The short answer is “yes” it can happen, but it’s not a particularly frequent occurrence. A recent example of adjacent volcanoes erupting at the same time happened in February 2010. Klyuchevskaya and Bezymianny volcanoes, situated on the Kamchatka Peninsula in eastern Russia, erupted simultaneously sending plumes of ash and steam into the atmosphere. Fortunately, these volcanoes are found in a remote region of the Pacific Ring of Fire, an area where two tectonic plates converge with one subducting beneath the other; the combined effects of the eruptions didn’t cause widespread disruption to air traffic over Europe, unlike a couple of months later with the eruption of the single Icelandic volcano, Eyjafjallajökull.
In the case of the two Russian volcanoes, the melted rock or magma, which originates at depths of around 100 km (62.1 miles) in the earthÂ’s mantle, makes its way to the surface via a complex series of fractures and possibly chambers where magma is stored. Given the general activity of subduction volcanoes, particularly around the Pacific, it is perhaps no surprise that two nearby volcanoes could erupt at the same time. In this instance, there is no reason to believe that the two Russian volcanoes share a common magma system so the eruptions must be completely independent of one another.
However, there have been times where an eruption at a particular location was influenced by a nearby eruption. At Rabaul Caldera in Papua New Guinea in 1994, there were simultaneous eruptions at volcanic cones situated on both sides of the caldera. A caldera is a circular depression formed when a large eruption empties out magma from a chamber below the earth’s surface. The starting times of the two eruptions were about an hour apart. Therefore, in this case it is highly likely that changes associated with the first eruption of the magma storage reservoir beneath the caldera and/or below-surface stresses helped initiate the second eruption.
— David Hilton, professor, Geosciences Research Division