Kilauea’s August 1968 eruption began in Hiiaka 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. (Photo courtesy of USGS)

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

Kilauea had been quiet for about six weeks in 1968 following the end of a 251-day-long eruption in Halemaumau 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.

The first indication of an impending eruption was a flurry of small earthquakes beneath Kilauea’s middle east rift zone that began the afternoon of Aug. 21 and continued through the night. The seismicity was most intense between 3 a.m. and 6 a.m., when several hundred earthquakes occurred near Hiiaka, one of the “Chain of Craters” in Hawaii Volcanoes National Park.

Then, shortly after 6 a.m. Aug. 22, lava erupted from a fissure within Hiiaka Crater on Kilauea’s upper east rift zone.

By the time USGS Hawaiian Volcano Observatory scientists reached the rim of Hiiaka at 7 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 Hiiaka, with active vents both high on the crater wall and beneath the lava lake.

Another small fissure soon erupted on Hiiaka 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 Hiiaka Crater stopped erupting shortly after 1 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 Kilauea’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 Kilauea’s summit.

Meanwhile, continued drainback of lava within Hiiaka Crater dropped the lake surface another 6 m (20 ft). By the time the eruption ended Aug. 26, about 85 per cent of the lava in Hiiaka 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 Kilauea’s east rift zone; (2) the active vents were the northernmost eruptive fissures along Kilauea’s east rift zone in at least 550 years; and (3) the fissures erupted the smallest volume of lava of any known Kilauea eruption.

More westerly and smaller eruptions have since occurred, but the 1968 vents remain the northernmost known fissures along Kilauea’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 Hiiaka 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 “Hiiaka.”