On the weekend of July 25 – 27, 2009, Jeff Witter and Ryan Wilson, made a trip to the Dorr fumarole field, high on the NE flank of Mt. Baker volcano, located in northern Washington State (Figure 1).
Figure 1. Mt. Baker is located in northern Washington State.
The goal was to make a map of the extent and geologic characteristics of the fumarole field as well as to assess current fumarolic activity for comparison with previous reports. A fumarole field is a geologic term for an area with volcanic steam vents in which the steam vent activity has converted the nearby rocks into clay and other minerals in a process called hydrothermal alteration. The Dorr fumarole field lies at an elevation of ~7800 feet near the head of the Mazama glacier and is relatively small compared to other fumarole fields (Figures 2 & 3). Other than the main center of steam vents at the Sherman Crater, near the Mt. Baker summit, the Dorr fumarole field is the only other known zone of steam vents on Mt. Baker. Access to the Dorr fumarole field is not easy (Figure 4) and requires a rope, an ice ax, and mountaineering experience.
Figure 2. Panoramic photo of the east and northeast sides of Mt. Baker taken from the top of Table Mountain at Artist Point.
Figure 3. The Dorr Fumarole Field is located high on the NE flank of Mt. Baker and is much smaller than the main area of steam vent activity at Sherman Crater.
Figure 4. Topographic maps showing access route to the Dorr Fumarole Field. The starting point is Artist Point, just uphill from the Mt. Baker ski area. The distance from Artist Point to Basecamp is 4.5 miles and the route is along a good quality trail. The distance from Basecamp to the Dorr Fumaroles is 3.3 miles and both mountaineering equipment and glacier travel experience are required.
Figure 5. Aerial photo of the Dorr Fumarole Field taken by John Scurlock on July 27, 2009 (one day after our visit).
Figure 6. View looking north across the hydrothermally altered rocks of the Dorr fumarole field. Note person in the center distance for scale.
The mapping program revealed that the Dorr fumarole field is an ~400 m long x ~100 m wide, N-S trending zone consisting of various types of hydrothermally altered rock (Figures 5 & 6). The central and southern portions of the fumarole field are also punctuated by numerous small steam vents with the most vigorous steaming activity concentrated in the south. During the July 2009 visit, no less than 12 individual steam vents were mapped. Several more steam vents were observed but not mapped in the southernmost sector of the fumarole field on a rubbly slope beneath an ice cliff considered too hazardous to approach (Figure 7).
Figure 7. View south across the west flank of the Dorr Fumarole Field. In the center distance is the ice cliff and hazardous, rubbly zone beneath it that remained unmapped. A wisp of steam can be seen rising from a vent at the base of the ice cliff.
The maximum temperature measured in the Dorr steam vents in 2009 was ~90 ºC, which is equivalent to the boiling point of water at that elevation. Steam emissions at the mapped vents were generally weak and wispy, easily dissipated by a light breeze. Observations at the Dorr fumarole field in July 2009 are in marked contrast to previous observations. In 1990, Dave Tucker reported “hundreds” of thumb-sized steam vents scattered about the fumarole field (Figure 8).
Figure 8. Photo of the steam vents in the central Dorr Fumarole Field taken in 1990 by Dave Tucker.
These qualitative observations suggest that activity at the Dorr fumaroles is lower in 2009 compared to activity observed in 1990. Whether the apparent decrease in activity is real or due to a difference in meteorological conditions is unknown. However, decrease in activity at the Dorr fumaroles is consistent with other studies which conclude that the overall activity at Mt. Baker volcano has been decreasing since the “failed eruption” of 1975 (Werner et al. 2009).
As part of the July 2009 fieldwork, we collected measurements of soil temperatures in the shallow subsurface as well as temperatures of steam vents. Results of these measurements are described below. We plan to return to the Dorr fumaroles in the summer of 2010 to make quantitative measurements of the steam emissions to serve as baseline values for comparison with future measurements.
Shallow soil temperature measurements were made by inserting an OMEGA-brand resistive temperature device (RTD) temperature probe into soft hydrothermally altered clay or non-steaming cracks. Accuracy of the soil temperature measurements was tested in the field by measuring snowpack temperature which gave 0.1 ºC. Table 1 lists soil temperatures and depths of measurement. Measurement locations are shown in Figure 9.
Table 1. Soil temperatures measured at the Dorr Fumarole Field.
The soil temperatures measured in the north central part of the Dorr fumaroles (Temp 0 to Temp 2) likely reflect: 1) near ambient air temperatures at depths within several centimeters of the surface and 2) cooler temperatures at slightly greater depths (e.g. 25 cm). The cooling with depth is apparently caused by an influx of ~0 ºC meltwater from the nearby snowpack. Significantly elevated temperatures (up to 77 ºC) were obtained in non-steaming cracks on the margins of the Big Sulfur Mound (Figures 10 & 11).
Soil temperature measurements made in the central part of the Dorr fumarole field, on the north and south sides of the Big Sulfur Mound, are consistent with one another, showing temperatures of 9 – 10 ºC at depths of 13 – 20 cm. It is difficult to say whether this 9 – 10 ºC measured temperature reflects upward conduction of heat from a broad, subsurface shallow thermal anomaly or is simply downward propagation of heat from surface sediments exposed to the sun. The more likely of these two options can be discerned by re-measuring soil temperatures at the Dorr Fumarole Field on a very cold day where surface temperatures are near 0 ºC. If soil temperatures remain above freezing on an overcast day with freezing air temperatures, then the shallow thermal anomaly measured in the soil is likely from the subsurface.
Based on the soil temperature measurements that we made, the largest thermal anomalies at the Dorr Fumarole Field are very localized around steam vents and non-steaming cracks. The broader thermal anomaly which has melted the snowpack lying on top of the fumarole field is of a lower magnitude.
Figure 9. Hydrothermal alteration map of the Dorr Fumarole Field annotated with locations of soil temperature measurements. White areas of the map are snow-covered.
Figure 10. Approaching the Big Sulfur Mound near the center of the Dorr Fumarole Field. View is to the south.
Figure 11. Measuring the temperature in a sulfur-encrusted crack near Big Sulfur Mound.
The locations of twelve steam vents were mapped and maximum measured vent temperatures were recorded at selected steam vents. The vigor of steam emissions ranged from weak and wispy to strong. Accuracy of the steam vent temperature measurements was tested in the field by measuring snowpack temperature which gave 0.1 ºC. Table 2 lists steam vent temperatures and other observations. Measurement locations are shown in Figure 12.
Table 2. Steam vent temperatures measured at the Dorr Fumarole Field.
Figure 12. Hydrothermal alteration map of the Dorr Fumarole Field annotated with locations of steam vents. White areas of the map are snow-covered.
Geologic Map and Hydrothermal Alteration
Overall, the Dorr fumarole field is dominated by acid-sulfate type hydrothermal alteration.
The fumarole field is separated into four distinct alteration zones. From north to south, these are: 1) competent andesite lava subjected to jarosite/limonite/goethite/hematite-type surface alteration, 2) a buff colored, clay-rich argillically altered zone probably consisting of mixed kaolinite and iron oxides/hydroxides, 3) a light grey-to-white, clay-rich, argillically altered zone probably dominated by kaolinite, and 4) a light grey argillically altered zone containing active steam vents and deposits of native sulfur (Figure 13). Some argillically altered zones exhibit a pinkish color suggesting the presence of the alteration mineral alunite. A fifth zone, lying at the southernmost end of the fumarole field, remained unmapped. While exhibiting the most vigorous fumarolic activity, any hydrothermal alteration in this zone appeared covered by recent rockfall and rubble. These observations suggest that an intense, long-lived acidic hydrothermal system has been centered in the vicinity of the twelve mapped steam vents resulting in the abundant white, kaolinite clay alteration and sulfur deposits.
Figure 13. Crystals of native sulfur up to 1.5 cm long exposed in a crack on Big Sulfur Mound.
This report summarizes preliminary work done at the Dorr Fumarole Field. We plan on returning in the 2010 to refine our geologic map of the area, make more temperature measurements of steam vents, and make quantitative measurements of steam emission from the most vigorous vents to provide baseline values for comparison with future steam flux measurements.
July 25, 2009: Jeff Witter and Ryan Wilson hiked in ~ 4 miles from the Artist Point parking area (above the Mt. Baker ski area) to base camp about halfway between Coleman Pinnacle and “The Portals”. Were hit by a thunder and lightning storm which lasted from ~4:30 pm until ~8 pm. Strong winds persisted until midnight.
July 26, 2009: Awoke at 5:40 am, had breakfast, prepared gear, and left camp by 7:30 am. Roped up across the Sholes Glacier and climbed up on top of the West Portal. Followed the crest of the West Portal until we dropped down onto the Mazama Glacier. Crossed and climbed up the Mazama Glacier on a more or less direct route to the Dorr fumaroles, zig-zagging around crevasses when necessary. Arrived at the Dorr fumaroles by ~1 pm. Discovered that there is cell phone reception at the Dorr fumaroles. Mapped out areas of altered rock and measured steam vent temperatures until ~4:30 pm. Arrived back at basecamp by 7:30 pm.
July 27, 2009: Dave Tucker and his team met us for breakfast at basecamp at 6 am. We passed on what we learned from the day before and they headed off toward the Dorr fumaroles. Jeff and Ryan break camp and hike back to Artist Point.
Werner C, Evans WC, Poland M, Tucker DS, Doukas MP (2009) Long-term changes in quiescent degassing at Mount Baker Volcano, Washington, USA; Evidence for a stalled intrusion in 1975 and connection to a deep magma source. Journal of Volcanology and Geothermal Research, vol. 186, p. 379–386.