Mechanical (physical) Weathering

• The process of breaking down sediment without changing the rocks chemical composition.

• Frost wedging

Physical Weathering

Biological activity (Mechanical Weathering) –

(sometimes chemical)

Tree roots splitting

rock

Biological activity

Exfoliation (Mechanical Weathering)

• Uplift of under rock causes the top hard rock, like granite, to split into layers.

Thermal Heating & Contraction

Chemical Weathering

• The transformation of rock into one or more new substances.

Oxidation

Chemical Weathering

– Oxidation : Elements reacting with Oxygen

ex. (Rust)

Hydrolysis

Feldspar +Water = Clay

Feldspar

A Clay Cliff

Acids

Lichen – Plant Acid

Sulfuric Acid & Carbonic Acid

Acids (chemical weathering)• Old tombstones made of marble will weather

due to the Carbonic Acid that is in rainwater.

Dissolution

• Dissolving a rock in water

Carbonation

What can affect Mechanical and Chemical Weathering?

Dissolving candy!!!! – I need a volunteer

Where does chemical weathering occur the fastest????????????

• WarmWarm and MoistMoist!!!!!!– Tropical rainforest

Where does Where does mechanicalmechanical weathering occur the fastest???weathering occur the fastest???

• Wet & temperate (warm day / cold night)

• Frost Wedging!!!!!

Buffalo, NY

Erosion – The process of moving weathered sediments from one location to another.

The four major Agents of Erosion are:

Gravity (Mass Movement)Gravity (Mass Movement)

Running WaterRunning Water

WindWind

GlaciersGlaciers

Types of Mass Movement (Gravity)

• Water erodes more sediments than any other agent of erosion, due to its great energy of motion.

Deposition

• When water flows downhill or wind slows down it loses energy of motion, & drops its sediments.

Large Sediment

Med Sediment

Small Sediment

http://www.classzone.com/books/earth_science/terc/content/visualizations/es1303/es1303page01.cfm?chapter_no=visualization

Mass Movement

• Gravity causes loose materials to move down a slope. When gravity alone causes materials to move down slope this erosion is called Mass Movement.

Mass Movements: Five Main Types

Slump

• occurs when loose materials or rock layers slip downward as one large mass. It happens because the material under the slump weakens.

Creep• occurs when sediments

slowly move downhill. As the ground freezes, small sediments are pushed up by the expanding water in the soil. As it thaws, the sediments fall down slope, often less than a millimeter at a time.

Rockslides

• occur when large blocks of rock break loose from steep slopes and tumble quickly to the bottom.

• Fastest form of Mass Movement

Talus

Mudflows

• usually occur in relatively dry areas where weathering forms thick layers of dry sediments. When heavy rains or rapid ice thawing happens, water mixes w/ the sediments & forms a thick mud. Gravity causes this mud to flow downhill.

• All types of Mass Movement happen where there are slopes. All are more likely to happen after a heavy rain because water makes the sediments heavier & slippery.

Wind Erosion

Areas most prone to wind Erosion

Deflation

• wind picking up and moving small sediments such as clay, silt, and sand.

Sediment Transport by Wind

Abrasion

• wind making sand grains roll and skip, bumping into other grains and rocks. The surfaces they strike become pitted and polished when small fragments are broken off. (sandblasting)

Glen Canyon, AZ

Wind Deposition

• Loess

• Dunes

LoessLoess• very fine sediment particles eroded by very fine sediment particles eroded by

wind that become packed together, wind that become packed together, creating a thick deposit. They are found creating a thick deposit. They are found in the farmlands of the U.S., especially in the farmlands of the U.S., especially the Mississippi River area.the Mississippi River area.

Dunes• sediments blown by wind that encounter a

barrier such as a plant, rock or some other obstacle and pile up behind it. These are the most common type of wind deposits.

Small scale

Large scale

Dune Movement

Running Water Erosion

Sheet Erosion Occurs when rainwater flows over a relatively flat area to lower elevations carrying sediments with it. The sediments left behind cover the soil like a sheet.

Rill Erosion

Begins when a small stream forms after a heavy rain. Water can carry away plants & soil, leaving a scar.

Gully Erosionbegins when a rill channel becomes broader & deeper. Large amounts of soil are removed from the area.

Most Famous GullyGrand Canyon

Sediment Transport by Streams

Alluvial Fan

a type of deposit shaped like a triangle that occurs when a river drops sediments on a floodplain. (land)

Delta

A type of Alluvial fan when the sediments are into a large body of water (lake, gulf or ocean)

ex. (Mississippi delta)

Vegetation Affects Erosion

• Roots hold soil in place!!!!!!!!!!!!!!!!!!!!!!!!!

Things people can do to reduce erosion

Build terraces. Terraces are broad, step-like cuts made

into the side of a

slope.

Things people can do to reduce erosionThings people can do to reduce erosion

Plant vegetationPlant vegetation

No till farmingNo till farming

Wind Breaks (fences/trees)Wind Breaks (fences/trees)

Video - dustbowlVideo - dustbowl

• Erosion can be slowed, but never stopped Erosion can be slowed, but never stopped completely.completely.

Rivers

River systems are referred to as dendtritic, like tree branches.

Small streams branching off of larger streams.

Tributaries

Where do streams get their water supply?

• Surface water runoff

• Groundwater (base flow)

Water has to go somewhere! It always follows the path of least resistance (generally downhill).

Drainage basin

• the land area from which a stream gets its water.

Mississippi Drainage Basin

Stream Characteristics

GradientGradient: The slope or steepness of a stream channel. Affects stream velocity and bedload (sediment deposition) size.

Discharge• The amount of water passing a point over a period

of time.

Which has a greater discharge?

Stages ofStream Development

Erosion of Deformed Sedimentary Rock

Stages of River Development

• Young streams flow fast through steep valleys.

• They are found in mountainous or hilly regions and may have white water rapids and waterfalls.

• They have high levels of energy and erode the stream bottom more than the sides.

Mature Rivers

– Mature rivers flows down a more gradual slope with curves called meanders.

The floodplain

Old-stage rivers flow very slowly through a very broad, flat floodplain

that is curved.

• A river in this stage mostly erodes its sides causing changes in its meanders, like the Mississippi.

• Meanders can eventually be cut off forming Oxbow lakes.

Erosion of Deformed Sedimentary Rock

Meanders (old rivers)

Meanders

Old Mississippi

Meander

Oxbow Lakes (Old Rivers)

Oxbow Lake Formation

Young stream

Mature stream

Old stream

http://www.dkimages.com/discover/previews/774/206778.JPG

Quiz – Water/Wind/Glacier Erosion

1. The beginnings of a stream is called a _.

2. Name the largest gully.

3. What is an Alluvial Fan?

4. Glaciers form this shape valleys.

5. Pieces of rock picked up by wind is called ____.

6. Name two methods of reducing erosion’s affects.

Shoreline and Sedimentation Changes