Mike Poland with the U.S. Geological Survey said Wednesday the plume seems to be made largely of rock dust.
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Because there’s little wind, the plume for the most part is rising vertically over the summit.
USGS scientists will not monitor the plume from a summit observatory because of fears of falling ash.
Instead, they will operate from a backup command center at the University of Hawaii at Hilo.
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Warnings to pilots are still in place because of the plume that reached 12,000 feet (3,658 meters) Tuesday.
The volcano has been spewing lava from fissures that opened up on its flanks for two weeks.