Sedimentation is the deposition of sediments. It takes place when particles in suspension settle out of the

fluid In physics, a fluid is a liquid, gas, or other material that may continuously motion, move and Deformation (physics), deform (''flow'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are M ...

in which they are entrained and come to rest against a barrier. This is due to their motion through the fluid in response to the

force In physics, a force is an influence that can cause an Physical object, object to change its velocity unless counterbalanced by other forces. In mechanics, force makes ideas like 'pushing' or 'pulling' mathematically precise. Because the Magnitu ...

s acting on them: these forces can be due to

gravity In physics, gravity (), also known as gravitation or a gravitational interaction, is a fundamental interaction, a mutual attraction between all massive particles. On Earth, gravity takes a slightly different meaning: the observed force b ...

, centrifugal acceleration, or

electromagnetism In physics, electromagnetism is an interaction that occurs between particles with electric charge via electromagnetic fields. The electromagnetic force is one of the four fundamental forces of nature. It is the dominant force in the interacti ...

Settling Settling is the process by which particulates move towards the bottom of a liquid and form a sediment. Particles that experience a force, either due to gravity or due to Centrifuge, centrifugal motion will tend to move in a uniform manner in the ...

is the falling of suspended particles through the liquid, whereas sedimentation is the final result of the settling process. In

geology Geology (). is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth ...

, sedimentation is the deposition of sediments which results in the formation of

sedimentary rock Sedimentary rocks are types of rock (geology), rock formed by the cementation (geology), cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or de ...

. The term is broadly applied to the entire range of processes that result in the formation of sedimentary rock, from initial

erosion Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust and then sediment transport, tran ...

through sediment transport and settling to the

lithification Lithification (from the Ancient Greek word ''lithos'' meaning 'rock' and the Latin-derived suffix ''-ific'') is the process in which sediments compact under pressure, expel connate fluids, and gradually become solid rock. Essentially, lithificati ...

of the sediments. However, the strict geological definition of sedimentation is the mechanical deposition of sediment particles from an initial suspension in air or water. Sedimentation may pertain to objects of various sizes, ranging from large rocks in flowing water, to suspensions of dust and pollen particles, to cellular suspensions, to solutions of single

molecule A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...

s such as

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

s and peptides. Even small molecules supply a sufficiently strong force to produce significant sedimentation.

Principles

Settling

Classification

Classification of sedimentation: *Type 1 sedimentation is characterized by particles that settle discretely at a constant settling velocity, or by the deposition of Iron-Rich minerals to streamlines down to the point source. They settle as individual particles and do not flocculate (stick to each other) during settling. Example: sand and grit material *Type 2 sedimentation is characterized by particles that flocculate during sedimentation and because of this their size is constantly changing and therefore their settling velocity is changing. Example: alum or iron coagulation *Type 3 sedimentation is also known as zone sedimentation. In this process the particles are at a high concentration (greater than 1000 mg/L) such that the particles tend to settle as a mass and a distinct clear zone and sludge zone are present. Zone settling occurs in lime-softening, sedimentation, active sludge sedimentation and sludge thickeners.

Sedimentation equilibrium

When particles settling from a suspension reach a hard boundary, the concentration of particles at the boundary is opposed by the

diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...

of the particles. The distribution of sediment near the boundary comes into sedimentation equilibrium. Measurements of the distribution yields information on the nature of the particles.

In geology

, the term ''sedimentation'' is broadly applied to the entire range of processes that result in the formation of sedimentary rock, from initial formation of sediments by

of particles from rock outcrops, through sediment transport and settling, to the

of the sediments. However, the term is more particularly applied to the deposition of sediments, and in the strictest sense, it applies only to the mechanical deposition of sediment particles from an initial suspension in air or water. Sedimentation results in the formation of depositional

landform A landform is a land feature on the solid surface of the Earth or other planetary body. They may be natural or may be anthropogenic (caused or influenced by human activity). Landforms together make up a given terrain, and their arrangement ...

s and the rocks that constitute the sedimentary record. The building up of land surfaces by sedimentation, particularly in river valleys, is called '' aggradation''. The rate of sedimentation is the thickness of sediment accumulated per unit time. For suspended load, this can be expressed mathematically by the Exner equation. Rates of sedimentation vary from less than per thousand years for pelagic sediment to several meters per thousand years in portions of major

river delta A river delta is a landform, archetypically triangular, created by the deposition of the sediments that are carried by the waters of a river, where the river merges with a body of slow-moving water or with a body of stagnant water. The creat ...

s. However, long-term accumulation of sediments is determined less by rate of sedimentation than by rate of subsidence, which creates accommodation space for sediments to accumulate over geological time scales. Most sedimentation in the geologic record occurred in relative brief depositional episodes separated by long intervals of nondeposition or even erosion. In estuarine environments, settling can be influenced by the presence or absence of vegetation. Trees such as mangroves are crucial to the

attenuation In physics, attenuation (in some contexts, extinction) is the gradual loss of flux intensity through a Transmission medium, medium. For instance, dark glasses attenuate sunlight, lead attenuates X-rays, and water and air attenuate both light and ...

of waves or currents, promoting the settlement of suspended particles.

Siltation

An undesired increased transport and sedimentation of suspended material is called

siltation Siltation is water pollution caused by particulate terrestrial clastic material, with a particle size dominated by silt or clay. It refers both to the increased concentration of suspended sediments and to the increased accumulation (temporary o ...

, and it is a major source of pollution in waterways in some parts of the world. High sedimentation rates can be a result of poor land management and a high frequency of flooding events. If not managed properly, it can be detrimental to fragile ecosystems on the receiving end, such as coral reefs.

Climate change Present-day climate change includes both global warming—the ongoing increase in Global surface temperature, global average temperature—and its wider effects on Earth's climate system. Climate variability and change, Climate change in ...

also affects siltation rates.

Human-enhanced sedimentation

In chemistry

In chemistry, sedimentation has been used to measure the size of large molecules ( macromolecule), where the force of gravity is augmented with centrifugal force in an ultracentrifuge.

In water treatment

Notes

{{Authority control Earth sciences Laboratory techniques Liquid-solid separation