Volcano Monitoring – Measuring Volcanic Gases: The Answer Is Blowing in the Wind

Volcano Watch is a weekly article and activity update written by scientists at the U.S. Geological Survey Hawaiian Volcano Observatory and its affiliates. This week’s article was written by Christine Sealing, a natural gas technician at the University of Hawaii Research Corporation.

The USGS Hawaiian Volcano Observatory (HVO) currently operates 19 permanent gas monitoring stations and seven portable instruments used for volcanic eruption response. These instruments can be divided into two categories based on what they measure: (1) gas concentrations; and (2) emission rates.

Gas concentration instruments include Multiple gas stations Measurement of various gases (CO₂H₂Oh, so₂and H₂S) and can measure a single gas (SO₂) to very low concentrations. These instruments inhale, or “sniff,” samples of the volcanic plume, telling us which gases are present and the ratios between them, which is important for understanding volcanic systems.

Emission rate instruments, including innovative Flyspec Array, UV Camera,as well as Vehicle-mounted differential absorption spectrometerthrough remote sensing, measuring the absorption of the sun’s ultraviolet light by the plume. This allows us to determine the amount of sulfur dioxide₂ It is pouring out of the volcano, but only during the day.

All of these instruments require the cooperation of the gas itself: the plume must pass through or over the instrument for a measurement to be made.

However, a volcanic plume does not move on its own. It relies on the wind to carry it in any particular direction. The job of a volcanic gas scientist is to Catching up And measuring this moving, transient mass of gas – no easy task!

Imagine a situation where seismometers stopped working every time it rained. Perhaps it was because the ground got too wet, weakening the seismic signal. This isn’t true, but let’s assume it. In this case, we could feel the earthquake and know when it happened, but we couldn’t measure its magnitude because the ground was wet. Thankfully, in the real world, seismometers work regardless of weather conditions, but gas instruments don’t. They need winds in the right direction and at the right speed to make useful measurements.

At Kilauea, the dominant trade winds mean that near-surface winds blow from the northeast most of the year. Therefore, HVO’s permanent gas monitoring station is located southwest (downwind) of Halemaumau, Kilauea’s summit crater.

If the wind is blowing in the opposite direction relative to the normal trade winds (we call these “Kona winds”), then while we can see the plume, smell it, and even taste it, we can’t easily measure it because the wind is blowing the gas away from our permanent sensors.

Likewise, if the wind is too slow (less than about 4 m/s, or 9 mph or 8 knots), then the plume may rise straight up, again missing our sensors. Alternatively, if the wind is too strong, then it effectively dilutes the plume, making it thin and difficult for our sensors to measure. How strong is too strong depends on the amount of gas in the plume, but during eruptions with relatively little gas, the cutoff speed is around 12 m/s, or 27 mph or 23 knots.

Another complicating factor is that volcanoes do not always erupt from the same location. Recent Eruptions At Kilauea, a fissure opened up in the upper part of the southwest rift zone—downwind of almost the entire gas monitoring network. Only one instrument, a high-resolution station called HRPKE, was located near the eruption vent, a few hundred meters west/northwest of the fissure. However, the winds that day were from the north, blowing the thick eruption plume southward and away from HRPKE. It wasn’t until several hours after the eruption that the wind turned easterly, finally blowing the plume toward the monitoring station, that it recorded a wisp of gas.

Effective gas measurements require a combination of four factors: wind direction, wind speed, sometimes daylight, and always luck. USGS volcanic gas researchers continue to develop new techniques to help us win this complex game of chasing so that we can inform the public about this ever-changing volcanic hazard. So if you check the public web page and see no gases reported, it may just mean the wind isn’t cooperating and we’re still chasing the plume.

Volcano Activity Update

Kilauea volcano is not erupting. The U.S. Geological Survey volcano alert level is “warning”.

Seismicity and swelling ground deformation rates continue to increase in the Kīlauea summit region, indicating that magma is re-pressurizing storage systems. Over the past week, about 650 earthquakes (mostly smaller than M2) have occurred in the Kīlauea summit region, extending southeastward into the upper East Rift Zone. Unrest may continue to wax and wane as magma input changes; changes may occur quickly, as may the potential for an eruption. Summit sulfur dioxide emissions were last measured at about 100 t/d on July 17, 2024.

Mauna Loa is not erupting. The U.S. Geological Survey volcano alert level is normal.

Two earthquakes were reported in the Hawaiian Islands over the past week: a M2.8 earthquake at 3:33 a.m. Hawaii Standard Time on July 16, 6 km (3 mi) south of the volcano at a depth of 1 km (1 mile); and a M3.0 earthquake at 5:50 p.m. Hawaii Standard Time on July 12, 2 km (1 mile) southeast of Pahala at a depth of 33 km (20 miles).

HVO continues to closely monitor Kilauea and Mauna Loa volcanoes.

Visit the HVO website for past volcano monitoring articles, the latest news on Kilauea and Mauna Loa, volcano photos, maps, recent earthquake information, and more. Please email questions to askHVO@usgs.gov.