Shishaldin Volcano is rumbling to life in the Aleutian Islands.The Alaska Volcano Observatory detected long tremors and an increase in surface temperatures at Shishaldin earlier Tuesday.Download AudioShishaldin Volcano with a typical steam plume, pictured on Sept. 14, 2013. Photo by Joseph Korpiewski, U.S. Coast Guard.Those could be signs of an eruption, says Robert McGimsey, a geologist at the AVO.“Typical eruptions of Shishaldin have involved what we call Strombolian eruptions, which are gas-charged emissions,” McGimsey said.Shishaldin, which is located on Unimak Island is unique among volcanoes in Alaska. It doesn’t have a lava plug or a dome – just a deep, open vent.McGimsey says that when Shishaldin erupts, “It’s gas bubbles coming up through the throat or the vent of the volcano. And when they pop, it just kind of throws magma up into the air. That’skind of what defines lava fountaining.”That lava glides down the flanks of the volcano, leaving a smooth layer. That’s why Shishaldin is the most symmetrical, conical volcano in the world.But for now, there’s no lava coming out of Shishaldin. Satellite images show steam, and some light traces of ash.Still, this is the most active that the volcano has been since 2009.The AVO started logging small explosions and ash clouds at Shishaldin this winter. They elevated the volcano’s official alert level in March.