The volcanic island that appeared off the coast of Japan in November last year could become a permanent feature as it continues to erupt and grow.

Niijima is now over eight times larger than when it first emerged just over two months ago and has since joined with its uninhabited neighbour island Nishino Shima.

At first, experts had said the island would erode away back into the sea from whence it came. However, this may not be the case.

Images from the Japan Coast Guard show how the island is becoming bigger, with the eruption showing no sign of stopping.

Dr Rebecca Williams, a volcanologist and lecturer at the University of Hull, told IBTimes UK that like Nishino Shima, Niijima has the potential to survive indefinitely.

"The more it keeps erupting, the more the island will grow. Normally, when [volcanic islands] are on their own they can get eroded away and disappear back under the sea, but because this one is now joined up with Nishino Shima, it has a much greater chance of sticking around.

"It's erupting lava flows, I think, which is much more sturdy material and is much more likely to stay around permanently. As to how big it will get it very much depends on how long the eruption continues."

When Niijima first rose from the deep, it was around 500m from its neighbour. However, photos of the two now show how they have joined together. The reddish pool of seawater that had separated them just two weeks ago has now gone.

Nishino Shima was also created from a volcanic eruption, Williams said: "The last time it erupted was in 1974 and that created the island it's joined up with at the moment. There's been suspected activity ever since then – there's been discoloured water around the area, which people have interpreted to mean that there's been activity deep in the ocean, but we don't know how long it's going to erupt for – it's something you can't predict.

"Now it's erupting these lava flows and getting to a bigger size, there's a good chance it will be around for several years if not permanently. I'd expect it to go on for a few years.

The lava being produced by the volcano is extremely hot, reaching temperatures up to around 1,000C. However, the tephra it produces cools down much faster. Williams said at present it appears the volcano is producing basalt lava, but said she does not know for certain.

"You can normally walk over the top of lava within several hours to a few days of the lava being in place, but it's still hot on the inside for up to several years depending on how thick they are – it really does depend on how thick the lava flows are. These ones I'd only expect to stay hot for a couple of days or weeks maybe."

Discussing the possible future of the island, Williams said that like Nishino Shima, Niijima may in all likelihood be colonised if it survives: "There's already four different species of plant that live there and flowering plants. They've got ants, bugs, flies and butterflies. So that's only 40 years but already life has started to take over.

"And that's quite a slow colonisation rate – it can happen much quicker but because here they are so far from other bits of land that it's taking a lot longer for life to turn up. If it sticks around, I'd expect it to be colonised within 30-40 years as well."