Volcano Watch: Volcanic gas studies in Hawaii — then and now

The left image shows Shepherd and Day’s hornito gas sampling set up in May 1912; the right images is the FTIR looking into the Halemaumau vent, acquiring the same sort of information today. Photo courtesy of USGS/HVO

The left image shows Shepherd and Day’s hornito gas sampling set up in May 1912; the right image is the FTIR looking into the Halemaumau vent, acquiring the same sort of information today. Photo courtesy of USGS/HVO

(Volcano Watch is a weekly article written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.)

What a difference a century (or even a few years) can make! As noted in an earlier Volcano Watch (June 5, 2011), 1911 was a dynamic year for science at Kilauea. With the arrival of Frank Perret, Thomas Jaggar’s vision of a volcano observatory perched on the rim of Kilauea began to take shape. By the time of Perret’s departure for Italy later that year, his efforts had stirred much interest in the volcano studies community worldwide.

Among the interested parties was E.S. Shepherd from the Geophysical Institute in Washington, D.C. Shepherd had worked with Perret to construct the cableway across Halema`uma`u from, which they collected the first molten lava lake samples and made the first molten lava temperature measurements.

Shepherd was also keenly interested in volcanic gases. He read about a study carried out by Albert Brun, a Swiss chemist, who had worked at Kilauea earlier. One of Brun’s conclusions about Kilauea was puzzling to Shepherd and his colleague, Arthur Day, also from the Geophysical Institute.

Brun, a careful scientist, had found that, on eruption, magma releases a number of gases including hydrogen, sulfur gases, and oxides of carbon, among others, but magmatic water was conspicuously missing. In fact, Brun was thoroughly convinced that volcanic exhalations were completely anhydrous—devoid of any water contributed by the magma from depth.

Science folks can get pretty competitive when it comes to showing that their measurements are more careful, rigorous, and therefore more valid than those of scientists with competing theories. In 1912, Shepherd returned to Kilauea with Arthur Day, intent on collecting and studying volcanic gases in the most pristine state possible. To do this, they needed more than scientific rigor and skill though; they needed luck.

Brun’s on-site gas measurements had been made by dangling a string of empty glass tubes over Halema`uma`u’s rim and pumping the local atmosphere, 250 feet distant from nearest molten lava, through them. Brun then carefully analyzed what was collected in the tubes.

Volcanic conditions smiled more kindly on Shepherd and Day. Next to Halema`uma`u, they found what might be described as a hornito—basically a dome-shaped hollow lava mound into which fresh lava was intruding, jetting, and burning through cracks in its side. They had hit a volcanic gas sampler’s jackpot. Placing a tube into the crack, they pumped the gas into a series of glass collection vessels.

What they collected into these bottles surprised even them. As the 1,000-degree C (1,832 degree F) gas cooled to the surrounding temperature, copious amounts of a clear liquid (which they later identified as magmatic water) immediately began to condense in the tubes. Intending to perform a rapid analysis of a subset of these samples, Shepherd and Day adjourned to The College of Hawaii in Honolulu, where they were able to quantify sulfur dioxide, carbon dioxide, and carbon monoxide.

The rest of the samples were analyzed at the Geophysical Institute at the end of the field season. For technical reasons related to the difficulty of trapping all volcanic gas species, Shepherd and Day were unable to precisely quantify the exact proportion of water to the other gases. But this early study put to rest the incorrect notion, at least at Kilauea, that volcanic gases were devoid of water of magmatic origin.

Studies carried out many years later, using chemical isotopes, have since confirmed the existence of magmatic water and have helped to refine our understanding of how Earth’s atmosphere and oceans were formed. Volcanoes play a significant role in these processes.

While we still collect gas samples in glass bottles intermittently as Shepherd and Day did, nowadays, HVO staff relies heavily on the use of remote spectrometers capable of measuring the amount of one or more volcanic gas species nearly instantly. One such technique, Fourier Transform Infrared (FTIR) spectrometry, is routinely used from the rim of Halema`uma`u to measure gases as they boil out of the lava lake within the Overlook vent.

The “remote” nature of these techniques help keep scientists a safer distance from an unpredictable volcanic vent while, at the same time, producing excellent data. These techniques help us assess a volcano’s eruptive state and provide information for assessing volcanic gas hazards. And while we appreciate what the new methods have done for our understanding of active earth processes, we salute the pioneering accomplishments of early workers like Shepherd, Day, Brun, and Perret.

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