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What Are the Effects of Underwater Landslides?

Underwater landslides -- also called submarine landslides -- are landslides that happen on a slope under the surface of the water. Far from being a flat, static plain, the ocean floor is a dynamic and restless place, subject to change and movement, some of it sudden and massive. Effects of this sometimes never reach the surface, so the existence of this phenomenon has only recently been the subject of focused research. Recent discoveries of massive seafloor changes have been documented by side-scan sonar, but research is still in its infancy.

Causes of Underwater Landslides
- There are several things that can cause underwater landslides. One of the most common are earthquakes. The slipping of the crust and the shaking that results can cause the wet substrate to break apart and slide downhill. Sediment loading is another cause. This happens when the substrate just gets too heavy and collapses. Another can be sea level change. Water is heavy, and changes in water pressure can unbalance the slope. Gas hydrates trapped underneath the sediment can also cause landslides if the pressure inside gets too high, or if changes in water pressure unleash them.
Tsunamis
- A lot of the time, underwater landslides will go completely unnoticed on the surface, but the really big ones can trigger tsunamis. This happens because the sudden movement of sediment displaces massive amounts of water, creating a series of large waves. These massive water movements happen for two reasons -- either from big changes on the sea floor, or giant above-ground landslides that fall into the water. Although changes on the sea floor don't have to involve submarine landslides, they frequently do, and the tsunamis that result can be devastating to people living on a coastline, as well as the shoreline ecosystem.
Underwater Infrastructure
- Underwater landslides can also have an impact on submarine infrastructure. Communication cables crisscross the ocean floor, and movement of the ocean floor can break them. The resulting water movement, especially if it produces a tsunami wave, can also break cables. Deep-water oil rigs also run risks from underwater slides. Slides happen most on steep slopes where sediments are deposited at an increased rate, and a lot of the time, oil rigs have to drill in these areas. Although they are built to withstand smaller slides, really big ones have destroyed entire rigs.
The Abyssal Plain
- The ecology of the deep sea floor isn't well understood, but enough is known about the abyssal plain to be able to say that it is the flattest place on Earth. Part of the reason for this is due to underwater landslides. The actual ocean floor is rock, mostly basalt, and it is uneven, but sediments from landslides have blanketed the sea floor and made it a vast, flat plain. The slides kick up sediments which are carried by deep ocean currents and deposited in the abyssal plain. It is thought that this has an effect on global temperatures, although exactly how is not understood.

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