Erosion and deposition play a pivotal role in shaping many landforms. Erosion wears away at tiny pieces of rock and soil, which then travel by water or wind currents to different places where they are eventually deposited as sedimentary layers.
Sand on beaches is often left behind after erosion from rocks and cliffs has taken place, leaving behind layers of sediment which eventually end up as deposits on beaches.
Sedimentation
Erosion occurs when rocks, sediment and soil are removed from one location and deposited elsewhere, creating the landscape we see today – from erosion-formed cliffs and shorelines, valleys and streams, rivers and lakes, glaciated areas as well as mountain tops being altered by this process.
Erosion occurs most rapidly where there is enough energy available to move the material being eroded away, such as steep mountain slopes. Gentler slopes tend not to erode as rapidly.
Sediment can be transported by water, wind or ice currents and depends on particle size and shape for its arrival at its new destination. Silt and clay particles have strong cohesive bonds which require greater flow velocities to break. Therefore, silt-clay mixtures need to travel much faster than sand particles before reaching their new location. When their transporting agent loses energy – be it wind, ice water or gravity – eventually they stop moving altogether and deposit themselves at their new site.
Runoff
Runoff refers to water that runs off land into streams, creeks and rivers – part of nature’s cycle that replenishes groundwater sources while transporting sediment and pollutants along its journey. Runoff can help replenish groundwater sources while transporting debris such as pollutants.
Water has an immense power to alter landscapes and carve canyons. Yet it can also transport dangerous chemicals and pollutant debris – both potentially toxic substances that pose great threats.
Urbanization increases surface runoff as more pavement and buildings replace fields, woods and grasslands that allow water to percolate through to aquifers through permeable surfaces like soil. The resultant increase in runoff results in flashy floodwater flows during rain events as well as no flow during dry conditions eroding stream banks and disrupting ecosystems. Runoff also transports lawn fertilizers, pet waste, sand sediment and chemical contaminants into streams rivers lakes which degrade water quality while harming fish and shellfish populations while organic material in runoff can add turbidity reducing sunlight reaching aquatic plants causing them to die off.
Weathering
Weathering refers to the chemical breakdown and degradation of rocks and minerals on Earth’s surface. It differs from erosion in that materials are carried away by wind, water or ice movement rather than through natural means such as weather.
Weathering can produce interesting geological features, including arches and pillars of rock. Furthermore, weathering contributes to the creation of mountains, canyons and other landforms – such as Grand Canyon which was formed from years of river flow through weathered rocks in its surroundings.
Thermal stress is one type of physical weathering, in which minerals in a rock expand and contract at different rates due to fluctuations in temperature causing it to weaken over time. It is particularly prevalent in environments with drastic temperature shifts like desert lands.
Chemical weathering can also contribute significantly to climate change, dissolving limestone and other minerals in the ground to form vast cave networks like Carlsbad Caverns National Park in the US. Chemical weathering also stores carbon in plants and soils – scientists believe this plays a crucial role in global climate change.
Erosion
Erosion refers to the gradual wearing away of surface materials like rocks, sediments and soil by wind, water or glaciers. Once this material has been worn away it is transported and deposited elsewhere.
Waves lapping beaches may sculpt them into arches, stacks and caves; or wind-driven erosion may transport dust over long distances to form towering dunes. Erosion also polishes rock faces until they look smooth – as seen with Arches National Park in Utah with its famed sandstone arches and gullies that give this park its name.
Globally, erosion is most often caused by flowing water. Soil texture such as its presence of silt or fine sand particles plays a part; clay soils tend to be less vulnerable. Loss of tree cover and leaf litter, as well as overgrazing by livestock also exacerbates erosion rates; current conservation agriculture practices may decrease it but climate change projections suggest low and middle income countries could experience higher erosion rates in future.