NEWS & PUBLICATIONS

Yellowstone Sound Survey
Presidents’ Day Weekend, 2000

   The opportunity to experience natural sounds and silence is rare in our modernized world. National parks are among the last refuges where people can experience natural quiet. Current use of snowmobiles in Yellowstone National Park undermines visitors’ opportunities to hear natural sounds and quiet as part of their park experience. Snowmobiles emit significant amounts of noise at higher frequencies than automobiles. This combination of volume and pitch makes snowmobile noise quantitatively and qualitatively different from other vehicle use in Yellowstone National Park.

   Despite strong policy guidance on noise impacts in parks and the appropriateness of using the human ear to measure natural quiet, the National Park Service (NPS) has failed to collect useful data on noise pollution in Yellowstone National Park. Anecdotal reports document degradation of natural quiet up to 20 miles into the backcountry (Yochim, 1999). Thus, current snowmobile use degrades large portions of Yellowstone Park for those seeking natural quiet.

Policy Requirements

   Natural quiet has been recognized as an integral and irreplaceable park resource that must be protected.

   The National Park Service will strive to preserve the natural quiet and the natural sounds associated with the physical and biological resources of the parks (for example, the sounds of the wind in the trees or of waves breaking on the shore, the howl of the wolf, or the call of the loon.). Activities causing excessive or unnecessary unnatural sounds in and adjacent to parks…will be monitored and action will be taken to prevent or minimize unnatural sounds that adversely affect park resources or values or visitors’ enjoyment of them. (National Park Service Management Policies of 1988).

   NPS further emphasized noise policy in a 1995 report to Congress, “Preserving natural quiet is an integral part of the mission of the NPS. This is confirmed in law, policy, and the beliefs of NPS managers.” (Report to Congress, p.76) NPS elaborated:

   Parks and wildernesses offer a variety of unique, pristine sounds not found in most urban or suburban environments. They also offer a complete absence of sounds that are found in such environments. Together, these two conditions provide a very special dimension to a park experience… Quiet itself, in the absence of any discernible source (especially man-made), is an important element of the feeling of solitude…In considering natural quiet as a resource, the ability to hear clearly the delicate and quieter intermittent sounds of nature, the ability to experience interludes of extreme quiet for their own sake, and the opportunity to do so for extended periods of time are what natural quiet is all about. (NPS Report to Congress on Effects of Aircraft Overflights on the National Park System, 1995, p.78).

In developing an approach to preserve natural quiet, NPS outlined several “important facts.” The first two are: “ 1. Natural quiet is a resource for preservation within the NPS mandate; and 2. The human auditory system is an excellent mechanism for determining the presence or absence of natural quiet. No available electronic device can duplicate human hearing for identifying audible sounds produced by non-natural sources.” (NPS Report to Congress on Effects of Aircraft Overflights on the National Park System, 1995, p.85.)

Map showing sites where measure- ments were taken.  Click here to  view the large-scale map.

Methods

   Percent-time-audible methodology uses the human ear to determine the percentage of time during which a targeted sound is audible. This methodology, used in parks such as Grand Canyon to assess impacts of overflight noise, fits well with park policy on natural quiet (cited above). In short, the human ear is the best way to measure whether artificial noise, in this case snowmobiles, disrupts natural sounds and natural quiet.

   For the Yellowstone percent-time-audible study, volunteers
were transported by snow coach to trailheads between Madison Junction and Old Faithful. 

   Volunteers skied or snow-shoed in pairs to 13 study sites marked on topographic maps. Listening sites were located in the Lower, Midway, and Upper Geyser Basins at well-known attractions accessible by trail in winter. Distances from the road ranged from approximately 0.5 miles to 2.5 miles. Percent-time-audible data were collected for 20 minutes of each hour for the four-hour period between 9AM and 1PM. Data were collected at the same sites and during the same time period on Saturday, February 19, and Sunday, February 20, by different teams of investigators.

   The listener and data recorder stood or sat quietly and noted noise present and the time when dominant noise changed or disappeared. The listener identified to the recorder what sounds were present, according to codes. Three codes were used for percent time audible data collection: “S” was marked if snowmobiles were audible; “O” if no snowmobiles were audible but other human sounds were present; and “N” if no human sounds were present. Snowmobile sound took precedence over all other sounds, and other human-generated sounds were recorded over natural sounds. Only when natural sounds were the only noise present was “N” recorded on data sheets. Volunteers recorded these codes and time of duration for each sound source throughout the 20-minute data-collection period. Natural sounds present at each site also were recorded.

   Data were compiled by Mountain West GIS Co-op using a spreadsheet program and the ratio of percent time with snowmobiles audible to percent time with natural sounds was determined for each collection period. Percent time audible for all collection periods for each site was calculated, and data for Saturday and Sunday were averaged, creating a final percent time audible for snowmobile noise for each listening site. A final map showing percent time audible by site was prepared by Mountain West GIS Co-op in Bozeman, Montana.

Results

   Thirteen sites were surveyed. Eleven sites had percent time audible for snowmobiles above 70 percent (Table 1), and eight of those had audible snowmobile sounds 90 percent or more of the time. Goose Lake had 41 percent time audible due to high winds that drowned out all other sounds. Lone Star Geyser recorded no snowmobile noise, most likely due to its topographical position in a river canyon at lower elevation than the road. Lone Star Geyser is approximately 1.5 miles from the road. The Nez Perce Creek site is more than two miles from the road and had 92 percent time audible for snowmobiles. Variation between sites seemed to be due to topographical variation, wind speed, and direction.

   Most sites had a mixture of snowmobile noise and ambient sounds, yet natural sounds often were rendered inaudible because of snowmobile noise. Ambient sounds heard included: geese, ravens, Clark’s nutcrackers, and other bird calls; waterfalls, rivers, and streams; wind; and geysers, mudpots, and other thermal features. Listeners described the snowmobile noise as a “constant whine” that escalated to a roar when several machines passed in a group, when machines were accelerating or revving in parking lots, or when an exceedingly loud machine passed. At Old Faithful, snowmobile noise was present 100 percent of the time surveyed (between 10AM and noon). Noise at Old Faithful consisted of a constant whine punctuated by louder, higher-pitched sounds both from the road and parking areas.

Discussion

   This percent time audible study for snowmobile noise in Yellowstone National Park on a busy winter weekend illustrates the problem encountered by winter visitors: it is virtually impossible to escape snowmobile noise. The only visitors who have any chance of finding quiet and experiencing natural sounds are those capable of skiing significant distances. Day visitors to Old Faithful and the geyser basins would find it exceedingly difficult to access an area not susceptible to snowmobile noise. Ambient natural sounds are abundant, yet overwhelmed by constant snowmobile noise. Volunteers for this study routinely commented that the noise was constant and of a pitch and intensity that was extremely disturbing and detracted from their enjoyment of park values.

Conclusion

   Yellowstone National Park is degraded by snowmobile noise at levels that conflict with park policy and visitor expectations. Current winter management of the park makes it impossible for visitors to encounter the natural sounds and quiet they seek, in a winter experience. Visitors in the most famous areas are inundated with snowmobile noise 90 percent of the time. The average visitor watching for Old Faithful over Presidents’ Day weekend could hear snowmobiles the entire time. Even visitors who are physically able to ski find that snowmobile noise follows them far into the backcountry.

Recommendations

   We recommend that the National Park Service adopt a winter management plan that complies with park policy on natural quiet. Current winter use renders it nearly impossible for the average visitor to experience natural sounds and quiet at many popular locations in Yellowstone. Implementation of a visitor mass-transportation plan using quieter vehicles in lower numbers is necessary. The snowcoach-only plan outlined in The Citizens’ Solution for Winter Access to Yellowstone, supported by the Greater Yellowstone Coalition and National Parks Conservation Association, would restore natural quiet to our first national park.

Report compiled by: 
National Parks Conservation Association and the Greater Yellowstone Coalition