WEATHERING, EROSION, AND MASS WASTING

WEATHERING

• Two types of weathering are mechanical and chemical.

• Mechanical weathering is the physical break up of rock exposing more surface area by:Frost wedging – common in mountains and middle latitudesUnloadingBiological activity

• Frost Wedging• When water

freezes it expands by about 9% and exerts tremendous force. This force breaks off rocks, tumble and pile up at the bottom of the cliff into large pies called talus.

• Unloading

• Exposed rock reduces pressure causing the outer layers to expand. The outer layers separate from the rest of the rock by a process called exfoliation.

• Biological activity

• Plant roots grow into rocks breaking rocks apart.

Chemical weathering is the transformation of rock into one or more new compounds.

• Water is the most important agent of chemical weathering

• The oxygen dissolved in water reacts with certain minerals forming oxides, such as iron oxides in soil (yellowish or red soils)

• Water falling through the atmosphere absorbs carbon dioxide forming weak carbonic acid. This acid reacts with many minerals, for example limestone.

• Water in the atmosphere reacts with sulfur oxides and nitrogen oxides from the burning of coal and petroleum to form acid rain. The acid rain reacts with many minerals.

Chemical weathering of granite forms the minerals feldspar and quartz. The feldspar reacts with the carbonic acid forming clay. The quartz is resistant to weathering and remains unchanged.

The rate of weathering is influenced by mechanical weathering, rock characteristics, and climate. For example

Granite weathers slower than marble or limestone.

Climate favorable to weathering have high

temperatures and abundant moisture.

Where is chemical weathering the slowest?

EROSION

• Soil erosion is a natural part of matter recycling.

• The rate of soil erosion depends on soil characteristics, climate, slope, and type of vegetation.

Types of Water Erosion

• Sheet erosion – thin sheets of water carriers away soil particles

• Rills – tiny streams of water

• Gully erosion – deep trenches

• Wind erodes soil much more slowly. However prolonged drought can remove large quantities of exposed soil.

• Human activities that increase the rate of soil erosion are land clearing due to development and road building. Sedimentation is the number one stream pollutant in North Carolina.

MASS MOVEMENT (WASTING)

• MASS MOVEMENT (WASTING) – the down slope movement of rock and soil due to gravity

Triggers of mass movements• Water-logged soils

• Over-steepened slopes from road building and development

• Removal of vegetation

• Earthquakes

Types of Mass Movements

• Rock falls – rock or rock fragments fall off

• Landslides – a block of material suddenly moves down along a flat inclined surface

• Slump – a block of materials move down along a curved surface

• Mudflows- contain a high amount of water, occur quickly, occur in mountainous areas

• Earth flows move relatively slowly, form a tongue-shaped mass

• Creep – the slowest type of mass movement, travels few millimeters to centimeters per year, freeze-thaw cycles contributes to creep.