Dying Glaciers of California

In August 1872, a 34-year-old John Muir climbed the snow and ice of Mount Lyell and Mount Maclure into the highest reaches of what is today Yosemite National Park. The journey to the high country was no pleasure trip, but an expedition intended to resolve a bitter scientific dispute. The climb chronicled in “The Living Glaciers of California,” published in the November 1875 issue of Harper’s Magazine, would hold great geological significance as Muir gathered evidence for the formation of the Sierra Nevada’s distinctive granite valleys.

At the time, no one had collected any evidence to suggest that the permanent ice and snowfields in the Sierra’s high basins were “living” glaciers. Muir believed they were. He posted that in a distant, colder past, these small glaciers once ran like great rivers of ice, carving the granite canyons of the western Sierra, including the majestic Yosemite Valley.

Muir’s most outspoken intellectual opponent was Josiah Whitney, an eminent geologist who derided the Scotsman as an “ignoramus” for straying into a field in which he possessed no formal training.  Whitney had a competing hypothesis. He believed Yosemite Valley had been created during a cataclysmic earthquake in which the massive granite uplift had been shaken violently – like a rising cake jostled in the oven – forming a deep furrow through its midsection.

Muir was undeterred. On August 21, 1872; he ascended the snowfield on the northern shoulder of Mount Maclure, joined by Galen Clark (the first appointed “guardian” of Yosemite) and University of California professor Joseph LeConte. The group hauled bulky stakes hewn from whitebark pine and drove them five feet into the ice. The experiment was simple but elegant. Using a plumb bob (rigged from a strand of horsehair and a stone) Muir surveyed the stakes, making sure they were in a straight line. Muir would return to the spot the first week of October. If the stakes had moved, he would have evidence that the patch of ice was not merely a permanent snowfield but a “living” glacier, pulled downhill by gravity and, in the process, gouging out the mountain below.

When Muir returned to Mount Maclure on October 6, 1872, he found that all his stakes had moved. One marker had traveled less than a foot, but several others slid nearly four feet. By his reckoning, the stakes that showed the greatest displacement had been moving downhill at a clip of one inch per twenty-four hours.

Muir’s scientific feud would drag on for several years after his discovery on the Maclure. Nearly a century and a half later, the debate mostly has been settled. Geologists agree that the granite of Yosemite’s famed cliffs was pushed up from great chambers of magma beneath Earth’s surface and over the next 50 million years, Yosemite Valley was simultaneously uplifted and cut by the Merced River. Then, around two to three million years ago, Earth’s climate rapidly cooled. The small glaciers of the Sierra became massive slabs of ice, 2,000 feet thick. Over the next 750,000 years, the glaciers would become the great shaping forces of Yosemite.

Today, new forces are shaping the Sierra, California, and the entire planet. In the 140-plus years since Muir came down the mountain, the Golden State has grown from 560,000 to 37 million people, and 4 million visitors arrive at the Yosemite Valley annually, the vast majority of them in automobiles spewing carbon dioxide. Global carbon dioxide concentrations have jumped from 280 parts per million in 1850 to 400 parts per million today-warming the planet and in the process, thawing the mountain snowfields.

These mid-latitude mountain glaciers, even more than their Arctic cousins, are indicators of global climate change. They also signal serious regional consequences, namely the decline in snowpack, the lifeblood of the state’s two heavily engineered river systems; the Sacramento and San Joaquin. Now that lifeblood is draining away as the Sierra’s ancient ice formations melt.

The task of measuring Yosemite’s fading glaciers has fallen to geologist Greg Stock. Unlike the bearded self-taught geologist Muir, the rangy, youthful 40-year-old goes clean- shaven and holds a PhD in earth sciences from UC Santa Cruz. Stock grew up in the town of Murphy’s (on the national park’s southern fringe) and spent much of his time exploring the region’s numerous caves. These days his work has pulled him upward, to the ailing ice formations atop the Range of Light. Stock recounts a recent hiking trip taken with his daughter through Yosemite backcountry, a reminder that his research holds generational significance. “It’s hard to believe, but the glaciers may be gone within her lifetime.” he says.

Stock’s glacier research began with an accidental discovery made nearly 30 years earlier by Pete Devine, one of Yosemite’s leading naturalists, during the mid-80s ascent of Mt. Lyell. As he made his way over a rugged ridgeline, he came upon a conspicuous letter ‘K’ and a circle inscribed on the rock in orange paint. Devine suspected that the marks were related to glacier research- a hunch confirmed after a visit to the park’s research library. The ‘K’ and a corresponding ‘L’ on the other side of the cirque were survey points established in the 1930s right at the edge of the ice.

Devine stumbled upon a trove of lost data: glacier surveys conducted by part naturalists between 1931 and 1975. The surveys, Devine says, succinctly describe the glacial retreat, though without the context of climate change. “There’s not that sense of alarm we here today,” Devine says. “The tone of the reports is much more, ‘We saw this. We measured this.’”


Shortly after Stock was hired in 2006, Devine showed him the reports and the Yosemite glacier surveys were reborn. One of Stock’s main objectives was to diagnose the condition of Lyell, Yosemite’s largest and most iconic glacier, which has lost so much ice that stock suspects it has stopped moving altogether-which is to say, it may no longer be a glacier.

Another of Stock’s investigation’s would replicate John Muir’s 1872 experiment on the Maclure Glacier to determine whether it is still a “living” glacier, as Muir proclaimed 140 years ago. Or has relentless melting taken its toll, reducing it to a stagnant patch of ice-a “dead” glacier? We would find out.

We set out on a glorious day in late September through the Tuolumne Meadows and toward the high peaks above. Within minutes, we cross a bridge over Rafferty Creek, barely a trickle in its rocky bed. Stock says this illustrates a key hydrologic characteristic of the Sierra Nevada. Though Rafferty Creek originates in an alpine basin, it lacks a glacier or permanent snowfield at its source and goes dry in late summer. “The glaciers act like buffers through the dry months,” Stock says, pointing out that glacier-fed waterways provide an invaluable resource to plants and animals, not to mention parched backpackers.

We press on through the constricting canyons as the temperature climbs. Unlike dry Rafferty Creek, the Tuolumne River runs clear and cold, filled with meltwater from glaciers above. About 35 miles downstream lies the Hetch Hetchy Reservoir, the massive water-engineering project that Muir tried to unsuccessfully halt in the early 1900s. The Tuolumne was damned and the great granite canyon (which Muir proclaimed the scenic equal of Yosemite Valley) was inundated to supply drinking water to San Francisco. Today Hetch Hetchy supplies water to 2.4 million people in the Bay Area.

A few miles farther on, we come to a bend in the trail. We plod into the frigid, thigh-deep Tuolumne River, balancing atop slick slabs of submerged rocks. At the head of the valley, 13,114-foot Mount Lyell (Yosemite’s highest point) thrusts upward, its namesake glacier slathered like frosting over the mountain’s swooping ramparts.

Even from the distance, it’s easy to see how much the Lyell has changed since geologist Israel Russell photographed it in 1883 from this very spot. Once an unbroken curtain of ice, the glacier has split into two separate lobes. The west lobe of the Lyell has lost about 30% of its area and the east lobe has lost 70% of its area. “But it’s not the area that matters as much as the volume,” says Stock. “From our models, the volume loss is more like 80%.”

The glaciers of the Sierra Nevada are remnants from the so-called Little Ice Age, an intervening period of cooling lasting from roughly 1350 to 1850. Many possible causes for the Little Ice Age have been offered, including altered ocean circulation patterns, weakening solar radiation, and volcanic eruptions that released vast plumes of sunlight-blocking ash and sulfate high into the atmosphere.

During Muir’s visit to Lyell and Maclure in the 1870s, the ice would have been near its maximum extent from the Little Ice Age glaciation. Since then the melting has been rapid and unrelenting. The surface area covered by the Sierra’s roughly 1,700 glaciers and permanent snowfields has dwindled by about 55% and now covers a mere 46 square miles. Glaciers throughout the American West and worldwide have experienced a similar ebb. In the Colorado Rockies, glaciers and snowfields have lost 42% of their area; the Cascades have lost 48% of their glaciers and snowfields and Glacier National Park has lost 66% of its glaciers and snowfields.

The date of the start of this mass retreat is conspicuous-1850 or thereabouts, the moment when humanity began generating huge quantities of carbon dioxide by burning coal to power the steam engines of the Industrial Revolution. Muir saw the fingerprint of warming and understood it to be part of a larger global trend. “Every glacier in the world is smaller than it once was.” Muir wrote. “All the world is growing warmer, or the crop of snow flowers is diminishing.”

We rise at dawn from our camp at a beautiful timberline lake and begin our climb, ascending to the high granite spine that will carry us to the glaciers of Mount Lyell and Maclure. Over a small rise, we encounter a strange, spaceship-like array of solar panels, temperature probes, and wind speed gauges affectionately known as the “met station.” During the last four years, this array of instruments has collected climate data on the 11,500-foot-high ridge. While snowfall is highly variable year-to-year, average precipitation in the Sierra has remained virtually unchanged since modern record keeping began more than 125 years ago.

The temperature records tell a different story. During the last century, California has experienced a one-degree Celsius rise in average temperature. Even the high country has not been immune to this uptick. In summers past, nighttime temperatures would often drop below freezing. These days, the lows rarely drop that far and between June and September the glaciers are in a state of near constant melting. As the amount of snow cover decreases, darker bedrock is exposed, absorbing sunlight and reradiating additional heat.

Although the glaciers are small from a water security perspective, the Lyell and Maclure glaciers play a huge role in the local ecology. The disappearance of a glacier can lead to a drastic drop in the biodiversity of the streams fed by those glaciers. An 11% to 38% drop in the number of species of micro-invertebrates (mainly insect larvae) is predicted. “You tend to lose organisms adapted specifically to the cold temperatures”, says an expert. Of course the loss of the ‘little’ things in the food web often results in a loss of whatever feeds on them, including fish, amphibians, and birds.

The glacial retreat is merely the most visible evidence of a larger and more troubling phenomenon for California’s human inhabitants: the state’s dwindling snowpack. Researchers speculate that warming temperatures could affect snowlines statewide, jeopardizing its water supply. As much as 75% of California’s drinking water comes from snowmelt.

In Yosemite, a shift in the snowline could reduce the volume and alter the timing of the spring melt that fills the Hetch Hetchy Reservoir. The snowline in the Hetch Hetchy watershed is expected to rise from 6,000 feet now to 8,000 feet by the end of the century. Other lower elevation watersheds may be even more vulnerable, including the Feather River, the largest tributary of California’s largest river, the Sacramento.

Snowpack is projected to decline 25% statewide by 2050. Shortfalls of snowpack means shortfalls of water deliveries- the consequences of which have been seen for the last several years including water rationing in Los Angeles and the Bay Area and the fallowing of massive swaths of the farmland in the Central Valley.

Of particular concern is the lack of freshwater flowing to the Sacramento-San Joaquin Delta, the vast and beleaguered tidal lowlands connecting the Sierra to the San Francisco Bay. The Delta is also the origin of the California Aqueduct, which delivers irrigation water to huge farms in the Central Valley and drinking water to 25 million Californians. The reduced snowpack could greatly reduce freshwater inflows, leading to an increased salinity of the Delta, further threatening ecosystems, farms, and municipal water supplies.

Once we arrive at the Lyell’s edge, our job is to find stakes Stock affixed across the mountains during the last four seasons. With ferocious melting, the few stakes we find upright are barely anchored to the ice. Others are lost. Stock calls our attention to a barely discernable, bright orange letter ‘K’ spray-painted on a boulder high on the east flank of the mountain-the survey point Pete Devine discovered nearly 30 years ago.

When the mark was established over 80 years ago, one could step right from K and onto the ice. During a subsequent survey in 1949, surveyors noted the surface of the ice had plummeted 35 feet below point K. Stock’s measurement revealed the distance between K and the ice had grown more than 120 feet. “I’m always reminded that these are not the same glaciers that Muir visited.” If Muir could somehow be teleported onto the landscape today, he’d be walking on a surface of ice more than 100 feet above our heads.

At a presentation Stock will give the following March for the Yosemite Conservancy, Stock reiterates his findings on the mountain. He projects a chart showing the movement of each of the stakes on the Lyell: Its columns are stacked with zeroes. “It’s not my place to rename features in the park,” Stock said to the small crowd assembled in the Yosemite Visitor Center. “But Lyell Glacier is probably not the best name for the feature we see today.”

The morning after our somber findings on the Lyell Glacier, we head to the Maclure Glacier. The Maclure Glacier covers a much smaller area and has lost about 65% of its surface area-the same as the Lyell. And for this reason, I assume the prognosis will be just as dire. And yet the “feel” of the Maclure Glacier is vastly different from the Lyell. There are many signs that that Maclure may still be a living glacier-but only measurements will tell for sure. Stock pores over the measurements and is astounded by what the data conveys. Not only does the Maclure appear to be moving, but it is moving at almost the same rate as John Muir measured in 1872-one inch every 24 hours.

How is this possible? With the extreme loss of ice, simple logic suggests that if the Maclure were moving at all it would be a fraction of its former rate. Stock believes that the physics of glacial motion may have shifted over 140 years, “You look at this thing and it looks solid. But in fact these objects are flowing.” Now that the Maclure has been reduced to a thin sliver of ice, sliding may have taken over.

The only way sliding is possible is if there is meltwater under the bed, which acts as a kind of lubricant allowing the movement of the entire glacier. As melting increases, so does the amount of water funneling through the crevasses to the bedrock below, in turn increasing the glaciers downhill velocity. In this case, the glacier’s movement might be a symptom of weakness rather than vigor.

But why has the Maclure continued to move while the Lyell has stopped? Turns out the steep, shaded topography may have played a key role in its survival to this point. The Maclure and nearby Dana Glacier- both of which are situated in steep, shaded basins-have been sheltered somewhat from warming temperatures. In contrast, the Lyell Glacier lies in a wide open canyon exposed to the full brunt of the sun.

Just how long the Maclure Glacier might be able to cheat death, hiding like a fugitive in its dark, remote basin-its glacial ‘womb’ as Muir called it-is unclear. But for now at least there is one glacier still living in the High Sierra.


  1. How did John Muir and Josiah Whitney differ on their theories of how Yosemite Valley was formed?
  2. In 1872, what was Jon Muir’s data collection method for testing if the glaciers are alive and moving?
  3. What is the data on the diminishing glaciers of the American West? What does this melting coincide with?
  4. Since record keeping began, what does the temperature record show for California and how does it affect the snow pack in the Sierras?
  5. When a glacier disappears, what are the effects on the local ecology?
  6. What did the research find about the difference between the Lyell and Maclure Glaciers in Yosemite?

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