Unit 1 – Earth’s Changing Surface
Chapter 2 – Water Erosion & Deposition
2.1 Surface Water
Runoff – water that doesn’t soak into the ground
- eventually lead to larger bodies (streams, lakes, oceans)
Factors – amount of precipitation
o slope
o amount of vegetation
Gravity – attracting force all objects have for one another
o more mass, greater forces of gravity
o energy of motion affects speed
Water erosion – weathering away of material w/ water
Rill – small stream forms during a heavy rain
- energy of water picks up & carries away plants & soil
- leaves a scar in land
Gully – a rill channel that becomes broader & deeper
- large amounts of soil are removed
Sheet – when rain water flows to lower elevations as a sheet
- not due to rill or gully
Stream – when water continues to flow along a low place it has formed
- over time, will continue to pick up sediments & move them down stream
River System – fed from ground water, streams, rills, & gullies
- forms a larger body
Drainage Basin – the land area from which a stream gets its water
- water in a river system eventually flows to one location – the main river
- largest basin in US is the Mississippi
River systems of the world
- http://www.rev.net/~aloe/river/
- http://www.waterencyclopedia.com/Re-St/Rivers-Major-World.html
Stages of stream development
- Young stream
o Swift current
o Steep slope
o Whitewater & rapids
o Erodes more at bottom than sides
- Mature stream
o Less swift than young
o Wider erosion begins
o Curves (meanders) develop
o Slope gradient decreases
o Leads to a floodplain
- Old stream
o Flows slowly
o Broad, flat floodplain
o Gradient is very small
Stream or river overflow – dams & levees are created
- dams – controls flow of water downstream
- mounds built along sides prevents overflow on banks
Deposition of surface water
- as energy (flow) decreases, sediments start to deposit
- varies from place to place along stream
- deltas form as the mouth of a river meets an ocean, lake or gulf
- river slows down immensely & allows sediment to deposit
- alluvial fan – mountain rivers empty to a flat plain
2.2 Ground Water
Ground water system development
Layers in ground: soil
Weathered rock
Pores (air holes)
-permeability – when water passes through soil and rock
ex. sandstone
- larger the rock, greater the permeability
- smaller the rock & soil particles, weaker the permeability
ex. clay
- no pores at all or very few pores – impermeable – water cannot pass
through it
Groundwater movement
- water filters down until it reaches impermeable rock
- water begins to fill up
- develops an aquifer – layer of permeable rock that allows water to move
freely
- zone of saturation – layers fill w/ water
- water table – upper surface of the zone of saturation
Water table
- average person in US uses ~400 L (397L) each day
- most drinking water comes from groundwater
Wells – goes through & breaks into the zone of saturation
- can go dry if a dry season occurs
- rain helps to replenish what is removed from the well
-
too much removed can “sink” the land – pore spaces fill w/ sediments
instead of water
- artesian well – needs no pump
o pressure induced
o needs a slope
o higher slope water presses on lower sloped water & causes water to
go through the well
o can create a fountain if pressure is great enough
Springs – where the water table meets the surface
- usually on hillsides
- usually cold but can be heated
- heated by rocks that come in contact w/ molten material
Geysers – a hot spring that erupts occasionally
- shoots water & steam into the air
- ex. Yellowstone “old faithful”
o shoots between 14-32000 L of water & steam one every 80 minutes
Groundwater erosion & deposition
- water mixes w/ CO2 – carbonic acid (weak acid)
- limestone is easily dissolved by this acid
- creates cracks that eventually create caves
Cave formation – water that drips slowly from walls & ceilings deposits
sediments
- contains Ca ions from the limestone that was dissolved
- water evaporates deposits calcite
o stalactites – ceiling deposits
o stalagmites – floor deposits
Sinkholes – dissolving of rock near the surface
- depression when a cave collapses
2.3 Ocean Shoreline
Shoreline forces
- surface waves continue to move sediments
- motions back & forth
- also affected by tides
Longshore currents – waves that collide w/ the shore at slight angles
- “runs along the shore”
- Carry metric tons of loose sediments
Rocky shorelines – rocks & cliffs are common features
- waves wear away rock & create caves
- rock fragments broken off are ground up by waves
- soft rocks erode more quickly than harder ones
- much more turbulent water
Sandy beaches – smoothly, gentle sloping beaches/shorelines
-
-
deposits of sediment that run farallel to the shore
will stretch as far inland as tides & waves go to deposit sediments
made up of different sediments
o rock fragments
o shell fragments
grain size 0.07mm to 2mm
constant motion of waves cause sediments to erode more & round ages
o ex. Hawaii – black sands
 composed of basalt
o ex. Jamaica – white sands
 coral & shell fragment
Sand erosion and deposition
- currents, tides, storms & manmade things
- barrier islands
o sand deposits that parallel the shore but are separated from the
mainland