What is "vog"? How is it related to sulfur dioxide (SO2) emissions?

Vog (volcanic smog) is a visible haze comprised of gas and an aerosol of tiny particles and acidic droplets created when sulfur dioxide (SO2) 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 volcanoes in particular. See the Hawaii Interagency Vog Information Dashboard for detailed information and current conditions.

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What gases are emitted by Kīlauea and other active volcanoes?

Ninety-nine percent of the gas molecules emitted during a volcanic eruption are water vapor (H2O), carbon dioxide (CO2), and sulfur dioxide (SO2). 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 Gas

Who monitors volcanic gases emitted by Kīlauea and how is it done?

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...

Does vog (volcanic smog) impact plants and animals?

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 (SO2) gas can also diffuse through leaves and dissolve to form acidic conditions within plant tissue. Farmers...

How much sulfur dioxide (SO2) gas does Kīlauea emit?

Kīlauea typically emits between 500 and 14,000 metric tons of sulfur dioxide gas (SO2) per day during periods of sustained eruption. During the 2018 eruption at Kīlauea’s Lower East Rift Zone, SO2 emissions were over 100,000 metric tons per day, in keeping with the increased vigor of that eruption. Methods for calculating emission rates for SO2...

Where and how do sulfur dioxide and volcanic gases (vog) affect air quality in Hawaii?

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...

Should I cancel my plans to visit to Hawai`i Island because of sulfur dioxide (SO2) and vog?

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,...

What health hazards are posed by vog (volcanic smog)?

Vog poses a health hazard by aggravating preexisting respiratory ailments. Sulfur dioxide (SO2) 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...

Does ash ever erupt from Kīlauea Volcano?

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...

How hot is a Hawaiian volcano?

Very hot!! Here are some temperatures recorded at different times and locations: The eruption temperature of Kīlauea lava is about 1,170 degrees Celsius (2,140 degrees Fahrenheit). The temperature of the lava in the tubes is about 1,250 degrees Celsius (2,200 degrees Fahrenheit). The tube system of episode 53 (Pu'u O'o eruption) carried lava for...

Why is it important to monitor volcanoes?

The United States and its territories contain 169 geologically active volcanoes, of which 54 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...

Is it dangerous to work on volcanoes? What precautions do scientists take?

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...
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Date published: June 21, 2018

Kīlauea Volcano Erupts

Today's update for June 21st, 2018 will be the last of the daily updates on this USGS feature story.  We encourage you to keep checking the USGS Hawaiian Volcano Observatory (HVO) Kīlauea status website for daily activity updates. You can also visit the USGS Facebook page and the USGS Twitter feed as updates become available. For press inquiries, please email volcanomedia@usgs.gov.

Date published: May 18, 2017


Just like smog and fog, this EarthWord is not what you want to see while driving...

Date published: August 18, 2016

Living with Vog on an Active Volcano: New Resources

New informational products about the health hazards of volcanic air pollution known as “vog,” are available through a new interagency partnership.

Date published: February 11, 2015

New Study Looks at How People Cope with Vog

A new study to examine how people who live downwind of Kīlauea Volcano cope with volcanic gas emissions, or vog, is currently underway.

Filter Total Items: 17
White gas plume rising straight up from Kilauea Volcano summit with distant, bright, full moon.
August 16, 2016

Gas plume from Halemaʻumaʻu Crater, Kilauea Volcano

With stagnant winds present, the plume from Halema`uma`u Crater at the summit of Kilauea Volcano, stands straight up, showing off the distant, but bright, full moon.

scientist with camera and spectrometer at the edge of smoking volcanic crater.
August 16, 2016

USGS HVO geochemist measuring gases released from Kīlauea Volcano

USGS Hawaiian Volcano Observatory geochemist measuring gases released from Kïlauea with a Fourier transform infrared (FTIR) spectrometer, an instrument that detects gas compositions on the basis of absorbed infrared light. The data obtained from FTIR measurements have been useful in identifying the many components of volcanic-gas emissions, which provide information on the

Image: Monitoring Volcanic Gases on Kilauea's East Rift Zone II
May 31, 2014

Monitoring Volcanic Gases on Kilauea's East Rift Zone II

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. Instrumentation at this site measures ambient concentration of noxious sulfur dioxide gas released from the volcano's vents, along with

Image: Monitoring Volcanic Gases on Kilauea's East Rift Zone
May 31, 2014

Monitoring Volcanic Gases on Kilauea's East Rift Zone

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. Instrumentation at this site measures ambient concentration of noxious sulfur dioxide gas released from the volcano's vents, along with meteorological

July 30, 2012

Volcano Hazards

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:

  • Volcanoes: Monitoring Volcanoes
June 30, 2011

The Air We Breathe…It’s a Gas!

We live at the bottom of an ocean of air. Most adults take around 29,000 breaths a day, children breathe a little faster; but what is in this air we breathe? What are the gases in the air? How much of each gas is there? Do these gases have different weights? How cold are liquid nitrogen and dry ice, and where did those names come from? Come join us to explore these

Image: Gas-Rich Lava Flow
December 2, 2010

Gas-Rich Lava Flow

A gas-rich lava flow on the northwest margin of the new shield.

Image: New Gas Vent of Pu’u ‘Ō’ō
June 21, 2010

New Gas Vent of Pu’u ‘Ō’ō

The new gas vent on the east wall of Pu`u `Ō `ō crater opening up next to an older vent (the dark opening to the right of the new gas vent) that sealed shut in the past few months. The new vent has been incandescent at night for the past few days.

Attribution: Natural Hazards
video thumbnail: Halema'uma'u Gas Vent Huffs and Puffs
August 9, 2009

Halema'uma'u Gas Vent Huffs and Puffs

The ongoing eruption in Halema'uma'u Crater at the summit of Kilauea Volcano has experienced several significant interruptions in activity since it began in March 2008. The latest disruption began on June 30, 2009, when a large collapse of the vent rim dumped rubble onto the lava surface and dramatically reduced gas emissions. This period of reduced activity persisted for

video thumbnail: Halema'uma'u Gas Plume Variations (November 17, 2008)
November 16, 2008

Halema'uma'u Gas Plume Variations (November 17, 2008)

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. While ashy plumes released by collapses and explosive events are

Image: The USGS Hawaiian Volcano Observatory Monitors Kilauea's Summit Eruption
September 3, 2008

USGS Hawaiian Volcano Observatory Monitors Kilauea's Summit Eruption

The USGS Hawaiian Volcano Observatory (foreground) is located on the caldera rim of Kilauea Volcano, Hawai'i—the most active volcano in the world.  The observatory's location provides an excellent view of summit eruptive activity, which began in 2008.