A volcanic eruption in Japan would usually have people living nearby reaching for their protective masks. But the recent formation of an island off the country's Pacific coast, after weeks of volcanic activity, has prompted more enchantment than fear at nature's volatility.

In the weeks since it rose from the sea 620 miles (1,000km) south of Tokyo, the island expanded amid continued volcanic activity, before merging with an existing island to create a new landmass with a remarkable resemblance to a cartoon dog – Snoopy.

The publication of aerial photos of Nishinoshima island and its new addition prompted an outpouring of delight online.

The Kotaku blog noted that @tekken8810, one of many Twitter users who posted visual comparisons, called the island and its canine likeness a "complete match".

User @etienneeshrdlu joked: "Exactly as Nostradamus predicted. A new Snoopy-shaped island rises from the sea near Tokyo," while @astralpouch declared: "Holy crap … Snoopy island … I don't care what they say I'm going over there."

Henceforth, the Japan-based Twitter-sphere deemed, the as-yet officially unnamed landmass would be known as Snoopy island.

Some speculated how long it would be before China claimed sovereignty over the island – a reference to a longstanding dispute over ownership of the Senkaku islands in the East China Sea.

Though meant as a joke, the comments did not entirely miss the mark: Japan plans to build port facilities and transplant fast-growing coral fragments onto Okinotorishima, a pair of tropical islets located even farther south of Tokyo in a resource-rich area of ocean coveted by China.

And Japan's chief government spokesman, Yoshihide Suga, welcomed the prospect that Japan's borders could stretch, if only by a few hundred metres. "If it becomes an island, our country's territorial waters will expand," he told reporters after the island was discovered last month.

By Christmas Eve, the island had expanded to about eight times its size when it was discovered, according to studies by Prof Fukashi Maeno of Tokyo University's earthquake research institute.

A massive undersea volcanic eruption had resulted in the new island linking with Nishinoshima at its two southern corners. In between sits of a pool of reddish seawater – Snoopy's perfectly positioned collar.

Experts said that volcano remains highly active, as red magma continued to rise, raising the possibility that it will lose its endearing shape as it expands.

Uncertainty surrounds the long-term future of the new island, which for now forms part of the Ogasawara chain, also known as the Bonin islands, that are administered by Tokyo despite their distance from the Japanese capital.

Hiroshi Ito, a volcanologist with the Japanese coastguard, said the island could erode after the eruptions cease. "But it could also remain permanently," he told the FNN news network.

The last recorded volcanic eruption in the area occurred in 1974, according to the meteorological agency. Much of the volcanic activity happens under the sea, which is thousands of metres deep at the site of the Izu-Ogasawara-Marianas Trench.

No doubt aware of the media buzz surrounding Snoopy island, Japan's coastguard warned that the area was still very dangerous and told would-be tourists to stay away.