Today marks the 25th anniversary of the last eruption of the Big Island of Hawaii’s Mauna Loa volcano.

At 1:30 a.m. on March 25, 1984, the largest active volcano on Earth woke up suddenly and spectacularly after nine years of slumber. The eruption sent several fast-moving fingers of lava down Mauna Loa’s gentle slopes, primarily over old flows and through upslope forests. One of the fastest of these molten Earth fingers immediately took direct aim at the Big Island’s largest city, Hilo, putting its residents on high alert in the days that followed.

The eruption ended three weeks after it began, its longest finger of lava coming to a stop just four miles from the nearest Hilo home. Mauna Loa has been quiet ever since.

Geologists at the Hawaiian Volcano Observatory on neighboring Kilauea volcano do not expect Mauna Loa to erupt any time soon. Near-surface earthquake activity that typically precedes Hawaii volcano eruptions by years or months isn’t being detected on Mauna Loa currently. (There were three years of such temblors prior to the 1984 eruption.) But though quiet for the moment, Mauna Loa is still considered as active as its younger, smaller and currently erupting sister mountain Kilauea.

Mauna Loa has erupted 33 times in the last 150 years. And though its current slumber has gone on longer than other periods of inactivity, geologists predict that another quarter-century isn’t likely to pass before the mountain erupts again.

On the occasion of March 2008's heightened eruptive activity at Kilauea and the 24th anniversary of the Mauna Loa eruption, I wrote a post from my memories of those exciting and frightening three weeks in Hilo in 1984.

Here it is again:

The current eruption of Kilauea is bringing back old memories for me.

I grew up on the Big Island of Hawaii. Mauna Loa awoke in the early morning hours 24 years ago this week, March 25, 1984.

The 1984 eruption on the 13,680-foot volcano’s southeast flank produced a river of lava that came within four miles of the upper slopes of Hilo before stopping.

I lived in Hilo at the time.

My friends and I joined other residents on Hilo’s bayfront or near the airport runway after dark, studying the suddenly strange-looking mountain looming over the city. The familiar placid evening silhouette was gone. Mauna Loa now had a glowing amber hot spot and a thin finger of orange lava moving downslope through its thick forests.

Twenty-four years ago we had a rare opportunity that even the current eruption does not afford: Two Hawaii volcanoes erupting simultaneously. Turn southeast at the Hawaiian Volcano Observatory and you’d see clouds lit up by the Kilauea eruption downslope. Turn west, and you could make out the curtain of 160-foot lava fountains upslope on Mauna Loa.

We became nightly volcano watchers over the three weeks that followed. Meanwhile, the intensely glowing orange finger of lava drew closer to the lights of Hilo each night. Fascination turned to fear. The town buzzed with talk of evacuation.

A friend’s house in upper Hilo was at least a dozen miles away from where the tip of the flow was mowing down vegetation. But sitting in his backyard gazing at the intense orange glow streaming through the forest beyond after dusk, you’d think it was just over the treeline, possibly arriving before morning.

In the end, the gentler slopes and thick forests of Mauna Loa’s lower elevations slowed the flow’s progression. The eruption ended around the same time, three weeks to the day it began. Hilo returned to its sedate pace. Mauna Loa has been quiet ever since.

Hawaiian Volcano Observatory’s most recent Mauna Loa report on March 15 showed no seismic activity or ground swelling—which means no lava is collecting in the mountain’s sizable below-surface reservoir.

One has to wonder, though, how long Mauna Loa will continue to let its younger sibling Kilauea continue to steal all the attention.

And so it remains today, as well.

Click here for Hawaiian Volcano Observatory Mauna Loa-related film and talk story events happening today through April 4 on the Big Island.

 


Check out these related HawaiiMagazine.com posts:
Remembering Mauna Loa's last eruption
The woes of Mauna Kea
Big Island of Hawaii's Mauna Lani Bay Hotel closing for renovations