Official websites use .gov
A .gov website belongs to an official government organization in the United States.
Secure .gov websites use HTTPS
A lock () or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.
Nearly all of Earth's alpine glaciers are losing mass, with consequences for freshwater resources, landscape stability, regional ecosystems, and global sea level. Rates of glacier mass loss in Western North America and Alaska are among the highest on Earth (The GlaMBIE Team, 2025).
Return to Glaciers and Landscape Change
The USGS Glaciers Project measures glacier change to inform understanding of water resources, landscape and ecosystem impacts, and infrastructure planning. With a focus on glacier mass balance, the USGS Glaciers Project provides long-term data on glacier change to the public, researchers, land managers, and policy makers.
Glaciers gain and lose mass primarily through winter snowfall and summer temperatures driving snow and ice ablation (melt). When more snow accumulates on a glacier than snow and ice ablate away, a glacier gains mass. Vice versa, if snow and ice ablation exceeds snow accumulation, a glacier loses mass. Glacier mass balance is defined as "the change in a glacier's mass, over a stated period of time” —akin to the accounting system for a glacier. Like balancing a glacier's checkbook, scientists measure the income (snow accumulation) of a glacier, and its expenses (snow and ice ablation), to calculate a glacier’s mass balance.
The U.S. Geological Survey Glacier Project's core glacier monitoring network stretching from Alaska to the Pacific Northwest, are known as the Benchmark Glaciers (Fig. 1). These five glacier sites — Gulkana, Wolverine, Lemon Creek, Sperry, and South Cascade glaciers — are among the longest-monitored and best-studied glaciers globally. Each year, project staff conduct field and remote sensing studies to measure each glacier's mass balance.
At each benchmark glacier, USGS researchers visit numerous field sites across each glacier's elevation range (Fig. 2).
In the spring, measurements are focused on determining the glacier's mass increase over the winter — largely due to snowfall — using snow probes, pits, and cores to measure both the depth and density of the winter snowpack (left image). Researchers then return in the fall to measure the mass loss of the glacier, using ablation stakes to measure snow and ice ablation during the summer (right image). These field measurements are extrapolated over the glacier area to calculate the glacier-wide annual mass balance, quantifying the change in the glacier's mass since the previous year.
The USGS Glacier Project additionally leverages remotely sensed data capturing multi-year and decadal changes. Data collected via aerial photography, Light Detection and Ranging (LiDAR), and commercial satellite imagery allow project staff to quantify glacier area (Fig. 3) and volume change through time. The remotely sensed data also serve as an independent check on field measurements, allowing researchers to identify and correct any potential bias in the glacier-wide annual mass balance record. Direct field measurements capture year-to-year variability and remotely sensed measurements capture long-term cumulative change. Combining methods yields high-confidence, quantitative assessments of mass change across both short and long-time scales for each glacier.
Finally, weather stations maintained adjacent to each glacier provide essential means of relating glacier mass balance field measurements to weather factors like winter precipitation (resulting in snow accumulation and mass gain) and summer temperatures (driving ablation and mass loss). These weather stations further inform USGS researchers the timing of when either the accumulation or ablation seasons of the glacier begin and end— important for accurately calculating glacier-wide mass balance.
The USGS Benchmark Glacier Project annually updates glacier mass balance time series data through a USGS data release. Data are submitted to the World Glacier Monitoring Service. The most recent Benchmark Glacier mass balance results are available on the executive summary webpage. For more detailed description of methods see: O’Neel et al., 2019, McNeil et al., 2020, and Florentine et al., 2023.
Aerial photograph of South Cascade Glacier, WA taken August 13th, 1958 (before image) and October 14th, 2015 (after image).
Aerial photograph of South Cascade Glacier, WA taken August 13th, 1958 (before image) and October 14th, 2015 (after image).
A core section from Kahiltna Glacier at 3,055 m (10,023 feet) on September 30, 2024, showing ice layers in finegrained snow. These "internal accumulation" layers form when water from surface melt percolates into the snowpack and refreezes.
A core section from Kahiltna Glacier at 3,055 m (10,023 feet) on September 30, 2024, showing ice layers in finegrained snow. These "internal accumulation" layers form when water from surface melt percolates into the snowpack and refreezes.
Emily Baker (USGS) sampling a snow-pit on Kahiltna Glacier at 3,055 m (10,023 feet).
Emily Baker (USGS) sampling a snow-pit on Kahiltna Glacier at 3,055 m (10,023 feet).
USGS scientist Louis Sass assesses an on-glacier weather station on the Kahiltna Glacier in Denali National Park, Alaska. This weather station is located at Kahiltna Base Camp, where climbers attempting to summit Denali begin their ascent. Sultana (Mt. Foraker) is visible in the background.
USGS scientist Louis Sass assesses an on-glacier weather station on the Kahiltna Glacier in Denali National Park, Alaska. This weather station is located at Kahiltna Base Camp, where climbers attempting to summit Denali begin their ascent. Sultana (Mt. Foraker) is visible in the background.
These are large glaciers, and even with a helicopter they make you feel very small. Here the scale of the crevasses is illustrated by the small helicopter shadow. This is typical of the complicated topography and significant relief that is common on larger glaciers in Alaska.
These are large glaciers, and even with a helicopter they make you feel very small. Here the scale of the crevasses is illustrated by the small helicopter shadow. This is typical of the complicated topography and significant relief that is common on larger glaciers in Alaska.
This is a 16 m (52.5-foot) core from Kahiltna Glacier at 3,055 m (10,023 feet), May 26, 2023. Kakiko Ramos-Leon (NPS, on the left) is standing where the core intersected the surface. Eric Ridington (pilot, in the middle) is pointing to the melt layers from summer 2022. The melt layers barely visible as grey stripes in the foreground are from summer 2021.
This is a 16 m (52.5-foot) core from Kahiltna Glacier at 3,055 m (10,023 feet), May 26, 2023. Kakiko Ramos-Leon (NPS, on the left) is standing where the core intersected the surface. Eric Ridington (pilot, in the middle) is pointing to the melt layers from summer 2022. The melt layers barely visible as grey stripes in the foreground are from summer 2021.
The surface of South Cascade Glacier, Washington is mostly exposed ice at the end of summer melt season.
The surface of South Cascade Glacier, Washington is mostly exposed ice at the end of summer melt season.
A scientist takes field notes on glacier mass change after measuring an ablation stake installed on the surface of South Cascade Glacier, Washington.
A scientist takes field notes on glacier mass change after measuring an ablation stake installed on the surface of South Cascade Glacier, Washington.
Students Stacey Edmonsond (left) and Audrey Erickson (right) of the Juneau Icefield Research Program, measuring glacier mass balance at the flow divide of Taku and Mendenhall glaciers during the summer of 2019
Students Stacey Edmonsond (left) and Audrey Erickson (right) of the Juneau Icefield Research Program, measuring glacier mass balance at the flow divide of Taku and Mendenhall glaciers during the summer of 2019
Aerial photograph of South Cascade Glacier, WA taken October 14th, 2015.
Aerial photograph of South Cascade Glacier, WA taken October 14th, 2015.
Aerial photograph of South Cascade Glacier, WA taken August 13th, 1958.
Aerial photograph of South Cascade Glacier, WA taken August 13th, 1958.
Nearly all of Earth's alpine glaciers are losing mass, with consequences for freshwater resources, landscape stability, regional ecosystems, and global sea level. Rates of glacier mass loss in Western North America and Alaska are among the highest on Earth (The GlaMBIE Team, 2025).
Return to Glaciers and Landscape Change
The USGS Glaciers Project measures glacier change to inform understanding of water resources, landscape and ecosystem impacts, and infrastructure planning. With a focus on glacier mass balance, the USGS Glaciers Project provides long-term data on glacier change to the public, researchers, land managers, and policy makers.
Glaciers gain and lose mass primarily through winter snowfall and summer temperatures driving snow and ice ablation (melt). When more snow accumulates on a glacier than snow and ice ablate away, a glacier gains mass. Vice versa, if snow and ice ablation exceeds snow accumulation, a glacier loses mass. Glacier mass balance is defined as "the change in a glacier's mass, over a stated period of time” —akin to the accounting system for a glacier. Like balancing a glacier's checkbook, scientists measure the income (snow accumulation) of a glacier, and its expenses (snow and ice ablation), to calculate a glacier’s mass balance.
The U.S. Geological Survey Glacier Project's core glacier monitoring network stretching from Alaska to the Pacific Northwest, are known as the Benchmark Glaciers (Fig. 1). These five glacier sites — Gulkana, Wolverine, Lemon Creek, Sperry, and South Cascade glaciers — are among the longest-monitored and best-studied glaciers globally. Each year, project staff conduct field and remote sensing studies to measure each glacier's mass balance.
At each benchmark glacier, USGS researchers visit numerous field sites across each glacier's elevation range (Fig. 2).
In the spring, measurements are focused on determining the glacier's mass increase over the winter — largely due to snowfall — using snow probes, pits, and cores to measure both the depth and density of the winter snowpack (left image). Researchers then return in the fall to measure the mass loss of the glacier, using ablation stakes to measure snow and ice ablation during the summer (right image). These field measurements are extrapolated over the glacier area to calculate the glacier-wide annual mass balance, quantifying the change in the glacier's mass since the previous year.
The USGS Glacier Project additionally leverages remotely sensed data capturing multi-year and decadal changes. Data collected via aerial photography, Light Detection and Ranging (LiDAR), and commercial satellite imagery allow project staff to quantify glacier area (Fig. 3) and volume change through time. The remotely sensed data also serve as an independent check on field measurements, allowing researchers to identify and correct any potential bias in the glacier-wide annual mass balance record. Direct field measurements capture year-to-year variability and remotely sensed measurements capture long-term cumulative change. Combining methods yields high-confidence, quantitative assessments of mass change across both short and long-time scales for each glacier.
Finally, weather stations maintained adjacent to each glacier provide essential means of relating glacier mass balance field measurements to weather factors like winter precipitation (resulting in snow accumulation and mass gain) and summer temperatures (driving ablation and mass loss). These weather stations further inform USGS researchers the timing of when either the accumulation or ablation seasons of the glacier begin and end— important for accurately calculating glacier-wide mass balance.
The USGS Benchmark Glacier Project annually updates glacier mass balance time series data through a USGS data release. Data are submitted to the World Glacier Monitoring Service. The most recent Benchmark Glacier mass balance results are available on the executive summary webpage. For more detailed description of methods see: O’Neel et al., 2019, McNeil et al., 2020, and Florentine et al., 2023.
Aerial photograph of South Cascade Glacier, WA taken August 13th, 1958 (before image) and October 14th, 2015 (after image).
Aerial photograph of South Cascade Glacier, WA taken August 13th, 1958 (before image) and October 14th, 2015 (after image).
A core section from Kahiltna Glacier at 3,055 m (10,023 feet) on September 30, 2024, showing ice layers in finegrained snow. These "internal accumulation" layers form when water from surface melt percolates into the snowpack and refreezes.
A core section from Kahiltna Glacier at 3,055 m (10,023 feet) on September 30, 2024, showing ice layers in finegrained snow. These "internal accumulation" layers form when water from surface melt percolates into the snowpack and refreezes.
Emily Baker (USGS) sampling a snow-pit on Kahiltna Glacier at 3,055 m (10,023 feet).
Emily Baker (USGS) sampling a snow-pit on Kahiltna Glacier at 3,055 m (10,023 feet).
USGS scientist Louis Sass assesses an on-glacier weather station on the Kahiltna Glacier in Denali National Park, Alaska. This weather station is located at Kahiltna Base Camp, where climbers attempting to summit Denali begin their ascent. Sultana (Mt. Foraker) is visible in the background.
USGS scientist Louis Sass assesses an on-glacier weather station on the Kahiltna Glacier in Denali National Park, Alaska. This weather station is located at Kahiltna Base Camp, where climbers attempting to summit Denali begin their ascent. Sultana (Mt. Foraker) is visible in the background.
These are large glaciers, and even with a helicopter they make you feel very small. Here the scale of the crevasses is illustrated by the small helicopter shadow. This is typical of the complicated topography and significant relief that is common on larger glaciers in Alaska.
These are large glaciers, and even with a helicopter they make you feel very small. Here the scale of the crevasses is illustrated by the small helicopter shadow. This is typical of the complicated topography and significant relief that is common on larger glaciers in Alaska.
This is a 16 m (52.5-foot) core from Kahiltna Glacier at 3,055 m (10,023 feet), May 26, 2023. Kakiko Ramos-Leon (NPS, on the left) is standing where the core intersected the surface. Eric Ridington (pilot, in the middle) is pointing to the melt layers from summer 2022. The melt layers barely visible as grey stripes in the foreground are from summer 2021.
This is a 16 m (52.5-foot) core from Kahiltna Glacier at 3,055 m (10,023 feet), May 26, 2023. Kakiko Ramos-Leon (NPS, on the left) is standing where the core intersected the surface. Eric Ridington (pilot, in the middle) is pointing to the melt layers from summer 2022. The melt layers barely visible as grey stripes in the foreground are from summer 2021.
The surface of South Cascade Glacier, Washington is mostly exposed ice at the end of summer melt season.
The surface of South Cascade Glacier, Washington is mostly exposed ice at the end of summer melt season.
A scientist takes field notes on glacier mass change after measuring an ablation stake installed on the surface of South Cascade Glacier, Washington.
A scientist takes field notes on glacier mass change after measuring an ablation stake installed on the surface of South Cascade Glacier, Washington.
Students Stacey Edmonsond (left) and Audrey Erickson (right) of the Juneau Icefield Research Program, measuring glacier mass balance at the flow divide of Taku and Mendenhall glaciers during the summer of 2019
Students Stacey Edmonsond (left) and Audrey Erickson (right) of the Juneau Icefield Research Program, measuring glacier mass balance at the flow divide of Taku and Mendenhall glaciers during the summer of 2019
Aerial photograph of South Cascade Glacier, WA taken October 14th, 2015.
Aerial photograph of South Cascade Glacier, WA taken October 14th, 2015.
Aerial photograph of South Cascade Glacier, WA taken August 13th, 1958.
Aerial photograph of South Cascade Glacier, WA taken August 13th, 1958.