VOLCANO MADNESS: [Geology2] Kilauea’s July 1974 summit eruption: fond memories of dinner by “lava-light”

Saturday, July 28, 2012

[Geology2] Kilauea’s July 1974 summit eruption: fond memories of dinner by “lava-light”

Volcano Watch: Kilauea's July 1974 summit eruption: fond memories of dinner by "lava-light"

Thursday, July 26, 2012.

Lava fountains, occasionally surging to heights of 45–55 m (150–180 ft), erupted south and north of Keanakako`i Crater (top and middle fissures, respectively) and on the floor of Kilauea Caldera (foreground fissure) in a spectacular summit eruption on July 19, 1974. A torrent of lava (largely obscured by fume at lower right) gushed to the caldera floor through a pre-existing gully. USGS photo.

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

At 3:45 a.m., Friday, July 19, 1974, a flurry of earthquakes on Kilauea triggered the USGS 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 in Hawai`i 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 121-m- (397-ft-) high 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 Keanakako`i Crater at Kilauea's summit.

Sure enough, at 12:30 p.m., lava fountains about 30 m (100 ft) high erupted from a small fissure at the base of the south wall of Keanakako`i Crater.

Minutes later, a second fissure erupted north of Keanakako`i, between Crater Rim Drive and the rim of Kilauea Caldera. Fountains 15-20 m (50-65 ft) 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 45–55 m (150–180 ft), thin lava flows spread rapidly eastward across the caldera floor.

Meanwhile, several fissures opened south of Keanakako`i Crater, erupting flows that traveled southward more than 2 km (1.2 mi), into an area west of the Park's Chain of Craters Road near Ko`oko`olau Crater. These fast-moving flows encased large `ohi`a trees in fluid lava, forming numerous "lava trees," many of which still stand today.

Flows from the southern fissures also streamed into Keanakako`i 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 5 m (16 ft) deep.

At 1:00 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 15 m (50 ft) of lava, much of which later drained back into the fissure, leaving a still-visible "high lava mark" half way up the crater walls.

Fifteen minutes later, two fissures broke out just north of the northern rim of Keanakako`i Crater. Most of this lava flowed into Kilauea Caldera, but some crossed Crater Rim Drive and spilled into Keanakako`i.

By 4:15 p.m. Friday, fissure activity in and south of Keanakako`i 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 tremor 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 Hawai`i 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 Keanakako`i and Lua Manu Craters and within Kilauea Caldera. Take a look!

http://www.hawaii247.com/2012/07/26/volcano-watch-kilaueas-july-1974-summit-eruption-fond-memories-of-dinner-by-lava-light/