Grinnell Glacier, Glacier NP, 1936/2010

1936 2010 20th century 21st 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 north america physical geography repeat photography sequence series side by side terminus united states geological survey usa usgs