Teachers should understand that deposition, along with erosion, is an integral part of shaping Earth’s surface. While erosion wears away rocks and soil from its surfaces, deposition creates landforms by depositing sediment.
Wind and water currents play an integral part in transporting sediment to its destination, while its weight and size determine its rate of deposition.
Sediment
Sediments are a conglomerate of materials that can be transported by wind, water or ice and include minerals (clay, silt and sand), decomposing organic matter as well as inorganic biogenic material like detritus or the remains of algae skeletons.
These particles can be separated according to grain size and can be classified as either lithogenous, terrigenous, or cosmogenous according to their origin: Lithogenous sediments contain weathered rocks; terrigenous ones come from erosion of terrestrial plants; while cosmogenous ones could include dust from windswept surfaces or small particles falling from space.
Deposited sediments reveal valuable information about their time of deposition, such as fossils found in sedimentary rock that provide insight into past climates. Layers of sediment also impact water chemistry, light penetration and bottom topography. Sediments contain contaminants like metals and organic pollutants which are then carried downstream in rivers or estuaries with high sediment accumulation – these pollutants often accumulate in environments rich in sediment such as estuaries or swollen rivers.
Weathering
The Earth’s rocky landscape is ever changing as rain, sun, wind, animals and plants combine forces to weather down rocks physically and chemically – often slowly. Sometimes rapid change may occur suddenly: for instance a road may become damaged by frost damage or stone monuments may crack under an earthquake’s force.
Weather-worn rock fragments can be transported through erosion and deposited elsewhere; for example, carried by wind they could end up as sand dunes on beaches; similarly eroded sediment from riverbanks may end up further downstream.
Physical weathering refers to rocks being broken down through mechanical forces such as abrasion. This causes their surface to crumble without changing their chemical structure; chemical weathering alters this composition of rocks by rearranges atoms or molecules into different substances with unique properties; for example turning limestone into salt. Chemical weathering takes much longer than mechanical weathering.
Erosion
Erosion refers to processes that dislodge rock and soil from one location and transport it elsewhere, typically by wind or water action. Rocks may be physically broken down by plant roots wedged into cracks in rocks or chemically, such as when iron rusts or limestone dissolves.
Erosion typically happens slowly, but in an emergency large volumes of rock and soil may quickly move downhill at once – known as mass movement – which can have devastating results for communities or landscapes alike.
Rainfall characteristics, soil factors, topography and land use all play an integral part in how erosion occurs. For instance, erosion from agricultural practices like tillage or strip cropping may compromise food production as well as harm rivers and lakes. Erosion caused by fast moving streams is known as rill or gully erosion – this form may even flood communities! Other forms of erosion may not pose as much of a risk.
Deposition
Deposition is the process by which particles move from one place to another, typically after being carried off by erosion. For instance, Egypt’s Nile river would deposit silt annually onto farmlands, helping people cultivate abundant crops each year.
Deposition can provide students with an effective means of exploring different states of matter and changes of state, beginning in year 4 (aged 8+).
Deposition in chemistry refers to the process by which gas changes directly to solid, bypassing liquid. A demonstration of this phenomenon might involve pouring purple iodine vapor onto an icy plate and watching as needle-like crystals of solid iodine form quickly – something you might have witnessed when pouring purple iodine vapor onto this surface!
Deposition in nature creates spectacular landscapes such as sand dunes and river deltas, as well as breathtaking cave formations such as stalactites and stalagmites. Deposition can also be used in 3D printing to build objects layer by layer.