This image from the Space Shuttle Atlantis shows distinct gas plumes rising from Kilauea Volcano in Halemaumau Crater and at Puu Oo, the two vents responsible for the vog that shrouds Hawaii Island. An ocean entry plume, created by molten lava from Kilauea’s east rift zone flowing into the sea, is also visible.

(Volcano Watch is a weekly article written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.)

To most Hawaii Island residents, the eruption of Kilauea Volcano has been something that is happening “over there.” Pele’s domain might be an attraction you show to visitors.

It might be a frustrating complication if you live in a high Lava Flow Hazard Zone area and you’re trying to get property insurance or a mortgage.

It’s what the volcano brings to people’s homes that understandably concerns them.

During the summer of 2007, Puna residents were worried about the possibility of active lava flows advancing north of Kilauea’s east rift zone and affecting many homes there.

Once the flows turned southward, the concerns of many shifted to the concerns of the few who resided in and downslope of the Royal Gardens subdivision. The ability to forecast where lava might invade has been very useful in planning responses and focusing on the most vulnerable.

We are forecasting lava hazards with increasing accuracy. Lava flows downhill. The path along which a lava flow advances is primarily a function of the terrain and can be confidently forecast, using the best and most recent digital-elevation models.

Details about the rate at which flows advance rely on understanding the physical and chemical nature of molten lava and its eruption rate. These are important items of research and monitoring for the Hawaiian Volcano Observatory and other institutions worldwide.

The current state of lava-flow forecasting provides accurate flow paths and somewhat less accurate flow dimensions and speed.

Lava, however, isn’t the only thing flowing out of Hawaiian volcanoes. In early 2008, Kilauea’s sulfur dioxide (SO2) emissions nearly doubled with the onset of the Halemaumau summit eruption, causing widespread public concern.

Like lava flow hazards, successful forecasting of gas hazards requires detailed knowledge of fluid properties, but, in this case, for gases. Most of Kilauea’s emissions are water vapor and carbon dioxide, but public concern understandably focuses on the irritating and readily detectable SO2.

Although heavier than air, this gas rises above ground level when released hot. To our eyes, SO2 itself is invisible. Reacting with sunlight, oxygen, and water vapor, however, SO2 converts to the visible, inhalable, acid sulfate aerosol droplets we “see” as vog.

According to the state Department of Health’s monitors, vog’s effects on the Island of Hawaii have recently diminished; air quality is somewhat improved.

In the first seven months of 2009, 24-hour SO2 health standards were exceeded four times, and inhalable aerosol particle (PM2.5) standards were exceeded 18 times.

This contrasts sharply with the last nine months of 2008, when the 24-hour SO2 standards were exceeded 37 times, and PM2.5 aerosol standards were exceeded 31 times.

The apparent improvement in air quality is welcomed but puzzling. Although Kilauea’s emissions were down in July, the long-term emissions have not decreased to the same extent.

Perhaps there’s something different about the winds.

Gases emitted by a volcano flow downwind the way lava flows downhill. Downwind movement of gas, however, is not as easily calculated as downhill movement of lava.

Local winds mix with regional winds, such as the trades (northeasterly) or konas (southerly). In addition, a thermal inversion layer in the atmosphere around 2,000 meters (6,000 feet) altitude effectively caps the highest vertical extent of emissions from Kilauea’s vents.

The downwind calculations for volcanic gas flow are not the expertise of most volcanologists, and HVO has benefitted by collaborating with atmospheric scientists.

Many different gas dispersion models are available, and a few have been tried with Kilauea’s emissions with some success.

An experiment run by the National Park Service and the National Oceanic and Atmospheric Administration through several months of 2008 showed promise and suggested a path for future work.

Native Hawaiian knowledge may also offer guidance on the wind issue in the way it has helped enhance our appreciation of volcanic processes.

In Hawaiian mythology, many deities influence volcanic phenomena, but Pele is clearly the one in charge. The hierarchy for wind deities, however, is more complex; winds are represented by a number of gods and goddesses, depending on locality.

So, for now, forecasting lava distribution is easier than forecasting gas distribution, but we are making some progress incorporating knowledge about the local wind deities while we refine our gas dispersion models.