EARTH SCI | Weathering and Mass Wasting

Chemical Weathering and Physical Weathering

As mechanical weathering breaks into smaller pieces, more surface area is exposed to chemical weathering. These two processes work together happening to the same rock at the same time

Frost Wedging

breakage resulting from the expansion of freezing water, which exerts outward force strong enough to wedge open a crack and split a rock

Talus

debris that piles up to a characteristic angle at the base of a cliff

Thermal Expansion and Contraction

• rocks are exposed to temperature fluctuations from the day-night cycle

• if the temperature changes rapidly, the surface of a rock expands or contracts faster than the interior, leading to the fragmenting of the outer part of the rock

Unloading/Pressure Release

• the weight of overlying rock puts pressure into the underlying rock (usually a volcanic rock)

• when the overlying rock is removed through other forms of erosion, the underlying rock is exposed and pressure is released through thermal expansion

Sheeting

when large masses of rock are exposed by erosion, slabs of rock begin to break loose, generating exfoliation domes

Abrasion

the mechanical wearing of rock by friction and impact

Biological Activities

burrowing animals, growing roots, and human activities contribute to physical weathering

Dissolution

minerals in a rock are dissolved by water; usually are dissolved more rapidly when the water is acidic or basic (e.g. carbonic acid rain)

Halite and Dissolution

When a crystal of halite (NaCl) is dropped in a glass of water, the negatively charged ends of water molecules pull the positively charged sodium ions away from the halite, while the positively charged ends of water molecules remove the negatively charged chlorine ions.

Hydrolysis

water reacts with one mineral to form a new mineral that has water in its crystalline structure

Granite and Hydrolysis

Feldspar and hornblende weathers easily as compared to quartz in granite. When granite weathers, the feldspar and other materials decompose to form clay but the unaltered quartz grains fall free from the rock

Oxidation

oxygen gas frequently reacts with iron and other metals to form mineral compounds to form rust, which easily crumbles and weakens rocks; they may react with aquatic resources, which harm aquatic environment

Biological Action

when mosses, lichens, algae, fungi, and bacteria forms on a rock; it obtains minerals from it, which is essential for its growth, producing chemicals that eat away at the rock

Mass Wasting

downslope movement of earth material by gravity

Water Saturation

it reduces the friction between soil particles, which are then easily set in motion by gravity; water adds weight to the mass of the material; the water saturation increases the cohesion among sand grains and reduces friction and causes the sand to flow

Over steepened Slopes

these unstable slopes that becomes prime sites for mass wasting due to the steep angle, these slopes are usually made to accommodate housing

Removal of Vegetation

when plants are lacking, mass wasting is enhanced especially if slopes are steep and water is plentiful since the roots of plants keep the soil in place

Ground Vibration

earthquakes and its aftershocks can dislodge enormous volumes of rock and unconsolidated material

Types of Motion

flow, slide, fall

Flow

Loose, unconsolidated soil or sediment moves as a fluid since the sediment is saturated with water

Slide

Movement of a coherent block of material along a fracture

Fall

Free-falling motion of loose material, it’s common on slopes that are too steep for loose material to remain on the surface

Rapid Forms of Mass Wasting

slump, rock slides, debris flow, earthflow,

Slump

downward sliding of a mass of rock or unconsolidated material moving as a unit along a curved surface, commonly occurs because a slope has been oversteepened

Rockslides

Occur when blocks of bedrock break loose and slide down a slope, usually takes place when the rock strata are inclined parallel to the slope

Debris Flow

Involves a flow of soil and regolith (fragments of parent rock) containing a large amount of water, sometimes called mudflows when the material is primarily fine-grained, example of this mass wasting is lahar

Earthflow

when water saturates the soil on a hillside, the material breaks away, forming a tongue or teardrop-shaped mass that flows downslope

Slow Forms of Mass Wasting

creep, soilfluction

Creep

Gradual downhill movement of soil and regolith, caused by alternate expansion and contraction of surface material caused by freezing and thawing or wetting and drying

Soilfluction

also known as soil flow, type of mass wasting is common wherever water cannot escape from the saturated surface layer by infiltrating deeper levels, usually in permafroist