This particular raft of pumice is believed to have come from an underwater volcanic eruption near Tonga on 7 August, and is now drifting towards Fiji.
The pumice is now drifting westwards towards Fiji, and is likely to pass New Caledonia and Vanuatu before potentially reaching Australia in a year's time.
Michael and Larissa Hoult were sailing from the Vava'u islands of Tonga to Fiji in the South Pacific Ocean when they saw it - a "total rock rubble slick" extending for miles around them.
Pumice is a lightweight, bubble-filled rock which can float on water, formed in volcanic eruptions when magma is rapidly depressurised and cooled.
"It was quite eerie, actually", Larissa Hoult told CNN.
Hoult describes the rocks as "closing in" around their catamaran. They said the raft covered the water "went as far as we could see in the moonlight and with our spotlight".
A giant mass of pumice stones, created from volcanic lava lighter than water, is now floating toward Australia. When ocean heat waves drive nutrient-rich algae from coral cells, they lose their color and begin to die.
According to Bryan, the raft of volcanic rock will arrive at the Australian shores in about seven months, passing by New Caledonia, Vanuatu, and touching the eastern Coral Sea along its way.
This particular "island" was detected earlier in August, and the image up above was captured by NASA's Landsat 8 satellite on August 13.
As such, the raft may turn out to be a stroke of luck for Australia's Great Barrier Reef, in whose general direction the raft is floating. When the pumice eventually reaches Australia's coastline, it will introduce millions of these organisms to the reef, potentially promoting regeneration of the coral and giving dead parts of the reef a second chance. Across the raft was discolored water, an indication that the volcano that produced it was slightly below, the Earth Observatory reported. "It's a home and a vehicle for marine organisms to attach and hitch a ride across the deep ocean to get to Australia", added Bryan.