What Are Underwater Landslides, and How Dangerous Are They?

By Heather Joseph
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Photo Courtesy: @mougrapher/Unsplash

Landslides on land are natural and relatively well-known phenomena that pose significant risks to surrounding areas and structures. We generally understand them, and they often occur in mountainous areas, especially after heavy rains. Landslides can also occur after significant seismic activity, like earthquakes.

Recently, scientists have found evidence to support the widespread existence of underwater landslides, also known as submarine landslides. While these disruptions don't pose as many immediate risks to human life as their terrestrial counterparts, underwater landslides can still be quite dangerous.

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Shifting Faults

Geologically speaking, the world is never still. In addition to constantly revolving around the sun, which itself is traveling through the Milky Way, Earth has a surface that is in constant motion. That's because the upper layer of the Earth's crust is composed of several large pieces, known as tectonic plates.

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Photo Courtesy: NASA/JPL-Caltech

These plates collide and form mountains, move apart to form rifts and canyons, and sometimes even push each other underground. Areas where these plates touch are called fault lines, and fault lines are famous hot spots for seismic activity, including earthquakes. In fact, when plates touch, it's rare for them not to produce some sort of reaction.

While many people assume that fault lines exist primarily above ground, that simply isn’t true. The Mid-Atlantic Ridge, for example, is a massive gap between plates that grows a little more with every passing year as the plates continue to shift in opposing directions. When these shifts occur rapidly — or with a lot of power — they can generate massive amounts of energy.

Triggering Underwater Landslides

Coastal cities and offshore oil rigs have the most risk of suffering damage as a result of shifting underwater tectonic plates. Underwater landslides play a huge part, as submarine earthquakes and volcanic eruptions alone don't tend to cause tsunamis or massive destruction.

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Photo Courtesy: @yannispap/Unsplash

However, when these earthquakes and eruptions trigger submarine landslides, the displaced earth and water can lead to gigantic waves that reach out in either direction, building momentum before reaching the shoreline. Those waves could also devastate an offshore platform. Because underwater landslides can trigger tsunamis and cause billions of dollars in damage, it's important to learn more about them and be aware of any activity in an area.

Dangerous Offshore Conditions

Offshore rigs are often located more than 100 miles from any shoreline, making emergency situations exceptionally hazardous. While rigs often have medical personnel on board to help and may even have a helicopter for expedited hospital transfers, natural disasters pose a more challenging type of threat.

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Photo Courtesy: PA3 Robert M. Reed/Wikimedia Commons

A tsunami caused by an underwater landslide can't be easily or quickly predicted, leaving those on board an offshore rig with very little time to prepare. Not only do they potentially have to contend with gigantic waves, but they could also be faced with a crumbling ocean floor. If the supporting floor beneath an oil rig begins to shift or collapse due to an underwater landslide, it’s impossible to predict how much structural damage could occur. In a worst case scenario, it could be possible to lose an entire offshore rig due to an underwater landslide. If the entire supporting ocean floor caved in or shifted a great distance, the results could be catastrophic for the humans on board.

Fortunately, most rigs are built far from underwater chasms or faults. In addition, engineers perform months or even years of oceanic testing before approving a site for construction. Unfortunately, when it comes to landslide-caused tsunamis, there's far less that people can do to protect themselves. This is especially true of those who live in coastal, low-lying areas.

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A Threat to Coastlines

Because the world is full of water and covered in shifting faults, submarine landslides are a fairly common occurrence. So, why don’t you hear about them on the news all the time? They can be particularly difficult to detect or track because the ocean is immensely vast, and most landslides only displace a small amount of sediment and don’t cause major catastrophes. Still, a massive underwater landslide that occurs fairly close to land could result in a surprising — but fortunately short-lived — change in tides.

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Photo Courtesy: Kommunikasjonsavdelingen NTFK/Wikimedia Commons

These tsunami-like conditions would most likely develop very quickly, possibly causing a significant amount of damage before anyone could react. That's part of what makes these natural phenomena so dangerous. Fortunately, most don't generate city-destroying waves; they merely form sudden riptides or tide rushes, resulting in dangerous conditions for beachgoers, swimmers, surfers and those who live directly on the coast. It's important to focus on developing technology that helps record and register these underwater events to help regional warning agencies protect the local population in the event of dangerous tides or a full-blown, deadly tsunami.

Submarine landslides may pose a threat to offshore oil rigs and coastlines, but a deeper ocean floor may help compensate slightly for rising ocean levels. We may be experiencing a heightened number of underwater landslides as a result of brimming oceans due to the effects of climate change. There could also be other factors in play, including the Earth’s core and mantle health and activity. Landslides are perfectly natural, and the underwater variety has been occurring for as long as the Earth has had oceans and steep cliffs, and that trend is unlikely to change as long as the planet has a mobile, shifting crust.

An Ever-Changing Earth

There are some things about our planet that we can change or manipulate — for the better and for the worse — but tectonic plates are far beyond our control. As long as these plates continue to shift, change and collide, different types of natural disasters will occur as a result. However, by educating ourselves on why underwater landslides occur, which areas they are likely to affect and possible early detection techniques, we can try to offset the financial and biological toll of catastrophic events. Fortunately, a lot of excellent research is underway to study the short-term and long-term effects of underwater landslides.

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Photo Courtesy: Phoenix7777/Wikimedia Commons

Current progress indicates we will have access to more information about these geologic events in the future, including possible advanced technology capable of detecting when and where a landslide could occur. However, considering we have only mapped about 5% of the ocean floor so far, it may still take quite some time to fully understand our incredible blue planet and its shifting ocean floors.