Tsunami are also known as tidal waves, although they have nothing to do with the tide, and are sometimes called seismic sea waves. Tsunami are great towering waves of massive destructive power. They are caused by large earth movements and unheavals beneath the oceans. In turn, these are caused by earthquakes, volcanoes (again often beneath the ocean) and underwater landslides which result in a sudden large movement of the water. The size of a tsunami is not always proportional to the size of the earthquake, and some of the most destructive ones have originated from quite small earthquakes. This can occur when a huge amount of ocean sediment on a sloping surface (such as the transition point between two different levels of ocean shelf) is disturbed by the earthquake and a very large undersea landslide occurs, triggering the tsunami.
Out in the deep ocean a tsunami wave may be only a foot high and would not be noticed by boats in the area. But they move at speeds between 500 and 800 kph. Yes, that's around 450 mph. FAST! When they reach shallow water however, the wave gets taller and slower, just like ordinary waves when they reach the beach. Typically 10 to 15 m in height. Notice that in the picture top right, the wave is going over the roof of the house - on top of the high sea wall!
Tsunamis occur all the time – perhaps thousands each year, the majority in the Pacific Ocean – but most are too small to notice. But every few years, however, large tsunami waves kill hundreds of people, most recently in 1998 when 2,000 people were killed in Papua, New Guinea. The dangerous ones occur in shallow water close to shore, because they hit the coast quickly without any warning, And if they hit in low-lying populated areas, the wave can travel far inland and cause serious flooding and loss of life.
As an example of how dangerous these waves are, in 1992 and 1993 alone, over 2,000 people were killed by tsunamis occurring in Nicaragua, Indonesia and Japan. Property damage was nearly one billion dollars. The 1960 Chile Earthquake generated a Pacific-wide tsunami that caused widespread death and destruction in Chile, Hawaii, Japan and other areas in the Pacific. Large tsunamis have been known to rise over 100 feet, while tsunamis 10 to 20 feet high can still be very destructive and cause many deaths and injuries.
Among the most famous tsunami are: -
If you wish to learn more about any of these famous tsunami events, just enter their name, tsunami and the year into your favourite search engine, and you'll find lots of information available.
|The Lituya Bay wave is generally described as the largest tsunami ever recorded in modern times, and has been given the special name of mega-tsunami. It was caused by a massive landslide, triggered by an earthquake of magnitude 8.3. When the wave rushed across the bay it ran up the valley walls to a height of 576 m at its maximum, (that's 1720 ft) and over 100 m for the rest of the bay area.|
Note the damage marks,especially top right of the picture,
where trees were stripped clean away from the valley walls from hundreds
of metres up the sides! For an excellent very detailed description and
pictures of the damage, visit the site of Dr
Lituya Bay was considered to be a safe haven for fishing boats, as it was always calm, even during storms. There were three boats in the bay at the time of the earthquake and the resulting massive landslide, and incredibly two of the boats and their crew survived the mega tsunami to tell the tale.
The Tokyo / Sendai tsunami of 2011 was possibly the first to be fully documented by hundreds of victims using mobile phones to record the dreadful damage. there are now many videos available on line showing the devastation, and the amazing sites of hundreds of cars being swept along together, houses being pulled down, and vast areas being inundated by the water.
Europe is not immune to tsunami, either. On 1 November 1755, a magnitude 8.6 earthquake (that's very powerful!) at Gorringe Bank (a ridge off the coast of Portugal) destroyed much of Lisbon. Then the tsunami arrived. At least three great waves about ten meters high swamped the city. The waves also hit the coasts of Spain and North Africa, with a great deal of damage occurring in the Azores, Madiera, and Canary Islands. Minor damage occurred as far north as Ireland (yes, Ireland!!) and as far west as the West Indies. Gorringe Bank presents a continual tsunami threat to Portugal - they don't tell you that in the holiday brouchures though.
We don't get too many of these giant waves in the UK, but who knows, so here's a few links to keep you amused and, more importantly, to educate you. Tsunami shouldn't be confused with tidal bores, which we do get in the UK. These occur in certain rivers, the Severn being the best known, due to interactions between the tide and the river flow where a wave runs up the river. They are predictable and crowds often gather to watch.
Welcome to Tsunami (What, welcome them? You must be mad!) is a good starting point for the ultimate surfer's experience, and is based at Washington University.It's also known as the WWW Tsunami Information Resource. They have a good set of links on this subject to keep you informed.
Tsunami and Earthquakes is another good site, includes some animations of tsunami, and lots of good information. The animations are VERY big files and you may decide not to view them. Some are for high level science lectures and probably not suitable for ordinary viewers. But it is well illustrated with pictures of how tsunami are formed.
The 1964 Alaskan Quake Centre is a site about the famous alaskan tsunami - the coast area was lifted 3.6 metres by the quake!!
Tsunami - The Big Wave is a NASA site and takes you through a series of good clear pages. Remember the general rule of thumb on the Internet - if it's a NASA site, it's a good site. A very informative site, use their Next link to work through the pages.
Tsunami - The Great Wave is a NOAA site, and like any NASA site, they are always worth investigating. Some good information here on how the waves form.
Tsunami Program Links, also a NOAA site, is an excellent jumping off point for those who wish to gather more information on this subject. They have so much information available, they had to provide a link at the bottom of the page to Even More Links. Exploring all the links provided here will turn up some good tsunami pictures.
Tsunami FAQ yet another NOAA site, answers lots of standard questions about the great waves.
Tsunami Info from NOAA is a site produced by, well, NOAA of course. Several links to good images can be found there.
Tsunami Pictures are a popular search topic and a very good source of lots of tsunami pictures can be found at this link. Pictures of the waves and the destruction caused by them are available as seven separate sets of slides. Just be aware that there are usually more pictures of the aftermath than the actual tsunami itself.
Pacific Tsunami Museum aims to promote public education of the people of Hawaii, especially as this general area is a tsunami hotspot. It includes another FAQ page, photos and good links. It even has a Tsunami Picture of the Month section (a beauty contest for tsunami??) which can throw up some stunning pictures. More tsunami pictures are available in their Archive link.
Scientific American Feature on Tsunami is a good article with some good links. Written by experts, you can trust these Scientific American articles to be factual, and like the NASA and NOAA pages, should always be looked at if they come up in a search.
Dr George P.C. has a vast site on tsunami, with literally hundreds of pages to investigate, well illustrated with graphics and pictures of tsunami and their origins. The site also covers earthquakes in detail, and the megatsunami at Liyuya Bay. This link takes you to the opening page of his site, the earlier link next to the picture takes you to his mega-tsunami section.
What is a Tsunami - tries to answer the question, and has links to other good sites.
Mega Tsunami: Wave of Destruction is the script of a BBC TV Horizon program on the famous tsunami that hit Lituya Bay, and the possibility that the east coast of america could be hit by something similar.
Mega Tsunami and East Coast America warns of the very real danger of a devastating great wave hitting America, and its know potential source. Includes some other good links.
Tsunami from Asteroid Impacts is a large document reporting on a scientific study of what might happen if an asteroid hits the sea. Okay, I know this isn't really weather, but I'm a scientist and it's my page, so there.