What physical factors determine the rate of weathering?

Answer 1

• Climate-

Climate, which is usually measured in terms of temperature and moisture, can drastically affect the rate of weathering.

High amounts of water and higher temperatures generally cause chemical reactions to run faster. Thus warm humid climates generally have more highly weathered rock, and rates of weathering are higher than in cold dry climates. Example: limestones in a dry desert climate are very resistant to weathering, but limestones in a tropical climate weather very rapidly.

A high temperature and high amounts of water also controls vegetation which indirectly affects rate.

Seasonality of precipitation affects rate to a degree.

· Organisms (Biota)

Animals- burrowing organisms like rodents, earthworms, & ants, bring material to the surface were it can be exposed to the agents of weathering.

• Time-

Weathering is a slow process. When we speak of time in a geologic sense, millions of years are often used as the units. The bedrock of Greenland has barely been weathered, and its age is over 3.5 billion years. The longer that a rock has been exposed to the weather, the faster it weathers.

• Mineral Composition-

All chemical and physical properties are determined by the mineral composition of the rock. Mineral composition is more important in determining the rate of chemical weathering. Those minerals that are most reactive with acids, water, and air are weathered at a more rapid rate.

Mineral composition also affects physical weathering. Minerals that are soft (hardness lower thaan six) can be easily abraided and blasted.

Slope - On steep slopes weathering products may be quickly washed away by rains. On gentle slopes the weathering products accumulate. On gentle slopes water may stay in contact with rock for longer periods of time, and thus result in higher weathering rates.

· Porosity and faults and shears in materials

Porous sediment equals better circulation and thus faster weathering process.

Impermeable rocks will mean that no or little circulation will take place in rocks and weathering will be slower.

Enhanced weathering rate occurs if faults and shears are present in rocks.

• Exposure-

Rock that is exposed to the atmosphere tends to weather much quicker. Bed rock that is covered by soil and vegetation may not weather as quickly.

• Particle Size-

The particle size of the material can affect the rate of weathering. The smaller the particle size, the faster it will weather. The more surface area that is exposed, the more it will weather.