A Tsunami
A tsunami is an ocean wave(s) with very long wavelengths caused by disturbances of the ocean, such as earthquakes, volcanic eruptions, landslides, or meteorite impacts. Earthquakes are the most common cause of tsunamis. Tsunamis can move at speeds up to 500 miles an hour. Tsunamis are not that tall in the ocean. They are only three feet tall in the open ocean on average. When they get close to the shore, they can get much taller they can get to over ten times the size of when they were out in the ocean. Sometimes it is not just one tsunami it might be two or more in this case the first wave is often not largest one out of all of the waves. A mega tsunami is caused when a large amount of rock or other substance gets into the water and displaces it. Mega tsunamis are much less common but can do much more damage in one blow. In some ways regular tsunamis are much more of a treat because they happen much more. The largest tsunami was in Alaska. It was caused by a landslide and 8.3 magnitude earthquake and was 1720 feet tall.
How to survive a tsunami.
The best way to survive a tsunami is to be far away from it. Look and listen for tsunami alerts. If you see the water level quickly recede or feel the Earth tremor then run to higher ground.
False tsunamis? False tsunamis can occur, looking like massive tsunamis. They are actually clouds, known as Tsunami clouds, or more known as shelf clouds. Shelf clouds are clouds that are at the leading edge (front) of a thunderstorm, but occur rarely. These clouds mainly fool people because of a strong resemblance to waves and how it moves fast. These clouds usually happen near coastal and ocean regions on a thunderstorm. Some tsunami clouds are roll clouds that are close to the ground. Even though now you know that you might be looking at a shelf cloud coming towards you, I think it'd be best to hide in your basement or something because it might be an actual tsunami.