Weathering

Weathering is the physical and chemical breaking down of rock material into smaller fragments due to exposure to processes that occur at Earth’s surface Weathering occurs when rocks in the lithosphere are UPLIFTED and is exposed to the atmosphere, hydrosphere, and biosphere

Weathering The most important agent involved in the weathering of material is WATER

Two Types OF Weathering: 1) Physical weathering is breaking rock by force into smaller pieces of the SAME material ex: hitting, scratching, cracking 2) Chemical weathering is the chemical reaction of water and water vapor breaking down rock by changing its chemical composition The minerals that make up the rocks are changed into another substance

4 Types of Physical Weathering 1) Frost action (ice wedging)- Water seeps into small cracks in rocks. When the water freezes it expands creating great pressure. The crack widens and allows water to seep deeper into the rock. Alternating Freezing and Thawing

Examples of Frost Wedging : Potholes

2) Plant action- Tiny root hairs seek out small cracks and pits in rock. Once the root hairs find a place they grow and expand. The expansion causes great pressure and cracks the rock.

3) Exfoliation Rocks formed deep in the Earth are made under high pressure. When the pressure is released the rocks expand & crack. May also be caused by alternate heating and cooling of rocks by weather conditions. This is basically the “peeling away” of rock

4) Abrasion- rubbing by other rocks Water 4) Abrasion- rubbing by other rocks Scraping, grinding, and wearing away other rocks during erosion WIND

Types of Chemical Weathering Oxidation Hydrolysis (water) Carbonation (acid rain)

Oxidation- Oxygen in the atmosphere chemically reacts with minerals. ex.: rusting

Much of the time these minerals will end up as clay Water (hydrolysis) Minerals are dissolved in water. ex.: Halite, calcite Much of the time these minerals will end up as clay

Acid- Carbonic acid: C02 dissolves in rain water forming a weak acid. This acid dissolves the calcium carbonate (calcite) in limestones and marbles

Acid Rain: Sulfur Dioxide in the atmosphere dissolves in rain water forming a strong acid (sulfuric acid).

Carbonation – Stalagtites and Stalagmites (karst topography)

Carbonation – Karst Topography Karst Topography is the name given to a region where the bedrock is easily chemically weathered This leads to the rock weathering away and forming sinkholes, caverns, disappearing streams

Karst Topography

Differential Weathering Masses of rock do not weather uniformly due to regional and local factors Results in many unusual rock formations Example: Bryce Canyon

Bryce Canyon National Park

Rates of weathering will be influenced by: Surface area exposed - weathering occurs on the surface. More surface exposed, the faster the weathering will occur.

A smashed piece has greatest surface area exposed A smashed piece has greatest surface area exposed. The interior can now be attacked. A full, solid block has the least surface area. The interior is safe from exposure.

Rates of Weathering will depend on: Mineral composition- some minerals are more resistant than others. ex.:Quartz is resistant to chemical and physical weathering.

Where is the rock more resistant to weathering? F A C E B D

Where is the rock least resistant to weathering? F A C E B D

You might also see it like this…

You might also see it like this…

Rates of Weathering will depend on: Climatic Conditions: Cold and/or dry climates favor physical weathering. Warm and wet climates favor chemical weathering. Frost action works best in areas where the temperature fluctuates wildly.

Soil - The product of weathering Soil- rocks, minerals (mainly sand and clay), and organic material (regolith and organic matter) Soil forms layers of different characteristics called horizons.

Soil Horizons