Weathering and Erosion

Weathering and erosion are two related processes that slowly change Earth's surface. Weathering breaks rocks into smaller pieces, while erosion moves those pieces from one place to another. Together, they shape the landscapes we see — valleys, canyons, beaches, and sand dunes.

Weathering

Weathering is the breaking down of rocks into smaller pieces by wind, water, ice, or chemicals. There are two main types: physical and chemical.

• Physical weathering — water freezing in cracks expands and splits rock apart (freeze-thaw).
• Physical weathering — wind abrasion scrapes rock surfaces with sand particles.
• Physical weathering — tree roots grow into cracks and slowly split boulders.
• Chemical weathering — acid rain dissolves limestone, forming caves and sinkholes.
• Chemical weathering — iron in rocks reacts with oxygen, forming rust and weakening the rock.

Erosion

Erosion is the movement of weathered rock or soil from one place to another by wind, water, or ice. Erosion can only move material that has already been broken down by weathering.

• Water erosion — rivers carry sediment downstream, carving valleys and canyons over millions of years.
• Wind erosion — wind blows sand particles, building up dunes and sculpting arches in deserts.
• Ice (glacial) erosion — glaciers scrape and drag rock and soil, carving U-shaped valleys and fjords.
• Ocean wave erosion — waves pound coastlines, forming sea cliffs and sea arches.
• Flood erosion — fast-moving water washes topsoil away from fields and hillsides.

Weathering and Erosion Together

• Weathering and erosion act together to shape landforms over very long periods of time.
• The Grand Canyon was carved by millions of years of river erosion after rock was weathered.
• Sand on beaches comes from rocks weathered and then carried by water or wind.