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

EarthWords is an on-going series in which we shed some light on the complicated, often difficult-to-pronounce language of science. Think of us as your terminology tour-guides, and meet us back here every week for a new word!

Side-by-side comparison of the northwest wall of Kīlauea Caldera on a clear day (left) and a day with thick vog (right).
Side-by-side comparison of the northwest wall of Kīlauea Caldera on a clear day (left) and a day with thick vog (right). HVO observation tower and building can be seen near the center in each photo. Credit: USGS.(Public domain.)

The EarthWord: Vog


  • Vog refers to the visible haze comprised of gas, tiny particles and acidic droplets created when sulfur dioxide and other gases emitted from a volcano chemically interact with sunlight and atmospheric oxygen, moisture, and dust.


  • Get ready, because this word’s pretty recursive. Vog is a contraction of volcanic smog, while smog is itself a pormanteau of smoke and fog.

  • Smoke likely comes from the Proto-Germanic smuk, which referred to the fumes given off from something burning.

  • Meanwhile fog comes from Scandinavian words for “snowstorm,” like the Danish fog and Norwegian fjuk.

Use/Significance in the Earth Science Community:

  • Vog is one of the side-effects of volcanic activity that can have a negative effect on humans and other wildlife. While not as immediate a threat as pyroclastic flow or lava, it can still lead to health effects, like aggravating existing respiratory conditions.

  • Physical complaints associated with vog exposure include headaches, breathing difficulties, increased susceptibility to respiratory ailments, watery eyes, sore throat, flu-like symptoms, and a general lack of energy.

  • Tiny droplets of sulfuric acid in vog creates acid rain, which can leach lead from roofing and plumbing materials, such as nails, paint, solder, and metal flashings. Leached lead poses a health hazard when it contaminates drinking water in rooftop rainwater-catchment systems.

  • Finally, vog can make it difficult to see while driving, piloting an airplane, or navigating a ship.


Next EarthWord: This EarthWord isn’t a new dance-move; it’s been around since we’ve had tectonic plates...

Hungry for some science, but you don’t have time for a full-course research plate? Then check out USGS Science Snippets, our snack-sized science series that focuses on the fun, weird, and fascinating stories of USGS science.

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