Water Erosion
Runoff and Erosion
• Moving water is a major agent of the erosion
that has shaped Earth’s land surface.
• When it rains, some water sinks into ground
and other evaporates or is taken up by plants.
• Moving water or water moving over Earth is
called runoff.
Amount of Runoff
•
•
•
•
•
•
Depends on 5 factors:
1. Amt of rain
2. vegetation- more plants=less runoff
3. type of soil- some absorb more
4. shape of land- slope or flat
5. how people use the land- paved areas do
not absorb water. Also, when farmers cut
down crops, it creates more runoff.
MORE RUNOFF MEANS
MORE EROSION
Rills and Gullies
• As the runoff travels, it
forms tiny grooves in
the soil called rills.
• As many rills flow into
one another, they grow
larger, forming gullieslarge grooves or
channels in the soil that
carries runoff after a
rainstorm.
Streams and Rivers
• Gullies join together to form a larger channel
called a stream (channel where water is
continually flowing down a slope.)
• Streams rarely dry up. Small streams are
called creeks or brooks.
• A large stream is called a river.
Tributaries
• Stream or river that
flows into a larger river.
• Ex: Missouri and Ohio
rivers are tributaries of
the Mississippi River.
• A drainage basin or
watershed is the area
from which a river and
its tributaries collect
their water.
Quick Check
• 1. What is a tributary?
• 2. What is a watershed/drainage basin?
• Of these items, which one(s) are NOT part of a
watershed/drainage basin? Rivers, oceans,
streams, rills, gullies
Valleys
• Through erosion, a river creates valleys,
waterfalls, flood plains, meanders, and oxbow
lakes.
• Steep slopes along a river erode rapidly,
forming a deep V- shaped valley.
• Rivers create
a V-shaped
valley.
• Glaciers
create a Ushaped
valley.
A. Waterfalls
• 1. Waterfall- softer rock is below harder rock.
The softer rock erodes first and the water
drops off.
Flood plain
• Lower down on its course, the river spreads
out and erodes the land, forming a wide river
valley called a flood plain.
• A river overflows into the floodplain during
floods.
Check up
1.How is a waterfall formed?
2.What creates a V-Shaped
valley? U-shaped valley?
B. MEANDERS
• 1. Meander- a curve in a river.
• 2. River curves around an obstacle (tree or
rock)
• 3. It erodes the outer bank and deposits on
the inner bank.
• 4. Over time, the meander becomes more
curved.
Meander
Meander
C. Oxbow Lake
• 1. Oxbow Lake- meander that has been cut off
from a river.
• 2. May form when river floods and deposits
sediments at the end of the meander.
• 3. Eventually, the meander is cut off from the
river forming an oxbow lake. (looks like a
horseshoe lake).
Oxbow lake diagram
Oxbow Lake
and
almost an
oxbow lake
Teach Time
• Explain to your neighbor what a meander is
and how it forms.
• Explain to your neighbor what an oxbow lake
is and how it forms.
III. DEPOSITS BY RIVERS
• A. Alluvial Fan- wide, sloping deposit of
sediment formed where a stream leaves a
mtn. range.(Shaped like a fan).
III. DEPOSITS BY RIVERS
B. Delta-Sediment deposited where a river flows
into an ocean or lake. It builds up a landform
called a delta.
Teach Time
• Compare and contrasts alluvial fans and
deltas.
• Draw a diagram to show the differences btwn
alluvial fans and deltas.
C. Soil on Flood Plains
1. River floods over land near it and deposits
new sediment.
2. The new soil is FERTILE and great for growing
things.
IV. Groundwater Erosion
1. Groundwater- Water that is UNDERGROUND.
2. Precipitation (rain, snow) soaks into cracks of
soil and rock and goes underground.
3. Groundwater erodes the land through
chemical weathering.
4. Water combines with Carbon dioxide to form
carbonic acid which breaks down limestone.
5. Limestone erodes away and leaves a hole
underground called a cave or cavern.
Karst Topography
• If the roof of a cave collapses because of the
erosion of the underlying limestone, the result
is a depression called a sinkhole.
• This type of landscape is called karst
topography.
A. Cave Formations
1. Cave formations occur when water drips
leaving behind calcite.
2. Stalactites- A deposit of calcite HANGING
from the roof of a cave.
3. Stalagmite- Slow dripping builds up calcite in
a cone-shape from the cave floor.
Stalactites and Stalagmites
Erosion- Rivers
Deltas