The images point to an erupting undersea volcano called the Havre Seamount in the South Pacific Ocean off the coast of New Zealand, SPACE.com reported Monday.
A New Zealand navy ship Thursday spotted the floating mass, 300 miles long by 30 miles wide.
"The rock looked to be sitting two feet above the surface of the waves, and lit up a brilliant white color in the spotlight. It looked exactly like the edge of an ice shelf," Lt. Tim Oscar, a Royal Australian Navy officer, said in a statement.
Pumice is lava that has hardened while trapping gas inside, making it light enough to float.
Researchers looking through images captured by NASA's Terra and Aqua satellites found a photo, taken July 19, that showed ash-stained water, gray pumice and a volcanic plume and identified Havre Seamount as the likely source.
Following the eruption winds and currents have spread the porous rocks into "a series of twisted filaments," a NASA statement said.