“In addition, we have detected more small magnitude (less than 3.0M) earthquakes beneath Mauna Loa than at any time since the previous eruption in 1984,” the USGS' post added. It’s these tremors that are worth keeping an eye on, as they are releasing about as much energy as they did prior to Mauna Loa’s last two major eruptions in 1975 and 1984.
However, the USGS cautions that although this is bizarre, there’s something missing from the volcano's shaky repertoire that means an eruption is likely not imminent. As the post explains, the USGS still hasn't detected any high-frequency quakes right at the summit of Mauna Loa yet – a sure sign that magma is about to breach the vent.
“But how certain is it that Mauna Loa will follow the script of 1975 and 1984?” it added. “That's the unknown.”
The USGS “cannot discount the possibility that Mauna Loa will move from current conditions to eruption more quickly than it did in 1975 and 1984,” but it also suggested that it’s possible that “the current unrest will gradually cease without the volcano erupting, as it did during periods of unrest in 2002 and 2004."
“And so, we must continue to live with uncertainty about the timing and details of Mauna Loa's next eruption.”
In short, there simply isn’t enough historical data to make the call either way. An eruption at Mauna Loa, if particularly effusive, would potentially trigger local evacuations of those living in the lava's path. As such, the USGS suggests that residents should “be prepared” just in case.