A weekly feature provided by scientists at the Hawaiian Volcano Observatory.
May 23, 2013
New studies help refine Kīlauea gas emission rates
There are times when the USGS motto, "Science for a Changing World," seems to be specifically crafted to describe studies at Hawaiian volcanoes. Without a doubt, changes recorded at Kīlauea during the past five years have produced some significant steps forward in our ability to understand and conduct volcano science. For example, by carefully observing changes in ground shaking (seismicity), ground surface expansion and contraction (deformation), gas emissions, and geology at Halemaʻumaʻu and at Puʻu ʻŌʻō, scientists at the Hawaiian Volcano Observatory (HVO) have been able to probe the inner workings of Kīlauea.
Several scientific and technical advances happened as the Overlook vent formed within Halemaʻumaʻu Crater in 2008. The vent appeared after a surge in magma supply that began years earlier, in late 2003, drove new material into the volcanic edifice. This set the stage for big changes at Kīlauea, and in the months leading up to the formation of the vent in 2008, summit seismicity and gas emissions both increased. Gas chemistry changes told us that either new gas pathways to the surface were forming or that magma was rising.
By mid-February 2008, air quality in the southern portion of the caldera had deteriorated to unhealthy levels, because noxious sulfur dioxide (SO2) emissions from Halemaʻumaʻu had risen markedly. To protect visitor safety, the National Park wisely chose to close the section of Crater Rim Drive normally downwind of the degassing sources.
Before the summit eruption actually began in 2008, Kīlauea's gas emissions were the highest HVO had recorded in over 20 years; in fact, they'd begun to exceed the range of our instruments. This sent us scrambling for ways to keep the readings on scale.
The instrumental technique we use to estimate SO2 emissions relies upon measuring the amount of ultraviolet sunlight energy passing through the volcanic gas plume. We do this by strapping a small upward-looking spectrometer on the roof of our field vehicle and driving it underneath the gas plume as it is blown across Crater Rim Drive. The spectrometer measures the amount of light absorbed by SO2 in the plume above us as we go. Conceptually, the more SO2 there is in the plume, the more ultraviolet light energy is absorbed. This seemingly straightforward measurement principle begins to break down, though, when gas amounts are very high. And by the beginning of March 2008, we were approaching that threshold.
Things got more complex in mid-March 2008, when the summit eruption was inaugurated by the forceful opening of the Halemaʻumaʻu Overlook vent. The summit plume suddenly became extraordinarily densealmost visually opaque. This was because, in addition to lots more gas in the plume, there was also a substantial amount of fine particles.
The interaction between sunlight energy and a dense volcanic gas and particle plume results in seriously complicated physics, especially when you're trying to quantify emission rates in near-real time. As a result, the high gas concentrations, along with the particle-rich plume, fooled our spectrometer into thinking that there was less SO2 in the plume than there actually was. While we knew this was happening as soon as the vent opened, until recently, we were unsure as to the degree of the problem.
On the positive side, although the exact amount of SO2 being released from the Halemaʻumaʻu Overlook vent has been uncertain, we've still been able to record changes in relative amounts. This has allowed us to estimate minimum summit emission rates for hazards purposes, and to track changes in eruptive activity by examining relative differences in SO2 through time.
In contrast, estimates of SO2 emission rates from Kīlauea's East Rift Zone are unaffected by the dense plume and high SO2 problems experienced at the summit. The East Rift Zone measurements are made 10 km (6 mi) downwind of the emission sources and, at that distance, the plume is substantially diluted.
Together with colleagues from the USGS Cascades Volcano Observatory and University of Hawaiʻi at Mānoa, we are refining our measurements to compensate for the complicated summit plume conditions. Until these improvements are finalized, we'll continue to report summit emission rates as minimum values, which consistently provide a relative measure of SO2 released from Kīlauea.
As ever, these developments show that Kīlauea continues to serve as a preeminent "laboratory" where "Science for a Changing World" benefits volcano studies worldwide.
Kīlauea Activity UpdateA lava lake within the Halemaʻumaʻu Overlook vent produced nighttime glow that was visible from the Jaggar Museum overlook and via HVO's Webcam during the past week. The lava lake rose and fell between about 50 and 70 m (165230 ft) below the crater floor, synchronously with cycles of deflation and inflation (DI events) at Kīlauea's summit.
On Kīlauea's East Rift Zone, breakouts from the Peace Day tube remain active on the pali and on the coastal plain. Small ocean entries are active on both sides of the Hawaiʻi Volcanoes National Park boundary. The Kahaualeʻa II flow, fed from a spatter cone on the northeast edge of Puʻu ʻŌʻō's crater, continues to spread at the northern base of the Puʻu ʻŌʻō cone.
One earthquake was reported felt on the Island of Hawaiʻi during the past week. On May 17, 2013, at 8:29 a.m., HST, a magnitude-3.0 earthquake occurred 17 km (10 mi) northwest of Kailua-Kona at a depth of 11 km (7 mi).
Visit our Web site (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.