Through earthquakes and sea level rise, climate change increases tsunami risks

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The most common cause of tsunamis is earthquakes. But 15% of tsunamis are caused by volcanoes or landslides. The effects of climate change, such as rising sea levels, the collapse of ice shelves, and increased volcanic activity are associated with the increased risk of a tsunami. Mitigation strategies, such as tsunami projection models and building codes for vulnerable infrastructure, are needed to improve preparedness.

The massive eruption of Tonga’s underwater volcano, Hong Tonga Hongga Hapai, triggered a tsunami that reached countries across the Pacific Rim, even causing a catastrophic oil spill along 21 beaches in Peru.

In Tonga, waves about 2 meters high were recorded before the sea level measurement failed, and waves up to 15 meters high hit the western coasts of the Tongatapu Islands, Iowa and Hapai Islands. Volcanic activity can continue for weeks or months, but it is difficult to predict if or when there will be another strong eruption.

The relationship between climate change and tsunamis

Most tsunamis are caused by earthquakes, but a large percentage (about 15%) are caused by landslides or volcanoes. Some of them may be interrelated – for example, landslide tsunamis are often caused by earthquakes or volcanic eruptions.

But does climate change play a role, too? As the planet warms, we are seeing more frequent and severe storms and hurricanes, melting glaciers and ice caps, and rising sea levels. However, climate change affects not only the atmosphere and oceans, but also the Earth’s crust.

Climate-related geological changes can increase the occurrence of earthquakes and volcanic eruptions, which in turn can exacerbate the risk of a tsunami. Here are five ways this can happen.

1. Sea level rise

If greenhouse gas emissions continue at high rates, the global mean sea level is expected to rise between 60 cm and 1.1 metres. Nearly two-thirds of the world’s cities with a population of over five million are at risk.

Sea-level rise not only makes coastal communities more vulnerable to storm floods, but also causes tsunamis. Even modest sea-level rises will greatly increase the frequency and intensity of flooding when a tsunami occurs, as the tsunami can travel inland.

For example, a 2018 study showed that a rise of just 50 centimeters would double the frequency of flooding caused by a tsunami in Macau, China. This means that in the future, smaller tsunamis could have the same effect as larger tsunamis today.

2. Landslides

Climate warming can increase the risks of subsea (underwater) and atmospheric (above land) landslides, and thus increase local tsunami risks.

Melting permafrost (frozen soil) at high latitudes reduces soil stability, making it more susceptible to erosion and landslides. Heavy rainfall can trigger landslides as well, as storms become more frequent under climate change.

Tsunamis can be generated on impact when a landslide enters the water, or when water is carried by a rapid underwater landslide.

In general, tsunamis from landslides or rockfalls dissipate quickly and do not travel as far as earthquake tsunamis, but they still result in massive waves locally.

In Alaska, United States, receding glaciers and melting permafrost have revealed precarious slopes. In 2015, this melting caused a landslide that sent 180 million tons of rock into a narrow strait, triggering a 193-meter tsunami – one of the highest rates ever recorded worldwide.

Other areas at risk include northwest British Columbia in Canada, and Barry Arm in Alaska, where an unstable mountain slope at Barry’s finger glacier is likely to fail and trigger severe tsunamis in the next 20 years.

3. Icebergs crushing and ice shelves collapse

Global warming is speeding up the rate at which icebergs are born – when chunks of ice fall into the ocean.

Studies predict that large ice shelves, such as the Thwaites Glacier in Antarctica, are likely to collapse in the next five to 10 years. Likewise, the Greenland ice sheet is shrinking and retreating at an alarming rate.

While much of the current research focus is on sea level hazards associated with melting and collapsing glaciers and ice sheets, there is also a tsunami risk from the process of calving and collapse.

Wandering icebergs can cause subsea landslides and tsunamis thousands of kilometers from the iceberg’s original source, where they collide with unstable sediments on the sea floor.

4. Volcanic activity of melting ice

About 12,000 years ago, the last glacial period (“Ice Age”) ended and melting ice led to a massive increase in volcanic activity.

The relationship between climate warming and more volcanic eruptions is not yet constrained or well understood. But it may be related to changes in pressure on the Earth’s crust as ice weight is removed, and a phenomenon called “static isothermal rebound” – a long-term rise of the Earth in response to ice sheet removal.

5. Increased earthquakes

There are a number of ways climate change can increase the frequency of earthquakes, and thus increase tsunami risks.

First, the weight of the ice sheets may dampen fault movement and earthquakes. When the ice melts, the static isometric recoil (ground rise) is accompanied by increased seismicity and fault movement as the crust adjusts to the weight loss.

We may have already seen this in Alaska, where melting glaciers reduced the stability of the faults, causing many small earthquakes and possibly the 7.2 magnitude St. Elias earthquake in 1979.

Another factor is the low air pressure associated with storms and hurricanes, which studies have also shown can trigger earthquakes in areas where the Earth’s crust is already under stress. Even relatively small changes in air pressure can lead to fault movements, an analysis of earthquakes between 2002 and 2007 identified in eastern Taiwan.

Prepare for the effects of climate change

Many climate change mitigation strategies must also include elements to improve tsunami preparedness.

This could include incorporating projected sea-level rise into tsunami forecast models, and into building codes for infrastructure along vulnerable coasts.

Researchers can also ensure that scientific models of climate impacts include the projected increase in earthquakes, landslides, and volcanic activity, and the increased tsunami risk that this will create.

This article was originally published on the World Economic Forum. You can view it here.

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