The Origins and Composition of Bermuda
The islands of Bermuda rest atop a truncated volcanic seamount that rises 4000 meters from the Atlantic ocean floor. Dating of basalt from the Bermuda seamount indicates that it began to form on, or near the mid-Atlantic ridge approximately 110 million years ago. It's position today, to the west of the ridge, is consistent with the westward movement of the plate, on which it is rooted. During the 30 million years since major volcanic eruptions ceased, weathering and erosion by the sea have removed virtually all surface evidence of this foundation. The volcanic rock is encountered at an average depth of 75 meters below sea level, while the shallowest known occurrence is at 30 meters below sea level. The seamount is capped by an oval limestone platform approximately 35 by 18 kilometers, part of which is submerged to form the shallow lagoon, bays and sounds that surround the emergent islands. The hills of Bermuda are old sand dunes, now solidified and covered with vegetation.