What can we learn from the lava level?

Considering the recent activity in Halema‘uma‘u Crater, just how reliable is its lava-lake level for judging the potential of an upcoming eruptive event? Lava level is one of the gauges of activity at Kilauea, and the recent build-up includes the highest levels recorded during the current summit eruption.

The current lava lake in the Overlook vent inset within the floor of Halema‘uma‘u Crater has been continuously present only since February 2010, two years after the eruption began in March 2008. HVO scientists have observed that the lava level rises and falls in concert with tilt, contractions, and extensions at the summit. Like the mercury level in an analog barometer, lava level is a good indicator of the pressure in Kilauea’s magmatic system.

In 2011, each of three episodes of rising lava levels culminated in an eruptive event on Kilauea’s east rift zone: the spectacular March 5-9 Kamoamoa fissure event, the Aug. 3 rupture of Pu‘u ‘O‘o’s west flank, and the Sept. 21 fissure event on the east flank of Pu‘u ‘O‘o cone. In each case, the eruptive event occurred at the time of peak summit lava level. There appears to be a direct correspondence between high summit lava levels and rift zone eruptive events.

But 2011 is just one year in Kilauea’s life, and it’s instructive to look at a longer timescale to see whether the timing is always that simple. Fortunately, HVO scientists in the early 1900s made detailed measurements of lava level in Halema‘uma‘u, from about 1911 through the end of that lava lake period in 1924. During that time, there were three rift eruptions: the 1919–1920 Mauna Iki eruption, the 1922 Makaopuhi-Napau, and the 1923 Makaopuhi eruption. In 1924, an intrusion in the lower east rift zone was followed by a collapse and steam (phreatic) explosions in Halema‘uma‘u Crater.

Each of the three rift eruptions and the 1924 intrusion was preceded by relatively high lava levels in Halema‘uma‘u. But the data from the 1900s also show that high summit lava-lake level and the onset of rift eruptions is not a simple one-to-one cause-and-effect relationship. Several episodes of rapidly rising lava levels peaked, but did not lead to eruptions or intrusions. The lava simply dropped back to lower levels without any obvious change elsewhere, suggesting that Kilauea has internal mechanisms for pressure adjustment (as discussed in last week’s Volcano Watch article).

The lava-level data from the early 1900s also show another interesting phenomenon. In two episodes, the eruptions did not occur at the peak lava level, as the three eruptive events did in 2011. Instead, the lava level peaked, then dropped for several months before the eruption occurred. Thus, the volcano can remain in a “charged” state for long periods after rapid lava-level rise.

The volcano’s ability to stay primed for weeks after reaching peak lava levels could have implications for the activity that we see today. The lava lake has dropped from its high level, measured on Oct. 26 (at 70 feet, below the floor of Halema‘uma‘u Crater). The summit is also no longer inflating at the steady rate it was through much of October. Earthquakes in the upper east rift zone, also indicative of elevated magmatic pressure, are much less frequent.

Only a couple weeks have elapsed since those high lava levels were recorded, but the summit is still in an inflated state. The build-up has drawn down a bit, but there’s an elevated likelihood of change in the ongoing activity and plenty of reasons to keep a watchful eye on Kilauea.

Kilauea activity update

A lava lake within the Halema‘uma‘u Overlook vent produced night-time glow that was visible from the Jaggar Museum overlook and by HVO’s webcam during the past week. Following several weeks of summit inflation and high lava levels during October, the lava lake has slowly dropped to more typical levels. In the past week, gradual summit inflation has resulted in a slight rise in lava level, but the lake remains deep within the Overlook vent.

On Kilauea’s east rift zone, surface lava flows are still slowly advancing across the coastal plain. As of Monday, Nov. 12, the flow front was .2 miles from the shoreline and advancing slowly. A very small portion of the active flows have entered the far eastern boundary of the National Park this past week.

Within the Pu‘u ‘O‘o crater, the northeastern pit still holds a circulating lava lake. Occasional small flows were erupted from several pits on the crater floor.

No earthquakes were reported felt across the Hawaiian Islands during the past week.

Visit the HVO website (http://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 (http://hvo.wr.usgs.gov/volcanowatch/) is a weekly article and activity update written by scientists at the U.S. Geological Survey‘s Hawaiian Volcano Observatory.


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