The first tremor event was recorded from 2:44 through 2:50 a.m., volcanologists said. A second, short burst occurred at 8:47 a.m.
"Since then a series of small, repeating earthquakes is ongoing," the observatory reports.
The 10,197-foot mountain 106 miles southwest of Anchorage has been under close observation for several days due to elevated seismic activity and the release of steam and gases near the summit.
Volcanologists say the mountain could explode with little warning and dust the region with ash.
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