Unit 4: Weathering, Erosion, and
Deposition
(Text ch.5, 6, and 7)
I Weathering: the breakdown of
rocks into sediments by exposure to
air and water.
(see text p.126)
\\hpnas-1\tfolders\ssmsteachers\bohman_ken\Earth Science 2009\Unit 3\vidclips unit 3\Weathering intro.asf
A. Physical (or Mechanical) Weathering:
changes the shape or size of a rock.
(How nature smashes rocks)
1. Frost Action (Wedging):
 During the day, liquid water
seeps into cracks in the rock.
 At night, water freezes and
expands, breaking rock apart.
[Diagram]
WEATHERING - FROST WEDGING ROLLOVER
Observe the effects of mechanical weathering.
(see text p.127)
2. Plant Roots grow into cracks,
breaking rock apart. (see text p.128)
Observe the effects of mechanical weathering.
3. Abrasion: sediments are
transported by water,or wind. They
wear away by bumping and grinding
together.
[diagram]
stream abraded rocks
YouTube - Bill Nye the Science Guy - Pet Rock Theatre
4. Exfoliation: occurs when heavy
pressure is removed from
underlying rocks.
(see text p.128)
exfoliation weathering - Google Images
5. Physical Weathering increases the
surface area and allows chemicals to
break rock apart faster.
(see text p.127)
[diagram]
Animation: particle size and surface area
\\hpnas-1\tfolders\ssmsteachers\bohman_ken\Earth Science 2009\Unit 3\vidclips unit 3\What_Is_Mechanical_Weathering_.asf
B. Chemical Weathering: changes
the chemical composition of the rock.
1. Water (H2O) is the most important
agent of chemical weathering
 H2O combines with minerals and
weakens them.
Ex. Feldspar + Water → Clay + Salt
(makes oceans salty)
Observe the chemical weathering of feldspar to clay.
 H2O speeds up the rate of all other
chemical reactions.
 H2O absorbs gases such as oxygen
(O2) or carbon dioxide (CO2) that
weaken or dissolve rock.
2. Oxygen combines with iron rich
minerals to form iron oxide or rust.
Iron + O2 → Iron Oxide (rust)
rock oxidation - Google Images
3. Carbon Dioxide dissolves in water
to form Carbonic Acid.
[Demo- carbonic acid formation]
This dissolves rocks, especially
limestone, forming caverns and
sinkholes (text p. 177, 179).
image karst topography
florida karst topography - Google Search
Observe an animation of cave formation.
Example: Howe Caverns in N.Y.
Howe Caverns: Year Round Adventure
Journey Into Amazing Caves (IMAX® Trailer) - Extreme Spelunk - YouTube
Cave of Swallows - Schwalbenhöhle in Mexico - YouTube
How Sinkholes like Guatemala happen - YouTube
C. Factors affecting how fast rocks
weather.
1. Mineral Composition
ex.: see text p.129 fig. 6
gravestone weathering - Google Image Search
 More resistant rocks stick out as
less resistant rocks weather away.
[Diagram]
See text p.132
buttes - Google Image Search
rock strata- grand canyon
2. Climate
 Rocks weather fastest in warm,
moist climates.
 Rocks weather slowest in dry
climates.
mayan pyramids - Google Search
egyptian pyramids - Google Search
3. Air Pollution, especially Acid
Rain, weathers rocks faster.
See text p.130
Acid Rain Students Site: Animation
Earth: Acid Rain Eating Washington, D.C. : Video : Discovery News
Cleopatra's Needle in Central Park- NYC
“Cleopatra's Needle, an Egyptian obelisk, has been used for
illustration of weathering processes in numerous geology
textbooks (Figure 15). The obelisk was donated to the United
States and erected at its site on the west side of the Metropolitan
Museum of Art in 1881.
The monument is easy to find by following any number of park
trails that lead toward the southwestern side of the museum. The
monument's name, Cleopatra's Needle," is somewhat of a
misnomer. Inscriptions on the monument include the names
Thutmose III and Rameses II from the 12th Century BC (more than
11 centuries before Cleopatra).
The obelisk is carved from a single piece of red granite derived
from a quarry at Aswãn, and weighs about 224 tons. The surface
of the stone is heavily weathered, nearly masking the rows of
hieroglyphs engraved on all sides.
closeup heiroglyph
Photographs taken near the time the obelisk was erected in the
park show that the inscriptions were still quite legible.
Cleopatra's Needle in Egypt 1880
The stone had lain in the Egyptian desert for nearly 3000 years but
undergone little weathering. In a little more than a century in the
climate of New York City, pollution and acid rain have heavily
pitted its surfaces.”
From: 3dparks.wr.usgs.gov/nyc/parks/loc1.html
D. Soil forms from the weathering of
rocks.
Soil "MovieTrailer" - YouTube
1. Composed of four parts
(see text p.133)
 Air
 Water
 Inorganic minerals: tiny
fragments of weathered rock
 Organic: decayed remains of
plants and animals. Also called
Humus. Makes soil dark colored
and fertile.
topsoil - Google Search
DIRT! The Movie TRAILER - YouTube
Dirt! The Movie Trailer - YouTube 2
Creating humus: compost pile
compost - Google Image Search
YouTube - Tips on Composting
2. The type of Soil that forms depends
on a number of factors
(see text p.135-137).
Residual Soil: forms in place.
[diagram]
Transported Soil: is carried into an
area by erosion.
[diagram]
3. Over time a mature soil forms
made of layers or Soil Horizons.
Soil Profile
[Diagram]
(See text p.138,148)
soil profile - Google Search
II Erosion: is the movement of
sediments by gravity, water, wind,
and/or ice.
A. Gravity is the driving force of
all erosion.
(Gravity makes water/ice flow and
wind blow)
Mass Movement occurs when
gravity transports sediment all by
itself.
1. Creep: slow movement of
sediments down a hill. (text p. 147)
[Diagram]
image: creep
2. Slumping: faster movement
downhill. (text p. 146)
3. Landslides and Mudflows: are
the fastest movement of sediment
downhill. Very dangerous. (See p.
143-145)
landslide vidclip- Japan
kayak landslide
YouTube - Landslides
B. Running Water, in streams and
rivers, transports more sediment than
anything else!
“Water is the main agent
of erosion on Earth.”
The River is Flowing .. A video presentation of Native American Indian Folk Song - YouTube
1. Stream Velocity is how fast the
water is flowing.
 The greater the slope (or gradient)
of the land, the greater the stream
velocity. (text p.157)
[Graph]
 Stream velocity is greatest in the
center, a little below the surface.
This is where friction is least
(text p. 160)
[Diagrams]
2. Stream Discharge is the amount
(or volume) of water being carried.
The greater the discharge, the greater
the stream velocity (text p.161)
[Graph]
Amazon: YouTube - The Mighty Amazon & River Dolphins -Wild South
America - BBC
C. Erosion by Flowing Water
1. Streams erode sediments in three
ways:
 Ions (salts) dissolve and are
carried in solution.
 Colloids, Clay, and Silt are
carried in suspension (floating)
 Sand, and larger sediment
bounce and roll along the bottom.
This is called the Bed-Load.
[Diagram]
Fig. 10.14 - Modes of Sediment Transport
YouTube - Sediment Transport Detail
YouTube - Sediment Transport, 50 g/m/s (12 mm), Detail 2
2. The greater the discharge, the
greater the total sediment load
transported.
image mississippi river
[Graph]
3. The greater the velocity of a
stream, the greater the size of the
sediment eroded.
(see ESRT p.6)
esrt page 6
Practice: Worksheet
4. The bed load can cut down through
the stream bottom forming
V-shaped canyons.
[diagrams]
v shaped valley - Google Search
Case Study: The Grand Canyon
grand canyon - Google Search
[Diagram formation of grand canyon]
Previous years\ES 2008-09\Unit 4 08-09\The_Geology_of_the_Grand_Canyon_asf.asf
YouTube - The Grand Canyon: How It Formed
YouTube - Grand Canyon Adventure: River at Risk IMAX Trailer
vidclip: formation of the grand canyon
D. Erosion by Wind is most
important in deserts.
(Very little water)
1. Sediment often deposited in Dunes.
(See Text p. 205-207)
2. Wind blown sediment can carve
rock into strange shapes.
Ex. “Hoodoo’s”
[Diagram]
wind erosion 1
wind erosion 2
wind erosion 4
vidclip: wind 2
E. Erosion by Ocean Waves
1. Waves erode rocky shorelines to
form cliffs, sea arches, and sea stacks.
(text p.464- read).
sea arch - Google Search
2. On sandy beaches, sediment is
transported by Longshore Drift.
See Text p. 463-464
[Diagram]
vidclip: wave erosion
YouTube - Longshore Drift 1
YouTube - Longshore Drift
Case Study: Long Island South Shore
http://www.fireislandmgm.com/00fi_beach.jpg
http://www.lib.utexas.edu/maps/national_parks/fire95.jpg
http://www.loving-long-island.com/image-files/fire-island-lighthouse-looking-west.jpg
http://lighthousegetaway.com/lights/NY/fire2.jpg
Google Maps- Long Isand South Shore
F. Erosion by Ice
1. Glacier: a mass of ice, formed
on land, that slowly flows down hill.
(See text p. 187-198)
vidclip- glaciers 1
Glaciers form when snow does not
completely melt in summer and builds
up from year to year.
Two Types:
 Alpine or Valley Glaciers: form in
mountains and flow slowly
downhill. (Text p.187,188, 190)
alpine glacier - Google Search
vidclip- lame lapse valley glacier
[diagram- ice movement in glacier]
Flowing ice carves V-shaped river
valleys into a U-shape. (text p.193)
[Diagram]
Image U shaped valley 1
u shaped valley 2
u shaped valley 4
 Continental Glaciers are huge
sheets of ice that cover all or part of
a continent. (text p. 189, 198)
glacier Animations and Movies: cross section
2. Glaciers erode sediments of all
sizes.
 Some sediments are carried on top.
(text p.195)
 Some rocks freeze into the sides or
bottom of ice and often scratch and
polish the underlying bedrock.
(see text p.192).
glacial striations- Central Park, NYC
[Diagram]
YouTube - Glacier Power
III Deposition: the laying down of
sediments in a new location.
A. Factors Affecting Deposition in Water
1. Larger particles, settle faster than
smaller particles.
[Diagram: Graphs]
2. Smallest particles may stay in
suspension (floating) or solution
(dissolved) and never settle.
3. If unsorted particles (a mixture
of sizes) are added to water…
Largest (most coarse)will settle on
bottom...
and smallest (most fine) on top.
[diagram: vertical Sorting]
This is called Vertical Sorting or
Graded Bedding.
graqded bedding 1
graded bedding 2.0
4. When a stream enters a lake or
ocean, it slows down and deposits
sediment.
 Largest particles are close to shore
 finest are furthest from shore.
 This is called Horizontal Sorting.
animation Observe how sediments are deposited.
YouTube - Particle Sorting and Settling Rate for Kids
[diagram]
5. Denser particles, settle faster
than less dense particles.
[Graphs]
6. Rounder particles settle faster
than flatter particles.
[Diagrams: Sorting by Shape]
[Graphs]
7. Life History of a Stream
 Youthful near the Source.
(See text p.157,167)
Steep slope, (high gradient)
High velocity,
Many rapids and waterfalls.
Bed load cuts steep V-shaped valleys
youthful 1
[Diagrams: Top / Streambed Profile]
 Mature Stage
Less slope, less velocity
Greater Discharge
Greater sediment load (text p.165)
Wide curves called Meanders form.
Meanders. Animation.
[Diagram:Top / Profile]
YouTube - Sticky - One Minute on Meanders
 Old Age Stage (text p.168)
Very low gradient (slope)
Very high discharge
Very high sediment load
Ox-Bow Lakes or Bayou’s form.
[Diagrams]
old age 2
old age 3
animation Meander Cut-Offs and Oxbow Lakes
8. Delta’s form when a stream or
river enters a lake or ocean.
(see text p.166)
[Diagram]
Nile river delta - Google Search
Mississippi river delta - Google Search
9. Summary DiagramEnergy and Rivers
 Potential Energy (PE) = stored energy.
In general, the higher up water is, the
higher the PE
 Kinetic Energy (KE) = Energy of
motion. In general, the faster water
moves the higher the KE.
[Diagram]
 Point A: Greatest PE at the Source.
 As river flows to the Sea, PE changes
into KE.
 If erosion = deposition, this called a
Dynamic Equilibrium
 Point B: Outside of meander, KE
increases. Erosion occurs.
 Point C: Inside of meander, KE
decreases. Deposition occurs.
 Point D: KE and PE = 0. Deposition
occurs. Delta forms.
B. Other Patterns of Deposition
1. Wind deposited sediments are
often
 Angular (pointy corners) with a
frosted appearance.
image- frosted grain sands
[Diagram]
 well sorted
 show cross bedding.
[Diagram]
Google images- cross bedding
sand dunes - Google Search
2. Evidence of Deposition by Glacial Ice
a.) Sediments are
 angular (have sharp corners)
and are
 poorly sorted (mixed up sizes).
These deposits are called Glacial Till.
(see text p.194)
glacial till 2
[Diagram]
glacial till 3
b.) Long hills of glacial till mark
furthest advance of glacier.
These called Terminal Moraines.
moraine 1
moraine 3
c.) Flat sandy areas, deposited by
streams flowing from melting glaciers
called Outwash Plains
outwash plain 1
outwash plain 2
d.) Many lakes form from melting
blocks of ice.
glacial lake 3
Example: Finger Lakes of New York
fill long, thin U-shaped valleys.
See ESRT p.3 link
google image: finger lakes
e.) Large boulders dropped by
melting ice called Glacial Erratics
[Diagram]
glacial erratics - Google Search
f.) Other glacial landforms include:
Text p.193: Cirques, Horns, Aretes, Tarns,
Hanging valleys.
p.197: Drumlins, Eskers
YouTube - Glacial Erosion Landforms
g.) Glacial Features of Long Island
text p.196
[diagram]
LI moraines
view of Ronkonkoma moraine
Ronkonkoma moriane- Montauk
Ronkonkoma moriane 2
long island glacial erratics - Google Search
lake ronkonkoma - Google Search
FORMATION OF LAKE RONKONKOMA