Over the Edge: Undersea Volcanic and Tectonic Activity  

For large stretches the deep ocean basin is flat. But seamounts, guyots, island arcs and trenches, all of which result at least in part from tectonic activity, break up the sameness.
Subject: volcano
Transcript: spreading centers Or what we call off-axis volcanoes. They're basically individual volcanoes that have-- Most of them form away from a ridge axis-- Not right