Fumarole gases are periodically sampled at Sherman Crater. For the past several years this essential volcano monitoring has been done by volunteer mountaineers and scientists organized by MBVRC. Sampling is done on behalf of the USGS Cascade Volcano Observatory. The purpose is to monitor gas chemistry as an indirect way of keeping tabs on changes in the magma reservoir, lying at an unknown depth below the volcano. Changing gas chemistry allows researchers to make some educated hypotheses about activity: Is new magma accumulating? Is different magma with different chemistry intruding below the volcano? Is existing magma cooling and putting out less gas?
Links to video are at the end of this essay.
Gas collection at Mount Baker
The first gas samples were collected at Sherman Crater during the‘failed eruption of 1975’. That excitement died down, attention was diverted to Mount Saint Helens in 1980, and monitoring of any kind at Baker lapsed to near zero. Gas was resampled in 1998, 1994, ’96, and ’97. The annual program was renewed in 2006, and gas has been collected every year since by volunteers.
Nitrogen (N) and Sulfur (S) are the principal gases strictly associated with magma. The principal sulfur gas coming directly from the magma is SO2; this is ‘scrubbed’ in wet environments such as Baker and reaches the surface as H2S (rotten egg hydrogen sulfide) and O, so is in very small concentrations at Baker. A big increase in SO2would indicate a large flux of gas directly from magma, and a change in magma volume beneath the volcano. Some of the sulfur ends up as sulfuric acid (H2SO4) which makes the rock in the crater pretty nasty- it is important to wash all clothing and gear when you get home so you don’t end up with clothes full of holes. It’s hard on climbing gear, too.
At Baker, we collect gas for chemical analysis directly from fumaroles. To do that, researchers first have to get to the crater. This is usually a two-day glacier ascent, although helicopters have been used. Even if a helicopter is available, it can’t land in the crater, since that is in the Mount Baker Wilderness. A landing must be made near the top of the Squak Glacier a few hundred meters south of the crater, inside the national recreation area. Then, the best way in is up the snow slope to the south crater rim, between “Pooch Peak” and Sherman Peak. This ascent is hazardous due to rock fall if it is put off too late in the summer. Once on the rim, we hope that the nasty bergschrund separating the rocky rim from the glacier inside the crater is not too wide, or we can’t get beyond the rim. It is nice to have an eye in the sky like MBVRC Air Wing Commander John Scurlock fly over shortly before to take some photos of the situation. Once inside the crater, it is a simple descent down gentle snow to the west rim fumaroles, the usual sample site.
The ideal fumarole to sample is big and hot- and accessible. The best ones at Baker are, alas, in pits melted in the crater glacier. One really vigorous one is directly below the West Rim. Another is the Sulphur Cone Fumarole, across the crater in the East Breach. Both of these have small cones of native sulfur built up around their vents. But, it isn’t too safe or too smart to go into a heavier-than-air gas-filled depression without separate oxygen [who wants to hump that up the hill?], so we content ourselves with the easily reached West Rim Fumarole Field, perfectly adequate for our purposes. There are dozens of fumaroles to choose from in the talus and mud just inside the West Crater Rim. We have names for the ones we typically sample: Smiley, Moto (named after a scientist who did gas studies in 1975). Other good fumaroles are a little further north in the Northwest Fumarole Field.
A titanium tube about 2 cm in diameter and a meter long is inserted into a fumarole’s vent, which is spewing gas and plenty of heat, and maybe spitting some water, too. The gas is principally water vapor, so the environmental is quite steamy. The gas is also fairly corrosive, so we have to be careful not to get cameras or other instruments too close or in the direct plume. Videos of Sherman Crater fumaroles are posted here and here and here. To collect as much gas as possible without sucking in ambient air, the tapped fumarole is plugged as best as we can with mud- there is usually plenty of that in the wet environs of Sherman Crater. As soon as that Ti tube goes into the fumarole vent, it gets hotter than hell, so very heavy asbestos mitts must be worn. Of course, once you have those on, you can’t do anything else requiring dexterity, so it really helps to have a couple of people working together. Once you see gas coming out of the end of the tube, a stopper surrounding clear tygon tubing is stuck into the end. The tygon tube is then attached to the fragile glass collecting flask, which has been backpacked up the mountain package in foam.
The flasks are prepared at the USGS Western Region Center in Menlo Park, California. The flasks are evacuated and weighed before they are sent to Baker. These flasks are about 30 cm long and 5 cm wide. There is a valve at the top. There are two glass tubing ‘ports’ on opposite sides near the top, just below the valve. These will allow gas to flow in and out when the valve is opened. A short length of tygon with a clamp is attached to one of these. With the valve closed, the other port is attached to the sampling tubing, which is hopefully spewing gassy steam. Since the valve is closed, gas immediately begins to enter the flask. Once a little pressure builds in the flask, the clamp on the ‘exit tube’ is opened, and gas begins to accumulate in the flask, which is sitting in a plastic bag filled with snow to keep the glass cool and to help the gas condense. It is important to do this in just the right sequence or the sample is contaminated with atmospheric air- bummer. If that happens, start over with another flask, which you had hoped to use to sample a different fumarole. (We usually have three flasks.) Eventually the flask will have a few cm of liquid in the bottom- this is water, but there is also gas in the flask. The valve is close, the tygon disconnected from the ports, the Ti-tube withdrawn. Then the temperature of the fumarole is taken with a thermister attached to a digital multimeter. Fumarole temperatures are written in a notebook, and you’re done. Temperatures are usually measured at many of the most vigorous fumaroles each sampling trip, but only three are sampled for gas chemistry.
Then, we backtrack out of the crater with the flasks carefully wrapped up in backpacks. The carrier(s) are reminded not to sit on their packs, or drop them- the poor soul just has to sit in the snow. Once back to Bellingham, the flasks are sent off to the lab at Menlo, the gas is analyzed, and the data is posted to a spreadsheet. Chemistry data from Baker fumaroles is posted over on the MBVRC main website for all the world to see.
An experimental ‘gas sniffer’ was tried out in 2011. This is a box fitted with inlets and battery-powered automated gas samplers. It passively ‘sniffs’ air in the crater, and measures concentrations of CO2, H2S, H2O, and SO2, rather than collecting a wide range of chemistries. The box can be set on the rocks inside the crater, but must be revisited before winter rolls around and packed out. More work is going in to this method. A comparison of the two sampling methods is presented on another page on this website.
What have we learned so far? Gas chemistry hasn’t changed substantially, though H2 and H2S have decreased a bit while CH4 has gone up. The changes are very small, but all are consistent with cooling temperatures of gas equilibration. In that sense, they are not surprising. Ar, O2, and N2 concentrations mainly reflect air contamination, so lower concentrations of these mean that sampling technique is better than at other times, or that the vent itself is a bit better sealed off from atmospheric inflow, or both. There is a component of N2 that does not derive from air contamination, i.e. is a magmatic signature, but it is very small. It seems that no new magma input has occurred at least since 1975, when the first gas samples were taken.
Temperatures have decreased somewhat since 1975, but overall thermal flux at Sherman Crater has not returned to pre-1975 levels, based on aerial photos showing much less thermal ground prior to 1975. Portions of Sherman Crater remain snow free virtually the entire winter, pretty impressive for 9500’ on a volcano that receives such a huge load of snow every year.
The next goal is to get some samples at Dorr Fumaroles at 7880′ (2400 m) on Mount Baker’s northeast flank; these appear to have never been sampled for gas, at least there are no data records.
Link to USGS webpage on Baker gas sampling.
A USGS website with a more general explanation about direct sampling of volcanic gases (nothing about Baker)
Another USGS website about indirect gas measurements from volcanic plumes. (no mention of Baker.). Some of these methods have been used at Baker.