Grinnell Glacier, Glacier NP, 1938/1981

1938 1981 20st century alpine glaciation america climate change research climate change climatology compare composite earth science ecological ecology environment environmental geography geology geomorphology geophysics glacial decline glacial loss glacial recession glacial retreat glaciation glacier national park glacier glaciology global warming gnp grinnell glacier montage montana mount gould mt gould north america physical geography repeat photography sequence series side by side united states geological survey usa usgs