This March, WHOI scientist Dan Fornari and a team of collaborators and students are returning to the East Pacific Rise at 9°50’ North to complete a map of an undersea volcano that they believe will erupt within the next five years—if it hasn’t already. The East Pacific Rise lies west of Costa Rica and is just one small part of a 60,000-mile-long mid-ocean ridge system—the longest mountain range on the planet. But to gain this new understanding, scientists need a detailed map of the area before a new eruption changes it dramatically. Sentry dove by night, and researchers followed in the human occupied vehicle (HOV) Alvin by day, using just-created Sentry maps to navigate to areas of scientific interest. The new Sentry map improves resolution by an order of magnitude, revealing bathymetric and morphological details of the volcanic terrain down to one meter.