Pumice raft

A pumice raft is a floating raft of pumice created by some eruptions of submarine volcanoes or coastal subaerial volcanoes.
Biologists suggest that animals and plants have migrated from island to island on pumice rafts.
Pumice rafts have unique characteristics such as the highest surface-area-to-volume ratio known for any rock type, long term flotation and beaching in the tidal zone, exposure to a variety of conditions, including dehydration, and an ability to absorb many potentially advantageous elements/compounds. For at least these reasons, astrobiologists have hypothetically proposed pumice rafts as an ideal substrate for the origin of life.
Notable examples.
Pumice rafts drifted to Fiji in 1979 and 1984 from eruptions around Tonga, and some were reportedly wide.
Volcanic activity in the South Pacific near Tonga on August 12, 2006 caused the emergence of a new island. The crew of the "Maiken", a yacht that had left the northern Tongan islands group of Vava'u in August, reported that they had seen streaks of light, porous pumice stone floating in the water—and then had "sailed into a vast, many-miles-wide belt of densely packed pumice". They went on to witness the ephemeral island known as Home Reef breaching the surface.
A very large pumice raft appeared near New Zealand in August 2012. It was reported to be spread on an area long and about wide, with pumice blocks poking up to above the ocean surface. On 10 August 2012 a raft with an estimated area of was observed near Raoul Island, north-east of New Zealand by the Royal New Zealand Navy. A possible source for the pumice was the July 2012 eruption of Havre seamount in the Kermadec Islands north of New Zealand. ("See: 2012 Kermadec Islands eruption)."
In August 2019, a large floating pumice raft covering was discovered in the tropical Pacific Ocean near Late Island in the Kingdom of Tonga. Sailors described a “rubble slick made up of rocks from marble to basketball size such that water was not visible,” as well as a smell of sulfur.