Blackfoot Glacier, in Glacier National Park north of Blackfoot Mountain near Jackson Glacier, is the park’s second largest remaining glacier and a striking measure of long-term ice loss in the region. In 1850, Blackfoot and the ice now counted as Jackson Glacier formed one body covering about 1,875 acres, while by 2015 Blackfoot alone had shrunk to 370 acres. The glacier has become an important site for scientific monitoring, with researchers using remote sensing and repeat photography to track change. Between 1966 and 2005 it lost more than 23 percent of its surface area, and in 2007 part of it broke away in an ice avalanche.