Volcanic gases can be harmful to health, vegetation and infrastructure
Magma contains dissolved gases, which provide the driving force that causes most volcanic eruptions. As magma rises towards the surface and pressure decreases, gases are released from the liquid portion of the magma (melt) and continue to travel upward and are eventually released into the atmosphere. Large eruptions can release enormous amounts of gas in a short time. The 1991 eruption of Mt. Pinatubo is thought to have injected more than 250 megatons of gas into the upper atmosphere on a single day. However, even if magma never reaches the surface, gases can often escape continuously into the atmosphere from the soil, volcanic vents, fumaroles, and hydrothermal systems.
By far the most abundant volcanic gas is water vapor, which is harmless. However, significant amounts of carbon dioxide, sulfur dioxide, hydrogen sulfide and hydrogen halides can also be emitted from volcanoes. Depending on their concentrations, these gases are all potentially hazardous to people, animals, agriculture, and property.
Carbon dioxide (CO2) trapped in low-lying areas can be lethal to people and animals
Carbon dioxide constitutes approximately 0.04% of the air in the Earth’s atmosphere. In an average year, volcanoes release between about 180 and 440 million tonnes of carbon dioxide. When this colorless, odorless gas is emitted from volcanoes, it typically becomes diluted to low concentrations very quickly and is not life threatening. However, because cold carbon dioxide gas is heavier than air it can flow into in low-lying areas where it can reach much higher concentrations in certain, very stable atmospheric conditions. This can pose serious risks to people and animals. Breathing air with more than 3% CO2 can quickly lead to headaches, dizziness, increased heart rate and difficulty breathing. At mixing ratios exceeding about 15%, carbon dioxide quickly causes unconsciousness and death.
In volcanic or other areas where CO2emissions occur, it is important to avoid small depressions and low areas that might be CO2 traps. The boundary between healthy air and lethal gas can be extremely sharp; even a single step upslope may be adequate to escape death. In 2006, three ski patrol members were killed at Mammoth Mountain ski resort after falling into a snow depression surrounding a volcanic fumarole and filled with cool CO2 gas. High concentrations of CO2 gas in soils can also damage or destroy vegetation, as is visible in several areas on Mammoth Mountain.
In addition to their direct hazard, volcanic CO2 emissions also have the capacity to affect the global climate, but scientific studies indicate that the average global volcanic output is insignificant when compared to emissions from human activity.
Sulfur dioxide (SO2) is irritating to eyes, skin and respiratory system
Sulfur dioxide is a colorless gas with a pungent odor that irritates skin and the tissues and mucous membranes of the eyes, nose, and throat. SO2 emissions can cause acid rain and air pollution downwind of a volcano—at Kīlauea volcano in Hawaii, high concentrations of sulfur dioxide produce volcanic smog (VOG) causing persistent health problems for downwind populations. During very large eruptions, SO2 can be injected to altitudes of greater than 10km into the stratosphere. Here, SO2is converted to sulfate aerosols which reflect sunlight and therefore have a cooling effect on the Earth’s climate. They also have a role in ozone depletion, as many of the reactions that destroy ozone occur on the surface of such aerosols.
Please see our discussion of volcanic gases and climate change for additional information.
Hydrogen sulfide (H2S) is very toxic in high concentrations
Hydrogen sulfide is a colorless, flammable gas with a strong, offensive odor. It is sometimes referred to as sewer gas. Interestingly, the human nose is more sensitive to H2S than any gas monitoring instrument we have today: air mixtures with as little as 0.000001% H2S are associated with a rotten egg smell. Unfortunately, however, our sense of smell is not a reliable alarm – at mixing ratios above about 0.01%, H2S becomes odorless and very toxic, causing irritation of the upper respiratory tract and, during long exposure, pulmonary edema. Exposure to 500 ppm can cause a human to fall unconscious in 5 minutes and die in an hour or less.
Hydrogen halides (HF, HCl, HBr) are toxic acids
When magma ascends close to the surface, volcanoes can emit the halogens fluorine, chlorine and bromine in the form of hydrogen halides (HF, HCl and HBr). These species have high solubility; therefore they rapidly dissolve in water droplets within volcanic plumes or the atmosphere where they can potentially cause acid rain. In an ash-producing eruption, ash particles are also often coated with hydrogen halides. Once deposited, these coated ash particles can poison drinking water supplies, agricultural crops, and grazing land.
While making observations at the coastal entry, those of us in the last group of observers are reminded of the unusual hazards posed by the interaction of hot lava and cool seawater. Nearly a half dozen people have died at the coastal entry in the past 10 years and scores more injured. Being prepared for the hazards can help us all to avoid becoming “statistics.” The U.S. Geological Survey, in cooperation with the National Park Service, has prepared a useful Fact Sheet on viewing Hawai`i’s lava safely, #152-00, available at the Kīlauea Visitor Center in the park.
There are two types of hazards discussed in the Fact Sheet that are especially important to consider right now as the new coastal entry evolves: collapse of the lava delta or “bench” and hazardous conditions associated with the coastal entry steam plume.
New land begins to form when molten (2,120°F, 1,160°C) lava encounters the comparatively cool seawater and disintegrates into rubble. The rubble piles up at the edge of the sea eventually gets plated over with more lava, and forms a delta. The actively growing part of the delta is a bench. And although this “bench” is located in a park, it is definitely not one you want to sit on—;or go near for that matter! In a cyclic process, part of the unstable bench collapses through ocean-wave erosion and then is rebuilt and extended a bit by the successive addition of fresh lava, thus continuing the build-erode-rebuild cycle. Eventually the active bench may substantially extend the size of the coastal entry delta.
A poignant hazard associated with new land formation involves being on, or near a delta when a bench collapse occurs. These collapses happen without warning and sometimes result in several acres of new land catastrophically breaking off into the sea in a matter of seconds. Literally all hell breaks loose. As the land slides into the ocean, the ocean responds by sending huge waves up over the shoreline that encounter, among other things, molten lava. Depending upon whether the lava is on the surface or in lava tubes, this interaction can produce anything from superheated steam clouds at ground level to explosions that hurl hundred pound rocks tens of meters (yards). Coastal entry visitors are implored to stay inland of the national park’s guard rope perimeter. Stay alert, stay off the new delta, and, if you hear unusual sounds, move inland quickly.
A subtler hazard posed by molten lava entering the ocean involves the evaporation of seawater to dryness and the associated series of chemical reactions that produce a dense white “laze” plume comprised of a suspended mixture of hydrochloric acid, concentrated seawater steam, and volcanic glass fragments. Hydrochloric acid (HCl) is toxic and extremely corrosive. It causes skin and eye irritation and can also cause breathing difficulties, as well. The mixture of tiny glass fragments, HCl, and seawater raining out of laze plumes has the stinging and corrosive properties of dilute battery acid.
Several years ago, a pair of visitors who ventured too near the coastal entry was found dead, apparently burned by acid-laced steam on the lava bench. Other people have been severely scalded by being near rogue waves washing over molten lava. Avoid being under, or close to, the coastal entry plume. Wear long pants and shirts, and bring plenty of water and a flashlight for each person. Watch for wind shifts, and if you’re caught off guard, put on a hat and raingear and rinse off any precipitation that gets on you as soon as possible.
While the foregoing advice may seem like overkill, it is important for all of us to remember that the coastal part of the park is certainly a wonderland but IS NOT Disneyland. With the right precautions taken, we can all witness this most amazing process of the formation of new land. It is enthralling to see it again for the first time!
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