https://en.m.wikipedia.org/wiki/1958_Lituya_Bay_earthquake_a...
The one you linked happened:
- in a narrow bay
- with a dual-slide that involved both a huge rockfall, and a huge release of sediment connected to a glacier breaking off
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It's also the first time I've heard of this event, and.... Just wow. Never thought it would be possible
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Edit: According to Wikipedia all megatsunamis recorded since 1900 were caused by landslides: https://en.m.wikipedia.org/wiki/Megatsunami Only some of the landslides were caused by earthquakes.
Edit: but I agree with the "wow". I can't even imagine what a wall of water that tall would look like. That is just so outside normal experience.
They are extremely rare.
12 megatsunamis in 123 years spread over the entire surface of the earth.