4 ms·
Simple picture for those who do not understand what makes a tsunami a tsunami. Gravity waves have a direct relationship between wavelength, the depth of the wa
by btilly 8y ago
Simple picture for those who do not understand what makes a tsunami a tsunami.
Gravity waves have a direct relationship between wavelength, the depth of the wave, and its speed. There is no such relationship with the height of the wave. You get a tsunami whenever a very tall column of water moves all at once, whether it is rising a little bit or a lot. The result is a very deep wave, with a correspondingly long wavelength, that travels at about the speed of a jetliner.
As a wave approaches land, it begins to rise and then break when the bottom of the wave hits the sea floor. It can then carry a volume of water inland determined by its overall size. This applies to all waves, but since tsunamis are so much deeper they rise more and carry much more water for their height. Hence they bring water in "like a tide". Thus the alternate name "tidal wave".
Most tsunamis are caused by earthquakes. They shake the sea floor, moving the entire column of water above, and off the tsunami goes.
They can also be caused by underwater mudslides, eruptions, or (rarely) large meteors - anything that moves the entire water column will do. And those causes often involve much larger vertical displacements, leading to a much taller wave and a lot worse tsunami.
Therefore the very largest tsunamis are caused in these alternate ways. See https://en.wikipedia.org/wiki/Megatsunami https://en.wikipedia.org/wiki/Megatsunami for information on some of the largest.
- arethuza 8y agoWe recently went for a walking holiday on El Hierro - which is a small volcanic island in the Canaries not far from La Palma where Cumbre Vieja is located. El Hierro, in addition to being generally lovely, has a particularly spectacular feature - a big chunk of the island is missing leaving behind El Golfo (The Gulf) - which is where a 150–180 km3 landslide(s) occurred leaving behind a flat bottomed area with a surrounding 1000m escarpment. The old paths up this escarpment make for interesting walking... https://en.wikipedia.org/wiki/El_Hierro#Landslides_and_tsunami https://en.wikipedia.org/wiki/El_Hierro#Landslides_and_tsuna...
- throwaway5752 8y agohttps://blogs.agu.org/landslideblog/2013/12/13/canary-islands-tsunami/ https://blogs.agu.org/landslideblog/2013/12/13/canary-island... Sounds like an amazing site to have visited, but just to be clear, this is not the kind of volcanic tsunami the linked article is talking about and the threat of them is exaggerated.
- arethuza 8y agoThe article does mention "Flank failures and sector collapses" - which sounds like El Hierro to me? (Mind you, there is no evidence that the El Golfo event actually caused any tsunamis).
- mc32 8y agoMegatsunamis requite special geography, typically an enclosed bay and steep walls and large material displacement (or rather introduction into thd body of water). Most coastal areas are not susceptible to megatsunamis (large meteors excepted).
- btilly 8y agoThe very biggest require proximity and geography. But you can get to many times larger than normal ones just by proximity to the thing that is causing the tsunami. See https://www.youtube.com/watch?v=k-DJkj5yr9E https://www.youtube.com/watch?v=k-DJkj5yr9E for a computer simulation of the Etna megatsunami that hit the Mediterranean 8,000 years ago. See https://www.youtube.com/watch?v=PQcpys0QHmA https://www.youtube.com/watch?v=PQcpys0QHmA for a different simulation that focuses on just the hardest hit areas. (The two simulations are of different models of the event with very different wave sizes. I have no idea which one is closer to what happened.)