( CNN ) -- Japan is getting bigger and bigger and bigger -- one volcanic blast at a time . The growth so far -- compared to the size of the Asian nation 's main Honshu island or the vast continent of Asia -- is minuscule , about 200 meters ( 650 feet ) long by about 50 meters wide . That 's small enough that , if the volcanic activity stops , the newly created island could wash back into the sea in months . But if it keeps going , it could enlarge even more and stick around for the long haul , expanding Japan 's footprint in the process . `` A lot of it depends on how fast it erodes , '' said Ken Rubin , a University of Hawaii at Manoa professor and expert in deep submarine volcanism . `` Until it shuts off , it 's too soon to tell . '' Even it slips away , and even if such volcanoes poke up from the sea floor like this every few years , what 's happened so far is exciting for volcanologists . And video of the steady eruption -- a stream of white smoke , interrupted by occasional blasts of blackish material -- is powerful imagery of what 's unfolding , even if what 's emitted does n't spew anywhere as high into the sky as land-based volcanoes like El Chichon or Mount Pinatubo . Unlike these deadly examples , this Pacific volcano started its eruption -- on Wednesday , according to the Japan Meteorological Agency , at the least -- in shallows off the small , remote island of Nishinoshima , hundreds of miles over sea due south of Tokyo . The national agency since issued a warning for those around the island crater . The most common type of volcano , by far , are those that erupt and spew material underwater : Rubin estimates `` probably more than 80 % happen in the oceans , and we never know about them . '' Volcanoes that erupt on land get the most attention , for good reason , given their impact on people , vegetation and ( by virtue of their expansive eruptions into the atmosphere ) on things like air traffic patterns and climate . What 's happening near these isolated Japanese islands is more of a sea-land hybrid . It is rooted on the flank of a string of underwater volcanoes a few hundred feet from the main island , Rubin explained . What 's being expelled into the air -- a mixture of water that appears as whitish , fluffy steam and darker coarse rock fragments -- is distinct from the magma , he adds . `` In the shallow sea water , ... it causes it to behave explosively , '' Rubin said . `` It 's kind of a short-term thing . If it kept growing , it would act differently . '' By `` differently , '' he means acting like a more traditional land volcano with the crater well out of the water . Whether or not that happens , people should be able to safely set foot on the island `` pretty soon after it stops erupting , '' Rubin notes -- assuming experts are 100 % sure it wo n't blow again . If it 's feasible , say , a year from now , remains to be seen . There was a similar case two years off the Canary Islands in 2011 where there was no breakthrough , and thus no new island . Two years earlier , a new island did emerge in such circumstances near the Pacific island of Tonga -- as happened in 1963 with Surtsey , an island that built up over four years in the 1960s off Iceland .
A volcanic eruption hundreds of miles south of Tokyo forms a new island . It shows white smoke mixed with black debris , including water . ` ` It 's too soon to tell '' if the island will grow or sink into the sea , expert says .