The following report and photos were provided to MBVRC by Dr. Jeff Witter, Vancouver, B.C. Jeff studies gas emissions at active volcanoes. He heads up the International Volcano Monitoring Fund, a non-profit organization that seeks to assist third world volcano monitoring programs.

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Mapping fumaroles at Baker’s Dorr Fumarole Field

Figure 1. The Dorr Fumarole Field is located high on the NE flank of Mount Baker and is much smaller than the main area of steam vent activity at Sherman Crater.

On July 25 – 27, 2009, Jeff Witter and Ryan Wilson crossed steep ice slopes and glaciers to map the little-known Dorr fumarole field. These fumaroles are at ca 7800 ft (2375 m) elevation at the base of the Cockscomb, the rocky, rugged northeast ridge of Mount Baker dividing the Park and Rainbow Glaciers (also see the map on the ‘About MBVRC’ page).

Figure 2. View looking north across the hydrothermally altered rocks of the Dorr fumarole field. Not much gas vapor is seen in this view. Note person in the center for scale.

Their 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 an area with volcanic steam vents. Other than the numerous steam vents inSherman Crater south of Mount Baker’s summit, the Dorr fumaroles are the only known center of fumarolic activity on Mount Baker. Access to the Dorr fumarole field is not easy and requires a rope, an ice ax, and glacier travel experience. An overnight camp on Ptarmigan Ridge is required if any time is spent working at the fumaroles.

Figure 3. Approaching the Big Sulfur Mound near the center of the Dorr fumarole field.

At Dorr, the steam vent activity has converted the nearby rocks into clay and other minerals in a process called hydrothermal alteration, the result of sulphur-rich gas emitted by the fumaroles.

Jeff and Ryan’s mapping revealed that the Dorr fumarole field is a ~400 m long x ~100 m wide N-S trending zone consisting of various types of hydrothermally altered ground; this is relatively small compared to other fumarole fields. The central and southern portions of the fumarole field are punctuated by numerous steam vents with the most vigorous steaming activity concentrated in the south.

Figure 4. View south to the most vigorous portion of Dorr Fumarole Field, in the ice-rimmed pocket. Fumaroles beneath the ice cliff remained unmapped. A wisp of steam can be seen rising from a vent at the right edge of the photo. This vent was steaming very strongly in 1990.

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 and on a rubbly slope beneath an ice cliff considered too hazardous to approach. The maximum temperature measured in the Dorr steam vents was 90 ºC, which is equivalent to the boiling point of water at that elevation, and comparable to most vents in Sherman Crater.

Figure 5. Measuring the temperature in a sulfur-encrusted crack (90 °C!) on Big Sulfur Mound. This is the boiling point of water at this 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 August 1990, Dave Tucker reported “hundreds” of thumb-sized steam vents scattered about the fumarole field. These qualitative observations suggest that activity at the Dorr fumaroles has decreased since 1990, consistent with studies concluding that the overall activity at Mount Baker volcano has been decreasing since the “failed eruption” of 1975 (e.g. Werner and others, 2009. See MBVRC References webpage.)

Figure 6. Preliminary geologic sketch map of the Dorr Fumarole Field, by Jeff Witter and Ryan Wilson, showing locations of mapped steam vents.

The team from the IVM-Fund plan to return to the Dorr fumaroles next summer to make quantitative measurements of the steam emissions to serve as baseline values for comparison with future measurements. A USGS-sponsored team also plans to visit the fumaroles in summer 2010 to collect gas samples for the first-ever chemical analyses of Dorr fumaroles gases.

Figure 7. Extremely delicate sulphur crystals up to 1.5 cm long exposed in a fumarole on Big Sulfur Mound. Photo taken in 1990 by Dave Tucker.