Perth, January 24
The huge eruption of Tonga’s submarine volcano, Hunga Tonga-Hunga Ha’apai, triggered a tsunami that reached countries around the Pacific Rim, even causing a disastrous oil spill along 21 beaches in Peru.
In Tonga, waves about 2 meters high were recorded before the sea level gauge failed, and waves of up to 15m hit the west coasts of Tongatapu, ‘Eua and Ha’apai. Volcanic activity could continue for weeks or months, but it is difficult to predict if or when there will be another such powerful eruption.
Most tsunamis are caused by earthquakes, but a significant percentage (about 15%) are caused by landslides or volcanoes. Some of them may be related – for example, landslide tsunamis are often triggered by earthquakes or volcanic eruptions.
But does climate change also play a role? As the planet warms, we are seeing more frequent and intense storms and cyclones, melting glaciers and ice caps, and rising sea levels. However, climate change does not affect not just the atmosphere and the oceans, it also affects the earth’s crust.
Climate-related geological changes can increase the incidence of earthquakes and volcanic eruptions which, in turn, can exacerbate the threat of tsunamis. Here are five ways it can happen.
1. Sea level rise
If greenhouse gas emissions remain at high rates, global mean sea level is expected to rise between 60 centimeters and 1.1 m. Nearly two-thirds of the world’s cities with more than five million inhabitants are at risk.
Sea level rise not only makes coastal communities more vulnerable to flooding from storms, but also to tsunamis. Even a modest rise in sea level will greatly increase the frequency and intensity of flooding when a tsunami occurs, as the tsunami can spread farther inland.
For example, a 2018 study showed that a rise of just 50 centimeters would double the frequency of tsunami-induced flooding in Macau, China. This means that in the future, smaller tsunamis could have the same impact as larger tsunamis today.
A warming climate can increase the risk of submarine (underwater) and airborne (above ground) landslides, thereby increasing the risk of local tsunamis.
The melting of permafrost (frozen ground) at high latitudes decreases the stability of the ground, making it more susceptible to erosion and landslides. More intense rainfall can also trigger landslides, as storms become more frequent with climate change.
Tsunamis can be generated on impact when a landslide enters water or when water is displaced by a fast moving underwater landslide.
In general, tsunami waves generated by landslides or rockfalls dissipate quickly and do not travel as far as tsunamis generated by earthquakes, but they can still locally cause huge waves.
In Alaska, USA, glacial retreat and melting permafrost have exposed unstable slopes. In 2015, this melting caused a landslide that sent 180 million tonnes of rock into a narrow fjord, generating a tsunami reaching 193m high – one of the highest ever recorded in the world.
Other areas at risk include northwestern British Columbia in Canada and the Barry Arm in Alaska, where an unstable mountain slope at the foot of the Barry Glacier could fail and generate a severe tsunami within the next 20 years.
3. Iceberg calving and collapsing ice shelves
Global warming is accelerating the rate of iceberg calving – when chunks of ice fall into the ocean.
Studies predict that large ice shelves, such as the Thwaites Glacier in Antarctica, will likely collapse within the next five to ten years. Similarly, the Greenland ice sheet is thinning and retreating at an alarming rate.
While much of the current research focuses on the sea level risk associated with the melting and collapse of glaciers and ice caps, there is also tsunami risk associated with the calving and breakup process. .
Wandering icebergs can trigger undersea landslides and tsunamis thousands of miles from the iceberg’s original source, as they strike unstable sediments on the seafloor.
4. Volcanic activity due to melting ice
Around 12,000 years ago, the last glacial period (“ice age”) ended and melting ice triggered a dramatic increase in volcanic activity.
The correlation between global warming and more volcanic eruptions is not yet well defined or understood. But it may be related to stress changes on the earth’s crust as the weight of the ice is removed, and to a phenomenon called “isostatic rebound” – the long-term uplift of land in response to retreating ice sheets.
If this correlation holds for the current period of global warming and melting ice at high latitudes, there will be an increased risk of volcanic eruptions and associated hazards, including tsunamis.
5. Increase in earthquakes
Climate change can increase the frequency of earthquakes and therefore the risk of tsunamis in several ways.
First, the weight of ice caps can suppress fault movement and earthquakes. When the ice melts, isostatic rebound (lifting of the land) is accompanied by increased earthquakes and faulting movement as the crust adapts to the loss of weight.
We may have seen it before in Alaska, where melting glaciers have reduced fault stability, causing many small earthquakes and possibly the magnitude 7.2 St Elias earthquake of 1979.
Another factor is low atmospheric pressure associated with storms and typhoons, which studies have found can also trigger earthquakes in areas where the earth’s crust is already under stress. Even relatively small changes in atmospheric pressure can trigger faulting movements, as identified in an analysis of earthquakes between 2002 and 2007 in eastern Taiwan.
So how can we prepare?
Many climate change mitigation strategies should also include elements to improve tsunami preparedness.
This could include incorporating predicted sea level rise into tsunami prediction models and into building codes for infrastructure along vulnerable coastlines.
Researchers can also ensure that scientific models of climate impacts include the projected increase in earthquakes, landslides and volcanic activity, as well as the increased risk of tsunamis this will cause. (The conversation)