There are four undersea mountains or seamounts within the monument: Bear, Physalia, Retriever, and Mytilus seamounts. The seamounts are steep undersea extinct volcanoes. These seamounts are part of the New England seamount chain that resulted from a mantle-plume hotspot. This same geologic event created New Hampshire’s White Mountains as it migrated eastward under the North American Tectonic Plate. The monument’s seamounts rise thousands of feet from the ocean floor, comparable to the height of the Appalachian Mountains. They are largely conical in shape, although wave erosion over time has caused some, including Bear and Mytilus, to have a plateaued summit. Seamounts with a flattened top are referred to as guyots.
The seamounts are considered biological "islands" in the deep-sea. They are ideal incubators for new life because of their isolation, unique topography, and water current patterns. As currents flow up and around the seamounts, eddies form, helping to keep larvae and other small organisms positioned over the seamount. These currents also bring food to the filter-feeding corals and sponges that grow in abundance here. Like the canyons, the substrate on these seamounts varies widely, resulting in a variety of species being found close together, leading scientists to refer to the seamounts as “ocean oases.”