failure; vegetation holds soil in place and slows the influx of water; tree roots
strengthen slope by holding the ground together
• f. Volcanic eruptions - produce shocks; may produce large volumes of water from
melting of glaciers during eruption, resulting to mudflows and debris flows
