Volcano may emerge from the sea

A volcanic island submerged for more than 170 years could soon reappear off the Sicilian coast.

The underwater volcano Ferdinandea, also known as Graham Bank, last emerged from the sea in 1831, but scientists think it may be about to make another appearance.

Just 20 kilometres out to sea, the top of the volcanic island lies about eight metres below the water surface.

The last time the island surfaced, diplomatic arguments arose over its ownership. This time, divers have acted swiftly to try to prevent a repeat of the disagreements - by planting an Italian flag on the rising mount.

Previous appearances

According to records, the island has appeared four or five times before.

The last time was on 2 July, 1831, when it remained above the water surface for six months.

On that occasion, the Sicilians claimed it for themselves - and so did the Spanish.

A British admiral who was passing thought the island might have some strategic importance, so he, too, staked a claim, calling it Graham Island.

This time, Italy is ahead of any potential rivals. Divers have planted the country's flag on the submerged island and hope to claim it for the country, if and when it breaks the surface.

Lava build-up

Professor Enzo Boschi, from the Institute of Geophysics and Volcanology in Rome, has been monitoring the situation.

He told BBC News Online: "We have observed minor seismic activity, gas emissions but this is quite normal."

Although Professor Boschi could not rule out an appearance of the volcano above the water surface, he said he did not expect one in the coming days.

It was much more likely that it would occur in a few weeks or even months, he added.

The above-surface island is formed when lava pushes out over the top of the volcano and solidifies in the cold water, increasing the height of the mount.

The last time the volcano came above water, it was 65 m tall and had a circumference of five kilometres.

Mount erosion

Dr Rex N Taylor, from the Southampton Oceanography Centre, UK, told BBC News Online that these types of re-emerging volcanic islands were formed in several ways.

"Magma can enter and inflate the region below [the volcano], lifting the island. As the magma deflates, the island will sink below."

They can also be lifted by the movement of tectonic plates. In 1967, volcanic eruptions caused the surfacing of Surtsey Island south of Iceland. It is 170 m tall and 1.5 km wide.

Another group of islands south of Tokyo is submerging again. Sumisu Jina and Miojin Sho are being eroded by the sea.