Rocks and Weathering

Rocks and Weathering

Which mountain range is older?

The Sierras are rocky and steep, higher than the Appalachians.

The Appalachians are more rounded and gently sloping, and are covered with soil and plants.

Which mountain range is older?

The Sierras formed within the last 10 to 20 million years ago.

The Appalachians formed more than 250 million years ago.

Q: How can you tell that the Sierra Nevadas formed much more recently than the Appalachians?

How is Earth's surface shaped?

1. Weathering- the process that breaks down rock and other substances at Earth's surface.

2. Erosion- the transportation of sediment by wind, water, ice, or gravity.

weathering vs. erosion video

Q: What is the difference between weathering and erosion?

The principle of uniformitarianism

-an assumption that the same processes that operate today operated in the past.

Two Types of Weathering

Mechanical-

When rock is physically broken into smaller pieces.

Keep the same chemical composition.

Chemical-

The process that breaks down rock through chemical changes.

Is this the cause of mechanical or chemical weathering?

Plant growth

Is this the cause of mechanical or chemical weathering?

oxidation

Is this the cause of mechanical or chemical weathering?

weak acid from plant roots or lichens

Is this the cause of mechanical or chemical weathering?

freezing and thawing

Ice wedging1st - water seeps into cracks of rocks2nd- water freezes 3rd - water expands when it freezes and

breaks rock

Is this the cause of mechanical or chemical weathering?

pressure release

The causes of mechanical weathering

• freezing and thawing

• release of pressure

• plant growth

• actions of animals

• abrasion

The causes of chemical weathering

• water dissolves minerals

• oxygen combines with iron in the presence of water forms rust (oxidation)

• carbon dioxide dissolves in water to form carbonic acid

• living organisms- root tips and lichens can form weak acid

• acid rain is formed when pollutants combine with water vapor

What determines how fast weathering occurs?

• surface area

• type of rock

• climate

Increasing the surface area of rock increases the rate of a chemical reaction

Q. Which type of stone weathers faster?

granite

marble - dissolves in acid, and is more permeable

Climate

Weathering is faster in hot and wet climate.