Weathering & Erosion

Weathering

• Process of chemically changing or physically breaking down rock.

• Water, ice, wind, & gravity weather rock.

• Weathering happens on the surface.

ErosionErosion = process that wears down and

carries away rock and soil fr. one place to another

Agents of Erosion (What’s doing the erosion?):

• Water – streams, rivers, oceans, glaciers

• Wind

• Gravity

End product of erosion = SOIL or SEDIMENT

TYPES OF Weathering

1. Mechanical: physically break down rocks into smaller fragments.

A. Frost wedging

B. Unloading

C. Biological activity

2. Chemical: Chemical reactions dissolve minerals in rock

Acidic water

Common in mountainous regions; Mid-latitudes w/ winter season (freezing and thawing required)

Talus = piles of rock at the base of a mt. or cliff produced by f.wedging

Mechanical Weathering: Frost Wedging

and expands

Expanding ice

Frost wedging produces rock spires

Frost wedging produces smaller rock pieces with MORE SURFACE AREA for CHEMICAL WEATHERING TO WORK.

Unloading & Exfoliation: Igneous rock are exposed b/c of uplift and erosion.

Unloading:

Outer layers of rock expand (b/c under less pressure; not buried anymore)

Examples or Mechanical Weathering

Exfoliation: Outer layers “shed” and break loose.

Produce domes; Usually granite

Unloading & Exfoliation: Produces …

Domes and Exfoliation Scabs

Examples or Mechanical Weathering

Biological Activity: Plant Roots

Examples or Mechanical Weathering

Shippensburg, PA, 1999 Shippensburg, PA, 2005

Gases that Dissolve in Water

From Reacts how?

Oxygen photosynthesis Reacts with metals in minerals to form oxides

Carbon dioxide Many sources Carbonic acid reacts with minerals

Sulfur dioxide Air pollution, volcanoes Sulfuric acid reacts with minerals

Nitrogen dioxide Air pollution, volcanoes Nitric acid reacts with minerals

Chem. Rxns break down rock when gases dissolve in water.

Acids in water react faster with carbonates (limestone, marble) than silicates (as in granite)

Chemical Weathering:

Examples of Chemical Weathering

1. ACIDIC RAIN WATER will dissolve calcium containing rocks (limestone, & marble). This is how caves are made.

2. Oxidation (chemical reactions w/ O2) of Iron containing rocks (Makes rust)

Iron reacts w/ oxygen to make blue soil.

Red rock layers formed by iron reacting w/

oxygen

Caves form when limestone is dissolved

by acidic water

Chemical Weathering of Granite

Quartz: Most resistant (unchanged) larger particles transported shorter distances (makes up beach sand)

Feldspar: Weathers to clay minerals clay = smaller particle size = transported by rivers out to sea deposited in ocean

Chemical Weathering of Silicate Minerals

Some things dissolve:Sodium(Na), Potassium (K), Magnesium (Mg) dissolve in acidic water become part of gound water.

Iron (Fe) reacts w/ O2 iron oxide (rust/red rocks)Si, O, Aluminum = resistant to chem. Weath (don’t dissolve in acids) bcm smaller clay minerals.Clay = Si, O, Al minerals

Weathering & Climate

Chemical Weathering & Climate• Carbonic acid weathers rock and particles usually

end up on the bottom of the ocean floor..

• Carbonic acid forms when CO2 is dissolved in water. This CO2 comes from the ATMOSPHERE.

• More chemical weathering = More CO2 removed fr. Atmosphere.

• When “NEW” land is exposed to Earth’s surface, weathering rates increase; temps. Decrease.

• Mt. Building exposes new land.

• Mt. Building = Cooling Climate

Rates of Weathering depend on…1. Temperature – • Warmer temps. Increase Chem.

Weathering• Alternating freezing & warm temps.

increase Mechanical Weathering.2. Availability of Water – More water, more

weathering3. Type of Rock – Calcium containing rocks

(limestone, calcite, marble) are prone to chemical weathering

Mass Movements= Transfer of rock and soil downslope due to gravity.

• Weathering weakens & breaks apart rock; gravity moves rock downslope to a valley.

• Streams at base of valley carry sediments away.

Types: Based on 1). Material 2). Speed

Rockfalls: Rocks fall freely thru. air down very steep slopes (esp. where mt. were blasted to make road); Fast; freeze-thaw loosens rock.

Slides: Block of material moves suddenly along flat inclined surface; FAST

• Rockslide/Landslide/ Mudslide

• Mt. regions• After heavy rain or

melting (destabilizes soil)

Mass Movements

Slumps: Block of material moves down curved surface (forms steps) (not fast; not far)• Oversteepened slopes w/ thick accumulation

of clay (that gets heavy after rains)

Mass Movements

Flows: Fast moving material w/ lg. amount of water, moving downslope (Muddy w/ debris)

• Semiarid mts. (no veg. to hold down soil after heavy rains)

• Base of snow. peaked volcanoes

• Very destructive

Mass Movements

Earthflow: Slow moving flows

• Hillsides in wet regions• “Tongue” shaped pile

Mass Movement

Creep: Slowest; few mm or cm/year; freeze-thaw separates and move soil.

TYPES OF MASS MOVEMENT:

Types of Mass Movement (aka, mass wasting)

More rain means greater chance of mass movement

Triggering Mass Movements

1. Water: Heavy Rainfall/SnowSoil gets saturated (pore spaces filled); rock/soil

layers get very heavy Gravity pulls downhill

2. Oversteepened SlopesMore than 40 degree angle; Stream cuts base of cliff;

people blast base of mountains for road/housing construction

3. Removal of VegetationNo roots to hold down soil; No roots to absorb water

4. Earthquakes/Volcano Eruptions

Videos• Landslides (National Geographic)• http://video.nationalgeographic.com/video/environment/

environment-natural-disasters/landslides-and-more/landslides/

• Mudflow (Austria) http://www.youtube.com/watch?v=ARkBJdsZw4w• Mudflow (Austria): http://www.youtube.com/watch?v=VMJiibdVYjE• Rockfall (Cornwall cliffs) http://www.youtube.com/watch?

v=QdsxtCtX5nk• Rockfall (Yosemite) http://www.youtube.com/watch?

v=H0YhlqP1BgE• Rockslide http://www.youtube.com/watch?v=ZVYGJYnJTi0

Creep

Slope

Landslide