# 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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### 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...

### What was the most destructive volcanic eruption in the history of the United States?

The May 18, 1980 eruption of Mount St. Helens (Washington) was the most destructive in the history of the United States. Novarupta (Katmai) Volcano in Alaska erupted considerably more material in 1912, but owing to the isolation and sparse population of the region, there were no human deaths and little property damage. In contrast, the eruption of...
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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.

January 31, 2008

### Vog from Kilauea

The rim of Kīlauea Volcano’s summit caldera, normally clear on trade-wind days (left), became nearly obscured by vog (right) on some non-trade wind days beginning in 2008, when sulfur dioxide emissions from the volcano’s summit increased to unusually high levels. (This photo has been edited.)

June 27, 2006

### Gas-Pistoning at Drainhole Vent in Pu'u 'O'o Crater (June 28, 2006)

Gas-pistoning is an interesting phenomenon seen at Kilauea and other volcanoes. It is caused by the accumulation of gas within, or the rise of a gas slug through, a column of lava. In either case, the gas pushes up the overlying lava (the "piston"). Eventually, the gas breaches the surface and escapes, sometimes as a forceful jet of fume and spatter. The lava then drains

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September 24, 1981

### Gas Sampling around the Mount St. Helens Dome

USGS geologists gathered samples by hand from vents on the dome and crater floor. Additionally, sulfur dioxide gas was measured from a specially equipped airplane before, during, and after eruptions to determine "emission rates" for the volcano.

June 21, 2010

### New Gas Vent of Pu’u ‘Ō’ō

The new gas vent on the east wall of Puu 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.