A huge "raft" of volcanic rocks with an extension of more than 150 km². (Scientists say the pumice sea – the size of 20,000 football fields – was reported for the first time earlier this month by Australian sailors Underwater Volcano near Tonga, which broke out after satellite images around 7 August.
Sailors were warned themselves
Pumice stone is a light, bubbly stone that can float in the water and is formed when magma has cooled rapidly.
Large "rafts" of volcanic rock tend to form when a volcano is located in shallower waters, experts say.
Massive volcanic & # 39; raft & # 39; found near New Zealand
Deep sea volcanoes found off Sydney
An Australian couple sailing to Fiji on a catamaran first reported the "pumice raft" after accidentally falling into the rubble at night.
"The waves were almost brought to rest and the boat slowed to a knot," wrote Michael Hoult and Larissa Brill online on August 1
"The debris slide went as far as we could see in the moonlight and with our headlights."
They were temporarily stuck after stones blocked their rudder, but were able to navigate out of the field.
Since then, they have sent samples of pumice stone – "ranging from marble to basketball size" – to Queensland University of Technology (QUT) researchers in Australia.
"Whole Surface Converted to Land"
Associate Prof Scott Bryan, a geologist who studied the samples at QUT, said such pumice stone might be seen in the region about every five years.
"It's a phenomenon that is reported over time, usually as islands in the middle of the ocean that people encounter but can not find again," he told the BBC.
"It may be as if the whole surface has landed [of the ocean]."