Cordilleran Section - 115th Annual Meeting - 2019

Paper No. 31-3
Presentation Time: 2:10 PM


O'CONNOR, Jim E., U.S. Geological Survey, 2130 SW 5th Ave., Portland, OR 97201

Glacier rephotography shows the remarkable shrinkage of glaciers in the Three Sisters Wilderness Area of central Oregon. The first known alpine photographs closely showing the glaciers in the area date from 1903, particularly a series of photographs made by USGS geologist I.C. Russell from vantage points on the east slope of Middle Sister. These were followed by dozens of photographs in 1910, mainly on the west side of the Three Sisters but including views from the summit of South and Middle Sisters by professional mountain photographer Clarence Winter and geologist Ira Williams. Early 20th century views were also made by Eugene studio photographer E.F. Martin and Forest Service planner Frederick Cleator; and Ruth Hopson Keen repeated photographs of Collier Glacier, the largest glacier in the Three Sisters area, nearly annually between 1934 and 1973. Colleagues and I have matched many of these photographs since 1993. Many matches are 100 years to the day (or so) after the originals. The changes shown in the photographs helps visualize findings borne from systematic mapping. Of the eighteen glaciers shown on 1920s-era maps of the Three Sisters Wilderness Area, about six are now doubtful. The 8 square kilometers covered by glacial ice shown by the 1920s maps (which was about half of the total area covered during the Little Ice Age maximum of about 1860) is now down to 4-5 square kilometers. The photos also show the greatest reduction glacier-covered area was between 1900 and 1950. Subsequent ice loss continues, but is manifest by slightly reduced area and ubiquitous thinning, locally as much as 50 m.