Water Erosion: How do processes involving water change Earth’s surface?
What is the MAJOR agent of erosion that has shaped Earth’s land surface? Water Erosion
Water moving over land’s surface is called runoff. This may cause sheet erosion.
The amount of water runoff in an area depends on 5 main factors:
1.
2.
3.
4.
5.
The amount of rain an area receives.
Vegetation - grasses, shrubs & trees reduce runoff
Type of soil - some absorb more water than others
Shape of the land – steep slopes has more run-off, which causes more runoff
How people use the land - paved areas increase run-off, crop removal increases run-off
Runoff overtime:
How does runoff over time affect the land and water?
Rills & Gullies:
Streams & Rivers:
Tributaries:
Rills are tiny grooves in
the soil that grow
larger forming gullies.
Gullies join together to
form a larger channel
called a stream
Streams grow together
by getting water from
tributaries
A gully is a large groove
or channel in the soil
that carries runoff after
a storm. It moves soil &
rocks.
Water continuously
flows here and rarely
dries up.
A tributary is a stream
or river that flows into a
larger river.
Small streams may be
called creeks or brooks
An example: The
Missouri & Ohio rivers
are tributaries of the
Mississippi river.
Tributaries collect their
water from the drainage
basin or watershed
Gullies only contain
water after it rains.
Small streams flow
together to form a large
stream called a river
Rivers cause erosion and create valleys, waterfalls, flood plains, meanders and oxbow lakes.
Rivers form on steep mountain slopes. They flow quickly & follow a narrow path so they erode rapidly. The result is that
rivers form deep, V-shaped valleys.
Features of rivers:
What are the features that erosion forms along a river?
Waterfalls:
Flood Plains:
Meanders:
Oxbow Lakes:
Occur where a river
meets an area of hard
& slowly eroding rock.
Lower down on the
river’s course, it flows
over a wide river
valley, an area of land
called a flood plain
Are loop-like bends in
the course of a river.
Sometimes
meandering rivers
form an oxbow lake a meander that has
been cut-off from the
river.
Then flows over softer
rock downstream.
The softer rock erodes
away faster & a
waterfall develops.
During flooding the
water in the river over
flows its banks into
this wide river valley
area.
They occur as the
outer bank of a river is
eroded & deposits are
dropped on the inner
bank of the bend in a
river.
Example: southern
stretch of the
Mississippi River
meanders on a wide,
gently sloping flood
plain area
They may form when
a river floods as high
water finds a
straighter path
downstream . As
flood waters fall,
sediments dam up
the ends of the
meander and a lake
forms
Deposits by rivers are made as the water slows down and the fine particles settle in the river bed. Larger stones quit
rolling and sliding. Deposition creates landforms such as alluvial fans and deltas and can also add soil to a river’s flood
plain.
Deposits by Rivers:
What features result from deposition along a river?
An Alluvial Fan is a wide, sloping deposit of sediment formed where a stream leaves a steep, narrow mountain
valley range. This deposit is shaped like a fan.
Deltas form when sediments are deposited where a river flows into an ocean or a lake.
A landform is built up as the
sediments drop.
Soil may also be added to Flood Plains during floods as sediments are deposited. This new soil added to the area
makes the river valley fertile. Forests and crops may be grown here.
Groundwater Erosion:
What results from water seeping into the ground & mixing with CO 2?
Not all rain water evaporates or becomes runoff. Some water soaks into the ground, filling openings in the soil and
trickling into cracks & spaces in layers of rock. Groundwater erosion is caused by the process of chemical weathering:
Carbonic Acid forms as carbon dioxide & water combine. This weak acid can break down limestone that will gradually
hollow out pockets in the rock. Over time, the pockets develop into large holes called caves or caverns.
Cave Formations:
What are the features found in a cave? How do they form?
Water containing carbonic acid & calcium drip from a cave’s roof forming stalactites (like icicles hanging from
the top) and stalagmites (drips the build up from the bottom of the cave floor)
Karst Topography:
What happens when land rich in limestone is weathered by groundwater?
In rainy regions where limestone near the surface is weathered and groundwater erosion can cause the roof of
the cave to collapse leaving a sinkhole – this type of landscape is called karst topography. In the U.S. regions of
Florida & Texas have these areas.
Erosion by Glaciers: How do glaciers cause erosion and deposition?
Glaciers:
A glacier is any large mass of ice that moves slowly over land and form in areas where more snow falls
than melts. (Watch Brain Pop – Free Movie - Glaciers)
What are the 2 types of glaciers? How are they alike? How are they different?
Continental Glaciers
Valley Glaciers
Covers Land or Continents
Spreads out over millions of
square kilometers, cover
about 10% of Earth’s land,
cover most of Greenland &
Antarctica, in the past these
Have covered larger parts of
Earth – times are called Ice Ages
Large
masses
of ice,
move
slowly on
land,
shape
the land
Forms high in
mountains when snow
& ice builds up in a
mountain valley
Stay narrow& long held
in by the sides of the
mountain, smaller than
Cont. Glaciers, form
U-shaped valleys
How do Glaciers shape the land?
They begin to move due to the force of gravity and erode the land by plucking & abrasion
Plucking happens as glaciers move across the land. They pick up rocks, the weight of the glacier breaks them
apart & they freeze to the bottom of the glacier and the glacier carries the rock fragments along with it. As the
glacier drags the rocks along, the land is gouged & scratched by the rocks. This process is called Abrasion.
Glaciers make deposits along the land as they melt and drop the sediments on their bottoms as till – particles of
different sizes – clay, silt, sand, gravel & boulders can be found in till. Till deposited along the edges of a glacier
forms a ridge called a moraine. Long Island in New York is a terminal moraine (it was the very last point reached
by the glacier that deposited it). As glaciers melt they leave their marks called kettles – small depressions left in
areas when chunks of ice are left in glacial till. They fill in with water and form ponds or lakes - called kettle
lakes (common in Minnesota)
Erosion by Waves: How do waves erode a coast? What features result
from deposition by waves?
Remember: Waves are caused by the energy from the wind being transferred to the water.
Erosion by Waves: Waves shape the coast through erosion by breaking down rock and transporting sand and
other sediment. They erode hard, rocky areas of the coast that jut out just like jagged mountains are eroded
over time.
Deposits by Waves: Waves deposit sediment as they slow down. Beaches, spits & barrier beaches are formed.
Beach:
Spit:
An area of wave-washed
sediment along a coast,
sands may be made of
coral or sea shells
A beach that projects or
sticks out like a finger
Sediments on the beach
are moved down the beach
as waves that move with
the current move down
the shore – this is called
the longshore drift
Spits form as a result of
longshore drift depositing
sediments along a coast
Sandbars or Barrier
Beaches:
Long ridges of sand that run
parallel to the beach
Storms deposit sand above
sea level
People build houses on the
large ones
DANGER: storms that build
them can also destroy them
Erosion by Wind: How does wind cause erosion? What features result from
deposition by wind?
Wind causes erosion by deflation & abrasion
Wind is the weakest agent of erosion, but can be powerful in shaping the land in areas where there are few
plants to hold the soil in place. Example: the deserts
Deflation:
Abrasion:
Wind blows across the land
and removes surface
materials, easily picks up the
smallest particles of
sediment, heavier particles
only bounce around for a
short time, does not usually
have a huge effect on the
land
Can polish rock, causes little
erosion, mostly a form of
weathering
Deposition by wind forms sand dunes (plant roots hold in place) and loess deposits (makes fertile soils, valuable
farmland)
Sand Dunes:
Loess Deposits:
Wind shifts sand from
one side of the dune
to the other slowly
Tiny particles of
sediments, deposited in
layers far from its source