Surface Processes & Landscapes

Unit 9Topics 9, 10 & 14 in your review book

I. WEATHERING

Weathering is the chemical and physical alterations of earth materials at or near the earth’s surface

A. Types of Weathering1. Physical Weathering

The mechanical breakdown of earth materials (rocks) at or near the earth’s surface.Changing the size/shape of the material.

Physical weathering does NOT change the characteristic properties of the material.Each time a material is made smaller, its surface area increases.

size es surface area

THANKS MOLLY

2. Chemical Weathering

The process by which chemicals such as oxygen, acids and water break down rocks and other earth materials.

Chemical weathering does change the characteristic properties of the material…new materials are created!

B. Agents of Weathering1. Wind: weathering is due

to the material carried by the wind (such as sand)

2. Water3. Temperature change4. Animals and Plants

C. Specific Types of Weathering1. Ice wedging/Frost Action:

Physical weathering occurs when the water contained within the material freezes, expands, melts and evaporates

Frost action requires moisture and temperatures ranging from above to below freezing

2. AbrasionPhysical weathering that occurs when different substances move against one another creating friction which results in sediment that is round and smooth.

3. Plant Action

Physical weathering that occurs when the roots of plants grow and enlarge breaking rocks apart.

4. Oxidation

Chemical weathering due to a reaction between the material and oxygenExample: rust

5. Acid RainChemical weathering caused by the gaseous by-products of industry that dissolve in rain water making it acidicMarble and limestone are most affected by acid rain.

6. HydrolysisChemical weathering that occurs when water reacts with the material.Usually some or all of the material is dissolved in the water.

D. Factors that influence the Rate of Weathering1. Temperature:

Most influences chemical weatheringChemical weathering occurs faster at high temperatures

As Temperature increases,Rate of chemical weathering increasesGraph:

As Temperature increases,Time for chemical weatheringdecreasesGraph:

2. Moisture

Most influences the rate of chemical weatheringChemical weathering occurs faster with more moisture

As the amount of moisture increases,The rate of c. weatheringincreasesand the time for c. weatheringdecreasesGraphs:

CHEMICAL WEATHERING OCCURS BEST IN HOT, MOIST (HUMID) CLIMATES

3. Size

Weathering of all types occurs faster as size decreases

As size decreases, surface area increases

Therefore, more of the material is exposed to the agents of weatheringallowing weathering to occur faster.

Decrease size:Increase surface area:increases rate of weatheringDecreases time for weatheringGraphs:

Increase size:Increases time for weathering

Increase surface area:Decreases time for weatheringGraphs:

4. Composition

Rate of weathering can be influenced by the mineral content of the rock.

A rock composed of minerals with a high hardness will be more resistant to weathering than one made up of “softer” mineralsAs resistance increases:Rate of weathering decreasesTime for weathering increasesGraphs:

5. Topography Rock structure can influence rate of weathering.Steep slopes may be more prone to physical weathering than grassy, gentle slopes

As slope increasesRate of weathering increasesTime for weathering decreasesGraphs:

6. Vegetation

As the amount of vegetation increasesThe rate of weatheringDecreasesThe time for weatheringincreases

E. Products of WeatheringSediments result from the weathering of earth materials

Biological activities add organic material (humus) to sediment creating soil

1. Soil Profile

A side view of the horizontal layers of soil.These horizontal layers are called soil horizons

Biological activity creates organic materialZone A: also called topsoilContains the most organic material and is most fertile

Zone B: also called subsoilContains a mixture of sediment and humusIs slightly fertile

Zone C: Contains sedimentIs infertileBedrock:The layer of impermeable rock which is weathered to create sediment

Infiltration: to soak into…the movement of water down through soil layers.Leaching: to bring organic material down through soil layers as water infiltrates

2. Types of Soila. Residual soil: soil that stays

soil that remains on top of the bedrock of origin (parent bedrock)The composition of residual soil is similar to the bedrock beneath it

b. Transported SoilSoil that goesSoil that has been moved from its location of origin.The composition of transported soil differs from that of the bedrock beneath it

Residual soils tend to be thicker and more well developed than transported soilsMuch of the soil in NYS has been transported by the glaciers that passed through

II. EROSION

move it

The movement of earth materials

The driving force of erosion isgravity

A. Mass MovementThe movement of earth materials by gravity alone

1. Landslides, mudslides, avalanches: large quantities of material moving rapidly down hill.

2. Slumping

occurs when the material slides along a curved surface

3. Hillside creep:a slow, imperceptible downslope movement of soil

Talus is the result of mass movement near steep slopesIt is a pile of rock fragments at the base of a cliff

Landslide

Mudslide

Slumping

Hillside Creep

Talus

B. Agents of Erosion1. Wind2. Water: • running water is the

dominant agent of erosion!

3. Glaciers

C. New TermSTRICKStands for:StreamRiverCreekIt will be used to refer to any moving body of water

D. Factors influencing rates/amount of erosion

1. VelocityAs the velocity of the agent of erosion increases,the amount of erosion increases

a. Factors influencing velocity

1. Slope• As slope increases• Velocity increases• Therefore, erosion

increases

2. QuantityDischarge is the amount of water flowing past a certain point (volume)As discharge increases,Velocity increasesTherefore, erosion increases

Discharge is greatest

tributary

Rainstorms and meltwater can increase dischargeWhen ppt > infiltration (it rains faster than it can soak in), runoff occurs and discharge increasesHuman activities such as dams, and development can also affect discharge

3. Shape of the Strick Bed

In a cross-sectional view, water flows fastest through the center

*

Surface tension between the air and the water molecules slows the water at the surfaceFriction between the water molecules and the strick bed slows the water along the sides and bottom

Direction of flow

Slowed due to friction along the sidesFastest at the middle of the leading edge

In a bird’s eye view:

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•Through the course of a strick

Water flows fastest near the source and along the outside of a curveWater flows slowest near the mouth and along the inside of a curve

Slow alongthe inside

Fast along the outside

Fast near the source

Slow near the mouth

4. AgeThe older a strick is, the wider it is, and the more it meanders (curves).Generally, as age increases, discharge decreases, and slope decreases…which decreases velocity and erosion

E. Carrying Capacity

The amount and size of sediment able to be transported by a strickis dependent upon the velocity of the strick.As velocity increases, transportable size increases

The material carried travels slower than the strick.The velocity needed to initiate erosion is greater than the velocity needed to maintain erosion.See ESRT page 6 for velocity and carrying capacities.

The stream can carry everything at and below the line

F. Methods of Transportation

1. Large particles are carried by bouncing and rolling along the bottom: in traction

2. Small particles are carried in suspension: in the middle (colloids)

3. Low density particles float on the surface

4. Soluble materials are carried dissolved in the water: in solution

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III. DEPOSITION

The release of sediments from the agent of erosion

AKA: sedimentation

A. Factors Influencing amount of deposition

1. Velocity of the agent of erosion:As velocity increases,the amount of deposition decreases

B. Factors influencing the rate of settling

1. Particle size: Large particles are deposited fasterLarge particles settle out firstWhen size increases,settling rate increases andsettling time decreases

2. Particle densityMore dense particles settle out first and fastest.When density increases, settling rate increases andsettling time decreases

3. Particle shapeRound particles settle out first and fastest.When roundness increases,settling rate increases andsettling time decreases

C. Location of deposition

1. At the mouth:Where the strick meets the larger body of water, velocity decreases and deposition increases

2. At the inside of a curveVelocity is slower along the inside of a curve,therefore, deposition is dominant

3. When the slope of the strick decreases, velocity decreases and deposition increases.

4. Older stricks experience more deposition than younger stricks

5. Deposition occurs more along the side banks of a strick …

• downcutting creates the characteristic V-shaped valley of a strick

D. Results of Deposition

1. In still water:Vertical sorting occursThis results in beds of sediment sorted according to size

Repeated depositional events result in graded beds … separate layers of sorted sediment

2. In moving water

Horizontal sorting occurs as velocity decreases in a strick

Resulting in a gradual decrease in particle size as the strick gets closer to the mouth

A delta forms at the mouth of a strick due to the rapid slowing of the strick as it enters the still water of a placean (pond, lake, ocean)This is a triangular shaped deposit of fine grained sediments

Memorizable:Deposits by water are:

sortedand the sediments aresmooth and round

Stream Valleys are V-shaped!

E. Deposition by glaciersand resulting landforms

Glacial deposits are unsortedSediments in glacial deposits are: angular and scratched (striations)Glacial valleys are U-shaped and the bedrock is striated

Unique features created by glaciers1. Moraines: irregular hills of

unsorted sediment created along the sides: lateral moraineand leading edge: terminal moraineand as it melts: recessional moraine

2. Erratic: a large boulder deposited by the glacier

3. Kettle: a round depression created when a buried block of glacial ice melts

4. Kettle lake: created when a kettle fills with water

5. Transported soil: soil relocated by a glacier … has unsorted sediments and a relatively thin A-layer

6. Esker: a long, winding ridge of layered sediment deposited by a stream flowing under a melting glacier

7. Drumlin: a long, smooth, canoe-shaped hill of till formed when a glacier moves over an older moraine. The steeper slope of a drumlin faces the direction the glacier came from.

8. Outwash: sediment deposited by the meltwater of a glacier. It contains gravel, sand, and fine silt.

9. Outwash plain: the area at the leading edge of the glacier where the meltwater streams flow and deposit outwash.

Memorizable:Glacial deposits areunsortedangularscratchedGlacial valleys areU-shaped!

F. Deposition by WindWind sorts sediment by sizeWind transports/deposits sand-sized sediments Wind blows sand into hills of sand called dunes

Wind blows particles of sand up the windward sidedepositing them on the downwind side

WIND

EEKS

G. Coastal Deposition

Sandbars are formed when waves advance and retreatcreating low ridges of sediment parallel to the shore

If a sandbar becomes connected to the beach, extending into deep water and rising above sea levelit becomes a barrier islandA lagoon is the section of the ocean between the beach and the barrier island

A peninsula is an area of land almost completely surrounded by water…connected to the mainland by an isthmus (a narrow portion of land connecting the peninsula to the mainland)

                                                                                                                                     

H. Erosional-depositional system

A system in which the amount of erosion is equal to the amount of deposition

Resulting in a

Dynamic equilibrium!

1. Energy of strick flowKinetic energy: energy of motion

Potential energy: energy due to position (stored energy)

As a strick flows from source to mouth:PE is highest at the source,and is converted to KE as the strick moves downslopeand is converted back to PE at the mouth

source

mouth

High PE Low KE

Changes to KE:

PE decreases

KE increases High PE Low KE

The PE at the mouth is less than the PE at the sourceEnergy is transformed by friction into heat and sound.

When KE is high, erosion is dominantWhen PE is high (KE is low), deposition is dominant

I. Erosional-Depositional features

1. The outside of a curve is faster; erosion is dominant; depth is greater

2. The inside of a curve is slower; deposition is dominant; depth is less

A B

A B

3. Oxbow lakes are created when a meander in a stream becomes cut off.

** see illustration!