Alpine Acoustical Zone
Wind is the most common natural sound heard in the alpine acoustical zone, but avalanches, flowing water, glacier movements, occasional mammals (caribou, sheep, and grizzly bears) and several species of birds (ravens and passerines) are audible. Intruding on the natural soundscape are the frequent high altitude overflights of commercial and military jet traffic, lower altitude general aviation, flight-seeing and air taxi traffic. Sounds originating from the ground near human activity (Don Sheldon Amphitheater, Eldridge Glacier, Little Switzerland, and at base camp on the Kahiltna Glacier) include human-generated sounds from voices, travelling and camping activity. Winter soundscapes differ by having fewer animal and low altitude aircraft sounds, and no flowing water. Sound often carries long distances in this zone because of the lack of sound attenuation from vegetation. Sound reflection and echoes are common from vertical faces of rock and ice. Fresh snow absorbs sounds well and therefore diminishes sound propagation, but snow loses this absorptive property upon compaction and metamorphosis.