Australia's only two active volcanoes have both erupted – and scientists on board a ship conducting research nearby caught the rare event on film.

The Big Ben volcano on remote Heard Island in sub-Antarctica, almost 1800 kilometres north of Australia's Antarctic base at Davis Station, erupted a combination of poisonous gases and red-hot lava. It was the first time it had done so in decades.

The other volcano, on the neighbouring McDonald islands, erupted gas only. Scientists on board the CSIRO's RV Investigator were visiting the islands to conduct research into the concentration of iron in Antarctic waters.

"We witnessed the lava descending Big Ben as it interacted dramatically with the snow and ice cover of the mountain," said ANU volcanologist Professor Richard Arculus, who witnessed the eruption first hand.