A giant pumice raft has been spotted in the Pacific Ocean, near Vava’u, Tonga. Pumice is a porous volcanic rock. Sailor Shannon Lenz shared footage of the phenomenon online. She wrote: “We sailed through a pumice field for six to eight hours, much of the time there was no visible water. “It was like ploughing through a field. We figured the pumice was at least six inches thick.” Scientists said the pumice was caused by an eruption of an underwater volcano which erupted off Tonga earlier this mon