The Changing Earth

Chapter Fourteen: Weathering and Erosion 14.3 Rivers Shape the Land

Investigation 14A Water Systems How does running water shape rivers and landscapes?

14.1 Weathering Mountains wear down over time. Due to the Sun’s energy, wind, and water, mountains begin to crumble as soon as they are formed.

14.1 Weathering The Smokey Mountains are much older than the Rocky Mountains. How do these two mountain ranges differ?

14.1 Weathering At one time, the Smokies were as tall as the Rockies and also had sharp peaks. How long did the weathering of the Smokies take?

14.1 Ways weathering occurs Mechanical weathering occurs when forces break or chip rocks and minerals into smaller pieces without changing their composition.

14.1 Ways weathering occurs Rock is also reduced to smaller pieces by chemical reactions between water and rock grains. This process is called chemical weathering.

14.1 Agents of mechanical weathering Changing conditions of wetness and dryness cause rocks and minerals to break down. Weathering occurs quickly when running water knocks rocks against each other.

14.1 Agents of mechanical weathering Frost wedging splits apart rock slowly as water freezes. When ice expands and water contracts, it causes more cracks in rock.

14.1 Agents of mechanical weathering Plants cause weathering when their roots grow into small cracks in a rock. Animals cause weathering when they dig into soil or burrow underground.

14.1 Agents of mechanical weathering Exfoliation is a weathering process that results in rock layers peeling away as they expand or contract.

14.1 Agents of mechanical weathering Even wind is a weathering agent. Wind-blown sand chips away tiny bits of rock from the surface of exposed rock.

14.1 Chemical weathering Moss and lichens on rocks and will eventually cause them to break down because of chemicals they release.

14.1 Chemical weathering Both physical and chemical weathering can affect rock at the same time.

14.1 Factors that affect weathering Weathering is slowest in dry, cold climates. Running water speeds up mechanical weathering and chemical weathering. The kind of minerals found in a rock also affects how fast it weathers. The greater the surface area of a rock or mineral compared to its volume, the faster it will weather.