Weathering

Weathering is the physical and chemical breakdown of rocks at the Earth’s surface.

The pieces or particles of rock (large and small) that

are weathered are known as sediments.

Weathering occurs when

rock is exposed to “weather events” (ex: wind, water,

pressure changes), as well as, the actions of organisms.

Chemical Weathering is the breakdown of rock through a change in the composition of

the rock..

The red color in this rock represents chemical weathering. The original composition of the rock has changed due to its exposure to rain. The iron

minerals in the rock combined with the oxygen molecules in rain water to create iron oxide (rust).

The iron oxide in the rock can weather easily.

The statue has gone through chemical weathering. Water combines with carbon dioxide in the air to create carbonic acid.

Carbonic acid will dissolve specific minerals, such as those found in limestone

or marble.

Physical (Mechanical) Weathering is the breakdown of

rock into sediments without chemically altering the rock. .

Frost Action: Water will make its way into a crack in the rock When the water freezes, it will expand widening the crack in the rock.

Frost action is responsible for damage done to roadways.

Abrasion: A form of physical weathering whereby rock particles grind against other rock particles.

An agent of erosion such as gravity, running water, wind, glaciers and/or tides are responsible

for abrasion.

Physical Weathering

In this example, the wind pushes small sediments against larger ones. This

leads to abrasion.

“How does abrasion work?”

Sometimes the weathering of rocks can be caused by biologic action.

Living organisms can weather rocks both chemically and physically.

Some organisms will release compounds

through biologic activity. These compounds will chemically breakdown

rocks.

The roots of plants will grow into cracks found in rocks. The growth of these roots physically

breakdown rocks.

Biologic Action

Factors that Impact Weathering Exposure The closer a

rock is to Earth’s surface, the faster it will

weather.

The exposed bedrock along the beach will weather quickly due

to:1. changes in

temperature2. exposure to wind

and precipitation3. exposure to

chemicals that can alter rock

4. tidal action

Factors that Impact Weathering

Particle Size and Mineral Composition

Smaller sediments have a larger surface area exposed to

weathering agents and will weather more quickly than

larger sediments.

Some minerals in rocks are more resistant to weathering

than other minerals.

The minerals that make up this vein of granite are more resistant to weathering than the dark parent rock surrounding it.

Factors that Impact Weathering Climate

Specific types of weathering and its intensity are prone to

certain climates.

PHYSICAL WEATHERING: Prone to climates that are

cool and dry.

CHEMICAL WEATHERING:Prone to climates that are

warm and humid.

Soil Formation Soil is a combination of organic (living) and inorganic (nonliving) matter that

accumulates at the Earth’s surface.

Sediments that have weathered from rocks become part of the soil.

Soil from parent bedrock can form

in horizontal layers over time. The upper layers

contain more organic material than the lower

layers.

Many soils are transported by water, wind or glaciers to new locations.

The soil may then become the parent material for new soils to form.