Being lucky enough to live near part of the US National Park system and travel to other parts on a regular basis I've always kept an eye out for classic and historical images. It's one thing to know changes are taking place but carries so much more of an impact when one can witness the long term affects. This can be both beneficial and depressing but overall it's a clear avenue of the power of photography.
Recently, I came across work that the National Park Service itself, or more specifically the USGS (US Geological Survey), has put together for their own records as well as public use. This specifically deals with Glacier National Park but I'm sure there are other similar projects out there.
Landscape Change Photography is made up of two main components in a series of ongoing photography projects. Panoramic photographs is a collection "of infrared and panchromatic photographs of Glacier National Park that were taken around 1935 with an Osborne photo-recording transit". The second, Repeat Photography, is the documentation of the namesake Glacier's in the park and their "dramatic glacial recession". (The current estimate is that every single one will be gone in our lifetime, sometime in the next 25 years.)
There is a fascinating description of how the images played out and have come to be available and interpreted today. Identifying features, fires, equipment - it's all there.
Chief Forester Coffman announces completion of a 4-year project for obtaining panoramic photographs from the 200 existing and proposed forest fire lookouts throughout the entire Federal Park System.
The photographic work, done by Junior Forester Moe, entailed many hardships not only in packing the necessary equipment weighing upwards of 100 pounds to lookout points, but also in climbing trees, poles, temporary towers, or roofs of lookouts with the equipment and facing the extreme winds that occur so frequently at high elevations.
Park Service Bulletin, June 1938, pg. 6"
Historical archives such as these that are with the Park Service and other government bodies are typically available for public viewing if not, non-commercial use. It's one way to visually explore and pick up a spot of history. After all we're paying for it.
Additionally, aside from the green photo opps locales such as Glacier National Park are known for, the 'face of use' as demonstrated by the above images is continually shifting these days. Glacier alone has been in a multitude of news pieces as a recognizable face of global warming. Most recently James Balog in a recent National Geographic Adventure feature (Portrait of a Meltdown - Oct 2007) has covered this issue and the park extensively. And in the realm of interesting and experimental photography James has carried this into a fascinating project involving 26 cameras and 300,000 images called Extreme Ice Survey.