Geophysicists recently have detected more seismic activity than normal beneath the surface of the slumbering volcano, located on the west side of Cook Inlet, 80 miles west of Anchorage.
Although some seismic activity is normal beneath a dormant volcano, up to 20 earthquakes per day are being registered beneath the mountain.
"That is quite a change from what we'd consider to be normal background activity," said John Power, a geophysicist with the Alaska Volcano Observatory.
The current activity is the most seen beneath the mountain since 1992, when Mount Spurr last erupted. However, the new activity is in a different location than the past eruption.
The current seismic activity is directly beneath the summit.
The 1992 eruption took place at Crater Peak, a vent on the flank of the mountain two miles south of the summit, as did an eruption in 1953.
The last known eruption of the summit dome of Mount Spurr was 5,000 years ago, which is a good indication that the current earthquake activity below the summit is not likely to lead to an eruption, according to Power.
"The most likely scenario at this point is this activity will just die out," he said.
Geologists flew over Mount Spurr on July 15 but found no indications of recent volcanic activity.
Even so, due to the volcano's increased seismic activity, the observatory raised its level of concern color code Monday from green to yellow which means the volcano has gone from dormant to "restless," according to a press release.
The earthquakes beneath Spurr are relatively small, registering less than magnitude 1.5, and relatively deep, centered between a half and 4 miles below sea level.
The quakes would have to become more severe, shallower and more frequent before the observatory would raise the level of concern color code to orange or, the highest code, red.
The ground likely also would bulge and vent steam, according to Power.
However, those kinds of changes in activity usually take some time. Mount Spurr's eruption in 1992 was preceded by nearly a year of small earthquakes.
"We don't see anything coming down the pike in two, three days, nothing like that," Power said. "We don't see any immediate short-term risks."
Peninsula Clarion
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