Ch 14 Weathering and Erosion

HS-ESS3-1 – Construct an explanation based on evidence for how the availability of natural

resources, occurrence of natural hazards, and changes in climate have influenced human

activity.

Section 1: What is Weathering? The natural process by which atmospheric and

environmental agents such as wind, rain, and temperature changes, disintegrate (break up) and decompose rocks.

What are the different types of weathering? Mechanical Weathering

is a strictly physical process (it does not change the composition of the rock).

agents of mechanical weathering include: ice, plants and animals, gravity, running water, and wind.

Chemical Weathering Chemical reactions act on the minerals in the

rock and break the rock down as a result.

• Oxidation: commonly occurs in rock that has minerals with iron. The iron in the rock combines with oxygen that is dissolved in water to form rust.• Hydrolysis: minerals from the rock react chemically

with water to produce another substance.• Acid Precipitation: Rain

contains high concentration of acids (due to the pollution of the atmosphere).

Section 2: Rates of Weathering

The process of mechanical and chemical weathering generally work very slowly.

Differential Weathering – the process by which softer, less weather resistant rocks wear away at a faster rate than harder, more weather resistant rocks do.

The rate at which rock weathers depends on a number of factors, include rock composition, climate, and topography.

How does rock composition affect the rate of weathering? The rate at which rocks weather depend

mostly on the material that holds the sediment grains together.

Some of the rocks that are strongly cemented together can resist weathering longer than other rocks.

How does climate affect the rate of weathering? Alternating hot and cold weather causes

weathering. Freezing and thawing can cause breakdown

of rock by ice wedging. The slowest rates of weathering occur in hot,

dry climates or in very cold climates.

How does topography affect the rate of weathering? Because temperatures are generally cold at

high elevations, ice wedging is more common.

On steep slopes, such as mountainsides, weathered rock fragments are pulled downhill by gravity and washed out by heavy rains.

How does human activity cause weathering? Mining and construction often expose rock

surfaces to agents of weathering. • Mining exposes rock to strong acids and

other chemicals used in the mining process.

• Construction removes soil and exposes unexposed rock surfaces.

Recreational activities also disturb rock.• Hiking or riding all terrain vehicles.

How do plant and animal activities affect weathering? Roots of plants and trees often break apart

rock.

Burrowing animals dig holes into rock and soil.

How does soil form?

Soil is a complex mixture of minerals, water, gases, and the remains of dead organisms.

The uppermost layer of rock fragments weather to form a layer of very fine particles which make up the soil.

Soil composition refers to the material of which it is made.

What is erosion?

The process by which the products of weathering are transported is called erosion. Farming and ranching practices increase soil

erosion. Clearing plants and animal overgrazing destroys

the groundcover and increases the rate of erosion.

What are the results of soil erosion?

Reduces the fertility of the soil. Impairs crop productivity.

Can lead to water pollution. Triggers landslides and mudflows.