The largest island in a lake on an island in a lake on an island is a nameless 1.6-hectare (4-acre) island at 69Â°47â²35â³N 108Â°14â²28â³W / 69.793Â°N 108.241Â°W / 69.793; -108.241, 121 kilometres (75 mi) inland from the south coast of Victoria Island, Canada.
A tsunami can travel across the open ocean at about 500-miles per hour, the speed of a jet airliner. As the wave approaches land and as the ocean shallows, the wave slows down to about 30 miles-per-hour and grows significantly in height (amplitude).
There are some instances where such a tsunami would probably only travel several miles while there are other scenarios where it may roar up a river way or bay and devastate far inland (e.g. 30 miles up Delaware Bay to Dover, another 30 to Wilmington and then 20 more to Philadelphia as it builds enormous height up the waterway).