Transcript Chapter 9: Water Erosion & Deposition

Runoff is water that doesn’t soak into the
ground or evaporate, but flows across
earth’s surface
 Factors that affect runoff
1. Amount of rain
2. Length of time
 Light rain over an hour has time to soak
up
 Heavy rain over less than an hour will
run off because it can’t soak into the
ground fast enough
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3.
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4.
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Slope of land
Gravity causes water to move down slope
Water moves quickly down steeper slopes
Water moves slowly down gentler slopes
Slower movement=water soaked up by
ground
Vegetation
Plants slow down runoff and help prevent
soil from being carried away
Runoff will carry more soil and sediments
in places lacking vegetation
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Streams are parts of river systems
Can compare to a tree
Water comes from rills, gullies and small streams
Drainage basin is the area of land from which a
stream or river collects runoff
All the water in a river system flows to the trunk
(main river)
Stages depend on the slope of the
ground over which the stream flows
 3 classifications:
1. Young
2. Mature
3. Old
 The stages of development do not
always coincide with the actual age of
the river
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Flows swiftly
 Slope is steep
 Has a rough bottom
 High level of energy
 Erodes bottom of stream faster than its
side
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Flows smoothly through its valley
 Rocks in the streambed over time are
eroded by running water and sediments
 Erosion takes place more on the sides
than the bottom
 This causes curves to develop called
meanders
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Flow through broad, flat floodplains
 Drops load of silt near its mouth
 Dropping of sediments forms a delta
 A delta is an area of flat, fertile land
extending into the ocean
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As water moves through a river system it
loses energy
 This lose of energy causes sediments to
be dropped along the way
 Some sediments are carried a long way,
while others only short distances
 When sediments are deposited as the
water empties into an ocean or lake, a
deposit called a delta forms
 Deltas are triangular or fan-shaped
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When a river empties from a mountain
valley into a flat plain, the deposit is
called an alluvial fan
Water that soaks into the ground collects
in the pores and empty spaces in the soil
or rock is called groundwater
 14% of all water exists as groundwater
 Groundwater system has connecting
pores
 Soil and rock are permeable if pores are
connected and water can pass through
them
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◦ Water flows easily through
◦ Ex: sandstone-permeable rock
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Impermeable rock or soil doesn’t have
well connected pores or few pore spaces
◦ Water doesn’t flow easily through
◦ Ex: granite, clay
Groundwater keeps going deeper into
Earth’s crust until it reaches a layer of
impermeable rock
 Zone of saturation is where all the pores
in the rock are filled with water
 The upper surface of this zone is the
water table
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The amount of groundwater is limited
 Many people get their water from wells
that have been drilled into the zone of
saturation
 During a draught, the water table drops
 This is why it is important to conserve
water
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A good well extends deep into the zone
of saturation
 Groundwater flows into a well and a
pump brings it to the surface
 If water is taken out of well faster than it
can be replaced, wells can go dry
 If too much water is pumped out in area,
the land can drop or sink
 Artesian well-doesn’t need a pump to
bring water to the surface
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Water in an artesian well rises to the
surface due to pressure
 Artesian wells are very rare because the
aquifer needs to be located between 2
impermeable layers that are sloping
 Water enters at the high part of the slope
and exits through a well at the low part
of the slope due to the pressure created
by the higher part of the aquifer
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Springs are found on hillsides where the
water table meets a sloping surface
 Water flows out of the spring
 Source of freshwater
 Usually water comes to the surface as a
cool temperature
 When water comes to the surface after
being heated by hot rocks, it is called a
hot spring
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Is a hot spring that erupts periodically
 Groundwater is heated to high
temperatures causing it to expand
underground
 The expansion forces some of the water
out of the ground
 Most of the water turns into steam
 Ex: Old Faithful, Yellowstone National
Park
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Groundwater mixes with carbon
dioxide to form carbonic acid (weak)
◦ CO2 is absorbed by groundwater in the
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soil
CO2 is absorbed by rainwater from the
air
Acidic water flows through rocks,
dissolving the rock (limestone)
Cracks in the limestone get bigger until
an opening is formed. This is called a
cave!
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Stalactites form from deposits of calcium
carbonate.
◦ Water dripping inside the cave has calcium
ions dissolved in it
◦ This water evaporates and deposits calcium
carbonate.
◦ When this happens over and over stalactites
form.
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Stalagmites form when the drops of water
fall to the floor of the cave
A sinkhole is a depression on the surface of
the ground that forms when the roof of a
cave collapses or when material near the
surface dissolves
3 forces shape shorelines
1. Waves
 Crash against the shorelines
 Very powerful force
 Erode and move away large amounts of
material
2. Currents
 Longshore currents are created by
waves that hit at a slight angle
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Carry tons of loose sediments
3. Tides
 Outgoing tides carry sediments away
from the shore
 Incoming tides bring new sediments to
the shoreline
 Work with waves to shape shorelines
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Rocky
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Consist of rocks and
cliffs
Waves and sediments
slowly wear away
rocks
Rock parts that break
off are carried away
by longshore currents
Sandy
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Smooth, gently sloping
beaches
Made up of grains of
quartz or shell
fragments
Fragments range from
stones to fine sand
Some beaches have
different colored sands
Ex: Hawaii-black, made
of basalt
Ex: Jamaica-white,
made of coral and shell
Are sand depositions that lay parallel to
the shore but are separated from the
mainland
 Start out as underwater sand ridges
 Hurricanes and waves help form the
islands
 Last only a few years to a few centuries
 Storms and waves also erode the barrier
islands and cause erosion to beachfront
developments
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