The Bolshaya Udina volcano in eastern Russia, long believed to be extinct, has shown signs of seismic unrest and has been re-classified as 'active'.
Its eruption could be severe enough to cause catastrophic damage.
It could be as bad as when the ancient Roman city of Pompeii was destroyed some 2,000 years ago.
It is impossible to predict when or whether Bolshaya Udina would erupt.
About 60 percent of the world’s seismically active volcanoes end up erupting.
Four temporary seismic stations were placed near the volcano.
Udina is a volcanic massif located in the central part of Kamchatka Peninsula, Russia.
It comprises two conical stratovolcanoes: Bolshaya Udina and Malaya Udina. The basaltic Malaya Udina rises above a low saddle at the eastern end of the complex; small lava domes also occur on its flanks.