Categorized | Sci-Tech

Volcano Watch: Nobody’s talking about the 800-pound gorilla

(Volcano Watch is a weekly article written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.)

March 25 marks the 25th anniversary of the most recent eruption of Mauna Loa volcano. Although Kilauea, Mauna Loa’s younger and smaller sibling, gets all the attention these days, we would like to remind readers that Mauna Loa is still an active volcano.  

An eruption from Mauna Loa is more likely to pose a significant threat to life and property than a Kilauea eruption. Furthermore, when this sleeping giant erupts, it has the capability of disrupting commerce islandwide.

Mauna Loa comprises slightly more than half of the surface area of the island. The volcano has erupted 33 times in the last 150 years, producing lava flows that have covered extensive areas on the flanks of the volcano and reached the ocean eight times along the south, west, and northwest coasts of the island. 

From our fieldwork and research, we have found that all historical eruptive activity commenced with a fissure eruption in Mokuaweoweo, the summit caldera. The eruption may consist solely of this summit activity or may progress to the flank when magma intrudes into the rift zone and opens additional vents. 

Preceding the outbreak in 1984, HVO observed 18 months of higher-than-average shallow- and intermediate-depth seismicity.  The number of larger earthquakes increased in a steady progression as the eruption approached.   

Likewise, summit-crossing survey lines showing signs of extension and outward tilt indicated that magma was accumulating in the volcano. We were in a heightened state of alert preceding the eruption; yet, in the last days before the outbreak, there was no clear change in gas emissions and deformation.   

Signs that an eruption was imminent came in the form of seismic precursors: a swarm of earthquakes (hundreds per hour) and volcanic tremor late in the evening of March 24.  At 10:55 p.m., the earthquake flurry commenced followed a half hour later by the onset of tremor. The eruption began March 25 at 1:30 a.m. with the opening of a fissure vent across the summit caldera. 

By 4 a.m., the eruption migrated into the upper northeast rift zone at around the 12,000-foot elevation, sending flows parallel to the rift. Concurrently, summit activity began to wane. The dike continued to propagate downrift to the 9,300-foot elevation. Here the eruption stabilized, and this region became the focal point of the eruption. 

Initially, three fast-moving flows advanced toward Kulani Correctional Facility. To the north, a fourth flow pirated lava from the “Kulani flows” as it swept rapidly down the mountain. It advanced 15 miles in threee days, down to the 3,000-foot elevation. Intense glow, fires, and occasional methane explosions contributed to Hilo’s anxiety. 

In the early hours of March 29, the first flow advancing to Hilo was thwarted by a channel breakout and the formation of a new flow north of, and parallel to, the first. This process repeated itself over and over in the next few weeks, sabotaging any chances that the flows would reach Hilo.  

Thereafter, the lava production began to dwindle, and the lavas became pasty, resulting in more blockages and breakdown in supply to the flow fronts. Throughout April, the supply continued to decrease, and flow lengths correspondingly shortened. The eruption lasted for 22 days, ending April 15.

Mauna Loa has great volcano-hazard potential for the Island of Hawaii. The population on the slopes of the volcano is growing rapidly increasing the risk of significant damage during the next eruption. In recognition of this fact, we are planning a series of public outreach events. The first event March 17 and March 24 is a pair of public “After Dark in the Park” lectures in Hawaii Volcanoes National Park,.  

On March 28, in conjunction with our colleagues at the University of Hawaii at Hilo and county Civil Defense Agency, we plan to hold an informational forum on the UH-Hilo campus at UCB100. Then, April 4, we will be at the Konawaena Intermediate School cafeteria.  

For daily updates, visit the HVO Web site:

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