Weathering, Erosion, & Deposition

part 1

Part I. WeatheringA. Weathering is the physical or chemical break-

down of rocks or minerals at or near the earth’s surface - Breaking rock into pieces

B. ONLY rocks at the surface can weatherC. Types

A. Physical – breaking rocks w/o changing composition

B. Chemical – breaking rocks by chemically changing the minerals

Chemical Weathering Agents

A. Water – dissolves certain rocks (salt)B. Air

a) Oxidation (rusting) – O2 combines w/ water and reacts with minerals containing iron

b) CO2 – combines w/ water to make carbonic acid, dissolves limestone

c) Plants – lichens make acid that dissolves rock

Chemical Weathering Agents

Lichens

Oxidation

Carbonic Acid

Oxidation

Oxidized rocks in Utah

Carbonic acid at work!

Hydrolysis of feldspar

Feldspar

Clay forming

from hydrolysis

of feldspar

Acid rain at work!

Review of chemical weathering• Oxidation (rust)• Acid rain• Carbonic acid

Water + Carbon dioxide Carbonic acid• Water dissolving rocks with acids mixed in it• Hydrolysis-water reacting with rock causing chemical

changefeldspar + water = clay

Physical WeatheringA. Frost action

1. Water enters cracks in rocks, as it freezes it expands breaking the rock

Physical WeatheringB. Abrasion

1. Grinding, rolling & scraping of rocks together. Breaks off sharp edges, rounding the rock

2. Caused by running water, waves, wind and glaciers

Physical WeatheringC. Plant action

1. Plant roots work into rocks breaking the rock apart as it grows

Physical WeatheringD. Exfoliation

1. Peeling off the outer layers of rock.2. Caused by repeated heating or cooling

Review of physical weathering

• Frost action-alternating temperatures above and below freezing causes rock to crumble

• Abrasion-the physical grinding of rocks along a surface

• Root action -roots break a part land as they grow into the ground

• Burrowing animals• Exfoliation-peeling of rock layers due to crustal

unloading

Exfoliation examples

Abrasion

Frost action at work!

Root action

Burrowing animals

Factors Affecting WeatheringA. Climate

1. Hot, dry climate – very little weathering

2. Warm, moist climate – rapid chemical

3. Cold, moist climate – strong frost action

Factors Affecting Weathering

B. Type of Rock1. Igneous and Metamorphic – react

SLOWLY, more dense2. Sedimentary – weather rapidly

Factors Affecting WeatheringC. Particle Size

1. As rocks break into smaller pieces, it weathers faster (more surface area exposed)

0

5

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35

1 2 3 4 5

Particle Size

Rate

of W

eath

erin

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Review Factors affecting rate of weathering

• Exposure to the elementsThe closer a rock is to the earth’s surface, the more weathering will occur

• Particle sizeWhen the rock particles are smaller, the rate of weathering increases

• Mineral compositionSome minerals are more resistant to weathering than others

• ClimateWarm, moist climates chemicalCold, dry climates physical

SOILS• Soils are a mixture of rocks, minerals and

organic material

SoilA. Final product of weatheringB. Soil composition

1. Inorganic material – pieces of weathered rock

2. Humus – organic material from decayed plants and animals; provides nutrients for growth

Classes of Soil

A. Soil Types1. Residual Soil

a. Soils that stay where they are formedb. Soil composition matches the rocks

underneath, granite rock = granite in soil

2. Transported Soila. Soils that were carried to other locationsb. Soil does NOT match, granite rock = NO

granite in soil

Soil development depends on…

• Climate• Biological activity• Slope of the land • Time

Soil profile

Know this profile!Know this profile!

Porosity and permeability of soils

• Porosity- amount of open spaces within soil particles

• Permeability- amount of water that passes through a soil

Weathering, Erosion, & Deposition

part 2

Part 2 - Erosion

A. Carries away pieces from weatheringB. Most soils are different from bedrock

under them (transported soils)C. Gravity is MAIN force behind erosion

What does erosion mean?

• Transport of weathered material.

• Agents of erosion are: wind, water, ice (glaciers) and gravity.

• Water is the most common erosional agent

Mass movement notes

What comes up, must come down!

What is mass movement?

• Mass movement: When gravity pulls geologic materials down slope

• Driving force gravity

• Resisting force friction

Soil creep

Velocity: Less than 1 cm/year

Debris flow

Velocity:1 mm/day to 1 km/hour

Mud flowVelocity:1-5 Km/hour

Rock fallsVelocity: Greater than 4 km/hour

Conclusion

• Mass movement is the downward movement of rock, snow, soil and ice as a result of gravity.

• When the driving force>resisting force slope failure occurs

• Order of increasing speed: soil creepdebris flowmud flowrock fall

Agents of Erosion

A. Gravity (Review)1. Landslides – rapid movement of rock

material down hill2. Slumping – small landslides3. Creep – VERY slow mvmt of material4. Talus – piles of rock found at base of

very steep slopes

Agents of ErosionSlumpingLandslide

Agents of ErosionTalus

Creep

Agents of ErosionB. Wind

1. Carries fine grained sediments about 1 meter above ground

2. Grains are lifted and bounced along

3. Wears away rocks at the base

4. Dunes – piles of wind blown sand

Agents of Erosion

Agents of Erosion

Agents of ErosionC. Glaciers

1. Masses of frozen water on ground2. Valley (alpine) glaciers

a. “rivers of ice”b. Found at high altitudes in mountains

Agents of Erosion

3. Continental glaciersa. Large sheets of ice covering large areas of

surface (Greenland, Antarctica)

Agents of Erosion

4. Formed in areas where snow does not melt, keeps building up and is compacted into ice

5. As Ice builds up, pressure increases at bottom, causing ice to flow (cm to m per day)

Agents of Erosion

6. As glaciers move, they carry materials of ALL sizes (sand to boulders)

7. Materials carried cause bedrock under glacier to be gouged and scraped

VIII. Agents of Erosion

Agents of Erosion

8. Glacier Landscapesa. U-shaped valleysb. UNSORTED rock material when glacier melts

(till)c. Drumlins – groups of long oval hillsd. Eskers – winding ridges formed in tunnels

under icee. Kettles – large piece of ice breaks off glacier

making a hole, ice melts leaving the hole. Kettle lake – hole is filled with water (Beaver Lake)

Agents of Erosion

VIII. Agents of Erosion

Kettle Lake

DrumlinGlacial Till

The Hydrologic (Water) Cycle

Water table

Agents of Erosion

D. Running Water1. MOST important (moves most material)2. Ways of carrying sediments

a. Solution – dissolved materials (salt)b. Suspension – very fine particles (silt)

suspended in water, looks muddyc. Bouncing – pebbles bounced along streamd. Rolling and sliding – largest particles moved

without being liftedParticle Transport

Agents of Erosion

3. Velocitya. Speed of the water flowb. Depends on slope and volume (stream

discharge)c. Greater slope = greater velocityd. Greater volume = greater velocity

Agents of Erosion

4. Sediments Carrieda. Size

1) FAST streams can carry LARGER sediments

b. Quantity (amount)1) MORE volume carries MORE sediment2) Even though a fast moving stream can carry larger

rocks, a slow moving stream with greater volume can carry more sediment (Mississippi River)

How fast does a stream need to be flowing to carry a cobble?

About 190 cm/sec

What kind of particle can a stream carry if it is going 400 cm/sec?

Boulder

How fast does a stream need to be flowing to carry a 1.0 cm particle?

50 cm/sec

Agents of Erosion

5. Effects of moving streamsa. Carry sedimentsb. Deepen and widen stream bed as it drags

and carries its sedimentsc. Abrasion happens (rocks becoming rounded)

Agents of Erosion6. Stages of Stream Development

a. Youth1) Steep gradients2) Rapid downcutting (carries rocks and pebbles)3) V shaped valley4) Has waterfalls or rapids5) Straight path

Agents of Erosionb. Mature

1) Less steep, less velocity2) Wind around obstructions forming loops3) Carries silt and clay (no rocks)4) Larger volume = more sediment than youth

Agents of Erosionc. Old

1) Very small gradient2) Only carries finest sediments3) Can flood4) Makes Oxbow Lakes

Agents of Erosion

Agents of Erosiond. Old streams can

become young again if the area is uplifted and gradient becomes steeper

e. Most streams have youth at source, mature in middle and old age at their mouth (where river dumps into a lake/ocean)

Weathering, Erosion, & Deposition

part 3

Part 3 - Deposition

A. Sediments are released or dropped from the agent of erosion

Factors Affecting Deposition

A. Size1. Large particles settle the fastest

Settling Time

Particle Size

Tim

e

Particle Size

Rat

e

Settling Rate

Factors Affecting Deposition

B. Shape1. Round particles settle faster than flat

particles

C. Density1. More dense particles settle faster

Sorting of SedimentsA. Graded bedding (vertical sorting)

1. Happens at ocean bottoms or landslides

Sorting of Sediments

B. Horizontal Sorting1. Large particles settle first as a stream

enters a body of water

Glacial Deposits

A. Till1. Dropped from glacier.2. UNSORTED!!!!! (all sizes mixed)

B. Outwash material1. Deposited from meltwater2. SORTED

Energy Changes

A. Kinetic Energy – energy of movementB. Potential Energy – stored energyC. High velocity = High KE = erosionD. Low velocity = Low KE = deposition

1. Streams slow when:a. Slope or volume decreasesb. Moves into a body of waterc. On the inside of a curve

Energy Changes

E. Streams have GREATEST PE at their source (highest point)

1. Loses PE as it turns to KE on the way down

Greatest PE, Less KE

Greater KE, Less PE

KE

PE

Erosion – Deposition System

A. Side View (profile)Erosion Dominates – water moving fast

Delta can form

Source

Mouth

A

B

C

Ocean

Deposition – river slows down

Erosion – Deposition System

B. Top ViewInside of curve, water moves SLOWER, deposition, shallow

Outside of curve, water moves FASTER, erosion, deeper water

OCEAN

A B C

Delta

Velocity within a Stream

A. Water moves fastest in the middle towards the top of the stream (less friction)

Stream Cross Section

AB

CD

D – Water moves fastest, smallest friction

Velocity within a Stream

B. Cross Section of a Stream Corner

Outside = Faster = More Erosion = Deep

Inside = Slower = More Deposition = Shallow

Velocity within a Stream

Effects of Climate on Landscape

A. Humid (wet)1. Worn down and rounded (more

weathering)

B. Arid (dry)1. More angled, sharper edges

Effects of Climate on Landscape

Humid Arid

Drainage PatternsA. Arrangement of

streams draining water in an area

B. Determined by type of bedrock