Megatsunamis
Megatsunami. The word accurately describes what it means. Where tsunamis are big, megatsunamis break all limits. Tsunamis are regular surfing waves compared to these guys. They can rise up to be 200 meter high wall of water, destroying everything on its path. Time to take a closer look.

On the subject tsunamis, Nathan posted this explanation:
QUOTE
In tribute to have died, I thought I'd post this!
A tsunami is a series of huge waves that happen after an undersea disturbance, such as an earthquake or volcano eruption. (Tsunami is from the Japanese word for harbor wave.) The waves travel in all directions from the area , much like the ripples that happen after throwing a rock. As the big waves approach shallow waters along the coast they grow to a great height and smash into the shore. They can be very high. They can cause a lot of destruction on the shore. They are sometimes mistakenly called "tidal waves," but tsunami have nothing to do with the tides. May god bless all those died.
(read it here)A tsunami is a series of huge waves that happen after an undersea disturbance, such as an earthquake or volcano eruption. (Tsunami is from the Japanese word for harbor wave.) The waves travel in all directions from the area , much like the ripples that happen after throwing a rock. As the big waves approach shallow waters along the coast they grow to a great height and smash into the shore. They can be very high. They can cause a lot of destruction on the shore. They are sometimes mistakenly called "tidal waves," but tsunami have nothing to do with the tides. May god bless all those died.
There is no scientific definition of a megatsunami, but informally the term has been used for tsunamis with waves of height from 40 m to over 100 m. They are a local effect, either occurring on shores extremely close to the origin of a tsunami, or in deep, narrow inlets. The largest waves are caused by a very large landslide, such as a collapsing island, into a body of water. They can potentially reach 20 km inland in low-lying regions.
However: there are some exceptions. For instance La Palma.
La Palma is a small island in the Atlantic Ocean near the 'head' of Africa. It's part of the Canary Islands. At first site this island may seem small and unimportant, but looks deceive the eye. This little island could change the earth drastically.
La Palma is a highly volcanic island, with quite some vulcanoes still active. The structure of the ground is that of a specific kind of hardened lava. It is very porous, and water can easily find its way through there. And what, ladies and gentlemen, can water do what clubs and axes etc. can't? Split stone in two. Even the egyptians knew that; they used this technique to break large rocks in two for better handling (in short: crack in stone, wooden wedge in crack, water over wooden wedge, stone splits due to expanding wedge). But it's also the water that hollows out a granite stone. Put this ingredient into a cauldron and mix it with two-three active vulcanoes, connected to each other underground, ensuring they will erupt at the same time. Now light it.
See the catastrofe? Tons of debris, destabilized by the water slowly grinding out the vulcanic rock, have slid into the water, pushing thousands of liters of water away. This water will form into a wave. A wave that grows and grows until...
...it hits the US. That means that cities like Boston, New York, Philadelphia, Washington DC, Miami, but also Toronto, Pittsburgh are destroyed completely. Not to mention small islands in the Atlantic. Furthermore there will be earthquakes, weatherchanges (such as heavy rain, etc.). Thousands of people will be killed. The world economy, which is currently heavily depending on the US will collapse.
Not very nice eh?
Of course, this is the so-called 'worst-case scenario'. Happily, according to this article, the threat is exaggerated. They argue that instead of one big landslide, there will be ten much smaller landslides. These will create waves of course, but not even close to a tsunami.
The question remains a mystery. Of course we hope that this will never happen, but who knows? The best solution I can think of is that the American Government will take precaution measurements (like evacuation plans, bunkers, etc.) to save the people, and start researching ways of how to make buildings survive this mighty blow.
Some interesting articles:
http://news.bbc.co.uk/2/hi/science/nature/3963563.stm -- "Tidal wave threat 'over-hyped'"
http://archives.cnn.com/2001/TECH/science/08/29/tidal.wave/ -- "Scientists warn for massive wave"


