A turbidity current is most typically an underwater current of usually rapidly moving, sediment-laden water moving down a slope; although current research (2018) indicates that water-saturated sediment may be the primary actor in the process. Turbidity currents can also occur in other

fluid In physics, a fluid is a liquid, gas, or other material that continuously deforms (''flows'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are substances which cannot resist any shear ...

s besides water. Researchers from the Monterey Bay Aquarium Research Institute found that a layer of water-saturated sediment moved rapidly over the seafloor and mobilized the upper few meters of the preexisting seafloor. Plumes of sediment-laden water were observed during turbidity current events but they believe that these were secondary to the pulse of the

seafloor sediment Marine sediment, or ocean sediment, or seafloor sediment, are deposits of insoluble particles that have accumulated on the seafloor. These particles have their origins in soil and Rock (geology), rocks and have been Sediment transport, transpor ...

moving during the events. The belief of the researchers is that the water flow is the tail-end of the process that starts at the seafloor. In the most typical case of oceanic turbidity currents, sediment laden waters situated over sloping ground will flow down-hill because they have a higher

density Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematical ...

than the adjacent waters. The driving force behind a

turbidity Turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality. Fluids can ...

current is gravity acting on the high density of the sediments temporarily suspended within a fluid. These semi-suspended solids make the average density of the sediment bearing water greater than that of the surrounding, undisturbed water. As such currents flow, they often have a "snow-balling-effect", as they stir up the ground over which they flow, and gather even more sedimentary particles in their current. Their passage leaves the ground over which they flow scoured and eroded. Once an oceanic turbidity current reaches the calmer waters of the flatter area of the

abyssal plain An abyssal plain is an underwater plain on the deep ocean floor, usually found at depths between and . Lying generally between the foot of a continental rise and a mid-ocean ridge, abyssal plains cover more than 50% of the Earth's surface. T ...

(main oceanic floor), the particles borne by the current settle out of the water column. The sedimentary deposit of a turbidity current is called a

turbidite A turbidite is the geologic deposit of a turbidity current, which is a type of amalgamation of fluidal and sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean. Sequencing Turbidites were ...

. Seafloor turbidity currents are often the result of sediment-laden river outflows, and can sometimes be initiated by

earthquake An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from ...

slumping Slumping is a technique in which items are made in a kiln by means of shaping glass over molds at high temperatures. The slumping of a pyrometric cone is often used to measure temperature in a kiln. Technique Slumping glass is a highly techni ...

and other soil disturbances. They are characterized by a well-defined advance-front, also known as the current's head, and are followed by the current's main body. In terms of the more often observed and more familiar above sea-level phenomenon, they somewhat resemble flash floods. Turbidity currents can sometimes result from submarine

seismic Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other ...

instability, which is common with steep underwater slopes, and especially with

submarine trench Oceanic trenches are prominent long, narrow topographic depressions of the ocean floor. They are typically wide and below the level of the surrounding oceanic floor, but can be thousands of kilometers in length. There are about of oceanic tren ...

slopes of convergent plate margins, continental slopes and

submarine canyon A submarine canyon is a steep-sided valley cut into the seabed of the continental slope, sometimes extending well onto the continental shelf, having nearly vertical walls, and occasionally having canyon wall heights of up to 5 km, from c ...

s of passive margins. With an increasing continental shelf slope, current velocity increases, as the velocity of the flow increases, turbulence increases, and the current draws up more sediment. The increase in sediment also adds to the density of the current, and thus increases its velocity even further.

Definition

Turbidity currents are traditionally defined as those

sediment gravity flow upright=1.25, This turbidite from the Devonian Becke-Oese Sandstone">Devonian.html" ;"title="turbidite from the Devonian">turbidite from the Devonian Becke-Oese Sandstone of Germany is an example of a deposit from a sediment gravity flow. Note th ...

s in which sediment is suspended by fluid turbulence. Meiburg, E. & Kneller, B. 2010, "Turbidity currents and their deposits", Annual Review of Fluid Mechanics, vol. 42, pp. 135–156. However, the term "turbidity current" was adopted to describe a

natural phenomenon A natural phenomenon is an observable event which is not man-made. Examples include: sunrise, weather, fog, thunder, tornadoes; biological processes, decomposition, germination; physical processes, wave propagation, erosion; tidal flow, and natur ...

whose exact nature is often unclear. The turbulence within a turbidity current is not always the support mechanism that keeps the sediment in suspension; however it is probable that turbulence is the primary or sole grain support mechanism in dilute currents (<3%).Kneller, B. & Buckee, C. 2000, "The structure and fluid mechanics of turbidity currents: A review of some recent studies and their geological implications", Sedimentology, vol. 47, no. SUPPL. 1, pp. 62–94. Definitions are further complicated by an incomplete understanding of the turbulence structure within turbidity currents, and the confusion between the terms

turbulent In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to a laminar flow, which occurs when a fluid flows in parallel layers, with no disruption between t ...

(i.e. disturbed by eddies) and

turbid Turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality. Fluids can ...

(i.e. opaque with sediment). Kneller & Buckee, 2000 define a suspension current as 'flow induced by the action of gravity upon a turbid mixture of fluid and (suspended) sediment, by virtue of the density difference between the mixture and the ambient fluid'. A turbidity current is a suspension current in which the

interstitial fluid In cell biology, extracellular fluid (ECF) denotes all body fluid outside the cells of any multicellular organism. Total body water in healthy adults is about 60% (range 45 to 75%) of total body weight; women and the obese typically have a lower ...

is a liquid (generally water); a

pyroclastic Pyroclastic rocks (derived from the el, πῦρ, links=no, meaning fire; and , meaning broken) are clastic rocks composed of rock fragments produced and ejected by explosive volcanic eruptions. The individual rock fragments are known as pyroc ...

current is one in which the interstitial fluid is gas.

Triggers

Hyperpycnal plume

When the concentration of suspended sediment at the mouth of a

river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wate ...

is so large that the density of river water is greater than the density of sea water a particular kind of turbidity current can form called a hyperpycnal plume.Mulder, T. & Syvitski, J.P.M. 1995, "Turbidity currents generated at river mouths during exceptional discharges to the world oceans", Journal of Geology, vol. 103, no. 3, pp. 285–299. The average concentration of suspended sediment for most river water that enters the

ocean The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wo ...

is much lower than the sediment concentration needed for entry as a hyperpycnal plume. Although some rivers can often have continuously high sediment load that can create a continuous hyperpycnal plume, such as the

Haile River Haile ( Ge'ez "the power of") may refer to: ;People with the given name Haile * Haile Selassie of Ethiopia (1892–1975), Emperor of Ethiopia * Haile Gerima (born 1946), Ethiopian filmmaker * Haile Gebrselassie (born 1973), Ethiopian distance runne ...

(China), which has an average suspended concentration of 40.5 kg/m³. The sediment concentration needed to produce a hyperpycnal plume in

marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military * ...

water is 35 to 45 kg/m³, depending on the water properties within the

coastal The coast, also known as the coastline or seashore, is defined as the area where land meets the ocean, or as a line that forms the boundary between the land and the coastline. The Earth has around of coastline. Coasts are important zones in n ...

zone. Most rivers produce hyperpycnal flows only during exceptional events, such as

storms A storm is any disturbed state of the natural environment or the atmosphere of an astronomical body. It may be marked by significant disruptions to normal conditions such as strong wind, tornadoes, hail, thunder and lightning (a thunderstorm), ...

floods A flood is an overflow of water ( or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are an area of study of the discipline hydrolog ...

glacier A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its Ablation#Glaciology, ablation over many years, often Century, centuries. It acquires dis ...

outbursts, dam breaks, and

lahar A lahar (, from jv, ꦮ꧀ꦭꦲꦂ) is a violent type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris and water. The material flows down from a volcano, typically along a river valley. Lahars are extreme ...

flows. In fresh water environments, such as

lake A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...

s, the suspended sediment concentration needed to produce a hyperpycnal plume is quite low (1 kg/m³).

Sedimentation in reservoirs

The

transport Transport (in British English), or transportation (in American English), is the intentional movement of humans, animals, and goods from one location to another. Modes of transport include air, land (rail and road), water, cable, pipeline, an ...

and deposition of the

sediments Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand a ...

in narrow alpine

reservoirs A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation. Reservoirs can be created in a number of ways, including control ...

is often caused by turbidity currents. They follow the

thalweg In geography and fluvial geomorphology, a thalweg or talweg () is the line of lowest elevation within a valley or watercourse. Under international law, a thalweg is the middle of the primary navigable channel of a waterway that defines the bounda ...

of the lake to the deepest area near the

dam A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use ...

, where the sediments can affect the operation of the bottom outlet and the intake structures.Oehy, C.D. & Schleiss, A.J. 2007, "Control of turbidity currents in reservoirs by solid and permeable obstacles", Journal of Hydraulic Engineering, vol. 133, no. 6, pp. 637–648. Controlling this

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

within the reservoir can be achieved by using solid and

permeable Permeability, permeable, and semipermeable may refer to: Chemistry *Semipermeable membrane, a membrane which will allow certain molecules or ions to pass through it by diffusion *Vascular permeability, the movement of fluids and molecules betwe ...

obstacles with the right design.

Earthquake triggering

Turbidity currents are often triggered by

tectonic Tectonics (; ) are the processes that control the structure and properties of the Earth's crust and its evolution through time. These include the processes of mountain building, the growth and behavior of the strong, old cores of continents k ...

disturbances of the sea floor. The

displacement Displacement may refer to: Physical sciences Mathematics and Physics *Displacement (geometry), is the difference between the final and initial position of a point trajectory (for instance, the center of mass of a moving object). The actual path ...

continental crust Continental crust is the layer of igneous, sedimentary, and metamorphic rocks that forms the geological continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called ''sial'' be ...

in the form of fluidization and physical shaking both contribute to their formation. Earthquakes have been linked to turbidity current deposition in many settings, particularly where physiography favors preservation of the deposits and limits the other sources of turbidity current deposition.Adams, J., 1990, Paleoseismicity of the Cascadia subduction zone: Evidence from turbidites off the Oregon-Washington Margin: Tectonics, v. 9, p. 569–584. Since the famous case of breakage of submarine cables by a turbidity current following the

1929 Grand Banks earthquake The 1929 Grand Banks earthquake (also called the Laurentian Slope earthquake and the South Shore Disaster) occurred on November 18, 1929. The shock had a moment magnitude of 7.2 and a maximum Rossi–Forel intensity of VI (''Strong tremor'') and ...

, earthquake triggered turbidites have been investigated and verified along the Cascadia subduction Zone,Goldfinger, C., Nelson, C.H., and Johnson, J.E., 2003, Holocene Earthquake Records From the Cascadia Subduction Zone and Northern San Andreas Fault Based on Precise Dating of Offshore Turbidites: Annual Review of Earth and Planetary Sciences, v. 31, p. 555–577. the Northern San Andreas Fault, a number of European, Chilean and North American lakes, Japanese lacustrine and offshore regions and a variety of other settings.

Canyon-flushing

When large turbidity currents flow into

canyons A canyon (from ; archaic British English spelling: ''cañon''), or gorge, is a deep cleft between escarpments or cliffs resulting from weathering and the erosive activity of a river over geologic time scales. Rivers have a natural tendency to cu ...

they may become self-sustaining, and may entrain sediment that has previously been introduced into the canyon by

littoral drift Longshore drift from longshore current is a geological process that consists of the transportation of sediments (clay, silt, pebbles, sand, shingle) along a coast parallel to the shoreline, which is dependent on the angle incoming wave direction ...

, storms or smaller turbidity currents. Canyon-flushing associated with surge-type currents initiated by slope failures may produce currents whose final volume may be several times that of the portion of the slope that has failed (e.g. Grand Banks).

Slumping

Sediment that has piled up at the top of the

continental slope A continental margin is the outer edge of continental crust abutting oceanic crust under coastal waters. It is one of the three major zones of the ocean floor, the other two being deep-ocean basins and mid-ocean ridges. The continental margin ...

, particularly at the heads of submarine canyons can create turbidity current due to overloading, thus consequent

and sliding.

Convective sedimentation beneath river plumes

A buoyant sediment-laden river plume can induce a secondary turbidity current on the ocean floor by the process of convective sedimentation. Sediment in the initially buoyant hypopycnal flow accumulates at the base of the surface flow, so that the dense lower boundary become unstable. The resulting convective sedimentation leads to a rapid vertical transfer of material to the sloping lake or ocean bed, potentially forming a secondary turbidity current. The vertical speed of the convective plumes can be much greater than the Stokes settling velocity of an individual particle of sediment. Most examples of this process have been made in the laboratory, but possible observational evidence of a secondary turbidity current was made in Howe Sound, British Columbia, where a turbidity current was periodically observed on the delta of the Squamish River. As the vast majority of sediment laden rivers are less dense than the ocean, rivers cannot readily form plunging hyperpycnal flows. Hence convective sedimentation is an important possible initiation mechanism for turbidity currents.

Effect on ocean floor

Large and fast-moving turbidity currents can

incise Incision may refer to: * Cutting, the separation of an object, into two or more portions, through the application of an acutely directed force * A type of open wound caused by a clean, sharp-edged object such as a knife, razor, or glass splinter * ...

and

erode Erode () is a city in the Indian state of Tamil Nadu. Erode is the seventh largest urban agglomeration in the state, after Chennai, Coimbatore, Madurai, Tiruchirapalli, Tiruppur and Salem. It is also the administrative headquarters of the E ...

continental margins and cause damage to artificial structures such as telecommunication cables on the seafloor. Understanding where turbidity currents flow on the ocean floor can help to decrease the amount of damage to telecommunication cables by avoiding these areas or

reinforcing In behavioral psychology, reinforcement is a consequence applied that will strengthen an organism's future behavior whenever that behavior is preceded by a specific antecedent stimulus. This strengthening effect may be measured as a higher freq ...

the cables in vulnerable areas. When turbidity currents interact with other currents, such as contour currents, they can change their direction. This ultimately shifts submarine canyons and sediment deposition locations. One example of this is located in the western part of the

Gulf of Cadiz A gulf is a large inlet from the ocean into the landmass, typically with a narrower opening than a bay, but that is not observable in all geographic areas so named. The term gulf was traditionally used for large highly-indented navigable bodie ...

, where the Mediterranean outflow water (MOW) current strongly influences turbidity currents, ultimately causing shifting of valleys and canyons in the direction of the MOW flow. This changes the erosion and depositional zones, ultimately changing the ocean floor topography.

Deposits

When the energy of a turbidity current lowers, its ability to keep suspended sediment decreases, thus sediment deposition occurs. These deposits are called

turbidites A turbidite is the geologic deposit of a turbidity current, which is a type of amalgamation of fluidal and sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean. Sequencing Turbidites were ...

. Turbidity currents are rarely seen in nature, thus turbidites can be used to determine turbidity current characteristics. Some examples:

grain A grain is a small, hard, dry fruit (caryopsis) – with or without an attached hull layer – harvested for human or animal consumption. A grain crop is a grain-producing plant. The two main types of commercial grain crops are cereals and legum ...

size can give indication of current velocity, grain

lithology The lithology of a rock unit is a description of its physical characteristics visible at outcrop, in hand or core samples, or with low magnification microscopy. Physical characteristics include colour, texture, grain size, and composition. Lit ...

and the use of

foraminifera Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists characterized by streaming granular Ectoplasm (cell biology), ectoplasm for catching food and ot ...

for determining origins, grain distribution shows flow dynamics over time and sediment thickness indicates sediment load and longevity. Turbidites are commonly used in the understanding of past turbidity currents, for example, the Peru-Chile Trench off Southern Central

Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...

(36°S–39°S) contains numerous turbidite layers that were cored and analysed.Völker, D., Reichel, T., Wiedicke, M. & Heubeck, C. 2008, "Turbidites deposited on Southern Central Chilean seamounts: Evidence for energetic turbidity currents", Marine Geology, vol. 251, no. 1–2, pp. 15–31 From these turbidites the predicted history of turbidity currents in this area was determined, increasing the overall understanding of these currents.

Antidune deposits

Some of the largest

antidunes An antidune is a bedform found in fluvial and other channeled environments. Antidunes occur in supercritical flow, meaning that the Froude number is greater than 1.0 or the flow velocity exceeds the wave velocity; this is also known as upper flow ...

on Earth are formed by turbidity currents. One observed sediment-wave field is located on the lower continental slope off

Guyana Guyana ( or ), officially the Cooperative Republic of Guyana, is a country on the northern mainland of South America. Guyana is an indigenous word which means "Land of Many Waters". The capital city is Georgetown. Guyana is bordered by the ...

, South America.Ercilla, G., Alonso, B., Wynn, R.B. & Baraza, J. 2002, "Turbidity current sediment waves on irregular slopes: Observations from the Orinoco sediment-wave field", Marine Geology, vol. 192, no. 1–3, pp. 171–187. This sediment-wave field covers an area of at least 29 000 km² at a water depth of 4400–4825 meters. These antidunes have

wavelengths In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tro ...

of 110–2600 m and

wave height In fluid dynamics, the wave height of a surface wave is the difference between the elevations of a crest and a neighboring trough. ''Wave height'' is a term used by mariners, as well as in coastal, ocean and naval engineering. At sea, the term ' ...

s of 1–15 m. Turbidity currents responsible for wave generation are interpreted as originating from slope failures on the adjacent

Venezuela Venezuela (; ), officially the Bolivarian Republic of Venezuela ( es, link=no, República Bolivariana de Venezuela), is a country on the northern coast of South America, consisting of a continental landmass and many islands and islets in th ...

and

Suriname Suriname (; srn, Sranankondre or ), officially the Republic of Suriname ( nl, Republiek Suriname , srn, Ripolik fu Sranan), is a country on the northeastern Atlantic coast of South America. It is bordered by the Atlantic Ocean to the north ...

continental margins. Simple numerical modelling has been enabled to determine turbidity current flow characteristics across the sediment waves to be estimated: internal

Froude number In continuum mechanics, the Froude number (, after William Froude, ) is a dimensionless number defined as the ratio of the flow inertia to the external field (the latter in many applications simply due to gravity). The Froude number is based on t ...

= 0.7–1.1, flow thickness = 24–645 m, and flow velocity = 31–82 cm·s⁻¹. Generally, on lower gradients beyond minor breaks of slope, flow thickness increases and flow velocity decreases, leading to an increase in wavelength and a decrease in height.

Reversing buoyancy

The behaviour of turbidity currents with

buoyant Buoyancy (), or upthrust, is an upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the pr ...

fluid (such as currents with warm, fresh or

brackish Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuari ...

interstitial water entering the sea) has been investigated to find that the front speed decreases more rapidly than that of currents with the same density as the ambient fluid.Hürzeler, B.E., Imberger, J. & Ivey, G.N. 1996 Dynamics of turbidity current with reversing buoyancy. J. Hydraul. Eng., 122, 230–236. These turbidity currents ultimately come to a halt as sedimentation results in a reversal of buoyancy, and the current lifts off, the point of lift-off remaining constant for a constant discharge. The lofted fluid carries fine sediment with it, forming a plume that rises to a level of neutral buoyancy (if in a

stratified Stratification may refer to: Mathematics * Stratification (mathematics), any consistent assignment of numbers to predicate symbols * Data stratification in statistics Earth sciences * Stable and unstable stratification * Stratification, or st ...

environment) or to the water surface, and spreads out. Sediment falling from the plume produces a widespread fall-out deposit, termed hemiturbidite
Experimental turbidity currents
and field observations suggest that the shape of the lobe deposit formed by a lofting plume is narrower than for a similar non-lofting plume

Prediction

Prediction A prediction (Latin ''præ-'', "before," and ''dicere'', "to say"), or forecast, is a statement about a future event or data. They are often, but not always, based upon experience or knowledge. There is no universal agreement about the exact ...

erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is distin ...

by turbidity currents, and of the distribution of turbidite deposits, such as their extent, thickness and grain size distribution, requires an understanding of the mechanisms of

sediment transport Sediment transport is the movement of solid particles (sediment), typically due to a combination of gravity acting on the sediment, and/or the movement of the fluid in which the sediment is entrained. Sediment transport occurs in natural system ...

and deposition, which in turn depends on the

fluid dynamics In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids— liquids and gases. It has several subdisciplines, including ''aerodynamics'' (the study of air and other gases in motion) an ...

of the currents. The extreme complexity of most turbidite systems and beds has promoted the development of quantitative models of turbidity current behaviour inferred solely from their deposits. Small-scale laboratory experiments therefore offer one of the best means of studying their dynamics. Mathematical models can also provide significant insights into current dynamics. In the long term, numerical techniques are most likely the best hope of understanding and predicting three-dimensional turbidity current processes and deposits. In most cases, there are more variables than governing

equations In mathematics, an equation is a formula that expresses the equality of two expressions, by connecting them with the equals sign . The word ''equation'' and its cognates in other languages may have subtly different meanings; for example, in F ...

, and the models rely upon simplifying assumptions in order to achieve a result. The accuracy of the individual models thus depends upon the validity and choice of the assumptions made. Experimental results provide a means of constraining some of these variables as well as providing a test for such models. Physical data from field observations, or more practical from experiments, are still required in order to test the simplifying assumptions necessary in

mathematical model A mathematical model is a description of a system using mathematical concepts and language. The process of developing a mathematical model is termed mathematical modeling. Mathematical models are used in the natural sciences (such as physics, ...

s. Most of what is known about large natural turbidity currents (i.e. those significant in terms of sediment transfer to the deep sea) is inferred from indirect sources, such as submarine cable breaks and heights of deposits above submarine valley floors. Although during the 2003 Tokachi-oki earthquake a large turbidity current was observed by the cabled observatory which provided direct observations, which is rarely achieved.

Oil exploration

Oil and gas companies are also interested in turbidity currents because the currents deposit

organic matter Organic matter, organic material, or natural organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have c ...

that over

geologic time The geologic time scale, or geological time scale, (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochrono ...

gets buried, compressed and transformed into

hydrocarbons In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ex ...

. The use of numerical modelling and flumes are commonly used to help understand these questions.Salles, T., Lopez, S., Eschard, R., Lerat, O., Mulder, T. & Cacas, M.C. 2008, "Turbidity current modelling on geological time scales", Marine Geology, vol. 248, no. 3–4, pp. 127–150. Much of the modelling is used to reproduce the physical processes which govern turbidity current behaviour and deposits.

Modeling approaches

Shallow-water models

The so-called depth-averaged or shallow-water models are initially introduced for compositional gravity currents Rottman, J.W. & Simpson, J.E. 1983, "Gravity currents produced by instantaneous releases of a heavy fluid in a rectangular channel", Journal of Fluid Mechanics, vol. 135, pp. 95–110. and then later extended to turbidity currents.Parker, G., Fukushima, Y. & Pantin, H.M. 1986, "Self-accelerating turbidity currents", Journal of Fluid Mechanics, vol. 171, pp. 145–181.Bonnecaze, R.T., Huppert, H.E. & Lister, J.R. 1993, "Particle-driven gravity currents", Journal of Fluid Mechanics, vol. 250, pp. 339–369. The typical assumptions used along with the shallow-water models are: hydrostatic pressure field, clear fluid is not entrained (or detrained), and particle concentration does not depend on the vertical location. Considering the ease of implementation, these models can typically predict flow characteristic such as front location or front speed in simplified geometries, e.g. rectangular channels, fairly accurately.

Depth-resolved models

With the increase in computational power, depth-resolved models have become a powerful tool to study gravity and turbidity currents. These models, in general, are mainly focused on the solution of the Navier-Stokes equations for the fluid phase. With dilute suspension of particles, a Eulerian approach proved to be accurate to describe the evolution of particles in terms of a continuum particle concentration field. Under these models, no such assumptions as shallow-water models are needed and, therefore, accurate calculations and measurements are performed to study these currents. Measurements such as, pressure field, energy budgets, vertical particle concentration and accurate deposit heights are a few to mention. Both

Direct numerical simulation A direct numerical simulation (DNS)Here the origin of the term ''direct numerical simulation'' (see e.g. p. 385 in ) owes to the fact that, at that time, there were considered to be just two principal ways of getting ''theoretical'' results r ...

(DNS) Necker, F., Hartel, C., Kleiser, L. & Meiburg, E. 2002, "High-resolution simulations of particle-driven gravity currents", International Journal of Multiphase Flow, vol. 28, pp. 279–300. and

Turbulence modeling Turbulence modeling is the construction and use of a mathematical model to predict the effects of turbulence. Turbulent flows are commonplace in most real life scenarios, including the flow of blood through the cardiovascular system, the airflow o ...

Kassem, A. & Imran, J. 2004, "Three-dimensional modeling of density current. II. Flow in sinuous confined and uncontined channels", Journal of Hydraulic Research, vol. 42, number. 6, pp. 591–602. are used to model these currents.

Examples of turbidity currents

* Within minutes after the

occurred off the coast of

Newfoundland Newfoundland and Labrador (; french: Terre-Neuve-et-Labrador; frequently abbreviated as NL) is the easternmost province of Canada, in the country's Atlantic region. The province comprises the island of Newfoundland and the continental region ...

transatlantic telephone cable A transatlantic telecommunications cable is a submarine communications cable connecting one side of the Atlantic Ocean to the other. In the 19th and early 20th centuries, each cable was a single wire. After mid-century, coaxial cable came into use ...

s began breaking sequentially, farther and farther downslope, away from the

epicenter The epicenter, epicentre () or epicentrum in seismology is the point on the Earth's surface directly above a hypocenter or focus, the point where an earthquake or an underground explosion originates. Surface damage Before the instrumental pe ...

. Twelve cables were snapped in a total of 28 places. Exact times and locations were recorded for each break. Investigators suggested that an estimated 60 mile per hour (100 km/h) submarine ''landslide'' or turbidity current of water saturated sediments swept 400 miles (600 km) down the

from the earthquake's epicenter, snapping the cables as it passed. Subsequent research of this event have shown that continental slope sediment failures mostly occurred below 650 meter water depth.Piper, D.J.W., Cochonat, P. & Morrison, M.L. 1999, "The sequence of events around the epicentre of the 1929 Grand Banks earthquake: Initiation of debris flows and turbidity current inferred from sidescan sonar", Sedimentology, vol. 46, no. 1, pp. 79–97. The

that occurred in shallow waters (5–25 meters) passed down slope into turbidity currents that evolved ignitively. The turbidity currents had sustained flow for many hours due to the delayed retrogressive failure and transformation of

debris flow Debris flows are geological phenomena in which water-laden masses of soil and fragmented rock rush down mountainsides, funnel into stream channels, entrain objects in their paths, and form thick, muddy deposits on valley floors. They generally ...

s into turbidity currents through hydraulic jumps. *The

Cascadia subduction zone The Cascadia subduction zone is a convergent plate boundary that stretches from northern Vancouver Island in Canada to Northern California in the United States. It is a very long, sloping subduction zone where the Explorer, Juan de Fuca, and ...

, off the northwestern coast of North America, has a record of earthquake triggered turbiditesGoldfinger, C., Nelson, C.H., Morey, A., Johnson, J.E., Gutierrez-Pastor, J., Eriksson, A.T., Karabanov, E., Patton, J., Gracia, E., Enkin, R., Dallimore, A., Dunhill, G., and Vallier, T., 2011, Turbidite Event History: Methods and Implications for Holocene Paleoseismicity of the Cascadia Subduction Zone, USGS Professional Paper 1661-F, Reston, VA, U.S. Geological Survey, 332 p, 64 Figures. that is well-correlated to other evidence of earthquakes recorded in coastal bays and lakes during the Holocene. Forty–one

Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togethe ...

turbidity currents have been correlated along all or part of the approximately 1000 km long plate boundary stretching from northern California to mid-Vancouver island. The correlations are based on radiocarbon ages and subsurface stratigraphic methods. The inferred recurrence interval of Cascadia great earthquakes is approximately 500 years along the northern margin, and approximately 240 years along the southern margin. *

Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia, at the junction of the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the nort ...

is a hot spot for submarine turbidity currents as there are large amounts of sediment suspended in rivers, and it is seismically active, thus large accumulation of seafloor sediments and earthquake triggering.Hsu, S.-., Kuo, J., Lo, C.-., Tsai, C.-., Doo, W.-., Ku, C.-. & Sibuet, J.-. 2008, "Turbidity currents, submarine landslides and the 2006 Pingtung earthquake off SW Taiwan", Terrestrial, Atmospheric and Oceanic Sciences, vol. 19, no. 6, pp. 767–772. During the

2006 Pingtung earthquake The 2006 Hengchun earthquakes occurred on December 26 at 20:26 and 20:34 local time off the southwest coast of Taiwan in the Luzon Strait, which connects the South China Sea with the Philippine Sea. The International Seismological Centre measure ...

off SW Taiwan, eleven submarine cables across the Kaoping canyon and Manila Trench were broken in sequence from 1500 to 4000 m deep, as a consequence of the associated turbidity currents. From the timing of each cable break the velocity of the current was determined to have a positive relationship with

bathymetric Bathymetry (; ) is the study of underwater depth of ocean floors (''seabed topography''), lake floors, or river floors. In other words, bathymetry is the underwater equivalent to hypsometry or topography. The first recorded evidence of water de ...

slope. Current velocities were on the steepest slopes and on the shallowest slopes. *One of the earliest observations of a turbidity currents was by

François-Alphonse Forel François-Alphonse Forel (February 2, 1841 – August 7, 1912) was a Swiss physician and scientist who pioneered the study of lakes, and is thus considered the founder, and the Father of limnology.Prof. F. A. Forel. Nature 89, 638–639 (1912). ...

. In the late 1800s he make detailed observations of the plunging of the Rhône river into Lake Geneva at Port Valais. These papers were possibly the earliest identification of a turbidity current and he discussed how the submarine channel formed from the delta. In this freshwater lake, it is primarily the cold water that leads to plunging of the inflow. The sediment load by itself is generally not high enough to overcome the summer

thermal stratification Lake stratification is the tendency of lakes to form separate and distinct thermal layers during warm weather. Typically stratified lakes show three distinct layers, the Epilimnion comprising the top warm layer, the thermocline (or Metalimnion): ...

Lake Geneva , image = Lake Geneva by Sentinel-2.jpg , caption = Satellite image , image_bathymetry = , caption_bathymetry = , location = Switzerland, France , coords = , lake_type = Glacial lak ...

. *The longest turbidity current ever recorded occurred in January 2020 and flowed for through the Congo Canyon over the course of two days, damaging two submarine communications cables. The current was a result of sediment deposited by the 2019–2020 Congo River floods.

References

External links

Turbidity current in motion

Depth-resolved simulation of turbidity currents
{{Authority control Sedimentology Fluid dynamics Ocean currents he:התנזלות קרקע#זרמי עכירות