Turbidity currents are a fascinating and significant phenomenon occurring beneath the ocean’s surface.
In this article, we’ll explore what these currents are, their causes, and the effects they have on aquatic environments.
By understanding turbidity currents, we gain valuable insights into the geological and ecological processes shaping our planet.
We encounter turbidity currents as underwater, rapidly moving flows of sediment-laden water, often found moving down slopes.
These currents result from an increase in density caused by high concentrations of sediment in water, leading to powerful flows capable of reshaping the seafloor.
Common triggers for turbidity currents include earthquakes, volcanic activities, collapsing slopes, and other geological disturbances.
As turbidity is a measure of a liquid’s relative clarity, turbidity currents play a crucial role in determining water quality.
The intensity of scattered light within a water sample is directly proportional to its turbidity.
Consequently, increased turbidity caused by movement of sediment affects marine ecosystems and can potentially impact human activities, such as water treatment and coastal engineering projects.
Table of Contents
What is a Turbidity Current?
Turbidity currents are underwater currents where sediment is suspended by fluid turbulence.
These currents typically result from geological disturbances, such as earthquakes, collapsing slopes or tsunamis.
As sediment gathers in water, it increases its density, triggering a rapid downhill flow known as a turbidity current.
Due to the high density of suspended sediment, turbidity currents are capable of traveling at great speeds, even reaching depths of several kilometers.
They play a key role in shaping the physical structure of the seafloor as they move along the continental slope, and across the upper parts of submarine canyons.
These currents form and dissipate quickly, making them transient phenomena. Their main triggers include:
- Volcanic activities
- Other sudden geological events
As turbidity currents move downslope, they erode material from canyons, contributing significantly to the formation and reshaping of submarine landscapes. While their occurrence is infrequent, their impact on seafloor morphology and sediment distribution is substantial and long-lasting.
Formation and Causes
Sediment gravity flows are one of the main causes of turbidity currents. They occur when sediments become saturated with water, resulting in a fluid with an increased density that flows downhill due to gravity.
When sediment piles up on continental slopes, particularly at the heads of submarine canyons, it can become unstable and trigger these flows.
These flows can be formed by sediment erosion, slumps, debris flows, and plunging sediment-rich river flows into the ocean, also known as hyperpycnal flows or plumes.
Earthquakes can also play a significant role in the formation of turbidity currents.
When an earthquake occurs, the shaking can destabilize underwater slopes and trigger the release of sediment into the water column.
The increased density of the water-sediment mixture produces a turbidity current, which can rapidly descend the slope, altering the seafloor’s physical shape and often transporting large volumes of sediment over vast distances.
Underwater landslides are another common cause of turbidity currents. These often result from geological disturbances, such as earthquakes or volcanic activities, which can weaken the sediment layers on underwater slopes.
When the sediment layers collapse, they release an enormous amount of sediment into the water column, creating turbidity currents.
These currents can be extremely powerful and impact the physical shape of the seafloor, potentially causing significant damage to underwater structures and ecosystems.
Characteristics and Components
Turbidity currents are composed of a mixture of water and sediments, leading to an increased density compared to the surrounding water.
The density of a turbidity current is mainly determined by the concentration and type of sediments present.
As the sediments in the current settle, the overall density of the current decreases, leading to a decrease in its flow speed.
The flow speed of turbidity currents can be quite high, as these currents are driven by gravity due to the increased density of the mixture.
As the current moves downslope, it can reach speeds of up to 100 kilometers per hour.
However, the speed of these currents tends to decrease as sediments settle and the density of the current diminishes.
The suspended sediments in turbidity currents primarily include sand, mud, and other debris.
The concentration and type of sediments in the current play a significant role in determining the overall properties and behavior of the turbidity current. For instance:
- Higher sediment concentrations lead to increased density and faster flow speeds.
- Coarser sediments, such as sand, are more likely to cause erosion during a turbidity current than finer sediments like mud.
It is important to note that the sediment composition within a turbidity current may change as the current moves downslope, altering its characteristics as it travels.
Types of Turbidity Currents
Broadly speaking, turbidity currents can be categorized into two main types: high-density and low-density turbidity currents.
High-density turbidity currents, as the name suggests, are characterized by a higher concentration of sediment within the water.
These currents are typically fast-moving and have a greater impact on the seafloor.
They are caused by major events such as earthquakes, underwater landslides, or collapsing slopes.
The density of the turbulent sediment-loaded water drives these currents, allowing them to travel at speeds ranging from 10 to 30 km/h on the seafloor.
High-density currents can travel for tens to hundreds of kilometers before dissipating.
Low-density turbidity currents, in contrast, have a lower sediment concentration within the water. They are typically caused by less dramatic events or smaller-scale geological disturbances.
These currents move at a slower pace and can still have an impact on the seafloor, though not as significant as their high-density counterparts.
The primary distinction between high-density and low-density currents lies in their velocity and sediment concentration.
In both cases, turbidity currents can alter the physical shape of the seafloor and create distinct geological features over time.
Importance and Effects
Turbidity currents play a crucial role in sediment transport processes as they move significant amounts of sediment from shallow water settings to deep ocean.
These currents are responsible for redistributing sediments across continental margins and contribute to the overall geomorphological context of the ocean floor.
They can also affect the nutrient availability in the ocean, which in turn impacts the marine ecosystem.
Submarine Canyon Formation
Submarine canyons are prominent geomorphological features found on the continental slope that cut through the continental shelf.
Turbidity currents are one of the major driving forces behind the formation of these canyons.
As turbidity currents travel downward, they erode the seafloor, creating channels and canyons.
Submarine canyons help store sediments that can be later transported to various regions of the ocean.
Impact on Marine Ecosystems
Turbidity currents directly impact marine ecosystems as they can cause disturbances in the water column, affecting the distribution and productivity of marine species.
For instance, high levels of turbidity can obstruct light penetration, thereby limiting the growth of photosynthetic organisms, which form the base of the food chain.
Additionally, turbidity currents can transport pathogens, which may lead to waterborne disease outbreaks, posing a threat to both human health and marine life.