Chapter 22 - Seamounts and Island Building

Abstract

Seamounts are the most abundant type of volcanoes on earth but only a miniscule fraction of them has been studied to this date. Seamounts may be found in any submarine tectonic setting and vary in size from abyssal hills (100m) to the largest mountains on earth (>8km). They evolve in distinct stages defined largely by size and eruption depth that control the abundance of effusive, clastic, and intrusive lithological rock types. Key effusive rock types include in particular pillow lavas and rare sheet or massive flows; clastic rock types include pillow breccias, pillow fragment breccias, and hyaloclastites; and especially large seamounts may include up to 50% intrusive rock types, including dikes, sills, and other intrusions. While the clastic processes may occur at any depth, the production of volcaniclastics markedly increases above 1000m water depth. Once both volcanic eruptions and sea-surface related erosion end, seamounts are among the most stable and long-lasting geomorphic features that ultimately will be subducted into the mantle and occasionally included into accretionary complexes.