Just an icefield

Arapaho Glacier, Colorado’s largest (and last) alpine glacier, has vanished in plain sight

The Arapaho Glacier as seen from Arapaho Saddle on October 2, 2021.

The air was thirty-four degrees Fahrenheit, and wind swept across the mountains at thirty miles per hour. A thin layer of snow covered the landscape, fallen overnight, blanketing tussock grasses and boulders of granite and gneiss; willows and cushion plants and dense thickets of knee timber. Six of us trekked amongst the snow, stone, and tundra. We hiked single-file, heads down, stumbling occasionally in the particularly powerful gales. Above us, clouds sped across the sky like cars on an interstate. Beneath us sat a U-shaped glacial valley, where Middle Boulder Creek flows from headwaters just beneath the Continental Divide. Beyond the valley floor and across the drainage, a hanging lake came into view. A creek cascaded down a steep and thickly timbered mountainside below the tarn. And just as quickly as it had emerged, the mountainscape was veiled by nimbostratus clouds.

With me was Dr. Ted Scambos, along with a team of glaciologists from the University of Colorado Boulder. Dr. Scambos is a Senior Research Scientist at CU Boulder’s Earth Science and Observation Center. He’s been conducting glaciology research for more than thirty years. He’s developed automated measurement systems to make remote observations of glaciers without the physical presence of scientists. He’s studied declines in Arctic sea ice. He’s studied glacial thinning in Antarctica. He’s studied ice discharges flowing from Greenland’s outlet glaciers. And, among many research projects throughout an exceedingly accomplished career, he’s studied the Arapaho Glacier—the largest and, as some have argued, the last alpine glacier remaining in the state of Colorado.

We climbed to the apex of Arapaho Saddle, to the ridge overlooking the cirque of the Arapaho Glacier. We looked down into the cirque, toward the glacier itself. What we were seeing—or rather, what we weren’t seeing—didn’t seem to add up.

“Where is it?” somebody asked.

There was a pause.

“There’s no glacier left,” Ted Scambos said.

The Arapaho Glacier, circa 1902. From the National Snow and Ice Data Center’s Glacier Photograph Collection. (Public domain)

The Arapaho Glacier sits in a bowl-shaped cirque between North Arapaho Peak and South Arapaho Peak, on the eastern slope of the Continental Divide, about twenty miles west of Boulder, Colorado. 

During the Pleistocene, which began about two and a half million years ago and came to a close at the end of the last Ice Age, roughly 12,000 years before present, much of Colorado was awash in snow and ice. Alpine glaciers layered the landscape. They moved and melted like slow-moving rivers of ice, carving valleys and gorges from the Rocky Mountains themselves. 

But Colorado’s glaciers have been steadily melting over the millennia, centuries, and decades.

A Google search will tell you that Colorado is home to 16 glaciers. Many of these “glaciers,” however, are only glaciers in name. When researchers from the United States Geological Survey surveyed Colorado’s remaining glaciers back in the mid-1980s, only seven permanent ice-fields in the state were larger than a tenth of a square kilometer. And this area—a tenth of a square kilometer, about the size of 15 city blocks—is a point at which glaciers become little more than sizable fields of snow and ice. “While there is no global standard for what size a body of ice must be to be considered a glacier,” reads a white paper from the United States Geological Survey, scientists typically “use the commonly accepted guideline of 0.1 square kilometers (about 25 acres) as the minimum size of a glacier. Below this size, ice is generally stagnant and does not have enough mass to move.” This brings us to the second criterion often used to define a glacier. A glacier has to be flowing beneath its own mass. It has to be massive enough to move. 

For a long time, the Arapaho Glacier had enough mass to move, and it certainly occupied an area larger than a measly 25 acres. At its largest, sometime between 19,000 and 26,000 years ago—an era known to glaciologists at the Last Glacial Maximum—the Arapaho Glacier was nearly nine miles long. It was a full-on, bonafide alpine glacier. And for a long time, it was deemed the last true alpine glacier in the state of Colorado.

The Arapaho Glacier was officially “discovered”—that is to say, recognized as a glacier—in 1900. Two years later, in 1902, a glaciologist by the name of N. M. Fenneman published the first study on the Arapaho Glacier in the Journal of Geology. Scientists have been studying the glacier ever since. 

As atmospheric temperatures have risen, the Arapaho Glacier has melted rather drastically over the last 120 or so years. Fenneman and other glaciologists of his time reported that the Arapaho Glacier occupied an area of about half a square mile by the turn of the twentieth century. Fenneman reported that the glacier was 16 meters thick—about the height of the average aspen tree. Half a century later, in 1951, a glaciologist named Ronald L. Ives reported a thickness between 25 and 130 meters. It’s a rather wide spectrum. On one hand, the glacier may have been as thick as the distance between first and second base on Coors Field. Or, it may have been as thick as the Great Pyramid of Giza is tall. By 1979, researchers estimated that the glacier was between 30 and 50 meters thick—as thick as a couple semi trucks are long. Others estimated that the glacier had lost more than half of its ice in the preceding two decades.

There is, however, a problem with the data referenced in the paragraph above. These numbers were calculated using outdated scientific methods and outright ancient technology. In some cases, these early glaciologists weren’t doing much more than guessing. “These area and thickness measurements were highly uncertain, and thus should be considered educated estimates at best,” Dr. Scambos and his colleagues wrote. 

By 2007, when Ted Scambos and his colleagues turned their attention to the Arapaho Glacier, the glacier occupied an area of about 0.16 square kilometers—an area about the size of Thoreau’s beloved Walden Pond. In 2007, the maximum thickness of the Arapaho Glacier, according to the team’s data, was 15 meters. They published their results in Arctic, Antarctic, and Alpine Research in 2010.

Two hikers explore the Arapaho Glacier, circa 1919. From the National Snow and Ice Data Center’s Glacier Photograph Collection. (Public domain)

Come August 2021, when Dr. Scambos and his colleagues and I trekked to the apex of Arapaho Saddle, we intended to carry out the first study of the Arapaho Glacier in over a decade. The researchers brought ice drills, ground penetrating radar equipment, and a drone to conduct an aerial survey of the glacier. Ted invited me along to write about the expedition. Typhoon-esque winds, frigid temperatures, and a snowstorm at altitude thwarted our attempts to study the glacier, however. 

And that day, our brief, fleeting view of the Arapaho Glacier was a gloomy one. Obscured by cloud cover, the glacier looked like little more than a sledding hill with a bright blue lake at its base—a hazard when it comes to sledding, to be sure. The remaining ice of the glacier was thin and darkened by settled particulate matter and rocky debris. Boulders were strewn about the lower reaches of the glacier, just above the lake. The stones had fallen in rock slides further up the mountain. Along the perimeter of the glacier, rock outcroppings emerged from the ice—outcroppings not seen in historical photographs, the glacier has grown so thin.

“A small group managed to get to the ridge, without any of the science gear, but we got a view of the glacier.” Dr. Scambos says. “There is not a lot of it left. It is small enough that there may only be a small area where the radar profile and ice core are possible . . . this really is the end for Arapaho.”

Confronted with our view of the glacier—or lack thereof—we hike around on the ridge for a time, searching for landmarks of historical perspectives from which the glacier has been photographed over the past century. Amidst the overcast clouds, however, the photographs would have to be snapped another day. We trekked down the mountain, into a thicket of subalpine fir in which we’d left our scientific equipment that morning. We gathered the gear, strapped it to our backs, and hiked on, down to the Fourth of July Trailhead. We reached our respective vehicles. I handed Ted an ice axe. I handed Mike MacFerrin—a research glaciologist at the University of Colorado Boulder’s Cooperative Institute for Research in Environmental Sciences—a pair of crampons. 

“Thanks again for lending these, Mike,” I said. “It’s a shame we couldn’t put them to use.” Had the weather cooperated, we would have needed the gear to collect our ice cores.

“No problem,” Mike said with a sigh. “I certainly wish we could have used them, too.” He took the gear and began packing it away.

Ted and I shook hands. “Thanks again for inviting me along, Ted.” We discussed dates for the upcoming historical photographs and drone survey of the glacier. I told him I’d do my best to be there.

“So, the Arapaho Glacier,” I said. “It’s just . . . not a glacier anymore?” I was seeking some kind of closure.

Ted looked up for a moment, in thought, toward the steep, timbered slopes of the glacial valley that enclosed us. “That ice doesn’t appear to be flowing,” Dr. Scambos said. “And by the looks of it, it isn’t 25 acres, either.”

“I’d say the Arapaho Glacier has safely entered permanent ice field status,” Mike MacFerrin noted as he loaded gear into the back of his crossover. 

“Yeah,” Ted Scambos agreed, nodding slowly. “It’s really just an ice field now.”

In September of this year, Dr. Ted Scambos and his team managed to collect some data on the Arapaho Glacier. “Time has not been good to this glacier: at least, not the most recent times,” Dr. Scambos writes via email.

“We collected probably a kilometer of radar data; and 1.4 meters of ice core; and while I have not seen any results, the completely soaked nature of the ice that day (the borehole filled with water to just 16cm below the surface; rivulets and gushing sub-surface streams everywhere) gives me some doubt that we will get much there—but I look forward to the actual results.” The results of the study have yet to be published. The team drilled core samples to a depth of 1.4 meters, but “below that, despite numerous tries, the ice simply dissolved into the meltwater before we could retrieve it.” Ted writes. “On the other hand, the historical-repeat photos, the drone SfM [Structure from Motion] data, and simply the record of the current activity on the glacier near the tarn lake, rock glacier, etc. will yield interesting results.”

The results, however interesting they may be, will prove empirically what Dr. Scambos, his colleagues, and I saw at a glance in August of this year. The Arapaho Glacier is no longer a glacier at all.