What is a megatsunami?

December 14, 2022 | Environment
Megatsunami: a rare and abnormally large tsunami | Photo: Shutterstock

Megatsunamis are a rare yet catastrophic natural event. Here's everything you need to know about the world's biggest wave.

A megatsunami is a huge and destructive ocean wave caused by a large-scale displacement of water.

Megatsunamis are typically caused by earthquakes, major landslides, volcanic eruptions, asteroid and comet impacts, and underwater earthquakes that create a water movement capable of generating a wave with a height of more than 328 feet (100 meters).

In addition, megatsunamis can travel up to 500 miles per hour (800 kilometers per hour) and reach distances of up to thousands of miles from their source.

The result is destructive waves reaching coastal areas on the opposite side of the ocean from their source.

Megatsunamis can also cause significant erosion and can create large bays and inlets in the coastline.

But what is the difference between a megatsunami and a tsunami?

Although there is no scientific definition for it, a megatsunami is an exceptionally colossal wave larger than a regular tsunami.

It could be hundreds or even thousands of feet high and travel across continents while harnessing and gathering energy on the way.

Megatsunami: a wave that can travel up to 500 miles per hour | Photo: Shutterstock

Biggest Megatsunamis

Megatsunamis have been part of Earth's long history, so most of them were not noted down or documented.

However, scientific research recently revealed the tallest walls of water to ever march across the five world oceans at least since 6225 BCE.

Here are some of the most notorious examples of megatsunamis:

Storegga Slides (6225-6170 BCE)

This megatsunami is believed to have been caused by a massive underwater landslide triggered by an earthquake off the coast of Norway.

The resulting wave hit Scotland and the Faroe Islands and is estimated to have been 83 feet (25 meters) high.

It is one of the largest and earliest known megatsunamis.

Minoan Eruption (1600 BCE)

This megatsunami is believed to have been caused by a meteor impact in the Mediterranean Sea and is estimated to have been up to 100 feet (30 meters) high.

It flooded the coastlines of Sicily, Crete, and the Greek mainland and is believed to have destroyed the Minoan civilization.

Jogan (869)

The 869 Jogan earthquake and tsunami was a large-magnitude earthquake and tsunami that struck the region around Sendai, Japan, on July 8, 869.

It was one of the largest earthquakes in recorded Japanese history and is estimated to have had a magnitude of 8.2 and a maximum tsunami wave height of up to 33 feet (10 meters).

The earthquake and tsunami caused extensive damage to the region and resulted in the deaths of an estimated 1,000 to 10,000 people.

Kamchatka (1737)

The Kamchatka earthquake was a magnitude 9.4 megathrust earthquake that struck the northern part of the Kamchatka Peninsula in Russia on October 4, 1737.

It is the largest historically recorded earthquake in the region and is believed to have been the largest earthquake in the world at the time.

It caused a tsunami that was observed across the Pacific Ocean, from Japan to South America.

The Great Lisbon Earthquake (1755)

The Great Lisbon Earthquake, also known as the Lisbon Earthquake, occurred on November 1, 1755, and was one of the most destructive and deadly earthquakes in history.

It had an estimated magnitude of 8.5-9.0 and caused a tsunami that reached the coast of Portugal and Spain and was even recorded as far away as Norway.

The earthquake and subsequent tsunami destroyed Lisbon and other towns along the coast, killing tens of thousands of people and leaving many more homeless.

The city of Lisbon was devastated, with the majority of its buildings either destroyed or severely damaged.

The earthquake and the tsunami also caused massive destruction in the Azores and in Spain, where the death toll was estimated to be in the thousands.

Krakatoa Eruption (1833)

The 1883 eruption of Krakatoa in Indonesia is considered one of the most violent volcanic eruptions in recorded history.

The eruption created a megatsunami, which is a large, destructive wave of water that is much taller than a typical tsunami.

The wave had a maximum height of over 40 meters (130 feet), and it caused massive destruction in the areas near the volcano.

It killed over 36,000 people, destroyed over 165 villages, and caused waves to reach as far as the coast of Africa.

The eruption also caused a loud noise that could be heard up to 3,000 miles (4,800 kilometers) away and created a large dust cloud that blocked out the sun in many parts of the world.

The Newfoundland Tsunami (1929)

The massive wave caused by the collapse of the Grand Banks landslide in Newfoundland in 1929 was one of the largest natural disasters in Canadian history.

It caused a wave of up to 35 meters (115 feet) high to crash ashore along the Burin Peninsula, obliterating communities and killing 28 people.

The megatsunami traveled over the Atlantic Ocean and was even reported in the United Kingdom, more than 2,000 kilometers away from the epicenter.

The collapse of the Grand Banks landslide was caused by an earthquake, which triggered a massive underwater landslide, resulting in the creation of the megatsunami.

The Lituya Bay Megatsunami (1958)

The Lituya Bay Megatsunami was a massive wave that occurred on July 9, 1958, in Lituya Bay, Alaska.

After a magnitude 8.3 earthquake triggered a landslide, an estimated wave of over 1,700 feet (520 meters) rushed through the inlet, destroying trees and homes in its path.

It is the largest wave ever recorded in human history.

The Great Chilean Earthquake and Tsunami (1960)

The Valdivia earthquake, also known as the Great Chilean Earthquake, was one of the most powerful earthquakes ever recorded.

It occurred on May 22, 1960, in the city of Valdivia, Chile, and had a magnitude of 9.5 on the moment magnitude scale.

This earthquake caused massive destruction throughout southern Chile and was followed by a devastating tsunami that caused damage in Chile, Hawaii, Japan, the Philippines, and other parts of the Pacific Rim.

The death toll from the earthquake and resulting waves was estimated to be more than 2,000 people, with 3,000 people injured, 2,000,000 homeless, and damage estimated at more than $500 million.

The Alaska Earthquake and Tsunami (1964)

The Alaska Earthquake and Tsunami was a catastrophic event that occurred on Good Friday, March 27, 1964.

The earthquake, which measured 9.2 on the Richter Scale, was the most powerful earthquake ever recorded in North America and the second strongest in the world at that time.

The resulting tsunami caused extensive damage in Alaska and killed over 130 people in Alaska, British Columbia, and California.

The Hokkaido Earthquake and Tsunami (1993)

The Okushiri earthquake and tsunami was an 8.3 magnitude earthquake that occurred off the coast of the island of Okushiri, Japan, on July 12, 1993.

The earthquake generated a devastating tsunami that killed 199 people and caused extensive damage to the island and its neighboring areas.

The earthquake was the largest to occur in the Japanese Sea since records began in the 19th century.

The Indian Ocean Tsunami (2004)

The Indian Ocean earthquake and tsunami was a series of seismic events that occurred on December 26, 2004.

It was one of the deadliest natural disasters in recorded history, with a death toll estimated to be between 230,000-280,000 people.

The earthquake off the coast of Sumatra, Indonesia, which had a magnitude of 9.1-9.3, was the third-largest ever recorded and triggered a series of devastating tsunamis that struck numerous coastal areas of the Indian Ocean, including Indonesia, Sri Lanka, India, and Thailand.

The earthquake and tsunami caused widespread destruction, with many areas being completely flattened.

In addition to the human casualties, the disaster caused significant economic damage, with estimates of the total cost ranging from US$10 billion to US$50 billion.

In response to the disaster, many countries and international organizations provided assistance in the form of humanitarian aid and reconstruction efforts.

The Sendai Earthquake and Tsunami (2011)

The Tōhoku earthquake and tsunami was a 9.0 magnitude earthquake that occurred off the coast of Japan on March 11, 2011.

It caused a massive tsunami that affected the coastal regions of the Tōhoku region of Japan and caused severe damage and loss of life.

The tsunami also caused a nuclear disaster at the Fukushima Daiichi Nuclear Power Plant.

Potential Dangers and Effects on Coastal Areas

A megatsunami has devastating effects on coastal areas and poses potential dangers to local communities.

Here are the main consequences of the abnormal walls of water:

1. Loss of Life

The power of a megatsunami is so immense that it can result in the loss of countless lives. It can quickly sweep away entire communities, leaving nothing but destruction and death in its wake.

2. Structural Damage

A megatsunami has the potential to cause tremendous amounts of structural damage to buildings, infrastructure, bridges, and other structures. The force of the wave can easily destroy anything in its path, including entire towns and cities.

3. Flooding

The sheer force of a megatsunami can cause massive flooding along coastal regions and even further inland. This flooding can result in the destruction of homes, businesses, and other essential structures, as well as the displacement of people from their homes.

4. Environmental Damage

A megatsunami can cause significant environmental damage by destroying ecosystems, contaminating water supplies, and killing off wildlife. The destruction of coral reefs and other habitats can have a long-lasting impact on the environment.

5. Economic Damage

A megatsunami can cause significant economic damage due to its destruction of infrastructure, property, and resources. In addition, the resulting damage from the flooding and environmental destruction can cause disruptions in trade and commerce, leading to a loss of revenue and jobs.

6. Devastation of Coastal Structures

A megatsunami can cause massive destruction to coastal infrastructures such as buildings, bridges, roads, ports, and other man-made structures. High-energy waves generated by the megatsunami can destroy or significantly damage these structures, resulting in serious economic losses.

7. Coastal Erosion

The powerful waves generated by a megatsunami can cause significant coastal erosion, removing large amounts of sand, land, and sediment. This can be particularly destructive for coastal regions and can destroy beaches and dunes, wetlands, and other habitats.

8. Loss of Wildlife

Megatsunamis can have a devastating effect on local wildlife, as the strong waves can displace and kill marine animals. Additionally, the destruction of coastal habitats can have a negative impact on fish and other aquatic species.

9. Spread of Contaminants

The powerful waves generated by a megatsunami can also spread contaminants, such as oil and sewage, to nearby areas. This can cause further damage to the environment and have a negative impact on the health of local people and wildlife.

Megatsunami: a source of destruction and death | Photo: Shutterstock

Predicting Future Megatsunamis

Predictions for future megatsunamis vary, but most experts agree that they will continue to occur as long as subduction zones remain active.

Areas where tsunamis are most likely to occur in the future include the Pacific Northwest, Hawaii, Alaska, Chile, Japan, and the Caribbean.

Scientists also predict that climate change may cause more extreme weather events, which could trigger bigger, more powerful tsunamis in the future.

It is important to note that predicting future megatsunamis is difficult due to the complexity of plate tectonics and the unpredictability of natural disasters.

Monitoring Technologies

Technologies such as seismic networks and tide gauges are used to monitor the potential for megatsunamis.

Here are some of the most relevant detection systems:

  • GPS receivers. They can track changes in ground elevation which can indicate a tsunami wave;
  • Seismometers. They can detect seismic activity, which can be used to predict tsunamis;
  • Tiltmeters. They can detect changes in the sea surface elevation, which can indicate a tsunami wave;
  • Pressure gauges: They can detect changes in air pressure, which can be used to determine the size and speed of a tsunami wave;
  • Tsunami buoys. They measure changes in the sea surface elevation, which can indicate a tsunami wave;
  • Radar systems. They can detect changes in the sea surface elevation, which can indicate a tsunami wave;
  • Satellite imagery. It can be used to detect changes in the sea surface elevation, which can indicate a tsunami wave;
  • Acoustic detection systems. They can detect changes in sound waves, which can indicate a tsunami wave;
  • Tide gauges. They measure changes in sea level, which can indicate a tsunami wave;
  • Computer models and simulations. They can be used to predict tsunamis by simulating the wave propagation and impact of a tsunami;

Mitigating Risks

What can authorities do to minimize the risk of megatsunamis? Here are a few options:

  • Construct tsunami walls. Tsunami walls, or coastal barriers, are large structures constructed along the coast to reduce the impact of incoming waves. They can be made from concrete, steel, or other materials and are designed to absorb the energy of a wave before it reaches the shore;
  • Install early warning systems. Early warning systems are designed to detect and alert people to the presence of a potential tsunami. They use sensors to measure changes in the ocean's temperature, pressure, and wave height and can provide a few hours of lead time for people to evacuate;
  • Manage coastal development. Coastal development can affect the strength of incoming waves. Building roads, bridges, and other structures can disrupt natural barriers such as coral reefs, which can weaken the wave's energy before it reaches the shore;
  • Plant mangroves. Mangroves are trees that grow in coastal areas and provide protection from waves. They act as a natural barrier, absorbing the energy of incoming waves and protecting shorelines from flooding and erosion;
  • Educate the public. Education is key to mitigating the risk of tsunamis. People should be informed about the signs of an incoming tsunami, what to do in the event of one, and how to protect themselves and their property;

Megatsunami: a massive ocean wave with a height of more than 328 feet | Photo: Shutterstock

Preparing for a Megatsunami

There is no guaranteed way to survive a megatsunami, as the waves can be incredibly destructive and may not be survivable.

However, people can prepare themselves by identifying and understanding the risks associated with the area they live in and being aware of any potential warning signs.

Citizens and authorities should also plan for evacuation routes and have an emergency kit ready in case of an emergency.

Additionally, people can seek out the high ground to avoid the worst of the wave.

Lastly, people should stay informed and listen to any warnings or advisories issued by their local authorities.

Preparing for a megatsunami requires a combination of common sense, planning, and the resources available to you.

It can include the creation of coastal defenses, such as seawalls and breakwaters, as well as evacuation plans.

Here are the main possible steps:

  • Research and plan. Research the areas that are most at risk from megatsunamis and have a plan in place in the event that one occurs;
  • Have an evacuation plan. Have an evacuation plan in place in the event of a megatsunami so that you know exactly where to go and how to get there;
  • Elevate your house. If you live in a low-lying area that is at risk for a megatsunami, consider elevating your house to provide more protection from the waves;
  • Stockpile emergency supplies. Make sure you have plenty of emergency supplies such as food, water, and medical supplies in your home;
  • Prepare to be self-sufficient. If necessary, prepare to be self-sufficient for a period of time if the infrastructure is affected by the megatsunami;
  • Stay informed. Stay up to date on the latest news and information about potential megatsunamis;
  • Listen for official warnings. Listen for official warnings from local authorities and follow their instructions;