Teacher Tip: Children explore states of matter and changing states starting in Year 4 (aged 8+). For instance, water vapour transforming into ice directly upon hitting a cold window pane.
Erosion occurs when pieces of the Earth are dislodged from their original locations and deposited elsewhere; deposition. As a result, this process creates natural features like river deltas and alluvial fans.
Earth is constantly shifting as rocks and minerals break down and move to new locations; this process, known as weathering, includes both physical, chemical, and biological components.
Longer periods of exposure to weathering increase its susceptibility to erosion. Rocks buried under other rocks such as lava flows tend to weather less quickly than those exposed for extended periods.
Physical weathering refers to the process by which rocks at the surface break down due to temperature extremes, rainwater, living or once-living organisms and organisms’ activity at their surfaces. This differs from erosion because physical weathering does not involve movement of rock materials.
Physical weathering occurs when water seeps into cracks and crevices of rocks, forcing expansion, cracking or crumbling. Water can also freeze and thaw in rock pores causing more flexibility which eventually makes more susceptible to erosion.
Erosion is the natural process of loosening, transporting and depositing weathered solid material by wind, flowing water, glaciers or gravity. Erosion also exposes fresh rock surfaces to weathering.
Physical erosion includes abrasion, chemical weathering and mechanical weathering (the physical breaking down of rock). Plant growth contributes to physical erosion as its roots and twigs rub against rocks. Rivers are most effective eroding agents – slowly wearing away soil and rock as they flow through landscapes – leaving behind features like waterfalls, flood plains, meanders and oxbow lakes in its wake.
Abrasion is the most prevalent form of erosion, occurring when pebbles rub against each other along a stream bank and bed. Water erosion can quickly erode surface sediments as well as break apart rocks by splashing, scouring, vibration or splashing; its energy also dissolving or entrainment particles into its streambed medium; these three processes often coincide and cannot easily be distinguished.
Sediment transport refers to the movement of erosion-eroded materials through waterways. It may be caused by wind, rain or waves; more commonly however it’s the result of all three. The rate at which sediment is moved depends on channel gradient, discharge capacity and its calibre load (i.e. the maximum particle size a stream can carry).
Regolith refers to the material carried by streams. This may include mineral-based or organic components and can differ depending on where you are. Rocks tend to erode faster than soil, and their composition determines which types of sediment a river carries downstream.
Geologic elements, like basalt near active volcanoes, tend to produce fine silts; other igneous and metamorphic rocks tend to produce coarse sands. Local terrain also influences how much sediment a river transports – bedrock streams are less vulnerable to fast erosion than alluvial channels 13. Longshore drift is another key source of sedimentation, especially in protected environments like estuaries or bays 13.