Monster Waves that Bring Havoc and Destruction
Catastrophe is sadly never far from the news headlines, with the major tsunami in Japan and the Chilean earthquake of 2010 continuing to loom large in the memories of millions.
A megatsunami is meant to refer to a tsunami with an initial wave amplitude (height) measured in several tens, hundreds, or possibly thousands of meters.
On July 9, 1958, a giant landslide at the head of Lituya Bay in Alaska, caused by an earthquake, generated a wave with an initial amplitude of 524 meters (1,719 ft).
This is the highest wave ever recorded, and surged over the headland opposite, stripping trees and soil down to bedrock, and surged along the fjord which forms Lituya Bay.
In the UK premiere of Doomsday Earth join experts who examine the likelihood of the planet being struck by both a mega-tsunami and a mega-quake.
Their findings are not good news. It seems a giant fault line beneath the sea is readying itself for a violent explosion of activity, and the race is on to calculate when rather than if, this 'megathrust' will do its worst.
They're focus is also on the terrifying trend that has seen the Earth struck by a series of devastating natural disasters. And they predict that the worst could still be yet to come...where do you think Mother Nature will strike next?
A tsunami is a series of water waves caused by the displacement of a large volume of a body of water, usually an ocean, though it can occur in large lakes.
On March 11, 2011, the city of Miyako in Japan was devastated by a tsunami caused by the 2011 Tōhoku earthquake. At least 401 lives were lost.
Tsunamis are a frequent occurrence in Japan; approximately 195 events have been recorded. Owing to the immense volumes of water and the high energy involved, tsunamis can devastate coastal regions.
Earthquakes, volcanic eruptions and other underwater explosions (including detonations of underwater nuclear devices), sciorrucks (underwater landslides), glacier calvings and other mass movements, meteorite ocean impacts or similar impact events, and other disturbances above or below water all have the potential to generate a tsunami.
Mega-tsunami is a term used by the popular media to describe gigantic tsunamis, which are very large and destructive waves that are generally caused by a tremendous disturbance in the ocean floor.
The term is used informally for tsunamis with wave heights of 40 meters or greater.
The Greek historian Thucydides was the first to relate tsunami to submarine earthquakes, but the understanding of a tsunami's nature remained slim until the 20th century and is the subject of ongoing research.
Many early geological, geographical, and oceanographic texts refer to tsunamis as "seismic sea waves."
Some meteorological conditions, such as deep depressions that cause tropical cyclones, can generate a storm surge, called a meteotsunami, which can raise tides several metres above normal levels.
The displacement comes from low atmospheric pressure within the centre of the depression. As these storm surges reach shore, they may resemble (though are not) tsunamis, inundating vast areas of land.
There have been studies and at least one attempt to create tsunami waves as a weapon. In World War II, the New Zealand Military Forces initiated Project Seal, which attempted to create small tsunamis with explosives in the area of today's Shakespear Regional Park; the attempt failed.
Megatsunami is an informal term to describe a tsunami that has initial wave heights that are much larger than normal tsunamis. Unlike usual tsunamis, which originate from tectonic activity and the raising or lowering of the sea floor, known megatsunamis have originated from large scale landslides or impact events.
Mega-tsunami: Wave of Destruction
Geologists searching for oil in Alaska in 1953 observed that in Lituya Bay, mature tree growth did not extend to the shoreline as it did in many other bays in the region.
Rather, there was a band of younger trees closer to the shore. Forestry workers, glaciologists, and geographers call the boundary between these bands a trim line.
Trees just above the trim line showed severe scarring on their seaward side, whilst those from below the trim line did not.
The scientists hypothesized that there had been an unusually large wave or waves in the deep inlet. Because this is a recently deglaciated fjord with steep slopes and crossed by a major fault, one possibility was a landslide-generated tsunami.
On 9 July 1958, an earthquake of magnitude 7.7 (on the Richter scale), caused 90 million tonnes of rock and ice to drop into the deep water at the head of Lituya Bay. The block fell almost vertically and hit the water with sufficient force to create a wave approximately 524 meters (1,719 ft) high.
Howard Ulrich and his son, Howard Jr., were in the bay in their fishing boat when they saw the wave. They both survived and reported that the wave carried their boat "over the trees" on one of the initial waves which washed them back into the bay, though the larger wave did not harm them much.
A similar tsunami out at sea could come tens of kilometers inland. This event and evidence of a potentially similar past event at the same location inspired the term megatsunami.