At 3:45 a.m., Friday, July 19, 1974, a flurry of earthquakes on Kilauea triggered the U.S. Geological Survey Hawaiian Volcano Observatory’s “tremor alarm.” In response, Bob Tilling, an HVO geologist, rushed to the observatory, located in what is now the Jaggar Museum within Hawaii Volcanoes National Park.
Reaching HVO within 15 minutes, Tilling saw, as expected, the distant glow from Kilauea’s middle east rift zone, where an active vent had been erupting almost continuously — and often spectacularly — since May 1969. For five years, this ongoing eruption had produced high lava fountains and sent numerous lava flows to the sea. It had also built a 397-foot lava shield called Mauna Ulu (Growing Mountain), which encompassed an active lava lake that, by July 1974, had become increasingly sluggish, with the lake level gradually dropping.
Tilling and other HVO staff quickly checked out the volcano monitoring data, which indicated that the onset of seismicity coincided with an abrupt deflation of Kilauea’s summit area. They also noted that the shallow earthquakes were centered beneath the uppermost part of Kilauea’s east rift zone and the southern part of its summit caldera, suggesting that the connection between Mauna Ulu and the summit magma reservoir was becoming clogged.
Around 10:30 a.m., the intense seismicity was accompanied by the start of strong volcanic tremor and a marked increase in the rate of summit deflation. This led Tilling and his colleagues to suspect that magma was rising toward the surface near Keanakakoi Crater at Kilauea’s summit.
Sure enough, at 12:30 p.m., lava fountains about 100 feet high erupted from a small fissure at the base of the south wall of Keanakakoi Crater.
Minutes later, a second fissure erupted north of Keanakakoi, between Crater Rim Drive and the rim of Kilauea Caldera. Fountains 50 feet to 60 feet high produced torrents of lava that poured over the caldera wall and gushed through a pre-existing gully to the caldera floor, where a third fissure soon opened to the west. As fountains surged to heights of 150 feet to 180 feet, thin lava flows spread rapidly eastward across the caldera floor.
Meanwhile, several fissures opened south of Keanakakoi Crater, erupting flows that traveled southward more than 1.2 miles, into an area west of the Park’s Chain of Craters Road near Kookoolau Crater. These fast-moving flows encased large ohia trees in fluid lava, forming numerous “lava trees,” many of which still stand today.
Flows from the southern fissures also streamed into Keanakakoi Crater in dramatic cascades of incandescent lava. The crater floor — previously covered by tephra erupted from Kilauea Iki in 1959 — was soon buried by molten lava about 16 feet deep.
At 1 p.m., a fissure opened east of the forested Lua Manu Crater, cutting across the Chain of Craters Road. This fissure and one on the crater’s east wall partly filled Lua Manu with about 50 feet of lava, much of which later drained back into the fissure, leaving a visible “high lava mark” half way up the crater walls.
Fifteen minutes later, two fissures broke out just north of the northern rim of Keanakakoi Crater. Most of this lava flowed into Kilauea Caldera, but some crossed Crater Rim Drive and spilled into Keanakakoi.
By 4:15 p.m., fissure activity in and south of Keanakakoi Crater had stopped. Low fountains continued to erupt from the caldera-floor fissures through Saturday morning but declined on Sunday. By Monday morning, July 22, all summit eruptive activity had ceased.
Volcanic tremors on Kilauea’s middle east rift zone also stopped after July 22, 1974, marking the end of the 1969–1974 Mauna Ulu eruption.
The July 1974 events provided thousands of Hawaii Island residents and visitors, as well as HVO scientists, an exciting opportunity to witness a spectacular Kilauea summit eruption from vantage points along the rim of Kilauea Caldera. Tilling fondly recalls taking a brief break from his HVO work to enjoy dinner by “lava-light” with his family at Volcano House, where the dining room afforded stunning views of the erupting fissures.
Today, you can still see abundant evidence of the 1974 eruption in and around Keanakakoi and Lua Manu Craters and within Kilauea Caldera.
Kilauea activity update
A lava lake within the Halemaumau Overlook vent resulted in night-time glow that was visible from the Jaggar Museum overlook and by HVO’s webcam during the past week. The lake level was fairly steady during the first half of the week at about 200 feet below the floor of Halemaumau Crater. The lake began to drop slightly late on Wednesday, however, with the onset of a deflation-inflation cycle.
On Kilauea’s east rift zone, surface lava flows on the coastal plain have been slowly diminishing over the past week, their front more than 0.6 miles from the ocean. There was no active ocean entry. Surface flows high on the pali, however, were more prominent and easily visible from the viewing area in Kalapana. Incandescence was visible from three degassing vents within Puu Oo, including the pit on the northeastern side of the crater floor which has held a small lava pond. The lava pond was too low to be directly visible via webcam.
No earthquakes were reported felt under the Island of Hawaii in the past week.
Visit the HVO web ite (hvo.wr.usgs.gov) for detailed Kilauea, Mauna Loa, and Hualalai activity updates, recent volcano photos, recent earthquakes, and more; 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.
