Volcano Watch: Eruption pause provides opportunity to probe volcanic pollution

  • M. POLAND/USGS photo from March 22, 2019 Only small amounts of sulfur dioxide (SO2) and hydrogen sulfide (H2S) are currently being released from Kilauea, but they chemically react with each other (oxidation-reduction reaction) to form the bright yellow sulfur deposits visible on the crater walls within Halema‘uma‘u. The current low sulfur emission rates at Kilauea have contributed to beautifully clear skies in downwind areas.

The end of Kilauea’s 2018 eruption this past September was accompanied by an enormous decrease in the amount of sulfur dioxide gas emitted from the volcano.

This led to beautifully clear skies gracing the Island of Hawaii, particularly noticeable on the west side, where the volcanic pollution known as vog chronically collected in past years.


During the peak of the 2018 lower East Rift Zone eruption, when the volcanic emissions and vog were much stronger, a team of academic researchers worked with the U.S. Geological Survey’s Hawaiian Volcano Observatory and the Hawaii Department of Health to study the intense volcanic air pollution events generated by the eruption.

The researchers, U.K. scientists from the universities of Leeds, Cambridge and Oxford, sampled volcanic particles and gases at the LERZ fissure 8 vent, the ocean entry and various sites downwind (Leilani Estates, Orchidland Estates, Volcano, Pahala, Ocean View and Captain Cook). To determine the nature and composition of the volcanic pollution, samples were collected by pumping air through filters, from the ground and from the air using drones.

The tiny particles captured on the filters were then analyzed in the laboratory for chemical composition and imaged using a powerful scanning electron microscope to determine the composition of individual particles. Other instruments determined the number or weight of particles of various sizes, which are associated with different health impacts in studies of human-caused pollution.

The samples were analyzed for pH (acidity); major components including sulfate, fluoride and chloride; and trace metals such as lead and arsenic.

These analyses targeted chemical species we know are present in volcanic plumes. Kilauea’s plume is composed primarily of water vapor, carbon dioxide, sulfur dioxide and entrained air, along with smaller amounts of other gases including hydrogen chloride and hydrogen fluoride.

SO2 reacts in the atmosphere with time to form tiny acidic and neutral sulfate particles, which are a major component of volcanic pollution in Hawaii. Small amounts of toxic metals also have been found in the volcanic gas plumes emitted from Kilauea’s vents (see https://vog.ivhhn.org/vog-fact-sheets).

The summer 2018 gas and particle sampling campaign was the first effort to look at how trace elements, such as metals, change over distance in the Kilauea plume. It was found that the amount of these elements was highly variable but not solely predicted by the distance of the plume from the vent.

Most of the particles (99 percent) were less than 2.5 micron in diameter — small enough to penetrate deep into the lungs.

The study’s findings also support previous observations regarding the chemical conversion of SO2 gas to particles.

Areas far from the gas source, such as along Hawaii Island’s Kona Coast, had high particle concentrations since much of the SO2 gas converted to particles as it traveled downwind. Ambient air quality standards for SO2 gas and particles were exceeded at various locations on the island during the three months of the LERZ eruption (https://health.hawaii.gov/cab/files/2018/08/exceedances_2018_08_01_04.pdf).

In contrast to last summer, Kilauea’s current lull in activity provides an excellent opportunity to study background air quality. This can help us distinguish between anthropogenic pollution, such as traffic exhaust, and volcanic pollution.

While controlling emissions from a volcano is not a practical proposition, understanding the contribution of human-made pollution, which can be controlled, is important on an island with a growing population.

To address the characterization of anthropogenic pollution, the same research team plans to return this coming summer to sample the background air without the volcanic contribution, using the same equipment and sampling sites.

The “before” and “after” snapshots will help isolate the chemical fingerprint of the volcanic particles. This will improve our understanding of the potential health, environmental and ecosystem effects of volcanic plumes.

The eruptive events of 2018 reshaped the land and the lives for many residents in Hawaii Island’s lower Puna District. The end of the eruption allows all of us around the island to breathe more easily, literally and figuratively, and provides an opportunity to better understand the chemistry and impacts of the Kilauea volcanic plume.

Volcano activity updates

The USGS Volcano Alert level for Kilauea, which is not erupting, is at Normal.

Rates of seismicity, deformation and gas release have not changed significantly during the past week. Deformation signals are consistent with refilling of Kilauea Volcano’s deep East Rift Zone magma reservoir. Sulfur dioxide emission rates on the ERZ and at Kilauea’s summit remain low and have been steady throughout the past several weeks.

Three earthquakes with three or more felt reports occurred in Hawaii during the past week: a magnitude-2.8 quake 26 km (16 mi) west of Pepe‘ekeo at a depth of 33 km (21 mi) at 9:42 p.m. April 1; a magnitude-3.4 quake 10 km (6 mi) northeast of Pahala at a depth of 31 km (19 mi) at 7:49 a.m. March 31; and a magnitude-3.7 quake 2 km (1 mi) southeast of Kapa‘au at a depth of 38 km (24 mi) at 8:29 p.m. March 29.

Hazards still exist at the lower ERZ and summit of Kilauea. Residents and visitors near the 2018 fissures, lava flows and summit collapse area should heed Hawaii County Civil Defense and Hawaii Volcanoes National Park closures and warnings. HVO continues to closely monitor Kilauea for any sign of increased activity.

The USGS Volcano Alert level for Mauna Loa remains at Normal.


Visit HVO’s website (https://volcanoes.usgs.gov/hvo) for past Volcano Watch articles, Kilauea and Mauna Loa updates, volcano photos, maps, recent earthquake info, and more. Call 808-967-8862 for weekly Kilauea updates. Email questions to askHVO@usgs.gov.

Volcano Watch (https://volcanoes.usgs.gov/hvo/hvo_volcano_watch.html) is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates.

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