Erosion is the processes that loosen sediment and soils and move it from one place to another on the Earth's surface. Erosion moves material away from its initial location and transports it by gravity, wind, waves, water and ice. Erosion of rocks, sediment and soils can occur in many different environments, which determines the processes of erosion that are active and their relative importance. The processes of erosion transport need to have sufficient energy to mobilise an object. Weathering of the object can reduce the size of an object and increase its surface area..
The energy of the transport medium (gravity, wind or water) needs to overcome the resisting forces (for example gravity and cohesion) on the object or surface to make the material move and erosion to occur.
There are a number of different types of erosion, including:
The transport energy in water can come from the water itself, or the abrasion of grains being moved by water hitting the object and dislodging and transporting it. Chemical dissolution of the original material means that water has the potential to transport the solute away. This is a common form of erosion in limestone and causes karst landscapes. Hydraulic action, that includes cavitation, is where water forces air into cracks in rocks or sediments. The increased pressure can force the sediment to disintegrate, reducing cohesion and particle size of the sediment.
In river systems, channel sediment can come from hillslope (sheet and rill) erosion, where overland flows and rain splash erosion are sufficient to entrain particles, or the hillslope fails as a landslide. The concentration of flow on hillslopes can be a factor in more efficient erosion in the form of gullies. Vegetation can increase the resistance of the surface by intercepting rain, slowing its impact on the surface, slowing overland flow through increasing surface roughness, and increasing the cohesion of the sediment and soils.
The boundary sediment in the channel can produce sediment from bed and bank erosion, such as from channel incision by entrainment and abrasion. The processes of streambank erosion can be divided into three main types: 1) sub-aerial, 2) fluid entrainment, and 3) mass failure. Sub-aerially eroded sediment comes from the processes of desiccation and frost heave decreasing the strength of sediment sufficiently so that gravity can erode it. Fluid entrainment can directly entrain riverbank sediment into the channel, with sand sized sediment the most easily eroded. Mass failures are when a block or unified mass of sediment is supplied to the channel. These are like mini landslides and can deliver pulses of sediment into the channel, sometimes after the flow has receded, so that there are readily available sources of sediment to be transported in subsequent flows.
Understanding the processes of erosion means that appropriate management strategies can be used when the risk of high sediment delivery downstream, or the threat of erosion to local infrastructure, becomes too high.
Links and references
Last updated: 24 October 2023
This page should be cited as:
Department of Environment, Science and Innovation, Queensland (2023) Erosion, WetlandInfo website, accessed 1 February 2024. Available at: https://wetlandinfo.des.qld.gov.au/wetlands/ecology/processes-systems/erosion/