Paradise Glacier in August of 2005.  Photo © Greg Louie
  Our Vanishing Glaciers  
  by Mauri Pelto  


he white expanse of the White Chuck Glacier graced the slopes south of Glacier Peak for thousands of years, experiencing periods of advance and retreat until the 20th century.   The last retreat, which began around 1930, culminated in the total disappearance of the north branch of the glacier in 2001. No more does this glacier dominate the headwaters of the White Chuck River, and its demise will alter the river’s hydrology to the detriment of late summer water supply and the salmon that return to this glacially fed river. So, why did this glacier disappear? And is the White Chuck indicative of the future of other Pacific Northwest glaciers?

Lower Curtis Glacier seen in 2003 (Mauri Pelto photo) and 1908 (Asahel Curtis photo).
Lower Curtis Glacier seen in 2003 (Mauri Pelto photo) and 1908 (Asahel Curtis photo). Enlarge
Behavior of Pacific Northwest Glaciers
Glaciers owe their existence to rates of snow accumulation that exceed rates of melting. If climate cools and/or snowfall increases dramatically, accumulation increases, which forces the glacier to expand and advance. When melting exceeds accumulation due to warmer and/or drier conditions, the glacier loses mass by retreating from the terminus and/or thinning. Since glaciers record climate 24 hours a day, year in and year out, they have long been recognized as key climate indicators.

The task of our North Cascades Glacier Climate Project (NCGCP) is to measure changes in the mass balance of North Cascade glaciers annually.  The mass balance is the remaining snow accumulation from the previous winter after the effects of the summer melt season.  The NCGCP has done this on ten glaciers every summer for 23 years.  We hike from crevasse to crevasse measuring the snowpack on the crevasse wall.  Much like reading tree rings, the thickness of each year’s snow layer is evident.  Where crevasses do not exist, we probe the glacier; the metal probe cannot penetrate the glacier ice or the previous year’s refrozen snowpack.  We also emplace stakes in the glacier to measure ice melt.  Each summer we also map the terminus position, and every few years we map a profile up the center of the glacier to evaluate thinning. 

Glacial Changes through the Holocene Period
To put recent changes into perspective, it is helpful to review past trends in glacier behavior throughout the Holocene period, the 11,000 years since the last continental glaciation in the region.

William Long, who served in World War II with the Tenth Mountain Division, was a teacher and Forest Service employee who observed North Cascade glaciers and moraines for fifty years from 1945 until 1995. By carefully observing ash layers on moraines and beyond, he noted no evidence of significant glacier advances between 10,000 and 5,000 years ago.

The Neoglaciation
After 5,000 years ago, a period of glacier growth in the region occurred that is referred to as the Neoglaciation. The Neoglaciation exhibited two distinct periods of glacial advance. Several overrun trees melted from the front of the retreating South Cascade Glacier have been dated to around 4,800 years ago, indicating the start of the Neoglaciation. Pollen records indicate the early Neoglaciation extended from 5,000 to 2,500 ago, and the youngest advance corresponds to the Little Ice Age of the last several hundred years.

Probing snow depth on a glacier. Photo © Mauri Pelto
Probing snow depth on a glacier. Photo © Mauri Pelto
The Little Ice Age
The Little Ice Age (LIA) was a global cooling trend that led to widespread glacier advances. Mean annual temperatures in the LIA were 1.0 to 1.5 °C cooler than at present in the Pacific Northwest, resulting in an average snowline lowering of 100 to 150m.

Depending on the glacier, the maximum advance occurred in the 16th, 18th, or 19th century. Pacific Northwest glaciers maintained advanced terminal positions from 1650 until around 1890, emplacing one or several LIA terminal moraines. At the Lyman, Columbia, and Lynch Glaciers in the North Cascades, William Long and I dated moraines using volcanic ash and found that the early Neoglaciation and Little Ice Age advances were similar in size. Early pictures by Cascade pioneers Israel Russell, C.E. Rusk, and Asahel Curtis show glaciers still close to their LIA maximum moraines at the beginning of the 20th century. Similar results were noted in the northeastern Cascades and on Mount Rainier.

Glacier Retreat in the Early 1900s
The Little Ice Age ended with a progressive temperature rise from the 1880s through the 1940s that led to glacier retreat around the world. A measuring tool for regional climate trends is the Pacific Northwest Index (PNI), which integrates annual values for snowpack at Mount Rainier, precipitation at Cedar Lake in the central Washington Cascades and temperature at Olga in the San Juan Islands. Negative PNI values indicate a cold and comparatively wet trend, while positive values suggest a warm and dry period. Although PNI values were initially low (average of -0.34 from 1895 to 1923), their upward trend generated retreat of glaciers from their LIA positions. The PNI increased sharply during the following decades (+0.44 from 1924 to 1944). This warm dry period was noted around the world, including the “Dust Bowl” in the midwestern US. In the Cascades, glaciers retreated substantially during this period.
Boston Glacier in 1967 (Austin Post photo) and in 2005 (Leor Pantilat photo).
Boston Glacier in 1967 (Austin Post photo) and in 2005 (Leor Pantilat photo). Note distinctly less crevassing and retreat of the central terminus of the glacier just right of center in 2005. Enlarge
Terminal retreat averaged 1400m among larger Mount Baker glaciers, 1200m for 38 other North Cascade glaciers examined by NCGCP, and 1900m for the Nisqually Glacier on Mount Rainier. Glaciers also retreated significantly on Mount Hood and in the Olympic Mountains.

Glacier Advance in the 1950s, 60s, and 70s
The 20th century’s second substantial climate change began in the mid-1940s, when conditions again became cooler and precipitation increased. The PNI dropped sharply (-0.37 average from 1945 to 1976) initiating a more positive trend in mass balance and the advance of some, but not all, North Cascade glaciers.

The Coleman Glacier on Mount Baker was noted to be advancing in 1948 and in short order all of the mountain’s major glaciers were advancing as well, by 480m on average. In 1950, Richard Hubley of the University of Washington initiated an aerial photographic survey of glaciers in Washington to document changes, and this was continued through the 1970s by Austin Post of the US Geological Survey (Post is profiled in this issue of NWMJ).

Major Cascade glaciers such as the Challenger, Boston, and Price became more crevassed as they accelerated and advanced. Most small North Cascade glaciers did not advance, but the large, steep glaciers generally did. For climbers during this period, the more rapid glacier flow led to substantially more crevassing and difficult glacier travel, though the greater snowfall also tended to fill in the crevasses. The change was notable on Mount Baker’s Rainbow Glacier. When we first mapped along the center of the glacier in 1984, we crossed over 300 crevasses; by 2006 the number had dropped to 120.

All the major Rainier glaciers advanced during this period. A wave of ice was noted moving toward the terminus of Nisqually Glacier in the 1940s, prompting it to begin advancing ten years later. Thomas Nylen recently determined from photographs that the Nisqually had advanced 700 to 800m by 1979. During the advance of this heavily debris-covered glacier, visitors watched young vegetation being buried by the advancing terminus.

Eldroado from Forbidden Peak in 1979 and 1996. Photos © Lowell Skoog
Eldorado from Forbidden Peak in 1979 and 1996. Note terminus position on the glacier’s right. Photos © Lowell Skoog Enlarge
Photography shows that approximately half the North Cascade glaciers advanced between 1950 and 1979. Among the 11 Glacier Peak glaciers that advanced, terminal moraines were 300m further downslope on average. However, of the 47 North Cascade glaciers observed by NCGCP, over half did not advance during this generally favorable period.

So, why the differences in glacier behavior during this period? This is because the faster a glacier moves, the faster its response to climate change. Factors causing rapid movement include steeper slopes, high elevation accumulation zones, thick glacier ice, and a narrow terminus. Glaciers that are slow to respond generally lack several of these characteristics. For instance, the flattest glacier on Mount Baker, the Easton, was the last to begin advancing after the 1940s and the last to begin retreating after the 1970s.

Global Warming Effects from Late 1970s to Present
A climate change to drier-warmer conditions in the Pacific Northwest began with the beginning of the sharp global warming trend in the late 1970s. The mean PNI from 1977 to 2005 rose to +0.47, even higher than the Dust Bowl era of the 1930s.

By the mid-1980s, all the Mount Baker glaciers that had been advancing in 1975 were again in retreat. Elsewhere, the termini of 35 of the 47 NCGCP-monitored glaciers were retreating and by 1992 the remaining 12 were as well. As of 2005, five glaciers we observe had melted completely away, including the Lewis in 1990, Milk Lake in 1992, Lyall in 1994, West Lynch in 1995 and North White Chuck Glacier in 2001. We mapped all of the glaciers around Glacier Peak to document changes since C.E. Rusk’s visit of a century before. Aside from glacial retreat, the most notable change from the 1984 USGS map was the formation of eight new lakes where glacier retreat exposed new basins.

This pattern of retreat is not confined to the North Cascades. The Wedgemount Glacier near Whistler, British Columbia has lost 75 percent of its area since 1895, with retreat most rapid since 1978. In the Olympics, the Blue Glacier has been continuously retreating since 1986 and the Anderson Glacier has lost a third of its area. The Hoh Glacier has retreated nearly 500m since its 1970s advance. Mount Hood’s White River Glacier has lost 40 percent of its area over the same time.

On Mount Rainier, the Nisqually Glacier has thinned by over 20m and the Kautz and South Tahoma Glaciers have retreated 800 to 1000m. Meanwhile, the Carbon Glacier has changed relatively little, its thick cover of debris slowing its response. The Paradise Glacier Ice Caves, which in 1978 had over seven miles of trails mapped by the National Speliological Society, no longer exist because the Paradise Glacier has nearly melted to bare ground, as shown in the opening photograph of this article.

White Chuck Glacier from Glacier Gap, looking down the north branch in 1973 (Neil Hinckley photo) and 2006 (Leor Pantilat photo).
White Chuck Glacier from Glacier Gap looking down the north branch in 1973 (Neil Hinckley photo) and 2006 (Leor Pantilat photo). Enlarge

Diagnosing a Dying Glacier
When the climate becomes unfavorable, a glacier responds by melting upward from the lowest and warmest terminus portion. If this new footprint does not stabilize, this indicates disequilibrium with current climate, and the glacier will ultimately disappear. The clearest symptom of disequilibrium is thinning, which indicates a lack of a consistent accumulation zone where at least part of the year’s snowfall can survive through the following melt season. In order to to survive, a glacier needs 60 to 70 percent of its area to be accumulation zone. Of the twelve North Cascade glaciers we have been systematically remapping, nine are thinning as much in the accumulation zone as near the terminus, indicating the extent of glaciers in disequilibrium.

Death of the North White Chuck Glacier
The changes felt by the White Chuck Glacier may provide a glimpse into the future of other struggling glaciers in the North Cascades.

The original USGS topographic map of the White Chuck Glacier shows northern and southern branches, each with separate accumulation zones, joining shortly above the terminus. At the peak of the Little Ice Age, the combined White Chuck Glacier covered an area of 4.8 square kilometers. The White Chuck Glacier retreated rapidly in the first half of the 20th century and by 1950, the glacier’s northern terminus had retreated 1050m and the southern terminus by 750m. More importantly, the glacier had thinned dramatically. Still, the updated 1958 topo shows the White Chuck Glacier with a sizable area of 3.1 square kilometers.

By 1988 however, the southern terminus of the glacier ended in a new lake which was absent from the 1984 topo. And in 2002, the northern branch of the glacier was entirely gone. What remains is a 1600m long boulder-filled basin that extends from the new lake all the way to Glacier Gap at the glacier’s former head. The retreat of this glacier has led to the development of five new lakes, though the two smallest may soon fill in with sediment. The 3.4 square kilometers of new bare bouldery surface will be slowly colonized by vegetation. The effects of this dramatic change upon local hydrologic and biological processes are sure to be profound, and the cumulative effect of many such transformations throughout the Cascades is even greater.

Meanwhile, the southern lobe of the glacier is still thinning slowly and retreating.  The total area of glacier ice left is 0.9 square kilometers, less than 30 percent of the area of just 30 years ago. At the current rate of decline, the last portion of this glacier is not likely to endure beyond the first half of this century.  

Honeycomb Glacier in 1977 (Bill Arundell photo) and in 2006 (Lowell Skoog photo).
Honeycomb Glacier in 1977 (Bill Arundell photo, courtesy Mauri Pelto) and in 2006 (Lowell Skoog photo). Enlarge

The Future
These observations make clear that retreat of North Cascade glaciers is rapid and ubiquitous. All 47 glaciers monitored by our project are currently undergoing a significant retreat or have disappeared altogether. Ongoing temperature rises combined with a reduction in snow accumulation in the North Cascades have resulted in widespread disequilibrium. Even the wet winter of 2007 yielded barely above-average snowpack in the mountains as more of that precipitation fell as rain.

The net loss over the last 20 years is a significant portion of the total glacier volume, estimated at 18 to 32 percent. Sadly, prevailing conditions provide little evidence that North Cascade glaciers are close to equilibrium. Their ongoing thinning indicates that all of the glaciers will continue to retreat into the foreseeable future.
Of the 47 North Cascades glaciers being tracked since the 1967, five have vanished. The following table summarizes the number of glaciers observed to be: advancing, in equilibrium, retreating, or vanished.
  advancing glaciers glaciers in equilibrium glaciers vanished
1967 19 8 20 0
1974 20 5 22 0
1985 5 10 32 0
1995 0 0 47 2
2005 0 0 42 5

Holocene Timeline

The Holocene period extends from 11,000 years ago (9000 BC) to present. The timeline below shows the recorded Northwest glacial advances and retreats during that time.

Glacier Mass Balance and Climate Trends

The chart below illustrates the accumulated decline in mass balance among North Cascade Glaciers. The increasingly downward slope illustrates the accelerating loss of glacier mass. The Y-axis on the left axis represents average change in glacier thickness (in m of ‘water equivalent’). Enlarge Chart
Chart of North Cascade Glacier Cumulative Annual Balance
The chart below illustrates the Cumulative Annual Mass Balance for selected individual glaciers. The Y-axis represents average change in glacier thickness (in m of ‘water equivalent’) relative to 1983.
The chart below tracks ablation (melt) season temperatures since 1984. Despite year-to-year variations, the regression line shows the rising trend. Enlarge Chart
Temperature Chart
The chart below tracks total snow depth (in ‘snow water equivalent,’ i.e. SWE) measured April 1 at eight North Cascade Snotel stations monitored by the USDA since 1946. Note the drop in snowpack after the mid-1970s. Enlarge Chart
North Cascade SWE Chart


Mass Balance
The retained snowpack accumulation at the end of the summer minus the ice and firn melt of the exposed glacier. If snow accumulation exceeds melt, this is termed a positive mass balance; negative indicates that melt is greater.

Period of time lasting 11,000 years ago to the present.

Little Ice Age (LIA)
A global cooling that led to global glacier advances affecting Northwest glaciers from 1650 to 1890.

About the Author

Mauri Pelto was attending graduate school at University of Maine in 1983 when he was instrumental in creating the North Cascade Glacier Climate Project. In 1984, he became, and remains, its director. He received his doctorate in 1989 and since then has been a professor of Environmental Science at Nichols College in Dudley, Massachusetts, where he expects to continue his work for another 20+ years.

North Cascades Glacier Climate Project