Volcano Watch: Comparing 1984 and 2022 Mauna Loa eruptions on the Big Island

Volcano Watch is a weekly article and activity update written by scientists and affiliates with the U.S. Geological Survey’s Hawaiian Volcano Observatory. 

Mauna Loa’s recent eruption is still fresh in the minds of Hawaiian Volcano Observatory scientists and Island of Hawai‘i residents. Now is a good time to reflect on this event, especially in comparison to the previous eruption — 38 years ago.

Despite the development of new volcano monitoring techniques, decades between the eruptions meant there were many uncertainties leading to the recent eruption. Did the unrest observed during the fall of 2022 mean an eruption would certainly occur? How soon would modern monitoring signals show signs of an imminent eruption?

At the same time, 33 previously observed Mauna Loa eruptions have demonstrated certain patterns that the observatory could be confident the volcano would follow if it erupted again. One patterns is that all previous eruptions began in the summit caldera.

Additionally, half of those eruptions stayed in the summit and half migrated to a rift zone or radial vent. If the eruption migrated out of the summit, where would it go? 

The answer to that question wouldn’t become evident until it happened. A Southwest Rift Zone eruption could impact infrastructure within hours; a Northeast Rift Zone eruption would take days, weeks or months to impact infrastructure downslope.

Throughout the fall of 2022, as Mauna Loa became more active, Hawaiian Volcano Observatory worked closely with the County of Hawai‘i Civil Defense Agency to educate the island residents.  We held community meetings, gave media interviews, published “Volcano Watch” articles, official notices and social media posts about the uncertainties and certainties of a Mauna Loa eruption.

We encouraged kamaʻāina living or working on the flanks of Mauna Loa to prepare for the possibility of an eruption. And as unrest continued, the Hawai‘i Volcanoes National Park closed Mauna Loa’s backcountry to hikers on Oct. 5.

When the eruption began, on the night of Nov. 27, events unfolded similarly to the 1984 eruption. Seismic signals indicating an impending eruption occurred less than an hour in advance of each eruption. Both eruptions occurred in the middle of the night, waking scientists and residents from their slumber.

In 1984 and 2022, bright glow from fountains within Moku‘āweoweo was visible around the island. Word of the eruption spread quickly — in 1984 via the coconut wireless and in 2022 via social media and digital news organizations.

In 2022, some residents living near the Southwest Rift Zone chose to self-evacuate in case the eruption migrated there. Fortunately, both the 1984 and 2022 eruptions migrated within hours from the summit to the Northeast Rift Zone, where there was no immediate danger to people or property.

Weather sometimes prevented observatory crews from making observations during both eruptions; however, technological advancements since 1984 allowed the observatory to provide remote views of the 2022 eruption in near real-time. Furthermore, the observatory deployed webcams and a livestream video that were available to the public.

Modern technology allowed the observatory to share, in near real time, accurate 2022 flow maps, derived from satellite imagery and overflights, with Civil Defense, our partners and the public.

Lava flow models used digital elevation models to evaluate lava flow paths and potential impacts. This information was shared during daily press briefings in 2022, a communication strategy that was also used during the 1984 eruption.

These observations and others were summarized at the International Association for the Volcanology of Earth’s Interior scientific assembly meeting that takes place every four years. This year, the meeting occurred in Rotorua, New Zealand, where Hawaiian Volcano Observatory staff were invited to present talks on the recent eruption.

Presentations described the buildup to the eruption, the magma system, flow mapping and modeling, and interagency coordination and messaging.

How do these eruptions compare physically? 

In 1984, about 58 billion gallons were erupted and covered an area of 11,860 acres. The 2022 eruption produced almost 40 billion gallons and covered an area of 8,900 acres. The volume and area covered was close to the average and median values for all historical Northeast Rift Zone eruptions. While it was spectacular to view, the 2022 eruption was ordinary by scientific standards.

Fortunately, these two eruptions have not greatly impacted infrastructure on the Island of Hawai‘i, but future eruptions at some point will. Hawaiian Volcano Observatory appreciates our community awareness and preparedness for eruptions, which are part of the dynamic and beautiful landscape of Hawai‘i nei.