In the past 100 years, 58 tsunamis have claimed more than 260,000 lives combined. The 2004 Indian Ocean tsunami, which ranks as one of the deadliest natural disasters in history, claimed around 230,000 of those lives. According to research facilitated by the UN, this combined body count surpasses any other natural hazard.

What is a tsunami?

A tsunami is a series of extremely long waves, sometimes reaching heights of over 100 feet. They are caused by large volumes of water being displaced within an ocean, often as a result of large undersea earthquakes at tectonic plate boundaries. Tsunamis can also be caused by coastal landslides, volcanic eruptions and asteroid or meteor strikes.

The speed a tsunami travels depends on the depth of the ocean. In deep oceans, such as the Pacific, they can reach speeds of over 500 miles per hour. At these speeds however, the wave is normally very long and very short, often only a few feet high, and relatively harmless. A tsunami is only dangerous when it approaches land. As it nears the shore, the wave will decrease in length and increase dramatically in height. It slows in speed and crashes over the land, often causing chaos and destruction, billions of pounds in damage, and loss of life.

Early warning systems and risk reduction

Several tsunami warnings systems are in operation around the world. The United States operates two major tsunami warning centres.

The Pacific Tsunami Warning Centre (PTWC) was established in the 1960s. The centre, located in Ewa Beach, Hawaii, monitors seismological and tidal stations throughout the Pacific Basin. It provides an early warning system for potential tsunamis to 46 member states, 25 of whom are official member states who help facilitate the system. These official states make up the International Coordination Group for the Tsunami Warning System in the Pacific.

The National Tsunami Warning Centre (NTWC), also established in the 1960s, provides a tsunami warning system to the US states of California, Oregon, Washington, and the Canadian province of British Columbia. Located in Palmer, Alaska, the centre’s scope was expanded in 2004 to include the Gulf of Mexico coasts, Puerto Rico, the Virgin Islands, and the Atlantic coast of Canada.

Unlike the Pacific, the Indian Ocean did not have a warning system in place prior to the 2004 Indian Ocean tsunami, which claimed over 200,000 lives.

Three weeks after this disaster, international organisations and governments met in the Japanese city of Kobe to discuss how they could prevent a disaster on this scale happening again. The conference resulted in the Hyogo Framework, the first comprehensive global agreement on disaster risk reduction, as well as an agreement to form what would become the Indian Ocean Tsunami Warning and Mitigation System (IOTWMS). The system became active in 2006, and uses a complex system of pressure recorders, tide gauges and sensors located on the seabed to provide enough warning to member states for a planned evacuation.

How much of a threat is a tsunami to the UK?

The threat the UK faces from tsunamis is minimal. The British Isles sits in the middle of the tectonic plate known as Eurasia. The nearest plate boundary is at the mid-Atlantic ridge, where the earthquakes are too small to generate tsunamis.

Despite this, Britain has experienced tsunamis in its history. Scientists have found evidence of a tsunami reaching the north-east coast of England around 8000 years ago. It is thought this was caused by an underwater landslide off the coast of Norway, known as the Storegga slide. This caused a wave that may have been around 20 metres high to crash over the Shetland Islands, before it decreased to around 1 metre in the north-east of England.

Several thousand years after the Storegga slide, Britain once again felt the impact of a tsunami. The 1755 Lisbon earthquake and tsunami left the Portuguese city of Lisbon almost totally destroyed. The effects of this disaster were felt in Mount’s Bay, Cornwall, with residents reporting several large waves crashing over the shore. Modelling has shown that the waves would have taken around 5 hours to reach Britain.

Research today is focused on tsunamis caused by landslides within the ocean, and how big a threat this poses to the UK. The Arctic Research Programme is currently researching the impact of climate change on the likelihood of landslide-tsunamis in the Arctic region. Early research shows signs that climate change occurring in the Arctic could significantly increase this risk of large landslides and tsunamis, which could potentially reach UK shores.

UN’s Sendai Seven campaign

In December 2015, the UN General Assembly designated 5 November as World Tsunami Awareness Day. In 2021, World Tsunami Awareness Day will promote the Sendai Seven Campaign, consisting of seven global targets for measuring progress on reducing disaster risk and loss of life by 2030. The targets take their name from the Japanese city of Sendai, which suffered catastrophic damage in the 2011 Japanese tsunami.

The Sendai Seven Campaign was launched by the UN in 2015 with the tagline “7 targets, 7 years”. The targets are designed to encourage implementation of the Sendai Framework for Disaster Risk Reduction, with the goal of saving lives, reducing disaster losses and improving management of disaster risk.

Each one of the targets is assigned a year. In 2021, the target is to “substantially enhance international cooperation to developing countries through adequate and sustainable support to complement their national actions for implementation of the present framework by 2030”.

Cover image: US Navy photo by Photographer’s Mate 2nd Class Philip A McDaniel from Wikimedia.