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The U.S. Geological Survey's Hawaiian Volcano Observatory (HVO) determines the amount and composition of gases emitted by Kīlauea Volcano. Changes in gas emissions can reveal important clues about the inner workings of a volcano, so they are measured on a regular basis.
HVO scientists use both remote and direct sampling techniques to measure compositions and emission rates of gas from Kīlauea Volcano.
To determine the rate at which sulfur dioxide (SO2) is emitted, HVO scientists measure the amount of ultraviolet (UV) radiation energy absorbed by the volcanic gas plume as sunlight passes through it. They do this by attaching a mini-UV spectrometer (Flyspec) to a field vehicle and driving beneath the plume.
The amount of carbon dioxide (CO2) emitted by Kīlauea is measured using a small infrared analyzer (LI-COR). Scientists drive this instrument through a gas plume, along with the Flyspec, while it continuously and directly samples the ground-level cross-section of the plume.
Another tool used to measure the relative abundance of some gases, including SO2, CO2, hydrogen chloride (HCl), hydrogen fluoride (HF), carbon monoxide (CO) and water vapor (H20), is the Fourier Transform infrared spectrometer (FTIR), which can continuously sample gas in a volcanic plume. The FTIR measures the amount of light absorbed by gases along an open path between the spectrometer and an infrared source, such as an eruptive vent.
Learn more:
The sulfuric acid droplets in vog have the corrosive properties of dilute battery acid. When vog mixes directly with moisture on the leaves of plants it can cause severe chemical burns, which can damage or kill the plants. Sulfur dioxide (SO 2) gas can also diffuse through leaves and dissolve to form acidic conditions within plant tissue. Farmers on Hawai`i Island, particularly in the Ka`u...
Predicting the vog levels that visitors might experience during a short stay in Hawai`i is as difficult as predicting the weather. Once volcanic emissions are in the atmosphere, they are distributed by prevailing winds. Where and how bad the vog is ultimately depends on several factors including wind direction, wind speed, air temperature, humidity, and rainfall, as well as the location of the...
Vog poses a health hazard by aggravating preexisting respiratory ailments. Sulfur dioxide (SO 2) gas can irritate skin and the tissues and mucous membranes of the eyes, nose, and throat, and can penetrate airways, producing respiratory distress in some individuals. Aerosol particles in vog can also penetrate deep into human lungs and, at elevated levels, can induce symptoms of asthma. Physical...
Vog (volcanic smog) is a visible haze comprised of gas and an aerosol of tiny particles and acidic droplets created when sulfur dioxide (SO 2) and other gases emitted from a volcano chemically interact with sunlight and atmospheric oxygen, moisture, and dust. Volcanic gas emissions can pose environmental and health risks to nearby communities. Vog is a hazard that's associated with Hawaiian...
The most critical factors that determine how much vog impacts an area are wind direction and speed. Air temperature, humidity, rainfall, location of the source, and the amount of sulfur dioxide (SO2) being emitted are also factors. During prevailing trade (from northeast) wind conditions, any SO2 emitted from Pu`u `Ō`ō is blown out to sea, while any SO2 from the summit vent often creates vog in Ka...
Ninety-nine percent of the gas molecules emitted during a volcanic eruption are water vapor (H 2O), carbon dioxide (CO 2), and sulfur dioxide (SO 2). The remaining one percent is comprised of small amounts of hydrogen sulfide, carbon monoxide, hydrogen chloride, hydrogen fluoride, and other minor gas species. Learn more: Volcanic gases can be harmful to health, vegetation and infrastructure
Kīlauea typically emits between 500 and 14,000 metric tons of sulfur dioxide gas (SO 2) per day during periods of sustained eruption. During the 2018 eruption at Kīlauea’s Lower East Rift Zone, SO 2 emissions were over 100,000 metric tons per day, in keeping with the increased vigor of that eruption. Methods for calculating emission rates for SO 2 can be complicated and challenging in the high...
Kīlauea Volcano is renowned for its relatively benign eruptions of fluid lava flows. Therefore, many people were surprised by the small explosions that occurred in Halema`uma`u Crater in 2008 and 2018, and even more surprised to learn that volcanic ash was being erupted from a new gas vent. However, ash emissions from Halema`uma`u Crater are part of the volcano's legacy. Kīlauea's summit has...
There are 161 potentially active volcanoes in the United States. According to a 2018 USGS assessment, 57 volcanoes are a high threat or very high threat to public safety. Many of these volcanoes have erupted in the recent past and will erupt again in the foreseeable future. As populations increase, areas near volcanoes are being developed and aviation routes are increasing. As a result, more...
Volcanoes are inherently beautiful places where forces of nature combine to produce awesome events and spectacular landscapes. For volcanologists, they're FUN to work on! Safety is, however, always the primary concern because volcanoes can be dangerous places. USGS scientists try hard to understand the risk inherent in any situation, then train and equip themselves with the tools and support...
There are many paths to becoming a volcanologist. Most include a college or graduate school education in a scientific or technical field, but the range of specialties is very large. Training in geology, geophysics, geochemistry, biology, biochemistry, mathematics, statistics, engineering, atmospheric science, remote sensing, and related fields can be applied to the study of volcanoes and the...
A USGS Hawaiian Volcano Observatory volcanic gas specialist sets up a Fourier Transform Infrared spectrometer, or FTIR, near Kīlauea summit during episode 46 of lava fountaining on May 5, 2026.
A USGS Hawaiian Volcano Observatory volcanic gas specialist sets up a Fourier Transform Infrared spectrometer, or FTIR, near Kīlauea summit during episode 46 of lava fountaining on May 5, 2026.
USGS scientists use an FTIR (Fourier transform infrared spectrometer) to measure the chemical composition of volcanic gas during episode 28 of the ongoing Kīlauea summit on July 9, 2025. USGS photo by M. Cappos.
USGS scientists use an FTIR (Fourier transform infrared spectrometer) to measure the chemical composition of volcanic gas during episode 28 of the ongoing Kīlauea summit on July 9, 2025. USGS photo by M. Cappos.
A USGS scientist aims the viewfinder of an infrared spectrometer to measure the chemistry of volcanic gas on the last day of the Nāpau eruption, September 20, 2024. USGS photo by P. Nadeau.
A USGS scientist aims the viewfinder of an infrared spectrometer to measure the chemistry of volcanic gas on the last day of the Nāpau eruption, September 20, 2024. USGS photo by P. Nadeau.
An HVO gas scientist carrying portable gas sensor (yellow box) near Mauna Loa summit in June 2023. The white material on the ground in this photo is snow. USGS photo by P. Nadeau.
An HVO gas scientist carrying portable gas sensor (yellow box) near Mauna Loa summit in June 2023. The white material on the ground in this photo is snow. USGS photo by P. Nadeau.
An HVO scientist samples the gas around a crack identified as emitting elevated levels of carbon dioxide (a volcanic gas) on the down-dropped block within Kīlauea caldera. The sample will later be analyzed to determine its complete chemical composition. This work was conducted within a closed area of Hawai‘i Volcanoes National Park, with park permission.
An HVO scientist samples the gas around a crack identified as emitting elevated levels of carbon dioxide (a volcanic gas) on the down-dropped block within Kīlauea caldera. The sample will later be analyzed to determine its complete chemical composition. This work was conducted within a closed area of Hawai‘i Volcanoes National Park, with park permission.
The 2018 Kīlauea Volcano eruption marked the first time the federal government used Unmanned Aircraft Systems (UAS) to assist in an eruption response in the United States.
The 2018 Kīlauea Volcano eruption marked the first time the federal government used Unmanned Aircraft Systems (UAS) to assist in an eruption response in the United States.
The 2018 Kīlauea Volcano eruption marked the first time the federal government used Unmanned Aircraft Systems (UAS) to assist in an eruption response in the United States.
The 2018 Kīlauea Volcano eruption marked the first time the federal government used Unmanned Aircraft Systems (UAS) to assist in an eruption response in the United States.
The 2018 Kīlauea Volcano eruption marked the first time the federal government used Unmanned Aircraft Systems (UAS) to assist in an eruption response in the United States.
The 2018 Kīlauea Volcano eruption marked the first time the federal government used Unmanned Aircraft Systems (UAS) to assist in an eruption response in the United States.
Hawaiian Volcano Observatory field crews establish a new MultiGAS volcanic gas monitoring station on the south side of Kīlauea Volcano's caldera. Currently, sulfur dioxide emission rates from the summit remain low. The station will collect data to track emission rates and concentrations over time. Photo by Frank Younger.
Hawaiian Volcano Observatory field crews establish a new MultiGAS volcanic gas monitoring station on the south side of Kīlauea Volcano's caldera. Currently, sulfur dioxide emission rates from the summit remain low. The station will collect data to track emission rates and concentrations over time. Photo by Frank Younger.
Title: What on Earth is going on at Kilauea Volcano?
Title: What on Earth is going on at Kilauea Volcano?
HVO's geochemist uses a Fourier Transform Infrared Spectrometer (FTIR) instrument to track volcanic gases emitted from the lava lake with Halema‘uma‘u Crater. These measurements help detect changes in gas composition, which can provide insight into the inner workings of Kīlauea Volcano.
HVO's geochemist uses a Fourier Transform Infrared Spectrometer (FTIR) instrument to track volcanic gases emitted from the lava lake with Halema‘uma‘u Crater. These measurements help detect changes in gas composition, which can provide insight into the inner workings of Kīlauea Volcano.
Hawaiian Volcano Observatory Geochemist Jeff Sutton and CSAV international volcanology students visit a continuous gas monitoring site on Kilauea's east rift zone during field studies portion of the summer training course.
Hawaiian Volcano Observatory Geochemist Jeff Sutton and CSAV international volcanology students visit a continuous gas monitoring site on Kilauea's east rift zone during field studies portion of the summer training course.
Hawaiian Volcano Observatory Geochemist Jeff Sutton and CSAV international volcanology students visit a continuous gas monitoring site on Kilauea's east rift zone during field studies portion of the summer training course.
Hawaiian Volcano Observatory Geochemist Jeff Sutton and CSAV international volcanology students visit a continuous gas monitoring site on Kilauea's east rift zone during field studies portion of the summer training course.
The United States has 169 active volcanoes. More than half of them could erupt explosively, sending ash up to 20,000 or 30,000 feet where commercial air traffic flies. USGS scientists are working to improve our understanding of volcano hazards to help protect communities and reduce the risks.
Video Sections:
The United States has 169 active volcanoes. More than half of them could erupt explosively, sending ash up to 20,000 or 30,000 feet where commercial air traffic flies. USGS scientists are working to improve our understanding of volcano hazards to help protect communities and reduce the risks.
Video Sections:
HVO gas geochemists deployed a FTIR spectrometer on the east rim of Pu`u `Ō `ō crater. The FTIR measures the composition of the East Wall vent gases by "looking" through the plume at an infrared lamp (obscured by fume in this photo)
HVO gas geochemists deployed a FTIR spectrometer on the east rim of Pu`u `Ō `ō crater. The FTIR measures the composition of the East Wall vent gases by "looking" through the plume at an infrared lamp (obscured by fume in this photo)
This photo was taken from the lamp on the other side of the plume. The FTIR is the small dark silhouette on the rim across the crater gap.
This photo was taken from the lamp on the other side of the plume. The FTIR is the small dark silhouette on the rim across the crater gap.
The erupting vent within Halema'uma'u Crater at Kilauea's summit (see http://hvo.wr.usgs.gov/kilauea/timeline/ for links describing eruptive activity at the summit of Kilauea Volcano) typically produces a white to gray gas plume dominated by steam.
The erupting vent within Halema'uma'u Crater at Kilauea's summit (see http://hvo.wr.usgs.gov/kilauea/timeline/ for links describing eruptive activity at the summit of Kilauea Volcano) typically produces a white to gray gas plume dominated by steam.
The sulfuric acid droplets in vog have the corrosive properties of dilute battery acid. When vog mixes directly with moisture on the leaves of plants it can cause severe chemical burns, which can damage or kill the plants. Sulfur dioxide (SO 2) gas can also diffuse through leaves and dissolve to form acidic conditions within plant tissue. Farmers on Hawai`i Island, particularly in the Ka`u...
Predicting the vog levels that visitors might experience during a short stay in Hawai`i is as difficult as predicting the weather. Once volcanic emissions are in the atmosphere, they are distributed by prevailing winds. Where and how bad the vog is ultimately depends on several factors including wind direction, wind speed, air temperature, humidity, and rainfall, as well as the location of the...
Vog poses a health hazard by aggravating preexisting respiratory ailments. Sulfur dioxide (SO 2) gas can irritate skin and the tissues and mucous membranes of the eyes, nose, and throat, and can penetrate airways, producing respiratory distress in some individuals. Aerosol particles in vog can also penetrate deep into human lungs and, at elevated levels, can induce symptoms of asthma. Physical...
Vog (volcanic smog) is a visible haze comprised of gas and an aerosol of tiny particles and acidic droplets created when sulfur dioxide (SO 2) and other gases emitted from a volcano chemically interact with sunlight and atmospheric oxygen, moisture, and dust. Volcanic gas emissions can pose environmental and health risks to nearby communities. Vog is a hazard that's associated with Hawaiian...
The most critical factors that determine how much vog impacts an area are wind direction and speed. Air temperature, humidity, rainfall, location of the source, and the amount of sulfur dioxide (SO2) being emitted are also factors. During prevailing trade (from northeast) wind conditions, any SO2 emitted from Pu`u `Ō`ō is blown out to sea, while any SO2 from the summit vent often creates vog in Ka...
Ninety-nine percent of the gas molecules emitted during a volcanic eruption are water vapor (H 2O), carbon dioxide (CO 2), and sulfur dioxide (SO 2). The remaining one percent is comprised of small amounts of hydrogen sulfide, carbon monoxide, hydrogen chloride, hydrogen fluoride, and other minor gas species. Learn more: Volcanic gases can be harmful to health, vegetation and infrastructure
Kīlauea typically emits between 500 and 14,000 metric tons of sulfur dioxide gas (SO 2) per day during periods of sustained eruption. During the 2018 eruption at Kīlauea’s Lower East Rift Zone, SO 2 emissions were over 100,000 metric tons per day, in keeping with the increased vigor of that eruption. Methods for calculating emission rates for SO 2 can be complicated and challenging in the high...
Kīlauea Volcano is renowned for its relatively benign eruptions of fluid lava flows. Therefore, many people were surprised by the small explosions that occurred in Halema`uma`u Crater in 2008 and 2018, and even more surprised to learn that volcanic ash was being erupted from a new gas vent. However, ash emissions from Halema`uma`u Crater are part of the volcano's legacy. Kīlauea's summit has...
There are 161 potentially active volcanoes in the United States. According to a 2018 USGS assessment, 57 volcanoes are a high threat or very high threat to public safety. Many of these volcanoes have erupted in the recent past and will erupt again in the foreseeable future. As populations increase, areas near volcanoes are being developed and aviation routes are increasing. As a result, more...
Volcanoes are inherently beautiful places where forces of nature combine to produce awesome events and spectacular landscapes. For volcanologists, they're FUN to work on! Safety is, however, always the primary concern because volcanoes can be dangerous places. USGS scientists try hard to understand the risk inherent in any situation, then train and equip themselves with the tools and support...
There are many paths to becoming a volcanologist. Most include a college or graduate school education in a scientific or technical field, but the range of specialties is very large. Training in geology, geophysics, geochemistry, biology, biochemistry, mathematics, statistics, engineering, atmospheric science, remote sensing, and related fields can be applied to the study of volcanoes and the...
A USGS Hawaiian Volcano Observatory volcanic gas specialist sets up a Fourier Transform Infrared spectrometer, or FTIR, near Kīlauea summit during episode 46 of lava fountaining on May 5, 2026.
A USGS Hawaiian Volcano Observatory volcanic gas specialist sets up a Fourier Transform Infrared spectrometer, or FTIR, near Kīlauea summit during episode 46 of lava fountaining on May 5, 2026.
USGS scientists use an FTIR (Fourier transform infrared spectrometer) to measure the chemical composition of volcanic gas during episode 28 of the ongoing Kīlauea summit on July 9, 2025. USGS photo by M. Cappos.
USGS scientists use an FTIR (Fourier transform infrared spectrometer) to measure the chemical composition of volcanic gas during episode 28 of the ongoing Kīlauea summit on July 9, 2025. USGS photo by M. Cappos.
A USGS scientist aims the viewfinder of an infrared spectrometer to measure the chemistry of volcanic gas on the last day of the Nāpau eruption, September 20, 2024. USGS photo by P. Nadeau.
A USGS scientist aims the viewfinder of an infrared spectrometer to measure the chemistry of volcanic gas on the last day of the Nāpau eruption, September 20, 2024. USGS photo by P. Nadeau.
An HVO gas scientist carrying portable gas sensor (yellow box) near Mauna Loa summit in June 2023. The white material on the ground in this photo is snow. USGS photo by P. Nadeau.
An HVO gas scientist carrying portable gas sensor (yellow box) near Mauna Loa summit in June 2023. The white material on the ground in this photo is snow. USGS photo by P. Nadeau.
An HVO scientist samples the gas around a crack identified as emitting elevated levels of carbon dioxide (a volcanic gas) on the down-dropped block within Kīlauea caldera. The sample will later be analyzed to determine its complete chemical composition. This work was conducted within a closed area of Hawai‘i Volcanoes National Park, with park permission.
An HVO scientist samples the gas around a crack identified as emitting elevated levels of carbon dioxide (a volcanic gas) on the down-dropped block within Kīlauea caldera. The sample will later be analyzed to determine its complete chemical composition. This work was conducted within a closed area of Hawai‘i Volcanoes National Park, with park permission.
The 2018 Kīlauea Volcano eruption marked the first time the federal government used Unmanned Aircraft Systems (UAS) to assist in an eruption response in the United States.
The 2018 Kīlauea Volcano eruption marked the first time the federal government used Unmanned Aircraft Systems (UAS) to assist in an eruption response in the United States.
The 2018 Kīlauea Volcano eruption marked the first time the federal government used Unmanned Aircraft Systems (UAS) to assist in an eruption response in the United States.
The 2018 Kīlauea Volcano eruption marked the first time the federal government used Unmanned Aircraft Systems (UAS) to assist in an eruption response in the United States.
The 2018 Kīlauea Volcano eruption marked the first time the federal government used Unmanned Aircraft Systems (UAS) to assist in an eruption response in the United States.
The 2018 Kīlauea Volcano eruption marked the first time the federal government used Unmanned Aircraft Systems (UAS) to assist in an eruption response in the United States.
Hawaiian Volcano Observatory field crews establish a new MultiGAS volcanic gas monitoring station on the south side of Kīlauea Volcano's caldera. Currently, sulfur dioxide emission rates from the summit remain low. The station will collect data to track emission rates and concentrations over time. Photo by Frank Younger.
Hawaiian Volcano Observatory field crews establish a new MultiGAS volcanic gas monitoring station on the south side of Kīlauea Volcano's caldera. Currently, sulfur dioxide emission rates from the summit remain low. The station will collect data to track emission rates and concentrations over time. Photo by Frank Younger.
Title: What on Earth is going on at Kilauea Volcano?
Title: What on Earth is going on at Kilauea Volcano?
HVO's geochemist uses a Fourier Transform Infrared Spectrometer (FTIR) instrument to track volcanic gases emitted from the lava lake with Halema‘uma‘u Crater. These measurements help detect changes in gas composition, which can provide insight into the inner workings of Kīlauea Volcano.
HVO's geochemist uses a Fourier Transform Infrared Spectrometer (FTIR) instrument to track volcanic gases emitted from the lava lake with Halema‘uma‘u Crater. These measurements help detect changes in gas composition, which can provide insight into the inner workings of Kīlauea Volcano.
Hawaiian Volcano Observatory Geochemist Jeff Sutton and CSAV international volcanology students visit a continuous gas monitoring site on Kilauea's east rift zone during field studies portion of the summer training course.
Hawaiian Volcano Observatory Geochemist Jeff Sutton and CSAV international volcanology students visit a continuous gas monitoring site on Kilauea's east rift zone during field studies portion of the summer training course.
Hawaiian Volcano Observatory Geochemist Jeff Sutton and CSAV international volcanology students visit a continuous gas monitoring site on Kilauea's east rift zone during field studies portion of the summer training course.
Hawaiian Volcano Observatory Geochemist Jeff Sutton and CSAV international volcanology students visit a continuous gas monitoring site on Kilauea's east rift zone during field studies portion of the summer training course.
The United States has 169 active volcanoes. More than half of them could erupt explosively, sending ash up to 20,000 or 30,000 feet where commercial air traffic flies. USGS scientists are working to improve our understanding of volcano hazards to help protect communities and reduce the risks.
Video Sections:
The United States has 169 active volcanoes. More than half of them could erupt explosively, sending ash up to 20,000 or 30,000 feet where commercial air traffic flies. USGS scientists are working to improve our understanding of volcano hazards to help protect communities and reduce the risks.
Video Sections:
HVO gas geochemists deployed a FTIR spectrometer on the east rim of Pu`u `Ō `ō crater. The FTIR measures the composition of the East Wall vent gases by "looking" through the plume at an infrared lamp (obscured by fume in this photo)
HVO gas geochemists deployed a FTIR spectrometer on the east rim of Pu`u `Ō `ō crater. The FTIR measures the composition of the East Wall vent gases by "looking" through the plume at an infrared lamp (obscured by fume in this photo)
This photo was taken from the lamp on the other side of the plume. The FTIR is the small dark silhouette on the rim across the crater gap.
This photo was taken from the lamp on the other side of the plume. The FTIR is the small dark silhouette on the rim across the crater gap.
The erupting vent within Halema'uma'u Crater at Kilauea's summit (see http://hvo.wr.usgs.gov/kilauea/timeline/ for links describing eruptive activity at the summit of Kilauea Volcano) typically produces a white to gray gas plume dominated by steam.
The erupting vent within Halema'uma'u Crater at Kilauea's summit (see http://hvo.wr.usgs.gov/kilauea/timeline/ for links describing eruptive activity at the summit of Kilauea Volcano) typically produces a white to gray gas plume dominated by steam.