Tsunamis are some of the most powerful and deadliest forces of nature. Within recent memory, you may recall both the 2004 Indian Ocean Tsunami and the 2011 Japan Tsunami, both of which in resulted catastrophic damage and loss of life. The Indian Ocean Tsunami happened after a massive earthquake struck here in the Indian Ocean. The earthquake itself released more energy than every single explosive detonated in the entire Second World War, including the nuclear bombs. This enormous amount of energy created a tsunami that reached heights of 30 meters high in some places, or about the height of 17 people stacked on top of each other. The wave smashed into Indonesia, South Asia, and the east coast of Africa, punching as deep as two kilometers inland from the coast in some places. As you can see from photos like this one, the damage in these places was often extensive. The tragedy claimed the lives of around 250 thousand people, making it the deadliest tsunami in all of history, while the 2011 Japan Tsunami was the costliest in terms of damage. That tsunami was also generated by an earthquake that created waves as high as 40.5 meters; just about five meters shorter than the Statue of Liberty, that came slamming into the Japanese east coast traveling up to ten kilometers inland away from the coast. As you can see from photos like this that look like something straight out of a Hollywood blockbuster, with what used to be a road stretching out into the endless ocean, the economic cost of Japan was enormous: an estimated 300 billion dollars in damages was done, more than the entire GDP of South Africa. But these are what are called “regular” tsunamis and there is an entire other class of gigantic waves that are simply called “megatsunamis”. Unlike a regular tsunami that is created by an earthquake, a megatsunami is usually created when a massive amount of material suddenly falls into water, which displaces that water into a huge wave. The most tragic and possibly terrifying instance of this happening in recent times was back in 1963, here in Italy, just 100 kilometers north of Venice. The Italian government and a construction company were building what at the time was going to be the largest dam on Earth; the only problem was that they were building this dam with a huge water reservoir the size of a large lake, right next to one of the most unstable mountains on the planet. For months leading up to the completion of the dam, there were several minor landslides and other signs that there could be a catastrophe coming, but rather than heed the numerous warning signs, the Italian government actually decided to sue the few journalists reporting on the issue for quote: “…undermining the social order”. The government and company continued to ignore all the warning signs until it was obvious that the mountain was actually going to collapse directly into the dam’s reservoir. Tthe engineers calculated the landslide that would likely occur, lowered the water in the reservoir to what they believed was a safe level, and then actually stood on top of the dam the night that they expected the landslide to occur to watch it all go down. The only problem was, the landslide ended up being over 10 times more powerful than what their calculations had predicted! This is a view of that mountain today: this right here used to be the reservoir, and all the land that’s there now came crashing off the mountain from these areas that are now exposed white rock. This tremendous amount of earth and rocks fell into the reservoir in a matter of seconds, completely filled the entire reservoir and generated a wave 250 meters high that flew over the top of the dam, and into the villages below. The wave was almost the same height as the TransAmerica building in San Francisco for some reference, and caused an impact crater 60 meters deep and 80 meters wide when it slammed into the ground on the other side of the dam! If you were standing from this angle looking up at the dam at the exact moment that the wave came over it, the entire sky that you see in this picture would be completely covered by water! This photo was taken in the town of Longarone, which before the megatsunami looked like this, but afterwards looked like this: completely destroyed. Around 2,000 people lost their lives in the accident, but it’s not actually the largest mega tsunami even in recent history. That distinction would have to go to a megatsunami that happened here in Lituya Bay, Alaska, back in 1958. A powerful earthquake caused a massive landslide to occur here at the back side of the bay. The huge amount of land that came crashing into the bay created a titanic wave 525 meters high that slammed into this part of the bay, completely went over it, and smashed into the other side here, causing huge amounts of damage to the rest of the bay and destroying millions of trees. The height of this wave was over 100 meters higher than the tip of the Empire State Building, and just 16 meters short of the recently built One World Trade Center in New York City, but even this is tiny in comparison to some prehistoric megatsunamis. The largest tsunami generated from a landslide happened around 1.5 million years ago in Hawaii.,on the specific island of Molokai. At some point around that time, about one-third of the northern portion of the volcano collapsed into the ocean and generated a wave 600 meters high, which would have completely inundated the entire island of Molokai and wreaked havoc on the rest of the island chain. This wave would have been about the height of four Great Pyramids of Giza stacked on top of each other… but even that pales in comparison to the largest ever known megatsunami, which was caused by an asteroid. About 66 million years ago, the same asteroid that likely killed the dinosaurs also caused possibly the largest megatsunami in all of Earth’s history when it crashed into the modern-day Gulf of Mexico. The asteroid was ten kilometers in diameter and released an unbelievable 100 TERATONS of TNT worth of energy. For comparison, the Tsar Bomba (which is the largest nuclear bomb ever detonated), released only 1/2,000,000th of that same amount of energy. You would need 2 million Tsar Bombs to release this same amount of energy, which caused an equally unbelievable wave of up to 5 KILOMETERS high that would have smashed into the Gulf Coast states of the modern-day United States. That’s higher than the Matterhorn in the Alps… by about 500 EXTRA METERS. In fact the height is higher than all of the mountains in the entire Alpine Mountain Range. These waves were so big that if they were to have happened in the Indian Ocean, the entire island of Madagascar would have been completely submerged underwater for a time. Imagine being on an island the size of Madagascar in this scenario, with absolutely no escape from the clutches of the ocean’s waves no matter how high on the land that you can get to! It’s a weird thought, but at least it happened 66 million years ago and there’s really no fear something like that ever happening again, right? Unless the 0.00001 percent chance of one of the Canary Islands collapsing into the ocean during your lifetime happens, which would cause a tsunami about 1 kilometer high and would probably wipe out the entire East Coast of the United States… unless that happens then no, probably not. But, it’s still fun to think about. 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