What Is Vog?

Vog, or volcanic fog, is a combination of gases and particulate matter droplets known as aerosols which act as an air pollutant around active volcanoes. The existence of vog may present a danger to humans, and is connected to an increased risk of respiratory illnesses and the aggravation of existing respiratory problems. One of the best examples of volcanic fog is found on the Big Island of Hawaii, where the plumes spewing from the regularly active Kilauea volcano can affect air quality, visibility, and health risks throughout the southern islands of Hawaii.

Deep within an erupting volcano, magma is filled with dissolved substances that become gases when the molten rock rises toward the surface. These gases include several known pollutants, including sulfur dioxide, carbon dioxide, and carbon monoxide. As the gases bubble out from the volcano, they form large plumes that can then settle over the surrounding areas or be carried by winds to distant locales. Volcanoes also spew out substances known as aerosols, which are small clumps of particles or liquid drops suspended in gas that are believed to be responsible for some instances of climate change.

High in the atmosphere, the gases can increase ozone depletion, and may fall to earth as acid rain. Closer to the surface, a haze of vog can significantly reduce visibility and is linked to the aggravation of some respiratory illnesses. During a period of significant volcanic fog, cases of bronchitis, pneumonia, and asthma attacks may increase. Minor symptoms, such as allergies, headaches, and fatigue, may also be the result of heavy volcanic fog. Some studies suggest that children who are raised in an area regularly exposed to volcanic fog may suffer an increased risk for developing asthma and other chronic respiratory disorders.

While vog can occur following a large volcanic eruption, it may be a daily feature in any active volcanic area. On the Big Island of Hawaii, vog is a regular occurrence despite generally mild volcanic activity. Since the Big Island has such a high, persistent rate of volcanic fog, it is often the epicenter of studies to determine the movement and resultant pollution of the smog-like haze. The local government of the Island takes many precautionary measures, such as publishing a daily vog level index, to help citizens avoid the nasty side effects of vog.

In a volcanic area, people can often detect the pollutant fog simply by examining the air quality. Unlike smog, which is distinguished by a yellow tinge, volcanic fog is recognizable by blue-tinged air and significantly decreased visibility. Health experts suggest limiting outdoor exposure when vog levels are high, and installing air purifiers inside homes to reduce passive exposure. Those who experience side effects from heavy vog need to hydrate, drink warm liquids to loosen any mucus caused by the air pollution, and should not exercise outdoors.