January 29, 2009
A weekly feature provided by scientists at the Hawaiian Volcano Observatory.
Seasonally enhanced aroma briefly fills the air near Halema`uma`u
It seems that something new and different is always cooking at Kīlauea. In December a change in the aroma coming from Pele's kitchen was noticed by the HVO and National Park staffs, along with nearby residents. The biting, choking odor of sulfur dioxide (SO2) from Halema`uma`u that had inundated Volcano Village and the Golf Course subdivision during trade wind disruptions started to change. The pervasive odor of rotten eggs or sewer gas that tainted the air was caused by an increasing appearance of hydrogen sulfide (H2S.)
The presence of H2S at Kīlauea's summit is not unusual in itself. Visitors to Sulphur Bank, located near Kīlauea Visitor Center, have long experienced the characteristic mix of odors. As Mark Twain quipped during his 1866 visit to Kīlauea, "The smell of sulphur is strong, but not unpleasant to a sinner."
Twainian humor aside, H2S gas, like SO2, can be hazardous at concentrations greater than 5-10 parts per million (ppm). Eye irritation and headaches are frequently reported symptoms. The human nose—very sensitive to H2S when first smelled—is able to detect it at concentrations well below 1 part per million. Unlike SO2, however, olfactory fatigue causes a loss of odor sensitivity upon prolonged exposure. The State of Hawai`i hosts a 1-hour ambient air standard for H2S of 0.025 ppm. California enacted a similarly protective standard in 1969, targeted at decreasing odor annoyance. The World Health Organization established a 24-hour average guideline of 0.15 ppm intended to protect human health.
H2S is formed at Sulphur Bank when SO2 escaping from Kīlauea's magma chamber rises and combines with ground water. The resulting chemical reaction, called hydrolysis, produces a mixture of SO2 and H2S at the surface. The amount of gas released is very small, and when the emissions are blown toward Halema`uma`u, they tend to affect only a small section of Crater Rim Drive.
Apart from the background Sulphur Bank gas emissions, HVO scientists have been watching carefully for appreciable H2S coming from the Overlook Vent at Halema`uma`u since the eruption began last March. A substantial increase in this gas, along with other eruptive indicators, might signal that a large amount of water was coming into close proximity of red-hot magma. The subsurface encounter of abundant groundwater and magma was the suspected culprit causing the explosive eruptions of 1924.
The lack of significant H2S presence at Halema`uma`u through late November reflected hot, dry conditions within the vent. And SO2 emissions remained high, as well, despite significant collapses of the vent rim and walls in September and October that added large amounts of rubble to the conduit bringing gas and other eruptive products to the surface.
This situation began to change in early December, when further collapses widened the vent rim to football playing-field size-100 m (110 yards) Accompanying the vent-widening was some seasonally notable rainfall. The gage at HVO recorded over a foot of rain in December, much of it during a single storm late in the month.
Hot, collapsed rim and wall rock accumulating in the vent, combined with the prodigious rainfall, provided good conditions to produce H2S from SO2 within the conduit. By mid-December, the vent had cooled somewhat, and the ratio of H2S to SO2 in the air near Halema`uma`u had climbed to higher levels than seen previously.
Despite the seemingly favorable H2S-producing conditions, the total emissions, while significant, were still less than one tenth those of SO2. HVO staff, however, watched the situation unfold with great interest, wondering what might happen next.
Pele's SO2 exhalations were not to be dampened by a little rainfall, though. By mid-January, the rains had tapered off, and magma heat and gas from below the rubble in the vent appeared to burn through. By late January, faint glow was once again seen in the vent, and the presence of H2S declined to near background as the vent heated up and dried out. And so, for now, it seems that hot liquid rock is once again what's cooking at Kīlauea's summit kitchen. Ah, pungent sinner soup! Can you smell it? Can you taste it?
Kīlauea Volcano continues to be active. A vent in Halema`uma`u Crater is emitting elevated amounts of sulfur dioxide gas and producing very small amounts of ash. Resulting high concentrations of sulfur dioxide in downwind air have closed the south part of Kīlauea caldera and produced occasional air quality alerts in more distant areas, such as Pahala and communities adjacent to Hawai`i Volcanoes National Park, during kona wind periods. Variation in glow, gas-rushing sounds, and ash production over the past week may indicate that conduit beneath the vent is periodically being closed with debris.
Pu`u `Ō`ō continues to produce sulfur dioxide at even higher rates than the vent in Halema`uma`u Crater. Trade winds tend to pool these emissions along the West Hawai`i coast, while Kona winds blow these emissions into communities to the north, such as Mountain View, Volcano, and Hilo.
Lava erupting from the Thanksgiving Eve Breakout (TEB) vent at the eastern base of Pu`u `Ō`ō continues to flow to the ocean at Waikupanaha through a well-established lava tube. Breakouts from a western branch of the lava tube were active on the coastal plain near the National Park boundary in the past week and reached the ocean again on January 28. This tiny, new ocean entry is located very close to the long-buried Waha`ula Heiau and National Park visitor center.
Be aware that active lava deltas can collapse at any time, potentially generating large explosions. This may be especially true during times of rapidly changing lava supply conditions. The Waikupanaha delta has collapsed many times over the last several months, with three of the collapses resulting in rock blasts that tossed television-sized rocks up onto the sea-cliff and threw fist-sized rocks more than 200 yards inland.
Do not approach the ocean entry or venture onto the lava deltas. Even the intervening beaches are susceptible to large waves generated during delta collapse; avoid these beaches. In addition, steam plumes rising from ocean entries are highly acidic and laced with glass particles. Call Hawai`i County Civil Defense at 961-8093 for viewing hours.
Mauna Loa is not erupting. Four earthquakes were located beneath the summit this past week. Continuing extension between locations spanning the summit indicates slow inflation of the volcano, combined with slow eastward slippage of its east flank.
One earthquake beneath Hawai`i Island was reported felt within the past week. A magnitude-2.3 earthquake occurred at 1:20 a.m., H.s.t., on Tuesday, January 27, 2009, and was located 9 km (6 miles) northwest of Kukuihaele at a depth of 42 km (26 miles).
Visit our Web site (http://hvo.wr.usgs.gov) for daily Kīlauea eruption updates, a summary of volcanic events over the past year, and nearly real-time Hawai`i earthquake information. Kīlauea daily update summaries are also available by phone at (808) 967-8862. Questions can be emailed to askHVO@usgs.gov.
Updated: February 2, 2009 (pnf)