We’ve learned a lot about Kilauea’s explosive history in the past 15 years. Once thought to be rare, explosive eruptions from the volcano’s summit are instead frequent and clustered into periods lasting several centuries. For example, between 1500 and the late 1700s, Kilauea’s eruptions were almost always explosive. We can be thankful that Kilauea is in a quiet period now, but we shouldn’t have an ostrich mentality about the future. If it happened yesterday, it can happen tomorrow.
Early residents of the island experienced only lava flows and accompanying lava fountains, during a period of eruptive activity similar to today’s. Some archaeologists now say the island was first populated in the early 1200s, 300 to 400 years later than previously thought. This is controversial, but it is true that, until about 1500, people on the island probably knew only about lava flows. The Pele concept may have arrived in the late 1300s, just before a giant lava flow — the largest erupted on the island since people have been here — lasted for about 60 years and destroyed much of Puna’s forest.
Things changed dramatically in about 1500, when the summit of Kilauea collapsed to form the caldera that, with some changes — mostly filling — remains today. The depression was so deep that it apparently intersected the water table, ushering in about 300 years of mostly steam-driven explosive eruptions. Imagine the impression that such a change, from quiet lava flows to violent explosive eruptions, must have had on island residents!
At least two elements of oral tradition tell of events during this time. The first describes when Hiiaka, digging for the body of Lohiau who was killed by Pele, was warned to stop digging or water would come in to drown Pele. This may record the dropping of the caldera down to the water table, so that standing water could be seen in places on the caldera floor. We now know that this happened in about 1500.
A second story tells of Kamapuaa trying to drown Pele during a lover’s tiff. Pele almost succumbed but eventually mustered all her strength, threw rocks at Kamapuaa, and chased him to the ocean. This is a colorful metaphor for a steam-driven explosive eruption.
The only eruption before 1790 strong enough to throw fine gravel into the ocean took place in about 1650. We determined this date by studying and dating several deposits left by explosive eruptions. One explosive eruption, with a carbon-14 charcoal age of 1650, dropped such rocks about where Chain of Craters Road meets the sea.
These events may seem minor, inconsequential curiosities in comparison to occurrences in today’s society. But imagine yourself caught in an explosive eruption at Kilauea’s summit. Major or minor doesn’t matter when ash or blocks are falling around you, the air is hot and choking, and hot ash-air-steam mixtures are surging across the ground surface at hurricane velocities.
That is just what happened in November 1790, when several hundred people were killed, likely between Namakanipaio and Jaggar Museum, during the deadliest eruption known to have occurred at a volcano now in the United States. The unfortunate victims were apparently caught by a hot, ash-rich surge that both suffocated and burned them to death.
Today most island residents and visitors are blithe to what happened in 1790, much less the preceding 300 years of violent but generally smaller explosive eruptions. Reading the geologic past, however, we think it almost certain that Kilauea will eventually return to a long period of mostly explosive activity, just as it did in about 1500. The explosive period will probably be initiated by collapse of the caldera floor down to the water table, which today is about 2015 feet below the high point on the caldera rim. For comparison, the caldera today is about 400 feet deep. During the next explosive period, which could last several centuries, the summit of Kilauea will often be a place to avoid. We can count our blessings now, but eventually our descendants will have to deal with a Kilauea that is very different from the one we know today.
Kilauea activity update
The summit lava lake within Halemaumau Crater produced nighttime glow visible via HVO’s webcam over the past week. The lava lake level was relatively steady at 100 to 115 feet below the rim of the overlook crater.
On the east rift zone of Kilauea volcano, the June 27 flow from Puu Oo continued to advance toward the northeast and reached 4.3 miles from the vent by midweek. Within Puu Oo crater, at least one small lava pond was active on the crater floor.
One earthquake was reported felt during the past week on Hawaii Island. At 12:08 a.m. Tuesday, a magnitude 3.2 earthquake occurred 19 miles northwest of Kailua-Kona at a depth of 16 miles.
Visit the HVO website, hvo.wr.usgs.gov, for past Volcano Awareness Month articles and current Kilauea, Mauna Loa and Hualalai activity updates, recent volcano photos and recent earthquakes; call 967-8862 for a Kilauea summary; email questions to askhvo@usgs.gov.
Volcano Watch is a weekly article and activity update written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.