10 Surprising Facts About the 1984 Mauna Loa Eruption

Mauna Loa’s 1984 eruption. Credit: R.B.M, USGS

Thirty years ago, Mauna Loa, the massive volcano that makes up more than half of Hawaii’s Big Island, kicked off a 22-day eruption that kept geologists, emergency managers and Hawaiian residents on their toes. Below are ten rocking facts about the event.

(If you want to read the full retelling of the eruption, check out my three-post series on WIRED’s Eruption Blog here.)

1. Worst (or Best?) Party Joke Ever: The night of the eruption, all the geologists from the volcano monitoring agency, the Hawaiian Volcano Observatory, were downing beers. The occasion? HVO’s head, Bob Decker, was leaving Hawai’i’s shores for a sister agency in California. At the sendoff, Decker’s colleagues joked about the scenario on everyone’s mind: What if Mauna Loa erupted that night? According to the HVO rumor mill, when Decker got the call about the eruption later that night, he thought it was an extension of the party joke.

2. Technical Difficulties: The piece of machinery that would have given the geologists an early heads-up—on the order of minutes, possibly hours—about the forthcoming eruption had been turned off. The equipment, a seismometer used to track earthquakes, located near Mauna Loa’s summit had been temporarily shut off due to disruptive high winds in previous weeks.

3. Where Ya Going?: In the eruption’s earliest hours, Mauna Loa’s lava flows proved fickle. Within a span of 10 hours, the eruptive source started at the summit, moved to the southwestern slope, returned to the summit and then finally committed to the northern slope.

4. Pack Your Bags: Early on in the eruption, several families living in the threatened Hilo town’s suburbs highest up on the mountain evacuated their homes voluntarily. Even though the flows were still several miles away, at night, when they glowed a terrible red, the lava seemed impossibly, stressfully close.

5. Data Disruption: On the eruption’s second day, lava devoured a terminal of power lines, shutting off the electricity at the meteorological Mauna Loa Observatory. The group’s carbon-dioxide emission data collection—the same data used in the famous Keeling curve tracking global warming—got temporarily disrupted, among other experiments. It was the first time that CO2 data had not been collected since the study began in 1958.

6. Double Rainbow Eruption: Nearly a week into Mauna Loa’s eruption, another Hawai’i volcano decided to follow suit. On Friday, March 30, 1984, the smaller Kilauea volcano started erupting within the confines of Hawai’i Volcanoes National Park, marking the first double-eruption in almost 116 years!

7. Did You Call?: Once the news had spread that Mauna Loa was erupting, HVO “was besieged” with phone calls, according to then-Mauna Loa geologist Jack Lockwood. At the time, the scientific group did not have a media person. So HVO’s head Bob Decker took on the role and got volunteers from the community to help him man the phones. During the eruption’s early days, Decker also gave regular press conferences about the volcano monitoring and threat-level.

8. Butting Heads: From the public’s perspective, the two agencies tag-teaming the lion’s share of the eruption response—HVO and Civil Defense—got along swimmingly. But behind doors, Civil Defense director Harry Kim and geologist Jack Lockwood disagreed on several issues, from volcano viewing to disaster outreach.

9. Don’t Touch This: As the lava flows pushed closer to Hilo, authorities cooked up a lava diversion plans, such as building a protective barrier around certain key buildings like the hospital, on the down-low. Then—and now—lava diversion is a sensitive topic in Hawaii. This is because according to Hawaiians who believe in the volcano goddess Pele, it is sacrilegious to obstruct the flows in any way because the flows are a physical extension of the deity. Fortunately, those diversion plans were never needed; the flows stopped around 4.5 miles north of Hilo, sparing the city.

10. One is the Loneliest Number: Only one geologist now working at HVO, current Mauna Loa geologist Frank Trusdell, was around to see the mighty mountain when it was last in action in 1984. At the time, Trusdell had been a temporary hire, who took time off from graduate school to help the HVO monitoring efforts.


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