This photograph shows the manipulator arm on one of MBARI’s
remotely operated vehicles (ROVs) holding what looks like a
chocolate brownie with a strange, spiky frosting. This is
actually a chunk of basalt, a common type of volcanic rock,
which MBARI geologists collected from the Endeavor segment of
the Juan de Fuca Ridge, 7,300 feet below the ocean surface and
180 miles off the coast of Washington state. This rock may have
been part of a hardened lava crust on a pool of molten lava
created by an underwater volcanic eruption. At some point the
molten lava drained out of the pool, leaving the hardened crust
behind. The lava spikes on this rock probably formed on the
underside of the crust (pointing downward), as the last remnants
of the molten lava dripped down from the ceiling of the pool and
solidified in the near freezing water of the deep sea.