WeatheringEssential Vocabulary

Weathering & Natural Erosion weathering – the processes

that breaks down rocks, soils, or minerals at Earth's surface. Types of weathering are mechanical and chemical.

mechanical weathering – type of weathering where rocks are physical broken down into smaller pieces.

chemical weathering – process that breaks down rock through chemical changes

Good to Know

Weathering and erosion work

together continuously to wear down

and carry away rocks at the Earth’s

surface.

Geologists make inferences based

on the principle of

uniformitarianism. That is a big

word that means the same

processes that operated today

operated in the past.

This means that, over time, even

the biggest, hardest rocks are

broken down by weathering.

abrasion – the grinding away of rock by rock particles carried by water, ice, wind, or gravity.

How to Know Mechanical Weathering When You See It?

Good to Know

The causes of mechanical

weathering include

freezing and thawing,

release of pressure, plant

growth, actions of animals,

and abrasion.

Weathering & Natural Erosion

ice wedging – process that splits rock when water seeps into cracks, then freezes and expands.

release of pressure– as erosion removes surface material, pressure is reduced on the rock, causing outer sheets to flake off (like onion layers)

animal actions – burrowing animals (moles, gophers, prairie dogs, and some insects) loosen and break apart rocks in the soil.

Good to Know

The causes of mechanical

weathering include freezing

and thawing, release of

pressure, plant growth, actions

of animals, and abrasion.

Weathering & Natural Erosion

plant growth trees (and other plant) roots enter cracks in rock and

force it apart as the roots grow and expand

The rate of weathering increases as more and more of the rock’s surface area is exposed.

water – most important cause of chemical weathering, because water dissolves rock.

oxygen – the process when iron combines with oxygen when water is present is called oxidation (rust)

Good to Know

The causes of chemical

weathering include the

actions of water,

oxygen, carbon dioxide.

Weathering & Natural Erosion

carbon dioxide – in the atmosphere, CO2 combines with rainwater. In soil, it becomes carbonic acid that easily weathers marble and limestone.

Good to Know

The causes of chemical

weathering include the

actions of water, oxygen,

carbon dioxide.

This creates holes or soft

spots in rock, which

helps with breaking

down the rock.

Weathering & Natural Erosion

living organisms – lichens grow on rocks and seeds sprout in cracks to produce weak acids.

Good to Know

The causes of chemical

weathering include the

actions of water, oxygen,

carbon dioxide.

This creates holes or soft

spots in rock, which helps

with breaking down the rock.

Weathering & Natural Erosion

acid rain – chemicals (sulfur, carbon, and nitrogen compounds) from air pollution mix with water vapor forming acids that fall with raindrops.

Weathering & Natural Erosion

Good to Know

The causes of chemical

weathering include the

actions of water, oxygen,

carbon dioxide.

This creates holes or soft

spots in rock, which helps

with breaking down the

rock.

Rates of Weathering climate - the average weather

conditions, including temperature, precipitation, and wind, most often occur in a particular region.

Good to Know

Some kinds of rocks weather

more rapidly than others

The most important factors that

determine the rate at which

weathering occurs are the

type of rocks and the climate.

Rates of Weathering permeable – material is full of tiny, connected air spaces that allow water to seep through it. Good to Know

Some kinds of rocks weather more rapidly than

others

The most important factors that determine the

rate at which weathering occurs are

the type of rocks and the climate.

Rocks that dissolve in water will

weather faster than rocks that

do not dissolve in water.

Chemical weathering happens

faster at high temperatures.

Both chemical and mechanical

weathering happen faster in wet

climates.

The End Products Of Weathering

Weathering breaks down rocks into particles of many sizes (clay, silt, sand, pebbles, cobbles, boulders)

Soil is a mixture of rock and organic material. Soils are the result of weathering and biological activity over long

periods of time. A mature soil profile shows three distinct horizons. The A-horizon

(topsoil) is dark and rich in humus. The B-horizon (subsoil) is lighter in color, has more clay, and less

humus. The C-horizon is made of slightly weathered bedrock (rock fragments).

Beneath the three horizons is the unweathered bedrock. Soils may be residual (form from underlying bedrock) or transported

(form from sediments that have been carried from some other place).

Different Climates, Particle Sizes, Composition & Exposure Affects the Weathering Process At high latitudes and high altitudes, where it is cold and humid, frost action is the major form of weathering.

In warm and humid climates chemical weathering is most important. In arid (dry) climates, very little weathering takes place. Local climatic conditions (winds, nearness to cities, etc.) can affect the

of weathering. Small rock particles will weather faster than a single large sample of

the same mass because more surface area exposed by the small particles.

Rocks containing more resistant minerals will weather at a slower rate. Rocks that are not exposed to the atmosphere and hydrosphere will

weather at the slowest rate.

It's a Hard Rock Life