Teaching weathering erosion and deposition to students is a fascinating way to introduce them to slow changes to Earth’s surface. This article includes several check-for-understanding opportunities as well as a tableau activity at its conclusion.
Erosion refers to the physical and chemical breakdown of rock and soil by wind, water, ice or gravity into sediment. The end product of erosion is known as silt.
Weathering
Weathering, or the deterioration of rocks and minerals on or near Earths surface, involves chemical and physical forces which often lead to sediments being formed from broken rock particles. Erosion refers to any process which erodes away these sediments – water, wind, glaciers and gravity are common forces causing it.
Mechanical (or physical) weathering breaks rocks into smaller pieces without altering their mineral makeup, like when plant roots penetrate cracks in rocks or glaciers slowly move ice along their path. Examples of such weathering include wedge-like action of plant roots within cracks in rocks, or slow movement of glacier ice.
Chemical weathering alters the molecular structure of minerals to make them easier for weathering agents like water, ice, acids, salts, plants and temperature changes to break them down. Air pollution speeds this process by reacting with carbon dioxide in raindrops to form sulfuric and nitric acids which quickly decompose rock.
Erosion
Weathering and erosion play an essential role in shaping Earth’s landforms. Erosion occurs when water, ice, wind, gravity or any combination thereof loosen or dissolve rock and soil material before transporting it along its course to depositing it at various places en route – as is evident by Arizona’s Grand Canyon carved by water erosion; wind also erodes rocks to shape them into mushroom shapes creating Badain Jaran Sand Dunes in China.
Water erosion is the most prevalent type of land degradation. Rainwater and melting snow erode bare land without vegetation to absorb its force or slow its pace of running water, particularly fast-flowing waters that erode more quickly than slower moving ones, carving channels into mountains or creating meandering rivers.
Waves batter coastlines, dislodging pebbles from beaches and eroding the rock that forms sea stacks and arches. Over time, plants that inhabit cracks in rocks such as mosses and lichens enlarge these existing cracks to further weakening it; while physical weathering occurs when its surface breaks apart due to heat or pressure.
Deposition
Earthquakes, glacial melt, water run-off and gravity all play their parts to break down rocks at Earth’s surface and transport weathered rock or soil from one location to the next.
Deposition can happen rapidly when mudslides move quickly across a river. We also witness it at beaches where ocean waves pound against rocks to deposit sand over time, creating beaches. Sometimes this also happens over exposed limestone due to chemical weathering.
Use this set of slides from Florida teacher and Teach Starter Collaborator Kaylyn Chupp to teach your students about weathering, erosion and deposition with various check-for-understanding opportunities and an engaging tableau activity at the end. This resource was made possible thanks to Teach Starter Collaborators like her!
Landforms
Landforms of various kinds are formed through weathering and erosion processes. While some landforms form from plate tectonic movement, others arise through endogenic forces like erosion, weathering and the accumulation of sediment.
Water is the greatest force at play when it comes to shaping landscapes, and erosion occurs through both mechanical (physical) and chemical (chemical) weathering processes. Mechanical weathering includes frost action – when rocks freeze and thaw multiple times over the course of an evening – and abrasion; chemical weathering encompasses acid rain (the pollution of air with sulfur dioxide, nitrogen and carbon compounds) as well as changes in rock composition such as iron reacting with oxygen to form rust.
Erosion is also affected by deposition. When rivers flow into still bodies of water they deposit sediment at their mouth creating deltas; ocean waves and wind also deposit material which contribute to deposition as do alluvial fans and gulleys.