In the Mariana region of the western Pacific Ocean, curving around the island of Guam, lies the Mariana Trench. Formed where the westward-moving Pacific tectonic plate subducts under the eastward-moving Philippine Sea plate, the trench is famous for being the deepest part of the sea, reaching depths of nearly 11 km. Yet the surrounding region, rife with exotic creatures and geological features, is equally fascinating.

This bathymetric three-dimensional image of the sea floor is based on data compiled from decades of surveying. The Mariana Trench is in the far lower right, in purple; the shallowest regions are red; and volcanic islands are green (the largest is Guam). The islands are the visible peaks of a long arc of mostly submerged volcanoes driven by subduction- generated heat. That submerged arc of fire is part of the Marianas Trench Marine National Monument established in 2009.

Contrary to what one might expect, the...

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