Satellites passing over the island have also picked up light steam emissions from the volcano, which sits at an elevation of about 5709ft.
The AVO said: “Renewed explosive activity or lava effusion remain possible outcomes of the current period of unrest.
“This is not certain and a decline in unrest to background levels of activity is also possible.
“Great Sitkin volcano is monitored by local seismic and infrasound sensors, satellite data, web cameras, and remote infrasound and lightning networks.”
The nearest city, Adak, is located about 26 miles away and boasts a population of more than 300.