# Volcano Watch — Expert on volcanic gases exsolves from USGS

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Hawaii is considered one of the best places on Earth to study gas release through active volcanism, and the process of gas release is a key to understanding how volcanoes work. As Thomas Jaggar, HVO's founder put it, "The observatory worker who has spent years watching lavas frothing in action, can't help but realize that gases are at the heart of the volcano magma problem."

This month, a leading expert on Hawaiian volcanic gases, Terry Gerlach, stationed at the Cascades Volcano Observatory (CVO), departs the USGS.

As the saying goes, "Great minds think alike," and some of Terry's 1980's work in Hawaii involved a thoughtful reading, recalculation and re-presentation of professor Jaggar's 1918-1919 gas analyses from Kīlauea. Jaggar was careful to collect high-quality gas samples from vents near the Halemaumau lava lake, but the technology of that time was lacking in the ways of chemical analysis that today we take for granted. So Jaggar and his colleague, E.S. Shepherd, reported these pioneering results as specifically as available methods of the day would allow-a hallmark of their own scientific excellence.

Gerlach showed that these early analyses could be made more valuable by reviewing and reinterpreting them through the lens of modern chemical thermodynamics--a potent tool used by scientists who model chemical processes. Terry's restoration of Jaggar's first analyses produced continuity between old and new work, answered some persistent questions about Kīlauea's eruptive process, and helped pave the way to the formulation of a volcanic gas "budget" for Kīlauea.

Factoring in the gases released through surface vents, he formulated Kīlauea's gas budget by making a careful accounting of the gas content of lavas held under high pressure and comparing these figures with those for lavas erupted out near Puu Oo. The geochemical accounting obtained when gas is sampled from a volcanic vent can provide insight as to the evolutionary state of magma deep beneath the surface of dangerous volcanoes, and often provides clues as to what the volcano might do next.

Terry's gas budget approach has us helped to better understand the workings of numerous other volcanoes, as well, such as Mount St. Helens, Mt. Spurr, Mt. Iliamna, and Mt. Redoubt on the U.S. mainland, and those located in far-flung places like Iceland, Ethiopia, Italy, Indonesia, and the Democratic Republic of the Congo.

Gerlach also applied his deep understanding of chemical thermodynamics to unravel a mystery about the eruption of Mt. Pinatubo in the Philippines. On June 15, 1991, Pinatubo erupted catastrophically, spewing an amount of sulfur dioxide into the stratosphere that it would take 10 years for Kīlauea to erupt at its current rate. The gas and ash from Pinatubo circled the Earth, causing significant global cooling for three years following the eruption. With his colleagues, Terry concluded that the magma beneath Pinatubo had more gas trapped in it than could simply dissolve in the liquid. Later, laboratory researchers conducted experiments confirming Gerlach's hypothesis. This finding represents a major advance in our understanding of how restless volcanoes can misbehave.

More recently, Terry led studies that improved our understanding of the release of carbon dioxide (CO2) from Kīlauea, Alaska, and Cascade volcanoes and Long Valley and Yellowstone calderas in the U.S., and Mt. Popocatepetl in Mexico. The results for Kīlauea, in particular, showed that previous emission rate estimates were off by about a factor of three to four. Although volcanic output of CO2 is dwarfed by the amount released when humans burn fossil fuels, volcanoes do contribute significantly to the natural carbon cycle of the Earth. Gerlach's leadership in enhancing the quality of these measurements and their interpretation is already improving the accuracy of global volcanic CO2 release estimates.

For these and his many other contributions, we, of the HVO ohana, join the other observatories and centers in the USGS in thanking Terry Gerlach, our colleague and teacher, for his many years of excellent and dedicated study of volcanoes, and we wish him and his wife Aniko well in their upcoming adventures. Aloha, Terry, and MAHALO! A hui hou!

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### Volcano Activity Update

This past week, activity levels at the summit of Kīlauea Volcano have remained at background levels. The number of earthquakes located in the summit area is low (usually less than 10 per day that are large enough to locate). Widening of the summit caldera, indicating inflation, continues at slower rates over the past few weeks.

Eruptive activity at Puu Oo continues. On clear nights, glow is visible from several vents within the crater. Over the last several weeks, many of the pits in and around Puu Oo crater have grown in depth and diameter, while the remnant spatter cones at some of the vents have partially collapsed. Lava continues to flow through the PKK lava tube from its source on the southwest flank of Puu Oo to the ocean. About 1 kilometer (1 mile) south of Puu Oo, the Campout flow branches off from the PKK tube. The PKK and Campout tubes feed two widely separated ocean entries, at East Laeapuki and East Kailiili, respectively. Both entries are located inside Hawaii Volcanoes National Park.

In the last few weeks, intermittent breakouts have occurred from the PKK tube just inland from the sea cliff at East Laeapuki. Scattered surface flows also have been active on the Campout flow on Pulama pali.

Access to the sea cliff near the ocean entries is closed, due to significant hazards. The surrounding area, however, is open. If you visit the eruption site, check with the rangers for current updates, and remember to carry lots of water when venturing out onto the flow field.

There were 11 earthquakes beneath Hawaii Island reported felt within the past week. A magnitude-2.1 earthquake occurred at 2:46 p.m. H.s.t. on Thursday, October 19, and was located 13 km (8 miles) southeast of Waimea at a depth of 33 km (20 miles). A magnitude-2.6 earthquake occurred at 8:41 p.m. on Friday, October 20, and was located 4 km (2 miles) east of Mountain View at a depth of 41 km (25 miles). A magnitude-2.5 earthquake occurred at 7:32 p.m. on Sunday, October 22, and was located 9 km (6 miles) northeast of Honaunau at a depth of 9 km (6 miles). A magnitude 2.0 earthquake occurred at 9:45 p.m. on Tuesday October 24, and was located 8 km (5 miles) southeast of Waimea at a depth of 13 km (8 miles).

Seven of the 11 were aftershocks of the October 15 magnitude-6.7 earthquake and were reported felt. They ranged in magnitude between 2.3 and 3.3, and depths to 44 km (28 miles). The aftershocks continue.

Mauna Loa is not erupting. During the past week, earthquake activity remained low beneath the volcano's summit (one earthquake was located). Extension of distances between locations spanning the summit, indicating inflation, continues at slow rates.