1984 eruption of Mauna Loa

The 1984 eruption of Mauna Loa was a Hawaiian eruption in the U.S. state of Hawaii that lasted from March 25 to April 15, 1984. It ended a 9-year period of quiescence at the volcano and continued for 22 days, during which time lava flows and lava fountains issued from the summit caldera and fissures along the northeast and southwest rift zones.

1984 eruption of Mauna Loa
Aa channel flow from Mauna Loa
Lava fountains and a'a channel flow during the 1984 eruption
VolcanoMauna Loa
DateMarch 25, 1984 – April 15, 1984[1]
Time1:30 a.m. HST[2]
TypeHawaiian
LocationHawaii, Hawaiian Islands
19°28′03″N 155°35′29″W / 19.46750°N 155.59139°WCoordinates: 19°28′03″N 155°35′29″W / 19.46750°N 155.59139°W
VEI0[1]
1984 Mauna Loa lava flows
Map showing areas covered by ‘a‘ā lava flows during the 1984 eruption of Mauna Loa

Precursors

Repeated deformation measurements showed that the summit area of Mauna Loa began to inflate shortly after a brief summit eruption on July 5–6, 1975. This was followed by a 3-year period of slowly increasing earthquake activity beneath the volcano that included a swarm of earthquakes 3 to 9 mi (4.8 to 14.5 km) deep in mid-September 1983. The earthquakes reached a maximum frequency just after a 6.6 magnitude earthquake took place beneath the southeast flank of Mauna Loa, in the Ka‘ōiki fault system, on November 16, 1983. Following the Ka‘ōiki earthquake, the number of earthquakes over 1.5 magnitude increased gradually as the time of eruption approached.[2]

The immediate precursors to the 1984 eruption consisted of an abrupt increase in small earthquakes and volcanic tremor recorded on seismic stations located near Moku‘āweoweo caldera. At 10:55 p.m. on March 24, small earthquakes began at a rate of 2–3 per minute. By 11:30 p.m., the seismic background increased, marking the onset of tremor. Just before 1:00 a.m. on March 25, the tremor amplitude increased to the point that the astronomical telescopes on Mauna Kea, 25 mi (40 km) to the northwest, could not be stabilized due to the constant ground vibration.[2]

Eruption

Mauna Loa erupting at night, 1984
Night time view of the 1984 eruption

At 1:25 a.m., a military satellite recorded a strong infrared signal from the summit of Mauna Loa, indicating that the eruption was underway. Within just a few minutes, people throughout Hawaii island were reporting an intense red glow above the volcano. Eruptive fissures migrated rapidly down the southwest rift zone to the 12,750 ft (3,890 m) elevation and across the southern half of Moku‘āweoweo (flow A on map). By 4:00 a.m., lava fountains extended across the northeast half of Moku‘āweoweo and into the upper reaches of the northeast rift zone (flow B on map).[2]

At 10:30 a.m., intense steam emissions began along a fracture 0.6 mi (0.97 km) long farther down the northeast rift zone between the 10,690 and 10,400 ft (3,260 and 3,170 m) elevation, but no eruptive fissure formed in this area. By mid-afternoon, eruptive activity began to decrease at the uppermost vents between 12,140 and 12,400 ft (3,700 and 3,780 m).[2]

At 4:41 p.m., a new fissure opened up at the 9,350 ft (2,850 m) elevation. This fissure rapidly migrated both uprift and downrift, so that by 6:30 p.m., a line of lava fountains slightly longer than 1 mi (1.6 km) was active. Eventually the fissure system condensed to four centers of activity with fountains up to 50 m (165 ft) high. Four parallel flows (flows D on map) moved down the northeast flank at speeds as fast as 300 to 700 ft (91 to 213 m) per hour. All vents uprift from these new ones quickly became inactive and the eruptive activity was confined to these vents for the next three weeks. Six large vent structures eventually formed in this area around the active vents. By daybreak on March 26, these vents were feeding lava to a fast-moving flow (flow E on map) that had advanced 5.5 mi (8.9 km) to the northeast and three less active, shorter flows (flows D on map) that were advancing east toward Kulani Prison. The prison was put on alert because the shorter lava flows were as close as 2 mi (3.2 km) to the prison. These flows, however, stopped advancing within 48 hours and never crossed the Powerline Road.[2]

1984 Mauna Loa Eruption (16285896735)
Hawaiian Volcano Observatory geologists board a helicopter as large lava fountains erupt in the background during the 1984 eruption. Helicopters provided access to remote areas of the eruption and were essential for safety.

The fast-moving flow (flow E on map) advanced as a relatively narrow, channelized ‘a‘ā lava flow. Its rate of advance slowed as it moved downslope, but by March 29 the flow had moved 15.5 mi (24.9 km) to an elevation of 3,000 ft (910 m). At this time, the flow front was about 4 mi (6.4 km) from the outskirts of Hilo. Smoke from burning vegetation, loud explosions caused by methane gas along the advancing flow front and the intense glow at night all contributed to a growing concern among Hilo's residents.[2]

Early in the morning of March 29, a levee along the lava channel broke at the 1,737 m (5,699 ft) elevation about 8 mi (13 km) upslope from the flow front (flow E on map). The lava was diverted into a new subparallel flow (flow F on map) and flow E stagnated, temporarily relieving emergency-response officials and residents of Hilo. This new ‘a‘ā lava flow moved at a comparable rate to the earlier flow E, yet did not extend beyond flow E until April 4.[2]

Another significant levee breakout occurred on April 5, forming a third subparallel ‘a‘ā lava flow (flow G on map) that moved downslope. Concurrently, lava output at the source vents diminished slightly, and the lava became more viscous, resulting in channel blockages and levee collapses that occurred more frequently. The collapses restricted the supply of lava to the flow fronts, which moved steadily higher and more distant from the outskirts of Hilo. By April 14, no active ‘a‘ā lava flows extended more than 1.25 mi (2.01 km) from the vents, and on April 15, the eruption ended.[2]

References

 This article incorporates public domain material from websites or documents of the United States Geological Survey.

  1. ^ a b "Mauna Loa". Global Volcanism Program. Smithsonian Institution. Retrieved 2019-06-21.
  2. ^ a b c d e f g h i "March 25 - April 15, 1984". United States Geological Survey. 2016-12-12. Retrieved 2019-06-23.

External links

1955 Hawaiian submarine eruption

The 1955 Hawaiian submarine eruption was a submarine eruption that occurred 90 km (56 mi) northeast of Necker Island on August 20, 1955. Steaming water, water discoloration and an eruption column took place during the eruption. A possible pumice raft was also witnessed. The eruption originated about 4 km (2.5 mi) below sea level from an unnamed submarine volcano. The eruption produced a column of smoke several meters high. It is probably the westernmost historical eruption within the Hawaiian Islands. Another but less certain submarine eruption may have occurred 60 km (37 mi) northwest of Oahu on May 22, 1956.

Kīlauea

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It is the second youngest product of the Hawaiian hotspot and the current eruptive center of the Hawaiian–Emperor seamount chain. Because it lacks topographic prominence and its activities historically coincided with those of Mauna Loa, Kīlauea was once thought to be a satellite of its much larger neighbor. Structurally, Kīlauea has a large, fairly recently formed caldera at its summit and two active rift zones, one extending 125 km (78 mi) east and the other 35 km (22 mi) west, as an active fault of unknown depth moving vertically an average of 2 to 20 mm (0.1 to 0.8 in) per year.

Kīlauea erupted nearly continuously from 1983 to 2018, causing considerable property damage, including the destruction of the towns of Kalapana in 1990, and Vacationland Hawaii and Kapoho in 2018. During the 2018 lower Puna eruption, which began on May 3, two dozen lava vents erupted downrift from the summit in Puna. The eruption was accompanied by a strong earthquake on May 4 of Mw 6.9, and nearly 2,000 residents were evacuated from the rural Leilani Estates subdivision and nearby areas.

On May 17, 2018 at 4:17 AM, the volcano explosively erupted at the summit in Halemaʻumaʻu, throwing ash 30,000 feet into the air. Continued explosive activity at the summit caused a months-long closure of the Kīlauea section of Hawaii Volcanoes National Park. Vigorous eruptive lava fountains in lower Puna sent destructive rivers of molten rock into the ocean in three places. The lava destroyed Hawaii's largest natural freshwater lake, covered substantial portions of Leilani Estates and Lanipuna Gardens, and completely inundated the communities of Kapoho, Vacationland Hawaii and all but three houses in the Kapoho Beach Lots. Lava also filled Kapoho Bay and extended new land nearly a mile into the sea. The County of Hawaii reported that 716 dwellings were destroyed by lava. By early August the eruption subsided substantially, and the last active lava was reported at the surface on September 4, 2018. Portions of Hawaii Volcanoes National Park reopened to the public on September 22. On December 5, 2018, after 90 days of inactivity from the volcano, the eruption that started in 1983 was declared to be over.

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Mauna Loa

Mauna Loa ( or ; Hawaiian: [ˈmɐwnə ˈlowə]; English: Long Mountain) is one of five volcanoes that form the Island of Hawaii in the U.S. state of Hawaiʻi in the Pacific Ocean. The largest subaerial volcano in both mass and volume, Mauna Loa has historically been considered the largest volcano on Earth, dwarfed only by Tamu Massif. It is an active shield volcano with relatively gentle slopes, with a volume estimated at approximately 18,000 cubic miles (75,000 km3), although its peak is about 125 feet (38 m) lower than that of its neighbor, Mauna Kea. Lava eruptions from Mauna Loa are silica-poor and very fluid, and they tend to be non-explosive.

Mauna Loa has probably been erupting for at least 700,000 years, and may have emerged above sea level about 400,000 years ago. The oldest-known dated rocks are not older than 200,000 years. The volcano's magma comes from the Hawaii hotspot, which has been responsible for the creation of the Hawaiian island chain over tens of millions of years. The slow drift of the Pacific Plate will eventually carry Mauna Loa away from the hotspot within 500,000 to one million years from now, at which point it will become extinct.

Mauna Loa's most recent eruption occurred from March 24 to April 15, 1984. No recent eruptions of the volcano have caused fatalities, but eruptions in 1926 and 1950 destroyed villages, and the city of Hilo is partly built on lava flows from the late 19th century. Because of the potential hazards it poses to population centers, Mauna Loa is part of the Decade Volcanoes program, which encourages studies of the world's most dangerous volcanoes. Mauna Loa has been monitored intensively by the Hawaiian Volcano Observatory since 1912. Observations of the atmosphere are undertaken at the Mauna Loa Observatory, and of the Sun at the Mauna Loa Solar Observatory, both located near the mountain's summit. Hawaii Volcanoes National Park covers the summit and the southeastern flank of the volcano, and also incorporates Kīlauea, a separate volcano.

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