WeatheringWeathering

Weathering the process that produces change

in the surface of rocks exposed to the atmosphere and/or hydrosphere.

Two Types OF Weathering:Two Types OF Weathering: Physical

weathering is breaking rock by force.

ex: hitting, scratching, cracking

Chemical weathering is where the rock material is changed into another substance by reacting with a chemical.

Frost action (ice wedging)-

Water seeps into small cracks in rocks. When the water freezes it expands creating great pressure. The crack widens and allows water to seep deeper into the rock.

Biological ActivityBiological Activity Plant action-

Tiny root hairs seek out small cracks and pits in rock. Once the root hairs find a place they grow and expand. The expansion causes great pressure and cracks the rock.

UnloadedUnloaded Exfoliation

Rocks formed deep in the Earth are made under high pressure. When the pressure is released the rocks expand & crack. May also be caused by alternate heating and cooling of rocks by weather conditions.

Chemical WeatheringChemical Weathering Oxidation-

Oxygen in the atmosphere chemically reacts with minerals. ex.: rusting of a nail

Water **** MOST IMPORTANT !!!!!Minerals are dissolved in water. ex.: Halite, calcite

Acid- Carbonic acid:C02 dissolves in rain water forming a weak acid

Acid Rain: Sulfur Dioxide in the atmosphere dissolves in rain water forming a strong acid (sulfuric acid).

Chemical WeatheringChemical Weathering

Chemical WeatheringChemical Weathering

Ex. Of Chemical WeatheringEx. Of Chemical Weathering

Rates of weathering will be influenced by:Rates of weathering will be influenced by:

Surface area exposed - weathering occurs on the surface.

More surface exposed, the faster the weathering will occur.

A full, solid block has the least surface area.

The interior is safe from exposure.

A smashed piece has greatest surface area exposed. The interior can now be attacked.

Mineral composition- some minerals are more resistant than others.

– ex.:Quartz is resistant to chemical and

physical weathering.

Rates of Weathering will depend on:Rates of Weathering will depend on:

Climatic Conditions:Cold and/or dry climates favor physical weathering. Warm and wet climates favor chemical weathering. Frost action works best in areas where the temperature fluctuates wildly.

Rates of Weathering will depend on:Rates of Weathering will depend on:

Soil - The product of weatheringSoil - The product of weathering

Soil- rocks, minerals (mainly sand and clay), and organic material (regolith and organic matter)

Soil forms layers of different characteristics called horizons.

oA

E

B

C

R

TOP SOIL

SUBSOIL

What are the main components of soil?What are the main components of soil?

Mineral Matter Air Water Organic Matter

Soil Components (volume basis)

What are the FACTORSthat make SOIL?What are the FACTORSthat make SOIL? TIME

1000’S TO 10,000’S OF YEARS

LAY OF THE LAND / “SLOPE”TOPOGRAPHY

LIVING ORGANISMSANIMALS AND PLANTS

CLIMATEHOT/COLD, WIND/RAIN

PARENT MATERIALROCKS AND MINERALS

Physical land features

Why is soil important ?Why is soil important ?

Necessary for the growth of rooted plants which support our life system !!!!

ErosionErosion

Movement of sediments (soil) from one location and deposition of it another place.

Can occur in 2 ways

2 ways erosion can occur ….2 ways erosion can occur ….

Earth processes which move material on the Earth’s surface over long periods of time, such as weathering and gravity

Human activity which moves material on the Earth's surface over short periods

Transport Agents of ErosionTransport Agents of Erosion

WaterRainStreams and riversOceanIce (glaciers)

Wind Gravity

Erosion by WaterErosion by Water

Erosion by WindErosion by Wind

Erosion due to gravityErosion due to gravity

Example of Human Made ErosionExample of Human Made Erosion

Erosion at Construction SiteErosion at Construction Site

Silt fencing during construction doesn’t necessarily stop all erosion

Silt fencing during construction doesn’t necessarily stop all erosion

How Erosion Effects the Environment

How Erosion Effects the Environment

#1 Pollutant to our Waters#1 Pollutant to our Waters

Sedimentation in Rivers Sedimentation in Rivers pollutes water with soil particles damages water ecosystems through reduced

sunlight for aquatic plants and animals increases water treatment costs for human

water consumption reduces the depth of rivers, thus creating

waterways that can't be navigated by commercial crafts

Removal of topsoil from land areasRemoval of topsoil from land areas

prevents plant growth alters ecosystems, thus reducing the

biodiversity of life destroys crops reduces agricultural food production reduces farming income

Wind ErosionWind Erosion

increases the amount of particles in the air reduces visibility reduces air quality causes breathing problems (asthma, etc.)

What can help prevent erosion?What can help prevent erosion?

Plants can help prevent erosion! Look at the roots on these grasses. Roots help hold the soil in place so that it doesn’t

wash away.

Plants can help prevent erosion! Look at the roots on these grasses. Roots help hold the soil in place so that it doesn’t

wash away.

Plant roots

Mass MovementMass Movement

The transfer of rock and soil downslope due to gravity

Triggers of Mass MovementTriggers of Mass Movement

Saturation of material with water Oversteepened slopes Removal of vegetation Earthquakes

Types of Mass MovementsTypes of Mass Movements

Based on:Kind of material that movesHow it movesSpeed of movement

RockfallsRockfalls

Usually happens on oversteepened slopes due to mechanical weathering (freeze-thaw)

SlidesSlides

Occur suddenly and can reach speeds of over 200 km/hr

Usually occur in the mountains

SlumpsSlumps

Do not occur suddenly Usually happens in clay soil

FlowsFlows Contains a large amount

of water Mudflows – move quickly Earthflows - slower

CreepsCreeps

Occur gradually over time Usually due to freezing and thawing of soil

The EndThe End

Chapter 5