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Report on Kilauea (United States) — July 1988


Kilauea

Scientific Event Alert Network Bulletin, vol. 13, no. 7 (July 1988)
Managing Editor: Lindsay McClelland.

Kilauea (United States) Lava bench collapse at seacoast

Please cite this report as:

Global Volcanism Program, 1988. Report on Kilauea (United States) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 13:7. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198807-332010



Kilauea

United States

19.421°N, 155.287°W; summit elev. 1222 m

All times are local (unless otherwise noted)


Through July, two lobes of lava continued to enter the ocean ~1 km E of Kupapau Point. Lava flowed intermittently into the ocean from a tube at the E edge of the lava field. The E lobe was active along a 200-300-m-wide front. As lava entered the ocean during the past few months, it formed wide lava benches extending the shoreline. Three nested littoral cones had formed behind the most active entry point and another was forming at the terminus of a different tube system ~50-100 m farther E. At 1212 on 9 July, the entire active lava bench at this entry point collapsed into the water. On 12 July at 0842 another area of ~100 x 25 m collapsed within 20-30 seconds, producing two large explosions as water rushed into the tube systems. Both events were evidently triggered by massive slumping of the underlying submarine fan. Thomas Wright (HVO) and two visitors reported that the normally white steam column turned black and spatter was thrown skyward and deposited within 30 m of the cliff edge. The 12 July collapse and explosions registered as a relatively large seismic event on the Waha'ula seismometer (> 1 km away) and the disturbance continued for the next hour.

Sometime during the night of 21 July approximately 1/2 of the active lava bench collapsed into the ocean. Seismic records from the Waha'ula station show a series of strong explosions during the night, but no single collapse event was evident. The collapse/explosion sequence lasted over an hour. A littoral cone began building the following day, and unusually large explosions sent spatter 25-30 m into the air.

By 22 July, the flow along the E edge of the lava field had ceased advancing. Backup of lava in the E tube system 20-29 July caused surface outbreaks between ~70 m elevation and the coast, at the junction of the two tube systems at 470 m elevation, and from the W system at ~365 m elevation. Some small spiny pahoehoe flows < 200 m long were produced.

The W lobe became inactive on 27 July. However, visible effusion at the eastern lobe entry point seemed less than the total output of the Kupaianaha lava pond, suggesting that another tube may have formed deeper in the subaerial part of the flow carrying lava directly to submarine extrusive vents. The lava pond level remained 10-20 m below the rim for the month.

Shallow tremor continued at low levels through July . . . near Pu`u `O`o and Kupaianaha. Amplitude variation reflected a pattern of lava movement and degassing in the vent region. Oscillating tremor related to fountaining in the bottom of Pu`u `O`o crater also continued the first week. A secondary source of tremor was . . . attributed to explosions caused by lava entering the sea. In addition to the background tremor, strong bursts were associated with collapse of the shoreline deposits. Both the 9 and 12 July slumping events were recorded as ~1 minute of strong tremor . . . and were followed by 45 minutes of suppressed background tremor. The signature was apparently triggered by the primary event. Except for a significant M 4.4 earthquake and some aftershocks deep beneath the offshore component of the Hilina fault, Kīlauea S-flank events were mostly local at crustal depths along the outlying seismic zone of the Southeast rift zone. Kīlauea summit earthquakes were mostly shallow at < 5 km but there were some scattered long-period events at ~5-13 km depth.

Geological Summary. Kilauea overlaps the E flank of the massive Mauna Loa shield volcano in the island of Hawaii. Eruptions are prominent in Polynesian legends; written documentation since 1820 records frequent summit and flank lava flow eruptions interspersed with periods of long-term lava lake activity at Halemaumau crater in the summit caldera until 1924. The 3 x 5 km caldera was formed in several stages about 1,500 years ago and during the 18th century; eruptions have also originated from the lengthy East and Southwest rift zones, which extend to the ocean in both directions. About 90% of the surface of the basaltic shield volcano is formed of lava flows less than about 1,100 years old; 70% of the surface is younger than 600 years. The long-term eruption from the East rift zone between 1983 and 2018 produced lava flows covering more than 100 km2, destroyed hundreds of houses, and added new coastline.

Information Contacts: C. Heliker and R. Koyanagi, HVO.