Japan 2011 earthquake and tsunami aftermath
Credit: Credit: From Wikipedia by Mitsukuni Sato, CC BY 2.0.

Rikuzentakata, a town on the coast of the island of Honshu, Japan after the massive March 11, 2011 earthquake and tsunami.  The tsunami completely wiped out 80% of the homes. Although a 6.5-meter seawall existed to combat the threat of a tsunami, the wave that came was actually 13 meters high, double the height of the seawall.[3]

Tsunami is a Japanese word that means "harbor wave"

With multiple recent dramatic examples, tsunamis constitute one of the biggest natural disaster threats to human beings along coasts worldwide. They can form due to earthquakes, volcanic eruptions, large explosions such as nuclear weapons, landslides, glacier calvings, meteor impacts, or any other powerful disturbance to large bodies of water. Waves can be hundreds of feet tall, and in some cases over 1,000 feet (300 meters).[1]

Tsunamis move through the water at up to 600 mph (370 km per hour), although slow down considerably when they approach shore and form their massive waves.[1] The speed of sound in the air by comparison is around 760 mph (470 km per hours).[2]

Tsunamis occur in the Pacific Ocean 80% of the time, which makes sense due to the size of the ocean, covering about one-third of the total surface of the Earth, and nearly half of its water surface – plus the fact that it is surrounded by volatile tectonic plate boundaries prone to earthquakes and volcanic eruptions. However, they do not occur only in oceans, and can occur upon lakes as well.[1]

Like earthquakes, a tsunami can form suddenly. Sometimes a few hours go by from the formation of the tsunami until it reaches shore somewhere. Other times it occurs close to shore with little opportunity for anyone to get out of the way.[1] Below are some examples of giant and destructive tsunamis from history, as well as examples of present day threats that need to be prepared for by the cities and nations that could be affected.

The water prior to a tsunami striking will suddenly recede out into the ocean, exposing ground that is normally always underwater. The sea level along a coast suddenly dropping considerably is a major warning sign to quickly get to higher ground if you can. There are typically a few minutes until the large wave strikes.[1]

Maldives during 2004 Indian Ocean tsunami
Credit: Public domain.

Tsunami generated from the massive 2004 Indian Ocean Earthquake, striking the Maldives island group.

Four examples of tsunamis from history

Example #1 - A tsunami more than 1,000 feet in height:

The Earth is a few billion years old, and we therefore obviously won’t know of a lot of large tsunamis that have occurred in the past. So the largest that we know of occurred in Alaska in 1958 in Lituya Bay.[1]

An 8.3 magnitude earthquake caused a massive slide of rock and ice into the bay, and damage included a cut communications cable and five people perishing. The tsunami wave is known to have been 1,720 feet (524 meters) high.[4]

Example #2 - The most destructive tsunami to ever occur

The massive 9.2 magnitude Indian Ocean Earthquake near Indonesia in 2004 by far created the most destructive tsunami ever known. This is the third-most powerful earthquake ever recorded, and one of the top ten natural disasters to have ever occurred.[5][6]

The death toll was somewhere between 230,000 and 300,000. Deaths occurred in countries around the Indian Ocean, although mostly in nearby Indonesia. Second-most affected was Sri Lanka, about 1,000 miles (600 km) northwest. Someone even died in Kenya, in Africa, nearly 4,000 miles (2,500 km) to the west.[5]

Many locations in Indonesia experienced waves between 80 and 100 feet (24 and 30 meters) in height. Warning systems were nonexistent, and therefore almost nobody knew the tsunami was coming. While the Pacific Ocean had a warning system in place at that time, since tsunamis are common in the Pacific, tsunamis are comparatively rare in the Indian Ocean – although after this, a disaster system for the Indian Ocean was created in 2006.[5]

Example #3 - A tsunami in a lake caused by a volcanic eruption

The 1980 Mount St. Helens volcanic eruption in Washington, USA was amazing in many ways. It was the largest volcanic eruption to ever occur in the contiguous 48 states, since the founding of the USA.[7]

One fact not commonly known is that it produced a tsunami wave across Spirit Lake that was 853 feet (260 meters) in height.[8] This was caused by a massive landslide as the side of the mountain basically fell off due to a magnitude 5.1 earthquake, and suddenly the magma was exposed to the air and exploded violently, greater than the energy released by six modern nuclear weapons.[7]

Example #4 - Tsunamis caused by meteor impacts

Near the beginning of the Pleistocene Epoch, about 2.5 million years ago, a large meteor landed in the southeastern portion of the Pacific Ocean. Evidence around the Pacific Ocean suggests this, and waves about 660 feet (200 meters) in height struck the coast of Chile, in South America, and also the Antarctic Peninsula.[8]

This was dwarfed though by the comet that hit the Earth 65.5 million years ago, killing all types of dinosaurs except for birds, and also mosasaurs, plesiosaurs, pterosaurs, ammonites, and some other ancient animal groups. This was the largest object to strike the Earth in the past 1.8 billion years, and caused a tsunami that scientists have estimate at over 16,000 feet (5,000 meters) in height.[8]

Tsunami wave from the 2004 Indian Ocean Earthquake
Credit: Credit: From Wikipedia by David Rydevik, and in the public domain.

The tsunami wave generated by the massive 2004 Indian Ocean Earthquake catches people off guard in Ao Nang, Thailand. There was no warning system anywhere in the Indian Ocean until after this disaster took place. In Thailand 5,395 people perished.[5]

Known present day tsunami threats

Certainly locations where tsunamis are known to have occurred before are locations that are easy to identify as places where they can occur again. For example, large earthquakes in Alaska have sent tsunami waves southward across the Pacific, and Hilo, Hawaii is positioned such that it gets hit by them – and so a breakwater has been built to lessen the impact, plus there are sirens which sound when a tsunami is coming.[9]

When the northeast coast of the island of Honshu, Japan was struck by a tsunami in March 2011, the size of the tsunami was larger than anyone had anticipated and this is why the Fukushima nuclear power plant failed. A wall meant to keep out tsunamis was far too small, and power was knocked out, and so was backup power.[10] This example shows how nature can surprise us and do things beyond what we knew were possible – and the results can be extremely devastating. Preparation for something totally unanticipated is not so easy.

So below are three threats I’d like to highlight, which are probably not well known, but should be. There are certainly others around the world, including some that no one has yet anticipated. Each of these has enormous potential for destruction, and may someday happen.

Present day threat #1 - Honolulu, Hawaii

The western side of Hawaii’s Big Island, which is the number one most volcanically active island on Earth, has Hualalai Volcano, which last erupted in 1801.[11] It is one of four shield volcanoes that intersect with Mauna Loa, which from the bottom of the sea floor is by far the largest and tallest mountain on Earth.[12]

Activity at Hualalai or Mauna Loa could potentially generate landslides and send a tsunami northwest into Honolulu and Pearl Harbor, an area with about one million residents and very busy beaches with many tourists. A wave 100 feet tall (30 meters) could slam into Honolulu in just 30 minutes. If this were to occur, hundreds of thousands of people would perish.[8]

For more about this scenario, see How Hawaiian Volcano Hualalai is a Potential Threat to Honolulu

Present day threat #2 - Washington, Oregon, and British Columbia

Off the coast of the state of Washington, USA is a fault very much like the one near Japan that caused the massive earthquake and tsunami in March 2011. The fault causes earthquakes up to magnitude 9.0 every few hundred years, and is thought due for another sometime soon.[13]

Besides causing massive damage to the coasts of Washington, Oregon, and British Columbia, like the Japan earthquake, the tsunami waves would spread across the Pacific Ocean. Although, they would be coming from the opposite side of the ocean as the tsunami waves that originated near Japan.

There is a large distance to the west between this potential point of origin for a major tsunami and other landmasses. Hawaii for example is about 2,500 miles (1,550 km) away. This would make the waves smaller as they lose energy along the length of their travel. Damage would occur in Hawaii, as it did with the Japan earthquake, although it would be nothing like what would happen to the coasts of the northwestern USA and southwestern Canada.

Present day threat #3 - East coast of North America, northeastern coast of South America, western coast of Africa, and parts of Europe

Volcanologists worry about a volcano that is part of the Canary Islands in the Atlantic Ocean near Africa. A massive landslide at La Palma, the most active volcano in the island group, could send tsunamis with an initial height of more than 3,000 feet (900 meters) across the Atlantic Ocean.[8]

The tsunami waves could slam into cities such as New York, Boston, Halifax, and Miami with waves still exceeding 150 feet (45 meters) tall. Caribbean islands would also be struck, and the northeastern coast of South America. Africa’s northwestern coast would be hit very hard, and in Europe the countries of Portugal, Spain, England, Wales, and Ireland could receive massive amounts of destruction.[8]

This particular scenario would cause destruction to human life never approached before by natural disasters. The death toll would certainly be in the millions if it were to happen.