Weathering How are the earth’s surfaces changed?

Weathering is the breaking down of rocks and other materials on the earth’s surface. There is no change in the rock’s chemical make-up or composition with this.

There are two There are two types of weathering.

Types of Weathering Mechanical or physical weathering ~ causes:  Temperature changes causing ice or frost wedging  Root, organic, or biological weathering  Gravity  Abrasion (scraping or sanding)  Unloading or exfoliating (like peeling) Skip ahead to details…

Second Type of Weathering Chemical or physical weathering ~causes:  Water wears down rocks  Acid dissolves Earth’s surfaces  Air pollution  Plant chemicals  Oxidation (exposure of minerals to oxygen)

Mechanical and chemical weathering can work together… Advance to chemical weathering

Causes of mechanical weathering include: TTemperature: which causes cycles of expansion and contraction Mechanical or physical weathering

Ice or frost wedging (frost action, freeze-thaw cycle): when liquid water goes into cracks and then freezes causing the cracks to get wider Mechanical/physical weathering

The power of the freezing and warming cycle

More mechanical or physical weathering Organic activity Organic activity root-pry, burrowing animals, human activities

A hearty growing plant can expand a crack in a rock until it splits! CRACK! Roots can also raise up cement slabs, crack sewer lines, and house foundations. Don’t you think they could also crack a rock?

Gravity Gravity causes rocks to fall and collide with other rocks Mudslides and sinkholes…

Landslides, rockslides, holes, and cracks

 Abrasion  Abrasion: wearing away by solid particles Wave rock, Australia – carved by wind blown sand. Phoenix, AZ

UUUUnloading: the expanding of high pressure rock when exposed to a lower pressure Classic sheeted granite in Yosemite National Park. It is broken into gently dipping plates by unloading joints.

Exfoliation or unloading - rock breaks off by layers or sheets along joints parallel to the ground surface; caused by expansion of rock due to uplift and erosion; removal of pressure of deep burial

Extreme exfoliation!

Contraction due to crystallization The surface pattern on this pedestal rock is honeycomb weathering, caused by salt crystallization. This example is on the island of Taiwan. Salt weathering of building stone on the island of Gozo, Malta Back to overview

The other kind of Weathering~ Chemical Weathering The altering of the composition or the make-up of minerals within a rock that results in a reduction in size.

Agents of chemical weathering include:  Water: Dissolves minerals out of rocks making them weaker. Example:

Acid: Dissolves minerals in rocks (examples: carbonic acid, acid rain, and plant acid) Cave wall Chemical weathering

Lichens such as these growing on the rocks in the pictures can produce weak acids that react with the rock.

Air polllution can produce acid rain.

3000 year old Egyptian Obelisk 3000 year old Egyptian Obelisk after 100 years in NY Picture it…

The ancient Parthenon in Greece shows discoloration and chemical weathering effects just from air pollution and acid rain.

 Oxidation: Oxygen combines with iron minerals and sulfur minerals changing the composition of the rock More chemical weathering Oxidation turned these rocks in Nevada's Valley of Fire red.

Look at factors that hasten weathering: 1. How much surface area is exposed to the elements?

2. Climate 2. Climate : Warm, wet climates + chemical weathering breaks down rocks rapidly, too. Mechanical weathering old climates + cold climates break down rocks rapidly.

3. Topography 3. Topography: the position of the rock (Is it in a position where gravity can pull it down?) 4. Air pollution 5. Exposure time (Will the elements have time to break down the surface?) Mechanical and chemical weathering work together to break down rocks and our earth surface.