Earth Science 1121H Physical Weathering

Weathering

the mechanical, biological, and or chemical breakdown of rocks

Products, sediment, and soil can be

transported and deposited by water wind, glaciers, ocean currents elsewhere

Weathering and transport are termed

erosion

Processes within the earth create

topography

Processes at the surface remove

topography
- weathering lowers topographically high features

Surface processes are driven by

earth's external engine

Material weathered at high altitudes is

transported and deposited elsewhere
- most of this material reaches the sea

The Geoid

the shape that the surface would have if the earth was entirely covered by oceans
- the idealized shape

prolate spheroid

the shape of the earth the earth's internal heat engine were shut down then the earth's surface would become smooth

Earth's energy sources

- internal heat (geothermal)
- tide energy (small)
- solar enegery

hydrologic cycle

The cycle through which water in the hydrosphere moves; includes such processes as evaporation, precipitation, and surface and groundwater runoff
- driven by solar energy
- water cycled between oceans, atmosphere, and land

Amount of water evaporated equals

amount precipitated

largest, second largest, and third largest reservoir of water

1. oceans
2. glacial ice
3. groundwater

Mechanical weathering

breakdown of rocks by physical means

chemical weathering

breakdown of rock by chemical attack

biological

breakdown of rock through the actions of organisms

Joints

fractures in rocks that allow access of water to the interior of the rock mass

If temperature drops below freezing in mechanical weathering

ice forms with an expansion in volume of about 9 percent
- rock mass is reduced to smaller particles
- some processes produces potholes in roads (frost wedging, freeze-thaw weathering)

How do potholes form

1. Water seeps through joints
2. water freezes and expands cause the road surface to rise
3. ice melts leaving a void
4. as traffic passes over, the tires collapse into the void

salt wedging

dissolved salt crystallizes and grows in open spaces wedging apart mineral grains
- clay can also absorb water, expand, and wedge mineral grains apart

sheeting

excavation of rocks by erosions results in a decrease in pressure
- rock mass expands
- rocs show cracks, joints, and fractures

pressure release

A significant type of mechanical weathering that causes rocks to crack when pressure is decreased

exfoilation

The mechanical weathering process where surface layers of rock peel off due to unloading of a heavy object

root wedging

In this type of physical weathering, the roots of a plant (typically a tree) wedge into a crack in a rock and, as the plant growns, splits the rock.

importance of mechanical weathering

Increases the surface area of a rock, providing more surface for chemical attack.