[FlyVet]

They can reach heights of 200 feet (61 metres) when they arrive on shore, with speeds of 150 miles per hour (241 kph), producing huge destructive force.

When I was in Hawaii, a tour guide told us they could move up to 500 mph, and sometimes only a few feet high, but at that speed could do a lot of damage. Now I wonder if he was correct.

[blam]

"When I was in Hawaii, a tour guide told us they could move up to 500 mph, and sometimes only a few feet high, but at that speed could do a lot of damage. Now I wonder if he was correct." If you were at sea in a boat you probably would not even know a giant wave had passed you, it's all under water, and 'rears' up near the shore. (Only when it hits shallow water)

[okie01]

"When I was in Hawaii, a tour guide told us they could move up to 500 mph, and sometimes only a few feet high, but at that speed could do a lot of damage. Now I wonder if he was correct."

Your tour guide was probably referring to their speed and amplitude in the open ocean. Tsunamis slow down and increase their amplitude as they begin to make contact with the bottom upon approaching the shore.

Both were correct.