Constructive and

DestructiveForces

Weathering and Erosion

Weathering - processes at or near Earth’s surface that cause rocks and minerals to break down

Erosion - process of removing Earth materials from their original sites through weathering and transport

WeatheringMechanical Weathering - processes that break a rock or mineral into smaller pieces without altering its composition

Chemical Weathering - processes that change the chemical composition of rocks and minerals

Agents of Mechanical Weathering

frost wedging thermal expansion and contraction mechanical exfoliation abrasion by wind and water plants and animals

Frost Wedging

Plant Wedging

Plant Roots

Friction and Repeated Impact

Burrowing of Animals

Chemical Weathering

The process that breaks down rock through chemical changes.

The agents of chemical weathering– Water– Oxygen– Carbon dioxide– Living organisms– Acid rain

Water

Water weathers rock by dissolving it

Oxygen Iron combines

with oxygen in the presence of water in a process called oxidation

The product of oxidation is rust.

Living Organisms

Lichens that grow on rocks produce weak acids that chemically weather rock

Acid Rain Compounds from burning coal, oil

and gas react chemically with water forming acids.

Acid rain causes very rapid chemical weathering.

Karst Topography A type of landscape in rainy regions

where there is limestone near the surface, characterized by caves, sinkholes, and disappearing streams.

Created by chemical weathering of limestone.

Features of Karst: Sinkholes

Features of Karst: Caves

Erosion

The process by which water, ice, wind or gravity moves fragments of rock and soil.

Water Erosion

Rivers, streams, and runoff

Ice Erosion

Glaciers

Wind Erosion

Mass Movements

Landslides, mudslides, slump and creep

landslide clip.mpeg

Streams

Stream Erosion and Deposition

Glaciers

Wind Transport of Dust

Wind Transport of Dust

Deposition Formation

Volcanoes

Earthquakes

Mountain Building

Weathering Controls The type, rate and extent of weathering

depends upon several controlling factors: • Climate dictates the type of weathering

processes that operate, largely by determining the amount of water available and the temperature at which the processes occur. Chemical reactions are faster at higher temperatures, while frost wedging occurs in colder climates.

Rock Type determines the resistance of the rock to the weathering processes that operate in that particular environment. Each rock type is composed of a particular set of minerals, which are joined together by crystallization, chemical bonding or cementing. When the forces of plate tectonics move these rocks from the environment in which they formed and expose them to the atmosphere they begin to weather.

Rock Structure: highly jointed or faulted rocks present many planes of weakness along which weathering agents (e.g. water) can penetrate into the rock mass (Figures 1 & 2).

Time: the duration of the period that the same type of weathering has been operating, uninterrupted by climatic change, earth movements, and other factors, determines the degree and depth to which the rocks have been weathered.

Topography: the slope angle determines the energy of the weathering system by controlling the rate at which water passes through the rock mass. Generally, higher, or tectonically active areas with steeper slopes have more dynamic weathering systems, whereas flat plains have slower weathering systems.

Erosion Processes Erosion processes are usually considered

under four distinct categories: • Mass Wasting: the processes that occur on

slopes, under the influence of gravity, in which water may play a part, although water is not the main transporting medium. Mass wasting, or landsliding

Rapid or Slow Changes Glaciers melt and form rivers. Wind weathers rocks into sand. Earthquakes move land and rocks. Rivers carry sediment and build deltas.

How does a river become more shallow over time?

Small amounts of soil is deposited each time the river current slowed down causing the river to become more shallow.