During World War II, seamounts were discovered by a ship captain, using the newly invented echo sounder. Volcanic activity began early in the Flood. But later, as the sea arose, the tops of the volcanoes were flattened out by storm and wave action. Seamounts point both to the fact that there once were lowered sea levels, but also to the extensive volcanic activity early in the Flood. Another evidence of the lowered sea levels, which gradually rose, are the continental shelves.
Corals can only live in shallow water, just below the ocean's surface.
Yet corals are to be found deep in the ocean. At some earlier time, corals were growing on those deeply submerged seamounts. As the rivers emptied into the oceans, canyons flowed down the sides of continents. Later, the oceans filled and these canyons, of which there are several hundred, are now as much as 1,500 feet below sea level. For example, you will find a canyon dropping down deeply off the outlet of the Columbia River.