In the spring of 1979 I was lucky enough to be on an expedition off the coast of Mexico to explore the East Pacific Rise – part of the globe-encircling system of ocean ridges where new sea floor is created. We used the small (3 man) research submersible Alvin to examine the EPR close up, at a depth of about two and a half kilometers, a part of the earth few people ever see. This photo illustrates one of new volcanic features found on the expedition (another was the now-famous ‘black smoker’ hot vents). If you look carefully you’ll see what appear to be layers of rock; actually they are features geologists refer to as ‘bathtub rings.’ They form when lava pours out quickly on the sea floor and ponds in a depression, forming a mini lava lake. The surfaces of such lakes solidify quickly into basalt rock at the low temperature of the sea floor, insulating the interior, which remains molten. If the lake eventually drains in pulses, the bathtub rings – small ledges of solidified basalt lava – are left around the sides. Because it’s no longer supported, the solidified ‘roof’ collapses, as it has done here. Near the bottom of this picture you can just make out some of the broken fragments of the collapsed roof.