Another nearby volcano that erupted in 2009, Mount Readout, showed volcanic tremor for two months before it blew its top. "If we see [tremor]," Haney said, "that will be the next sign that Spurr ...

Mount Spurr, located about 75 miles West of Anchorage, has been acting up in recent weeks, prompting officials at the U.S. Geological Survey and Alaska Volcano Observatory to issue a yellow alert.