Sailor calls it "the weirdest thing I've seen in 18 years at sea."
Described by a witness as "the weirdest thing I've seen in 18 years at sea," the New Zealand Royal Navy is currently investigating a vast swath of white pumice found floating atop the South Pacific Ocean.
Pumice is a lightweight stone that you may have encountered as a food scrub. This lava rock's light weight and sharp microscopic edges make it perfect for this purpose. Pumice is formed when lava cools very quickly, as might happen when a lava flow encounters the ocean, or from an underwater volcano. The super-fast cooling causes the rock to puff up, in principle not unlike a marshmallow in the microwave. When the rock cools, this puffed-up shape causes it to be incredibly light and buoyant. Which explains why it is floating atop the ocean.
The raft of pumice in the South Pacific Ocean is roughly 250 nautical miles long by 30 nautical miles wide. (One nautical mile equals 1.15 miles.) The sailors encountered the mysterious occurrence at night. When they hit it with their spotlights to see what it was, it lit up brilliant white as far as they could see in either direction. In aerial photographs, the floating pumice raft looks like an exceptionally thick, frothy series of white caps on the surface of the ocean - until you realize the scale of what you are seeing.
The rock is "brilliant white," and is floating in a large raft about two feet high above the surface of the ocean, comprised of lumps of pumice each of which is about the size of a golf ball. The New Zealand Royal Navy's ship was able to safely sail into the middle of the floating rock, because it was too lightweight to damage the ship's hull. This allowed the sailors to gather samples from several different points, for the scientists to analyze back at the lab.
Researchers speculate that this floating pumice slab is most likely the result of an underwater eruption. (Perhaps because there is so much of it, surely we would have noticed an eruption that large if it were above sea level!)
Initial reports were that the floating pumice raft originated from the underwater volcano Monowai. However, it will likely be impossible to track down the source of the pumice with 100 percent certitude. The pumice will no doubt travel far on ocean currents, being so buoyant. Pumice from the colossal eruption of Krakatau in 1886 "washed up on African beaches months later."