Dense, large rocks roughly 60 centimetres in diameter were found in a vehicle park a few hundred metres away from Kilauea's summit crater, and "reflect the most energetic explosions yet observed and could reflect the onset of steam-driven explosive activity", the Hawaiian Volcano Observatory said in a statement.
A 4.2 magnitude quake at the volcano at 8.36am (2:36pm EDT) prompted authorities to issue an alert reassuring rattled Big Island residents that there was no risk of a tsunami from the volcanic activity.
The United States Geological Survey (USGS) posted an aviation red alert for the first time for the Kilauea volcano in Hawaii as explosions intensified on Tuesday.
Scientists say earthquakes may shake loose rocks underground and open up new tunnels for lava to flow. The troops may be needed for emergency evacuations, search and rescue, clearing debris and other duties.
The Hawaiian County Civil Defense Agency said rock falls and gas explosions from one of the craters on Kilauea had caused the ash plume which was drifting downwind to the southwest.
A shift in winds was expected to bring ash and vog inland on Wednesday and make them more concentrated, said John Bravender of the National Oceanic and Atmospheric Administration (NOAA). "The plume, it's not near as ashy as it was yesterday, and it's rising more or less vertically over the summit region".
"We're observing more or less continuous emission of ash now with intermittent, more energetic ash bursts or plumes", Steve Brantley, a deputy scientist in charge at the Hawaiian Volcano Observatory (HVO), said while on a conference call with reporters.
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"They're just in disarray and frantic", Adele Tripp, an employee at the Kilauea General Store, said of other residents.
The plume is separate from the lava eruptions occurring about 40 kilometres away from summit, where about 20 lava fissures in the earth have destroyed more than two dozen homes and forced the evacuation of about 2,000 residents.
Geologists have warned that Kilauea's summit could have an explosive steam eruption that would hurl boulders and ash miles into the sky. Residents and scientists are keeping a close watch for more violent activity. But it's not certain when or if that might happen.
The Hawaii Fire Department said there is a high alert level for air quality near Lanipuna Gardens estates because of fissures.
The area taking the brunt of the eruption is about 40km down Kilauea's eastern flank, near the village of Pahoa.
Several fissures remained active Wednesday, producing lava spatter.