Glacier National Park is losing its glaciers.

The flowing sheets of ice scattered throughout the Montana park shrank by more than a third between 1966 and 2015, according to new data from the United States Geological Survey and Portland State University in Oregon.

Using aerial and satellite imagery, researchers traced the footprints of 39 named glaciers in the park and surrounding national forest. They found that 10 had lost more than half their area over 50 years.

Ice extent for every glacier in Glacier National Park in 1966 and 2015 Lost 50 percent or more coverage area Agassiz Lost 213 acres (54%) 2015 1966 Sperry Lost 133 acres (40%) Jackson Lost 129 acres (41%) Grinnell Lost 113 acres (45%) Kintla Lost 107 acres (33%) Harrison Lost 98 acres (19%) Rainbow Lost 93 acres (26%) Two Ocean Lost 87 acres (82%) Blackfoot Lost 83 acres (18%) Logan Lost 70 acres (56%) Stanton Lost 65 acres (49%) Chaney Lost 57 acres (41%) Boulder Lost 48 acres (85%) Shepard Lost 44 acres (72%) Dixon Lost 41 acres (57%) Whitecrow Lost 34 acres (57%) Herbst Lost 34 acres (81%) Ipasha Lost 33 acres (41%) Carter Lost 32 acres (37%) Harris Lost 28 acres (77%) Vulture Lost 27 acres (27%) Pumpelly Lost 26 acres (10%) Miche Wabun Lost 25 acres (49%) Sexton Lost 25 acres (25%) Siyeh Lost 25 acres (33%) Old Sun Lost 20 acres (19%) Ahern Lost 19 acres (13%) Red Eagle Lost 18 acres (53%) Grant Lost 17 acres (20%) Weasel Collar Lost 14 acres (10%) Lupfer Lost 13 acres (42%) Salamander Lost 13 acres (23%) Swiftcurrent Lost 13 acres (23%) Baby Lost 10 acres (36%) Hudson Lost 9 acres (42%) Piegan Lost 9 acres (13%) North Swiftcurrent Lost 8 acres (26%) Thunderbird Lost 7 acres (21%) Gem Lost 2 acres (24%)

Ice extent for every glacier in Glacier National Park in 1966 and 2015 Lost 50 percent or more coverage area Agassiz –213 acres (54%) 2015 1966 Sperry –133 acres (40%) Jackson –129 acres (41%) Grinnell –113 acres (45%) Kintla –107 acres (33%) Harrison –98 acres (19%) Rainbow –93 acres (26%) Two Ocean –87 acres (82%) Blackfoot –83 acres (18%) Logan –70 acres (56%) Stanton –65 acres (49%) Chaney –57 acres (41%) Boulder –48 acres (85%) Shepard –44 acres (72%) Dixon –41 acres (57%) Whitecrow –34 acres (57%) Herbst –34 acres (81%) Ipasha –33 acres (41%) Carter –32 acres (37%) Harris –28 acres (77%) Vulture –27 acres (27%) Pumpelly –26 acres (10%) Miche Wabun –25 acres (49%) Sexton –25 acres (25%) Siyeh –25 acres (33%) Old Sun –20 acres (19%) Ahern –19 acres (13%) Red Eagle –18 acres (53%) Grant –17 acres (20%) Weasel Collar –14 acres (10%) Lupfer –13 acres (42%) Salamander –13 acres (23%) Swiftcurrent –13 acres (23%) Baby –10 acres (36%) Hudson –9 acres (42%) Piegan –9 acres (13%) North Swiftcurrent –8 acres (26%) Thunderbird –7 acres (21%) Gem –2 acres (24%)

“One of the reasons we study glaciers is because they have a simple, visual and easily understood response to climate,” said Daniel Fagre, a U.S.G.S. research ecologist who led the study. “If it gets warmer or if they get less snow, they shrink.”

Glacier National Park’s eponymous ice formations have been around for more than 7,000 years, and have survived warmer and cooler periods. But they have been shrinking rapidly since the late 1800s, when North America emerged from the “Little Ice Age,” a period of regionally colder, snowier weather that lasted for roughly 400 years. (At its founding in 1910, the park had at least 150 glaciers, most of which are now gone.)

Agassiz Grinnell Gem Glacier National Park MONTANA

After the end of the Little Ice Age, glaciers across the Western United States, Canada and Europe lost ice as temperatures rebounded. But scientists have attributed more recent melting to human-caused global warming.

“With each decade that we go, more of what we see can be attributed to humans, and less to natural variation,” Dr. Fagre said.

Dr. Fagre noted that even under natural conditions, these small, vulnerable mountain glaciers would have lost ground over the past 50 years — but they would have eventually stabilized at a reduced size. Instead, the park is on track to lose its glaciers within a generation.

Larger, thinner glaciers have lost the most ground

Agassiz glacier. John Scurlock/U.S.G.S.

Agassiz glacier, pictured above, has lost more ground than any other glacier in the park: over 200 acres.

The relatively large glacier — which covered nearly 400 acres in 1966 — is also relatively thin, making it more vulnerable to rising temperatures.

“The analogy here is, think of the shoreline where the water is shallow and the slope of the beach is flat, and we have a small drop in sea level, which immediately reveals a whole lot of beach. Take that same amount of sea level drop with a steep slope and deep water, and you don't expose much more beach,” said Joel T. Harper, a glaciologist at the University of Montana. “The same is true of these glaciers.”

But smaller, thicker glaciers have lost mass, too

Gem glacier. John Scurlock/U.S.G.S.

Unlike Agassiz, the smallest glacier in the park — appropriately named Gem — has not ceded much ground over the past 50 years. But that doesn’t mean it hasn’t lost ice.

Gem is positioned at the top of a cliff, in a small area on a ledge, which means it never had much room to spread out. The glacier formed by accumulating ice upward, becoming thicker. But Gem has visibly thinned in recent years.

“Repeat photographs show it losing volume over time,” Dr. Fagre said. He added that, today, many of the park’s glaciers were “noticeably thinner than they were in the past.”

The recently published U.S.G.S. data measured only coverage area, but a coming study by Dr. Fagre’s team will measure the glaciers’ volume.

“Both processes are going on: thinning and contracting,” he said.

The park’s most visited glacier lost nearly half its footprint in 50 years

Grinnell glacier. John Scurlock/U.S.G.S.

The park’s most visited glacier, Grinnell, lost 45 percent of its footprint — more than 100 acres — from 1966 to 2015.