Denali National Park & PreservePage 127 of 192
Repeat Photography in Alaska’s Parks: Rephotographing a Century of Landscape Change
Reid Glacier, Glacier Bay, June 12, 1899 (G.K. Gilbert, U.S. Geological Survey).
Historical photographs can be revisited to document change. Ronald D. Karpilo of Colorado State University, writing in the National Park Service's Alaska Park Science, explains how to relocate the spot a historical photographer stood, take the picture again and compare. Around the turn of the 20th century, explorers and scientists in Alaska made thousands of high-quality photographs, and a few saw that returning to the same station would reveal change. Harry Fielding Reid, a geophysicist who visited Glacier Bay in 1890 and 1892, wrote in 1896 that any photograph of a glacier's end is useful, especially from an easily described station, since later photographs from it would show what changed.
Karpilo says repeat photography has been used for the 125 years since, and it is a well-established way to document and evaluate changes in natural and cultural resources, to study landscape-scale change, and to explain climate change to visitors, managers and scientists. The information matters for managing Alaska's national parks and keeping people safe.
The five phases
The author has run projects in Denali, Gates of the Arctic, Glacier Bay and Klondike Gold Rush over two decades, relocating and repeating hundreds of photos.
| Phase | What happens |
|---|---|
| Visit archives and gather images of the glaciers, vegetation or other subjects. The pictures must show stable landmarks, such as peaks and rock outcrops, and notes, journals, letters, maps and publications help to find the location. Sources include park archives, the Library of Congress, the National Archives, the Royal BC Museum, several universities, the USGS and private collections |
| Rank photos by quality, subject, season (snow-free summer is usually preferred), access, safety and how repeatable they are, then map the sites. Park staff, pilots, bus drivers and residents can pinpoint locations, and Google Earth, GIS data and topographic maps can simulate the view |
| The author's "think like a photographer" technique asks where he would stand for a good picture, which often points to overlooks and hills. Then he moves until the position of rocks, ridges and peaks matches a printed copy of the old photo. A GPS records latitude, longitude and elevation, along with camera height and bearing, and a 360-degree panorama and reference photos are made |
| Layer the old photo, partly transparent, over the new one in editing software, rotate and resize it with the aspect ratio locked, and crop the modern photo to the old field of view |
| Experts from different fields look at each pair, since each notices different things. Pairs show changes in vegetation, ecosystems, rivers, glaciers, landforms and human impact, and can be analyzed qualitatively or quantitatively depending on the repeat's quality |
Why it works
It is low cost, needing only a basic camera and GPS skills, so it suits citizen science projects and field courses. The resulting pairs serve research, education, outreach and management, can flag features that need closer monitoring, and well-documented stations are easy to revisit. People grasp the point quickly and are drawn into complex subjects. The author argues that pairs satisfy a human yearning for time travel.
What the pairs show
The original article shows each historical photo beside its modern repeat; only the historical photographs are shown here.
| Place | Old photo | Notable changes |
|---|---|---|
| Reid Glacier, Glacier Bay | June 12, 1899 (G.K. Gilbert, USGS); repeated June 27, 2004 | The glacier has retreated several kilometers and plants have colonized the bare ground |
| Tarr Inlet, Glacier Bay | Summer 1931 (C.W. Wright, USGS); repeated June 26, 2004 | Margerie Glacier has advanced into the inlet, Grand Pacific Glacier has thinned and stagnated with a debris-covered end, and vegetation covers the foreground |
| Polychrome Pass, Denali | July 18, 1916 (S.R. Capps, USGS); repeated June 26, 2011 | Polychrome Glaciers have melted significantly, a large pond dried while new ones formed from melting permafrost, low tundra gave way to brush, and the park road was built |
| East Fork Toklat River, Denali | August 22, 1919 (S.R. Capps, USGS); repeated June 30, 2011 | The glacier retreated and thinned, cirque glaciers in side valleys melted, and the river moved from the east bank of its outwash plain to the west |
| Windy Creek, Denali | August 31, 1919 (S.R. Capps) | Cirque glaciers at the head of the creek have melted significantly by July 30, 2011 |
| Nutuvukti Lake, Gates of the Arctic | August 13, 1901 (W.C. Mendenhall, USGS) | White spruce are denser and larger on the foreground slope and midground ridge by 2019 |
| Walker Lake, Gates of the Arctic | August 12, 1901 (W.C. Mendenhall, USGS) | Trees have grown in size and number, shrubs have filled open areas and thickened along the shore and in stream channels (2018) |
| Skagway Harbor, Klondike Gold Rush | July 26, 1897 (F. La Roche, Library of Congress) | Slopes are more thickly vegetated, the shoreline was altered by dredging and fill, and housing, businesses and a small boat harbor were built |
| White Pass, Klondike Gold Rush | August 1899 (H.C. Barley, Yukon Archives) | Rock was blasted for the railroad, vegetation along the river thickened, spruce forest shifted to deciduous species, and the ice on the peak shrank slightly |
| Chilkoot Pass | Late summer 1906 (International Boundary Commission, Library and Archives Canada) | Glaciers on both sides of the pass have retreated, the lake level changed slightly, and historic structures at the pass have deteriorated |
Tarr Inlet, summer 1931 (C.W. Wright, USGS).
Polychrome Pass, July 18, 1916 (S.R. Capps, USGS).
Walker Lake, August 12, 1901 (W.C. Mendenhall, USGS).
Sources
- Ronald D. Karpilo, "Repeat photography: A visually compelling tool for documenting natural resource change," Alaska Park Science 20(1), National Park Service, 2021, https://www.nps.gov/articles/000/aps-20-1-6.htm; rewritten in hubnx's own words. The modern photographs in the original are the author's and are not reproduced.