Hawaiian Volcano Observatory scientists have raised the volcano alert level at Mauna Loa to "advisory" from normal, the U.S. Geological Survey announced Thursday. 

The change in status for the Big Island volcano means it "is showing signs of unrest that are above known background levels, but it does not mean that a Mauna Loa eruption is imminent or certain," according to the announcement. 

The USGS said that HVO’s seismic stations have recorded elevated rates of "shallow, small-magnitude earthquakes beneath the summit, upper Southwest Rift Zone, and west flank of Mauna Loa for at least the past year." The scientists have also measured inflation on Mauna Loa that is indicates a recharge of the volcano’s shallow magma storage system, which led them to raise the alert level to yellow, or advisory. 

"It’s possible that the increased level of activity at Mauna Loa could continue for many months, or years, without leading to an eruption," said Tina Neal, HVO’s Scientist-in-Charge. "It is also possible that the current unrest could be a precursor to the next eruption of Mauna Loa. But at this early stage, we cannot determine precisely which possibility is more likely." 

The scientists stressed that "progression toward an eruption is by no means certain, but the volcano is closely watched to track how the unrest develops. 

The last time HVO changed the status for Mauna Loa to advisory was in 2004-05 after another period of rapid inflation of the volcano. No eruption resulted and after the inflation slowed the status of Mauna Loa was returned to green, or normal. 

The most recent eruption of Mauna Loa began on March 25, 1984 and lasted just over three weeks. It was preceded by up to three years of increased earthquake activity, scientists said. 

HVO said it continues to closely monitor Mauna Loa, and will notify Hawaii County Civil Defense, the National Park Service and the public, if significant changes are detected.