1.
Wearing Down and Building Up
•Weathering breaks down earth’s surface into sediments.
“Breaks”
•Erosion is when sediments are transported. “Takes”
•Deposition is when sediments “settle out” or are “dropped”
by whatever is carrying them. This can build up landforms or
fill in areas. “Makes”
•Principle of Uniformitarianism- Weathering, erosion, and
deposition act together in a cycle that wears down and builds
up Earth’s surface today and in the past.

2.
• Have you ever seen a “muddy” stream or river?
• The water appears “muddy” because it is carrying
small particles of sediment! Erosion from running
water is at work!

3.
Runoff and Erosion
•After it rains, some of the water that does
not soak into the ground becomes runoff.
•More runoff = more erosion.

4.
Streams and Rivers
•Streams and creeks form from
runoff.
•Rivers form when streams come
together.
•A tributary is a stream or river that
flows (along with any sediment it is
carrying) into a larger river.
•Exs. Pine creek is a tributary to the
Allegheny river.
•As water moves through streams
and rivers, it picks up sediment and
carries it! Erosion is happening!

5.
Today you are going on a river trip!
You are going to follow a river from start to finish and discover
many things along the way!
Pick your boat of choice:

6.
River Erosion
•You start your journey at the river’s source which
is often a steep mountain stream. You will end your
journey at the river’s mouth which is when it
reaches the sea.

7.
River Erosion
•Wow! At the river’s source, you
notice the water is fast flowing and
follows a straight and narrow
course. You barely have to paddle!
•It erodes deep into the mountain,
eventually forming a V-shaped
valley. As it cuts into the earth, the
water continues to pick up
sediment.

8.
River Erosion
• You are at the bottom
of the mountain and
you notice a fan-
shaped deposit. You
realize that this must
be an Alluvial fan.
• When a stream comes
to the bottom of a
mountain water slows
down, spreads out,
and drops or deposits
its sediment in a fan
shape.

9.
River Erosion
•As the river flows, you notice there are deep canyons,
gorges and waterfalls carved by the river.
•The “Grand Canyon” was slowly carved out of the Colorado
Plateau by the Colorado River over millions of years.
Grand Canyon of PA

10.
River Erosion
•Waterfalls are created when softer rock erodes
before overlying harder rock, creating a steep drop.
•Be careful, rocks that have broken off create rapids!
World Record Holder-Costa Rica

11.
Erosion by Rivers
•The paddling is getting tough!! Now
you are lower on the river’s course and
closer to the sea, you notice it slows
down and spreads out. It is no longer
fast and narrow. It erodes a wide area
on its sides called a flood plain. This is
where water goes when it overflows the
river banks.
•You notice that the land along the flood
plain is flat and you notice a lot of farms
so it must be very fertile.
•Although land along a floodplain may
be appealing, what are some potential
problems with living along it?

12.
Erosion by Rivers
• You are moving so slowly and you
notice you are no longer taking a
straight path! Instead, the river
meanders or forms loop like bends.
•You move to the outside of the curve
because you notice the water moves
faster on the outside and slower on the
inside curve.
•Therefore erosion happens along the
outside and where the water is slowing
down, along the inside, sediment that
the water is carrying gets deposited and
forms cute little beaches!
•Yum! You stop along one of these
beaches for a snack!

13.
Erosion by Rivers
•As you are moving, you notice a strange C- shaped lake!
•When meanders get too curved, the river is able to “break
through” and takes a straight course again. The meander gets
cutoff as sediment builds up. This is called an oxbow lake.
The lake
looks like
a C!

14.
Deposits by Rivers
•You made it! You have reached the ocean!
•Sediment that is eroded away by rivers and streams is
deposited at the river’s mouth as a river slows down forming
a landform called a delta.
•Delta -Rivers slow as they meet the sea. The sediment is
deposited which forms new land. They take on a triangular
shape and are named after the Greek letter ∆.
•The city of New Orleans is built on land created by a river!

15.
Groundwater Erosion
•Rain water that does not evaporate or become
runoff soaks into the ground and is called
groundwater.
•Groundwater can be in the form of underwater
streams but most of the time it is held in the
pore spaces of rocks.

16.
Groundwater Erosion
•Carbon dioxide can dissolve in water making it acidic. This
acidic water can weather and dissolve limestone underground
forming a cave.
•Once the groundwater in the cave lowers, the cave is filled with
air.
•When water containing dissolved limestone (main mineral is
calcite) drips from the ceiling and hits the air, the water
evaporates and leaves behind the limestone again forming a
Stalactite.
•When this water drips to the floor it builds up a Stalagmite.

17.
Ceiling - Stalactite
Ground - Stalagmite

18.
Groundwater Erosion
• Karst topography is found in many parts of the
United States where the bedrock is made up of layers
of limestone that have been eroded by acidic water.
• Karst topography has caves and sinkholes
(sinkholes are caves where the roof has collapsed)

19.
Glaciers – “Rivers of Ice”
•Glacier-A large, slow moving mass of ice. Glaciers
form when more snow falls each year than melts so it
builds up.

20.
How Glaciers Form and Move
•A continental glacier is a glacier that covers much
of a continent or large island. Antarctica and
Greenland are large continental glaciers!
•Continental glaciers move by spreading outwards
in all directions towards the sea.

21.
How Glaciers Form and Move
•The last Ice Age ended
around 12,000 years
ago. Most of Earth’s
water was in the form of
ice. During the last ice
age, a continental glacier
covered most of northern
North America.
•Most of the land and
water were covered
under an ice sheet that
was 2.5 miles thick in
some places.

22.
Valley Glaciers
•Valley Glaciers form when snow and ice pile up high
in the mountains. The ice slowly begins to move
downward because of gravity.
•Ex. Alaska and Glacier National Park in Montana

23.
How Glaciers Form and Move
•Like the force of gravity and running water, glaciers
too cause both erosion and depositional features
which scar and shape the land!

24.
Glacial Erosion Features-How Glaciers shape the
land
**Remember, erosion is the transportation of
sediment**
1. As a glacier moves, plucking breaks and
picks up pieces of bedrock from the ground and
carries them.

25.
Glacial Erosion Features
2. V-Shaped valleys become U-Shaped as
glaciers erode old river valleys. Glaciers can
also carve a mountain peak into a sharp horn or
sharp peak and leave bowl shaped depressions
along mountains called cirques.

26.
Glacial Erosion Features
3. Glaciers also carved depressions in the land which can
fill with water to create lakes (ex. Great Lakes)

27.
Glacial Erosion Features
4. As glaciers move across the land, they
scratch the bedrock (remember they are
carrying rocks). These are known as glacial
striations.

28.
Glacial Deposition Features
*Remember, deposition is the dropping of
sediment.*
1. As glaciers melt and retreat,
they deposit the sediment that
they were carrying which is a
mixture of clay and boulders
known as Till.
How did this rock get here?
2. Many big boulders were
dropped as the ice melted
away at the end of the last
ice age. These big, out of
place boulders are known as
glacial erratics.
Glaciers can move huge
rocks that wind or water
could not move!

29.
Glacial Deposition
3. The very end of the
glacier pushes along a lot of
rocks, so when it quits
moving and begins to melt,
it leaves the till in a pile.
This is known as a terminal
moraine.

30.
Glacial Deposition
•Moraine State Park, about 40 minutes
North of Shaler, is the southernmost
point in Pennsylvania that the glaciers
reached during the last ice age.
•The soil in the park is full of boulders
and a mixture of rock that was stuck in
the ice as it moved across Canada!

31.
Glacial Deposition
• Lateral moraines are parallel ridges of
sediment deposited along the sides of a
glacier.

32.
Glacial Deposition Features
4. Often when glaciers retreat (begin to melt) they leave
behind chunks of ice. These melt and create lakes called
kettle lakes. Ex. Conneaut Lake in PA & Walden Pond in
Concord, Massachusetts!

33.
Erosion by Waves
•Many ocean waves are caused by wind
and can have tremendous power (we will
talk about tides later this year which are
caused by something else!). Some of the
world’s biggest storms happen at sea!

34.
Erosion by Waves
•Due to constant erosion by wave action,
there are many unique landforms found
along the edges of the continents.

35.
Erosion by Waves
•Waves shape the coast through weathering
(abrasion), erosion, and deposition. Waves
carry sand and gravel which wear away rock
like sandpaper breaking it down, transporting
the sediment, and depositing it.

36.
Erosion by Waves
•Weathering, erosion, and deposition creates a
variety of unique landforms along a coast.
1. Wave-Cut Cliffs
2. Sea Caves
3. Sea Stack
4. Sea Arch
5. Headland-land
that stands out
from the coast
because it is
made of erosion-
resistant rock.

37.
Deposits by Waves
•Waves shape a coast when they deposit sediment, forming
coastal features such as beaches, spits, and barrier beaches.
1. Beaches
2. Spit
3. Sandbar
4. Barrier Beach-
large sandbar
Ocean City MD
and
Outer Banks, NC
and Cape Cod

38.
Outer Banks, NC
Barrier Beach
Ocean City, MD
Spit
Sandbar

39.
Deposits by Waves
•Beaches are constantly being moved around and
reshaped by a process known as longshore drift.
•Because waves often hit the shore at an angle,
then move straight back due to gravity, sand often
travels down a beach in a zig-zag manner.

40.
Deposits by Waves
•Beaches are constantly being
changed by longshore drift.
•Sometimes in heavily developed
areas beaches have to have sand
added to them or have structures
called jetties built to reduce erosion.

41.
Deposits by Waves
•You can tell a lot about a beach by examining
its grains of sand.
•What do the shape of the sand grains tell you?
How much weathering the grains have been
exposed to.
•What do the different colors in sand tell you?
What minerals/materials the beach is made
from.

42.
How Wind Causes Erosion
•Wind erosion usually occurs in dry
areas where there is little
vegetation to keep sediment in
place.
•Ex. deserts and recently plowed
farmland.
•Wind erosion led to the Dust Bowl!

43.
How Wind Causes Erosion
•Wind wears down rock, kind of like a natural
sandblasting. This is known as abrasion.

44.
Wind Deposition
•Wind erosion and
deposition may form
giant piles of sand
dunes.
Erg Chebbi, Morocco

45.
Mass Movement- Gravity
•Mass Movement is
when rock is eroded by
gravity.
•Gravity pulls everything
toward the center of the
earth.
•Mass movement can be
triggered by
earthquakes, volcanoes,
heavy rainfall, etc.
•The different types of
mass movement include
landslides, slump, creep
http://www.youtube.com/watch?v= and mudflows.
K1qY8nPqcCw
http://www.youtube.com/watch?v=mknStAMia0Q

46.
Landslides - Problems Around Pittsburgh
•Every year, tumbling rocks called
landslides along Route 28 near
Harmarville cause nightmares for
motorists!
•Also a few years ago a landslide
caused Rt 65 to close for weeks after
the construction of a new Walmart
destabilized the land!
•Pittsburgh is especially prone to
landslides and mudslides because
our local rocks contain a lot of clay so
they easily crumble when wet.

47.
Mudslides
•Mudflows or mudslides - can occur when
loose sediment becomes drenched after
heavy rainfall. (Hurricanes)
•Can also happen around volcanoes
(when snow and ice melt rapidly after a
volcanic eruption.)

48.
Mudslide from the May 1980 eruption of Mount St. Helens.