14 minute read

Farewell to Oregon’s Central Cascade Glaciers?

by Anders Eskil Carlson, Ph.D., Nicolas Bakken-French, and Erin K. Hennessy, Oregon Glaciers Institute

In 1939, Kenneth Phillips waxed whimsically in the closing of his Mazama Bulletin article Farewell to Sholes Glacier: “perhaps mountaineers of the fairly near future may look upon the empty cirques of Mt. Hood as a normal condition, much as climbers of today may pardonably consider those of Mt. McLoughlin.” Phillips was discussing the departure of Sholes Glacier from Mt. McLoughlin, the first glacier disappearance documented in Oregon, not knowing the remarkable prescience his poetic closing contained. A little over 80 years later, that “fairly near future” is the modern here and now, at least for the glaciers in the Oregon Central Cascades.

Above: Photograph of Collier Glacier on September 25, 2021. The snow cover is from a mid-September snowfall that hides the bare ice of the entire glacier. Photograph by Nicolas Bakken-French.


The Oregon Glacier Institute, with generous support from the Mazamas, had planned in 2021 to resume seasonal surface mass balance measurements on Collier Glacier on the northwest side of the North Sister volcano in the Oregon Central Cascades (above). Surface mass balance is the measurement of a glacier’s “ins” and “outs.” One measures the amount of summer melt using PVC pipes drilled into the glacier’s surface (the outs; the term for glacier mass loss is ablation) and the amount of snow remaining at the end of the summer using snow pits (the ins; the term for glacier mass gain is accumulation). That end-of-summer snow is then slowly turned into firn (granular ice crystals) that eventually compacts into glacier ice. The snow-firn-ice metamorphosis takes many years.

Thus, in summer on a normal glacier, one would walk up the glacier on bare ice in the ablation zone. As the elevation increases, one crosses from bare ice onto last winter’s snow in the accumulation zone. Under that snow are many prior winters’ snows and then firn resting on glacier ice. The transition between the ablation and accumulation zones is called

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the equilibrium line and its altitude is equivalent to the elevation where the mean annual temperature is freezing (32 °F, 0°C). Another way to think of the equilibrium line is that it is also the end-of-summer snowline on the glacier.

On a healthy glacier in equilibrium with climate, accumulation equals ablation. The mass of the prior winter’s snow remaining at the end of the summer above the equilibrium line is equal to the mass of ice melted during the summer below the equilibrium line. The ins match the outs and the glacier’s overall mass does not change. On most glaciers in equilibrium with climate, about 55 percent to 75 percent of the glacier’s area should be in the accumulation zone above the equilibrium line, with the range reflecting individual glacier geography, geometry, and climate. That is, at the end of the summer roughly two-thirds of the glacier should still have some snow cover from the prior winter. On an unhealthy glacier, the accumulation zone is consistently less than two-thirds of the glacier area. And to kill off a glacier, the equilibrium line must rise due to a warming climate so that it is higher than the upper reaches of the glacier and the glacier has no accumulation zone. The glacier is now starving and will cease to flow once it has lost so much ice that it is no longer 100 feet (30 meters) thick, the threshold thickness for ice to deform under its own weight.

Surface mass balance measurements are critical for documenting how seasonal weather drives long-term changes in climate and glaciers. If a glacier retreats, was it due to warmer summers causing more melt? Or has there been less snowfall? Or a combination of the two? Without such measurements, one is left with just speculation on what is driving glacier changes. At present, only glaciers in Alaska, Washington, and Montana have surface mass balance measurements conducted on a seasonal to annual basis, leaving the glaciers of Oregon, California, Wyoming, and Colorado unmonitored (the lone glaciers of Utah and Nevada are most likely gone).

Professor Peter Clark and his students at Oregon State University made surface mass balance measurements on Collier Glacier in the late 1980s into the mid1990s with one more set of measurements made in 2009–2010. These measurements indicated that Collier had to have an accumulation zone ratio of 70 percent to be in equilibrium with climate. However, the consistent measurements were abandoned due to lack of support from the State of Oregon. Despite the incontrovertible evidence of global warming and its impact on glaciers, as of 2021 the State of Oregon still shows no interest in documenting, monitoring, or understanding the retreat of Oregon glaciers and their attendant consequences to the environment and water resources of the state. For instance, the frequent state climate assessments never mention Oregon’s glaciers and their changes; the state’s 100-Year Water Vision makes no acknowledgment of glaciers’ roles in the hydrologic cycle. Research support from groups like the Mazamas is therefore critical to make up for our government’s neglect of their constitutional duty to protect our environmental trust. Indeed, the Mazamas maintained surface mass balance measurements on Mt. Hood’s Eliot Glacier from the 1960s up to the mid-1980s, showing the organization’s commitment to glacier science. COLLIER GLACIER IN 2021

We headed out in mid-September to scout Collier Glacier. We planned to determine proper locations for the PVC melt stakes on the glacier and return in a week to install the stakes. Instead of the normal glacier profile described above, what we found halted our work in its tracks.

As I mentioned, a hot summer can drive glacier retreat through increased melting and consequently more outs than ins. That heat also melts the snow and thus reduces the ins. Oregon had experienced an unprecedented heatwave a month and a half earlier in late June to early July, which the World Weather Attribution group found to have a 1-in-1000 chance of occurring, with grater than 99 percent of the heatwave due to human greenhouse gas emissions. In addition to its unprecedented nature, the heatwave was also devastating to Oregon’s glaciers and snowpack. While a

Figure 2. Accumulation area ratio of Collier Glacier (top) and nearby summer temperature (bottom). Top: accumulation area as percent of total glacier area. Dashed line indicates equilibrium ratio of 70 percent: above 70 percent is a positive mass balance year; below 70 percent is a negative mass balance year. Pink are data from satellite observations; red are data from surface mass balance measurements. Bottom: McKenzie Pass summer (June, July, August) temperature in blue. Dashed line is average temperature of 1990s.

dusting of new September snow lay over Collier Glacier signaling winter’s encroachment, the heatwave had not only melted ice in the ablation zone, but also all the prior winter’s snow in the accumulation zone, leaving the glacier in a state of starvation. Collier Glacier had no accumulation zone for the 2020–2021 water year (a water year begins October 1 and ends September 30).

Without an accumulation zone, Collier Glacier lost mass at every elevation for the 2020–2021 water year. With such drastic conditions, we decided against installing the surface mass balance equipment on the glacier as the lack of an accumulation zone violates basic assumptions that go into the technique. The equilibrium line altitude was above the glacier’s highest reaches—8,920 feet above sea level. At its 1990s extent, the equilibrium line altitude on Collier Glacier should be at about 8,050 feet above sea level for the glacier to have 70 percent of its area in the accumulation zone. The temperature of 2021 over Collier Glacier was therefore quite extreme to drive the end-ofsummer snowline more than 900 feet higher than where it would typically reside in a climate that would sustain the glacier. We therefore switched focus and used the Mazama financial support to investigate the extent of the accumulation area on Collier for the last five years with satellite imagery to place the 2021 summer in historical context.

Figure 2 shows the accumulation area record for Collier Glacier. At present, Collier Glacier is about 110 football fields in area. Remember that for Collier to be in equilibrium, about 70 percent of its area should be in the accumulation zone, or around 75 football fields of snow remaining at the end of the summer. However, Collier Glacier lacked an accumulation zone in 2021 (0 percent ratio). When we visited Collier Glacier on September 7, 2020, we found only about a foot of snow remaining on the upper reaches of the glacier (above). It did not snow on the glacier until mid-October of 2020, making for a long summer. By mid-October, all the snow on Collier was melted away and the glacier had an accumulation zone ratio of 0 percent in 2020 as well as in 2021. In 2019, the accumulation zone was 85 football fields in size (a ratio of 78 percent), marking a positive mass balance year for Collier. However, 2018 was another bad year with an accumulation zone covering only about 8 percent of the glacier (nine football fields). Conversely, 2017 was another healthy year with an accumulation zone of 97 football fields (88 percent ratio). In summary, two of the last five summers had significant melting with no accumulation zone: 2021 and 2020. In addition, 2018 had an accumulation zone that covered less than 10 percent of Collier Glacier. In fact, we would be shocked by the 2018 year if it wasn’t for how much worse 2020 and 2021 were. In contrast, 2017 and 2019 were years continued on next page

with large accumulation zones and the glacier gained net mass. Nevertheless, three out of the last five years were bad to abysmal. We then compared the last five years against the Collier surface mass balance record from the early 1990s (Figure 2). For 1990–1994, Collier Glacier had an accumulation zone that covered about two-thirds (1990, 1991) to 80 percent of the glacier (1993). Two other years had negative surface mass balances, with accumulation areas of around 50 percent (1992) to 35 percent (1994). The one-off 2010 year measurements indicated that Collier had about 75 percent of the glacier in the accumulation zone. Head of Collier Glacier on September 2, 2020, showing only about 1 foot of snow remaining from the prior winter. Photograph by Anders Carlson. This limited record points toward the 2017 and 2019 years for Collier being nothing out of the normal while also highlighting the severely negative 2018 year (nine percent accumulation area ratio) and extremely negative 2020 and 2021 years as unprecedented. EXTREME SUMMERS While Collier Glacier did not have an accumulation zone in 2020 and 2021, an additional phenomenon occurred in 2021: The heatwave melted through all the prior winter’s snow and into the pre-2020 snow/firn that had accumulated. Those snow gains of 2019 and 2017, along with the little snow of 2018, were obliterated, leaving an entire glacier the size of 110 football fields of bare ice. One analogy to this phenomenon is a political prisoner on a two-week hunger strike being forced by the guards to undergo liposuction to hasten a morbid end to the hunger strike. The year 2021 is not the only extreme summer we have experienced in recent memory. There is 2015. Until 2021, 2015 was the hottest summer on record that followed the lowest endof-winter snowpack on record, which set up dire conditions for Oregon’s glaciers. In fact, the summer (June, July, August) average

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temperature at the nearest weather station to Collier Glacier, McKenzie Pass, recorded equal average summer temperatures for 2015 and 2021: 57.3°F (bottom of Figure 2). For comparison, the average summer temperature in the 1990s at McKenzie Pass was 52.2° (bottom of Figure 2).

We find on many glaciers in the Central Oregon Cascades evidence of that 2015 year. In the summer of 2020, only three to four layers of snow rested above bare glacial ice on some Oregon Central Cascade glaciers. The photo to the right shows three of these snow layers on Crook Glacier on Broken Top. These snow layers above glacial ice indicate that the 2015 summer melted away the pre-2015 accumulated snow and firn, just like the 2021 heatwave wiped out the post-2015 accumulated snow on Collier. Thus, one hot summer can remove the positive mass gains from prior cooler summers and/or snowier winters.

Another force multiplier from these hot summers is the change in the glacier’s reflectance: the glacier’s albedo. Albedo is a measure of how much of the sun’s energy (shortwave radiation called insolation) is reflected versus absorbed by a surface. An albedo of 1.0 would reflect all insolation. Snow has a very high albedo around 0.8–0.9, which explains why one burns the underside of one’s nose on a blue bird powder day despite wearing a billed cap and temperatures well below freezing. That high albedo snow reflects the insolation back upwards where it then burns one’s nostrils. Old snow/firn has a lower albedo of around 0.6. Glacier ice absorbs even more insolation with an albedo of 0.4–0.5 These differences are apparent in the photo above where the older snow layers and the glacier ice itself are darker than the 2020 snow layer.

Absorbed versus reflected insolation matters. Just think about running from the car to the swimming pool as a kid. While sprinting on the parking lot blacktop, one’s feet burn like the dickens with the heat abating somewhat once one can hop onto a cooler cement sidewalk. The blacktop has a lower albedo than the lime-gray cement and absorbs more insolation that then burns one’s feet more than the higher albedo cement.

Burned-feet childhood memories aside, heatwaves can switch how reflective a glacier’s surface is. A heatwave removes the highly reflective snow surface, burns through the less-reflective old snow and firn to expose the low albedo, absorptive glacial ice. A snow/ firn-free glacier now melts even more thanks to the hot summer and change in the glacier’s albedo that absorbs more of the sun’s energy. The heat switched the glacier from being cement to asphalt. LOOKING FORWARD

Unfortunately, unless humans immediately cease to emit greenhouse gases AND start to reduce the level of carbon dioxide in the atmosphere from the current 412 parts per million level towards a sustainable target below 350 parts per million, glaciers will soon cease to exist in Oregon. At the 2021 level +1.2°C (+2.2°F)

The accumulation zone of Crook Glacier on Broken Top on August 28, 2020. Only three years of snow are visible above bare glacier ice, showing the loss of all prior years’ accumulation during the summer of 2015. Photograph by Anders Carlson. of global warming, that 2021 heatwave had a 1-in-1000 chance of occurring, which would have been 150 times rarer if not for that +1.2°C of global warming. At +2.0°C (+3.6°F) of global warming, which we will likely surpass even with global nations’ current carbon emission pledges, the heatwave is estimated to occur every five to 10 years. Human greenhouse gas emissions have taken the 2021 heatwave from being a 1-in-150,000-year event to a 1-in1000-year event, and will make it a less than 1-in-10-year event in the coming decades if we do not change our collective behaviors starting at the top and fully divest the United States from fossil fuel use. What we are doing now and are planning to do in the future is clearly not enough to keep Oregon as the Oregon we know and love. The fact that three out of the last five summers were extremely bad for the health of Collier Glacier shows that even +1.2°C of global warming at 416 parts per million carbon dioxide in the atmosphere is too much. Reducing carbon dioxide levels to below 350 ppm (the level in the 1980s) would return Oregon back to a time when glaciers were more or less happy with their winter snowfall and summer temperatures. The Mazama surface mass balance measurements for Eliot Glacier on Mt. Hood documented slight glacier growth between 1963 and 1983, meaning that the climate of the early 1980s could sustain glaciers near to what the U.S. Geological Survey depicts on their maps. We could bring the landscape back into accord with the maps, saving the federal government much time and money in updating the physical geography of the maps! Nevertheless, the climate that will result in Kenneth Phillips’ vision of “empty cirques” may already be here, at least for Oregon’s Three Sisters Wilderness. The carbon dioxide level in the atmosphere may be already too high to sustain glaciers in the central part of the Oregon Cascades. There are some good snow years with positive mass balances, but the bad years are really bad and growing ever worse.