There was a FR thread awhile back (with pics) of a island of pumice in the Pacific Ocean.
Thanks. Found this just now...
An island of floating pumice rocks bigger in area than Israel has been spotted in the South Pacific, New Zealands Royal Navy said.
Officers on a Royal New Zealand Air Force ship saw the rock raft southwest of Raoul Island yesterday (Aug. 9). It measures an astounding 300 miles (482 kilometers) in length and more than 30 miles (48 km) in width, the Navy said.
https://www.livescience.com/22268-huge-pumice-island-floats-in-pacific.html