Continuous Gas Monitoring Tracks Volcanic Activity at Mount St. Helens

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Detailed Description

Volcano gas geochemistry has been around for a long time. Scientists can make gas measurements using very large, very expensive Correlation Spectrometers or collect samples in the field and bring them back for analysis in the lab. But it’s possible we’re missing out on a lot of information because our monitoring capabilities don’t include continuous observation.

To solve the problem, researchers at the USGS-Cascades Volcano Observatory developed a MultiGAS analyzer that was installed in the crater of Mount St. Helens. The “SNIF” site continuously monitors gas plumes at Mount St. Helens and sends data to USGS-CVO. This video shows the SNIF station and USGS Research Geologist Peter Kelly discusses how it works.

By continuously monitoring volcanic gases at Mount St. Helens and other volcanoes, scientists hope to pick up on the earliest signs of unrest. The data will be used in combination with other monitoring data such as seismicity and ground deformation to piece together a comprehensive model for what we think is going on at the volcano. The information will be used to issue warnings of impending eruptions and deliver eruption updates to local governments, public officials, the media and the public.


Date Taken:

Length: 00:07:02

Location Taken: Vancouver, WA, US

Video Credits

Narration by Peter Kelly
Images by Amberlee Darold, Peter Kelly, Rebecca Kramer and Liz Westby

Music by David Szesztay, Sunny Street,; 
Kevin Macleod, Dirt Rhodes,;
David Szesztay, Take Off,




Mount St. Helens SNIF Monitoring Station:  Continuous gas monitoring improves our ability to track volcanic activity and detect early indications of volcanic unrest

Crater of Mount St. Helens (WA)

Latitude: 46.196626

Longitude: -122.188482

Elevation: 7500 ft



Here we are.  Mount St. Helens.  In the crater.  This is the Mount St. Helens “SNIF” site.  This is a gas monitoring site that was put in at the end of August 2014, and its purpose is to monitor gas plumes at Mount St. Helens.

This plume here contains mostly water vapor, but also contains carbon dioxide, sulfur dioxide and a really trace amount of hydrogen sulfide.  And its composition is consistent with a very shallow, hot, oxidized melt.  And so it’s a magmatic gas essentially, that’s being emitted into the atmosphere.  It has a very low carbon-sulfur ratio, which is consistent with low pressure degassing and it also has mainly sulfur dioxide—very little hydrogen sulfide, which is also consistent with high temperature, low pressure degassing.

This is the only place in the Cascades where we presently get sulfur dioxide degassing.  Everywhere else, there is hydrothermal systems that are in-between the point where the gas separates from the magma and then makes its way to the surface.  It interacts with hydrothermal fluids and rocks and water.  And during that process any sulfur dioxide that is degassed gets converted into hydrogen sulfide and other species so it’s not actually emitted to the atmosphere.

And so this station, which you can see in front of you, is actually a station to monitor just those four gases—water vapor, carbon dioxide, sulfur dioxide and hydrogen sulfide.

Looking at the exterior of the site, this is the north side. On the south side here, we have solar panels to power the site.  Then we have a mast over here that consists of, on the far right, the black thing is an ultrasonic anemometer for wind speed and direction.  There’s a white radiation shield, which has a temperature and relative humidity sensor for ambient air temperature and relative humidity.  And there’s a box with an inlet that serves as an inlet for the gases.  So there’s pumps inside that actively pull plume gas through a tube into the instrument inside.

I’ll open it up now.

So, inside of the station is the gas instrument, which is a self-made instrument, combining several different sensors for the purpose of monitoring water, CO2, sulfur dioxide and hydrogen sulfide.  That’s in this box right here.  And it also contains an array of other diagnostic sensors so we can tell how well the station is working, tracking things like flow, are the pumps working, the temperature of the station, the pressure—all these sorts of things.  And it also has an array of chemicals in small gas bottles which allow us to do automated sensor verifications.  The chemicals are used to check the baseline of the sensors, so it scrubs out water, CO2, SO2 and H2S so we can see if there is any significant baseline shift in the sensors.  And then the gas bottles contain mixtures of gas containing CO2 (carbon dioxide), sulfur dioxide and hydrogen sulfide in known concentrations, which we periodically sample automatically, so that we can verify the response of the sensors—are they changing with time, is there a problem with the sensors of any kind?

And so in this orange box next to the gas instrument—the gas instrument is referred to as a MultiGAS.  This orange box contains additional equipment, such as a solar charge controller, which controls the charge of the batteries.  There is about 10 lead-acid batteries in here.  Hopefully, which will help us get through the winter.  And the orange box also contains a 900-megaHertz radio, which provides a link back to the CVO so we have two-way communications.  We are constantly downloading data but we can also interact with the station in the same way as if it were plugged in on our desktop.

And, another measurement, sort of charismatic measurement that the station makes, is that it measures the temperature of a fumarole just over here to the south of us, here to the left, which currently is about 370 degrees C or around 700 or 750 degrees Fahrenheit.  So there is actually a long cable that runs down the other side of this ridge and you might be able to see some of that heat shimmer there, above those sort of white/pink altered rocks.  And this is a remnant from the dome, one of the spines that was extruded during the 2004-2008 eruption of Mount St. Helens.  And presently, it is the only place we are aware of that emits sulfur dioxide in the Cascades.

This is a very challenging place to make gas measurements or to make any measurements for that matter.  It’s a high elevation site, we’re at about 7500 feet, in the Cascade mountains, so we receive crushing snow loads, ice, wind, rain.  And to add to that mix, we also have corrosive volcanic gases.  So this is a very challenging place to do business.  It’s a challenging place to make instrumentation run for any period of time and it’s also an even more challenging place to get good quality data.

We’ve done this sort of work elsewhere in the world, around the Equator and Southeast Asia, and colleagues have done this sort of work in Italy and other places.

By improving our capabilities for continuous gas monitoring we are better able to track activity and detect early indications of volcanic unrest.  When used in combination with other monitoring data, such as seismicity and ground deformation, we can piece together a comprehensive model for what we think is going on at the volcano.  In this way, we are able to provide the public, government agencies, and the media with comprehensive information regarding the present state of the volcano as well as forecasts of volcanic activity in the event of unrest.  Ultimately, these data contribute to the overall understanding of how these incredible, explosive, volcanic systems work.


For more information about Mount St. Helens visit

Narration by Peter Kelly

Images by Amberlee Darold, Peter Kelly, Rebecca Kramer and Liz Westby

Video by Liz Westby

Music by David Szesztay, Sunny Street,;

Kevin Macleod, Dirt Rhodes,;

David Szesztay, Take Off,