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Volcanowatch

December 9, 2010

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.


Halema`uma`u lava lake spectacularly disappears in 1923

The lava lake deep within Kīlauea's currently active summit vent is known for being a bit capricious. It is not uncommon for the lava lake's level to change up to about 30 m (100 ft) over periods of minutes to hours. These cycles of rise and fall are apparently driven by vesiculation of the shallow magma system. Basically, a layer of foam is created, then destroyed, at the top of the lava column.

But the dramatic drop of the lava lake during Kīlauea's August 1923 east rift zone eruption, which was driven by a deeper process, puts today's rise-fall changes to shame. During the August 1923 eruption, the lava lake—which, at the time, filled the entire bottom of Halema`uma`u Crater—dropped about 110 m (360 ft) over the course of just a few days.

On August 23, 1923, the lava lake in Halema`uma`u was within 63 m (206 ft) of the crater's northeast rim—a height it had roughly maintained for the previous few weeks. Small lava fountains and other points of weak spattering played nearly constantly atop the lava lake. By August 24, however, the level of the lava lake had begun to drop visibly in coordination with a swarm of earthquakes from the summit to the east rift zone.

The scale of the change became apparent when lava level measurements were made the following morning. By then, the lake had dropped some 37 m (122 ft) and continued to drop through the day as lava began to fountain from fissures on Kīlauea's east rift zone.

This new eruption was localized in the forest between `Alae and Makaopuhi craters amidst a broad zone of cracking that was nearly 1.6 kilometers (1 mile) across. Frothy lava spread over an area of just a few acres, and clots of lava were tossed into the tops of trees on both sides of the erupting fissure. The dense plume of noxious fumes billowing from the eruption site prevented geologists from approaching the area for several days.

The eruption was short-lived, however, probably ending some time on August 26. By that time, the lava lake in Halema`uma`u—having dropped another 64 m (211 ft)—had disappeared. Only a small stream of lava was visible near the southeast edge of the crater. The crater floor was composed of huge cracks and tilted blocks.

Minor subsidence of the crater floor continued over the following days until it was a chaotic jumble of rubble 172 m (565 ft) below the rim of Halema`uma`u. Only a faint glow could be seen at night through thick fume at the bottom of the crater. Occasional rock falls sent up swirling dust clouds as they crashed down into the crater.

Then, just as easily as the lava lake drained, it filled back up again. A dull glow was reported on September 4, and, by the following morning, lava had begun to refill Halema`uma`u. By the end of September, the lava lake was 51 m (167 ft) deep; by the end of 1923, it had reached its early August level.

While the drop in the lava lake level during the August 1923 eruption was impressive, it was not entirely unusual. A similar drop in level, also corresponding to an east rift zone eruption, occurred in May 1922. In May 1924, the lava level dropped dramatically again, resulting in the famous steam explosions that littered the summit with boulders. Earthquakes and ground cracking in lower Puna indicated that magma had intruded into the east rift zone but did not erupt to the surface.

After the 1924 explosions, massive draining events like those in 1922, 1923, and 1924 ceased. Without profound changes in Kīlauea's current eruptive activity, the likelihood that we will be witness to an incredible draining event at Halema`uma`u again is close to nil.

Kīlauea Activity Update

The low shield that began to form on November 30 at the top of the pali was no longer producing lava flows, but was hosting a perched lava pond. On the pali, there were several active breakouts reaching the 600-foot level, as of December 9. The coastal plain and ocean entry remain inactive.

At Kīlauea's summit, the circulating lava lake in the collapse pit deep within the floor of Halema`uma`u Crater has been visible via Webcam throughout the past week. The circulation pattern was interrupted sporadically by abrupt increases in the height of the lava surface. These periods of high lava level have been short-lived, lasting up to several hours, and each ended with a sudden drop of the lava surface back to its previous level. By the end of the week, the lava high stands had temporarily ceased. Volcanic gas emissions remain elevated, resulting in high concentrations of sulfur dioxide downwind.

No earthquakes beneath Hawai`i Islands were reported felt during the past week.

Visit our Web site (http://hvo.wr.usgs.gov) for detailed Kīlauea and Mauna Loa activity updates, recent volcano photos, recent earthquakes, and more; call (808) 967-8862 for a Kīlauea activity summary; email questions to askHVO@usgs.gov. skip past bottom navigational bar


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Updated: January 4, 2011 (pnf)