Surprising as the picture may be, the simultaneous eruptions of the Kamchatka Peninsula's Klyuchevskaya and Bezymianny volcanoes isn't all that shocking, according to geologist James Quick of Southern Methodist University in Texas.
"Kamkatcha [map] volcanoes are very active, so it's not uncommon for more than one of these volcanoes to be erupting at the same time," Quick said.
In fact, the volcanoes' close proximity makes it more, not less, likely that they'd explode in unison, he said.
Though there's no "great pool or pipe of lava connecting them," he said, the volcanoes lie above the same active subduction zone, an area where one tectonic plate is diving under another. So if the gnashing of the plates sends heat, lava, gas, or ash up through the earth toward one of the volcanoes, chances are the other might get it too. (See plate tectonics pictures.)
(Also see: "Pictures: Chile Volcano Erupts With Ash and Lightning.")
Among the Most Active Volcanoes on Earth
The recent simultaneous eruption began on February 11, when 16,000-foot-tall (4,835-meter-tall) Klyuchevskaya erupted.
Scorching lumps of rock shot more than 1,000 feet (300 meters) into the air, and tall plumes of gas and steam billowed up to 20,000 feet (6 kilometers) above sea level.
Around the same time, 9,500-foot-tall (2,882-meter-tall) Bezymianny was sending up plumes that were smaller and thinner than its neighbor's but still dangerous to low-flying aircraft.
Volcanoes on Kamkatcha are among the most active anywhere on Earth, in part because they lie along the Pacific Ring of Fire—an seismically active arc stretching roughly northward from Chile to Alaska, then westward to Japan and southward to the South Pacific.
Twenty Volcanoes Erupting Right Now?
On a global scale, simultaneous volcanic eruption is a constant.
According to the Smithsonian Institution's Global Volcanism Program, there are about 20 volcanic eruptions happening at any given moment. Some, like Italy's Stromboli volcano, have been erupting continuously for more than a thousand years.
"At one point in 2005, there were five eruptions within the United States all happening at the same time," Quick said.