MAUNA LOA, HAWAII (HawaiiNewsNow) - Two years ago, the Hawaiian Volcano Observatory upgraded the volcano alert level for Mauna Loa from normal to advisory.
That's where it remains today.
And officials are urging residents not to put their guards down.
The 2015 upgrade followed more than a year of inflation, as magma filled reservoirs beneath the summit.
That was new behavior for a volcano that had been quiet for years.
At the same time, the observatory said, the rate of shallow, small earthquakes in the area increased.
"Since then, rates of inflation and seismicity have waxed and waned, but have remained above what we consider to be long-term background levels," the observatory, in a recent publication. "In addition, we have detected more small magnitude earthquakes beneath Mauna Loa than at any time since the previous eruption in 1984."
That 1984 eruption — the most recent for Mauna Loa — attracted spectators from around the state and world. Lava flows advanced 15 miles in three days, and got within about four miles of the outskirts of Hilo.
There have been previous eruptions, too.
In 1881, lava almost reached Hilo. In 1926, a fast-moving flow 50 feet high wiped out the fishing village of Ho'opuloa. In 1950, lava covered homes in Pahoehoe.
Today, Mauna Loa remains the largest active volcano in the world.
While officials say an eruption isn't likely in the next few weeks or months, one could be a reality at some point soon.
"If Mauna Loa follows the 'script' of 1975 and 1984, before the volcano ramps up to an eruption, we would expect to see lots of small earthquakes occurring frequently beneath the summit — many more than are currently recorded — over a period of months," the observatory said.
"We would also expect at least an hour, or hours, of tremor (constant ground vibration) as a final warning that magma is on its way to the surface."