by S.T. Paxton
Repeat photography, or rephotography, is the act of photographing a scene from the same or comparable vantage point over a period of time. The main reason for this activity is to observe and document change (or the lack thereof) in a subject of interest, such as a person, object, or landscape. In the earth sciences, documenting landscape change is a popular activity among conservationists and to those interested in the rates at which weathering and erosional processes take place. Collectively, these observations are useful for evaluating and estimating changes in the landscape. In addition, some members of the climate change community are relying on repeat photography to document retreat of mountain glaciers as evidence for warming.
The USGS Photographic Library has historical images that can by used as reference images for rephotographing the landscape. However, a challenge with these images is determining, after the fact, precisely where the photographs were taken – that is, the geographic location, the elevation, and the angle of the camera relative to the object of interest. For the State of Oklahoma, the USGS photoarchive has some images for Platt National Park (known today as Chickasaw National Recreation Area, or CNRA) and for the Cushing Oil Field.
Specifically, tor the Chickasaw National Recreation Area, the USGS photoachive has a photograph of Antelope Springs. This USGS photograph was taken by N.C. Glover in 1910 (actual date uncertain). Antelope Springs is located near the far eastern boundary of the park. The springs emerge from just beneath a rocky ledge of conglomerate, referred to as the Vanoss Conglomerate. The Vanoss Conglomerate is very hard and resistant to erosion. The conglomerate is considered the confining layer to the Arbuckle-Simpson Aquifer, an aquifer of regional significance in terms of geology, hydrology, ecology, drinking water, public activism, and emerging water policy for the State of Oklahoma.
Including the most recent attempt, I have tried rephotography of Antelope Springs three times. The first two sessions were during the summer and fall seasons and leaves were on the trees. Therefore, modern comparison to a former view of Antelope Springs is difficult because the 1910 Glover photograph was taken during the winter or very early spring (when leaves were off the trees). Moreover, since the time of Glover, the size and abundance of vegetation surrounding Antelope Springs has increased greatly. Invasion of eastern red cedar to the park has been camoflauging the 1910 appearance of the springs. To a degree, the encroachment of vegetation at CNRA is being remedied by an active program of eastern red cedar and brush removal throughtout the park. The removal of trees around Antelope Springs has the area looking similar to 1910.
During my first two attempts at rephotography of Antelope Springs, my shots were from a vantage point located just slightly to the west of the stream issuing from Antelope Springs (left side of the spring). My most recent attempt (below) was shot from the eastern, or right side of the stream. No matter how hard I try, I cannot get the two images sized correctly. I now conclude that Glover must have been standing in the stream when he took this 1910 photograph.
I will try another round of repeat photography at CNRA next winter (2012/13). Standing in the stream has alway been an option for me, but an option of last resort.
Comparison of the two photographs with an eye to the position of the boulders, rock slabs, and bedrock outcropping of Vanoss Conglomerate indicates remarkable stability in the backbone of the landscape over the past 102 years. The most obvious change in the vicinity of the spring appears to be erosion and lowering of the stream banks by about 30 centimeters (12 inches). To evaluate this conclusion yourself, find the small tree on the left bank of the creek (in the top photograph). Note the base of the tree and the elongated roots, reaching down and out for stability. Note also that just to the left of the tree roots is a slab of rock and to the left of the slab, soil is visible on the creek bank. Now drop your eyes to the bottom image and attempt to find where the tree and soil should be located in February, 2012. The bottom image indicates that the firm ground upon which the tree was rooted has been removed. Regarding water level in the stream, based on the size of cobbles (protruding from the stream) and vegetation in the stream (visible just below the water surface in both images), the depth of the stream appears comparable, then and now. However, the water level of the creek appears to have dropped in comparison to the surrounding boulders.
This exercise in repeat photography indicates little visble change has occurred in the bedrock and boulders surrounding Antelope Springs. In contrast, the immediate springs area appears to have undergone normal landscape erosion – that is, loss of soil on the stream banks of the spring and an overall lowering of the creek bed that issues from Anterlope Springs.