Kīlauea's 1968 Hi‘iaka Crater eruption was a ground-breaking (literally) event

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Kīlauea had been quiet for about six weeks in 1968 following the end of a 251-day-long eruption in Halema‘uma‘u Crater. But the summit area had been steadily swelling for almost three years and, by August, the volcano was in a highly distended state, ready to erupt again.

Kīlauea's 1968 Hi‘iaka Crater eruption was a ground-breaking (lite...

Kīlauea's August 1968 eruption began in Hi‘iaka Crater but soon migrated down the northern part of the volcano's east rift zone. A month after the eruption ended, USGS Hawaiian Volcano Observatory scientists investigated the aftermath of a still-fuming fissure that erupted in dense forest about 5 km (3 mi) northeast of the crater.

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The first indication of an impending eruption was a flurry of small earthquakes beneath Kīlauea's middle east rift zone that began on the afternoon of August 21 and continued through the night. The seismicity was most intense between 3:00 and 6:00 a.m., HST, when several hundred earthquakes occurred near Hi‘iaka, one of the "Chain of Craters" in Hawai‘i Volcanoes National Park.

Then, shortly after 6:00 a.m. on August 22, lava erupted from a fissure within Hi‘iaka Crater on Kīlauea's upper east rift zone.

By the time USGS Hawaiian Volcano Observatory scientists reached the rim of Hi‘iaka at 7:00 a.m., a lake of lava 18 m (60 ft) deep had formed on the crater floor. Lava fountains 20 m (65 ft) high—with occasional bursts up to 45 m (150 ft) high—erupted from a fissure cutting the eastern wall of Hi‘iaka, with active vents both high on the crater wall and beneath the lava lake.

Another small fissure soon erupted on Hi‘iaka Crater's southwest wall but was short-lived. Its abrupt end at 8:40 a.m. was accompanied by a 5-minute-long "blowtorch" of roaring hot gas that caused upslope vegetation to burst into flames.

As the small fissure died, lava fountains along the main fissure peaked, and the lava lake reached its maximum depth of 27 m (89 ft) at about 9:15 a.m. The eruption then slowly declined over the next three hours.

As the fountains weakened, the lake developed a solid crust, with sluggish lava flows advancing across it. Molten lava beneath the crust began to drain back into drowned parts of the fissure and, within hours, the sinking lake surface was about 12 m (40 ft) below the high-lava mark.

The fissure within Hi‘iaka Crater stopped erupting shortly after 1:00 p.m. But the eruption was not over.

During the next three days, active vents migrated 20 km (12 mi) down the northern part of Kīlauea's middle east rift zone, erupting in six different places. These new fissures emitted billowing clouds of steam and sulfurous gas, which, along with smoke from burning trees ignited by small lava flows, were visible from Kīlauea's summit.

Meanwhile, continued drainback of lava within Hi‘iaka Crater dropped the lake surface another 6 m (20 ft). By the time the eruption ended on August 26, about 85 per cent of the lava in Hi‘iaka had drained back into the crater-floor fissure.

The August 1968 eruption was noteworthy—at the time—for several reasons: (1) No other fissures documented in written records had opened so far west on Kīlauea's east rift zone; (2) the active vents were the northernmost eruptive fissures along Kīlauea's east rift zone in at least 550 years; and (3) the fissures erupted the smallest volume of lava of any known Kīlauea eruption. More westerly and smaller eruptions have since occurred, but the 1968 vents remain the northernmost known fissures along Kīlauea's east rift zone.

Despite the small output of lava during the August 1968 eruption, ground cracking was extensive. Nine sets of cracks opened across the Park's Chain of Craters and Escape Roads near Hi‘iaka Crater, with many more cutting through the dense forest. The cracks likely opened during the seismic swarm prior to the eruption as magma wedged its way upward. Most cracks were less than 1 cm (0.4 in) wide, but a few were large enough to cause a temporary road closure until it could be repaired.

Interestingly, in 1968, maps showed the crater's name as "Heake." The crater had been named "Hiiaka" by a U.S. Geological Survey mapping team in 1912, but apparently, in the 1930s, the name morphed into Heake. During the August 1968 eruption, an HVO geologist found a weathered Park sign reading "Hiiaka" along an old trail past the crater. His discovery triggered a series of events that ultimately resulted in the U.S. Board on Geographic Names officially naming the crater "Hiiaka" in 1970. Today, its name is more commonly spelled "Hi‘iaka."


Volcano Activity Update

The lava level within the Halema‘uma‘u Overlook vent dropped below the level of the vent floor last weekend, leaving behind a few incandescent openings that sometimes issued short lava flows. This general decrease in activity was in response to the onset of DI deflation at the summit. Just after noon on Wednesday (August 17), the deflation switched back to steep inflation, and a small lava lake reappeared at the bottom of the vent overnight. This should result in a corresponding increase in the night-time glow visible from Jaggar Museum.

Following the August 3 crater floor collapse and flank eruption, lava had begun to very slowly fill the bottom of Pu‘u ‘Ō‘ō crater. This activity slowed and stopped in the past week in response to the DI event at Kīlauea's summit. Lava output from the Episode 60 flank vent also slowed dramatically, stopping almost completely by mid-week. As of this writing (Thursday, August 18), Pu‘u ‘Ō‘ō had not yet responded to summit inflation.

Six earthquakes beneath Hawai‘i Island were reported felt this past week. A magnitude-2.5 earthquake occurred at 3:48 p.m., HST, on Friday, August 12, 2011, and was located 13 km (8 mi) northeast of Hualālai summit at a depth of 14 km (9 mi). A magnitude-3.1 earthquake occurred at 4:21 a.m. on Saturday, August 13, and was located 4 km (2 mi) southwest of Kapoho at a depth of 1 km (1 mi), followed by a magnitude-1.8 earthquake at 5:18 a.m. on Sunday, August 14, in the same area. A magnitude-2.7 earthquake occurred at 05:55 a.m. on Sunday, August 14, and was located 8 km (5 mi) northeast of Pāhala at a depth of 36 km (22 mi). A magnitude-2.6 earthquake occurred at 2:40 p.m. on Monday, August 15, and was located 4 km (3 mi) northeast of Waikoloa Village at a depth of 8 km (5 mi). A magnitude-3.5 earthquake occurred at 11:19 a.m. on Wednesday, August 17, and was located 2 km (1 mi) northwest of Pāhala at a depth of 8 km (5 mi).