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 posited 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 defile of Yosemite Valley itself.
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 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 ploughs 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 from the mountain, the Golden State has grown from 560,000 to 37 million people, and 4 million visitors arrive at Yosemite Valley annually, the vast majority of them in automobiles spewing CO2. 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 powerful indicators of global climate change. They also signal serious regional consequences, namely decline in the 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 the University of California-Santa Cruz. Stock grew up in the town of Murphys, 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 the 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 a 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 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 also stumbled upon a trove of lost data: glacier surveys conducted by park 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 hear 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. Last July and September, I had a chance to participate in two of these surveys, joining Stock, his colleague Bob Anderson, a glacier researcher from the University of Colorado, and several volunteers on two trips to the Lyell and Maclure Glaciers, among the last in a four-year study began in 2009.
One of Stock’s main objectives was to diagnose the condition of the 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 investigations 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 earlier. 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 Tuolumne Meadows and toward the high peaks above. Before beginning, we divvy up a high-tech array of gear – three-foot lengths of PVC pipe, temperature sensors, tripods, titanium ice augers, collapsible shovels, GPS receivers, laser surveying equipment – a collection that little resembles Muir’s makeshift equipment.
Within minutes, we cross a bridge over Rafferty Creek, barely a trickle in its rocky bed. Stock says this illustrates a key hydrological 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.
Is the Maclure still a “living” glacier, as John Muir proclaimed? We would find out.
We press on through the constricting canyon as the temperature climbs. Unlike dry Rafferty Creek, the Tuolumne River runs clear and cold, filled with meltwater from the glaciers above. About 35 miles downstream lies Hetch Hetchy Reservoir, the massive water-engineering project that Muir tried unsuccessfully to halt in the early 1900s. The Tuolumne was dammed 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 across the Bay Area.
A few miles farther on, we come to a bend in the trail marked by a cairn. We plod into the frigid, thigh-deep Tuolumne, balancing atop slick slabs of submerged granite to another cairn concealed in ankle-high grasses. 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. (The mountain and its glacier are named for famed nineteenth-century geologist Charles Lyell, friend and colleague of Charles Darwin, who, ironically, was resistant to the idea of “ice ages” when it was first introduced in the 1830s.)
Even from a distance, it’s easy to see how much the Lyell has changed since geologist Israel C. Russell photographed it in 1883 from this very spot. Once an unbroken curtain of ice, the glacier has split into two separate lobes. Stock relays the findings of Hassan Basagic, a glacier researcher from Portland State University who found that the west lobe of the Lyell has lost about 30 percent of its area, the east lobe, 70 percent. “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 percent.”
Contrary to common thinking, the glaciers of the Sierra Nevada are not holdovers from the Pleistocene, or Ice Age, an epoch that began 2.6 million years ago and ended 11,000 years ago as Earth entered its current period of warming. Today’s glaciers are remnants of 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 the 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. According to Andrew Fountain, a geology professor at Portland State, the surface area covered by the Sierra’s roughly 1,700 glaciers and permanent snowfields has dwindled by about 55 percent 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 percent of their area; the Cascades, 48 percent; and Glacier National Park, 66 percent. According to the National Oceanic and Atmospheric Administration, alpine glaciers around the globe have been in a state of “negative mass balance” – a condition in which melting exceeds snow accumulation – for 21 years. NOAA also reports that the world’s alpine glaciers have lost, on average, 50 feet of thickness since 1980.
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, too, 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 a high granite spine that will carry us to the glacial cirques of Mount Lyell and Maclure. Stock is tall and lean and walks with economy but a sense of urgency. “Just over this rise and we’ll get a view,” he says, gripping the straps of his daypack from which several lengths of white PVC pipe jut like arrows from a quiver.
We press upward over granite slabs cleaved into massive rectangular flakes. Other sections are polished smooth or covered in “chatter marks,” deep scars left by boulders raked across the surface by the glacier that once covered this slope. Over a small rise, we encounter a strange, spaceship-like array of solar panels, temperature probes, and wind speed gauges affectionately known by the team 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 record-keeping began more than 125 years ago. The temperature records, however, 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 into the alpine bowl.
Meltwater from the Lyell and Maclure feeds directly into the Lyell Fork of the Tuolumne River, the main artery to Hetch Hetchy Reservoir. Stock estimates the two glaciers hold about 20 acre-feet, a mere teardrop in the 360,000-acre-foot bathtub of Hetch Hetchy Reservoir.
Although the glaciers are small from a water security perspective, the Lyell and Maclure glaciers play a huge role in the local ecology. According to Alexander Milner, a professor of river ecosystems at the UK’s University of Birmingham, the disappearance of a glacier can lead to a drastic drop in the biodiversity of the streams fed by those glaciers. A 2012 report he coauthored in Nature Climate Change found that the disappearance of glaciers could lead to an 11 to 38 percent drop in the number of species of macro-invertebrates, mainly insect larvae. “You tend to gain generalists, species that can survive in many conditions, and lose organisms adapted specifically to the cold temperatures,” Milner says. Of course, the loss of the “little” things in the food web often results in a concomitant crash 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. According to Yosemite’s hydrologist, Jim Roche, as much as three-quarters 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 Hetch Hetchy Reservoir. According to a 2008 paper from Bruce McGurk, a former hydrologist for Hetch Hetchy Water and Power, 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 that of Feather River, the largest tributary of California’s largest river, the Sacramento.
Snowpack is projected to decline 25 percent statewide by 2050, according to the Department of Water Resources. Shortfalls of snowpack mean shortfalls in water deliveries – the consequences of which have been seen in the last few years, including water rationing in Los Angeles and the Bay Area, and the fallowing of massive swaths of farmland in the Central Valley. Of particular concern is the diminution 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 the huge farms of the Central Valley and drinking water to 25 million Californians. According to a Scripps Institution of Oceanography report, reduced snowpack could greatly reduce freshwater inflows, leading to increased salinity of the Delta, further threatening ecosystems, farms, and municipal water supplies.
After leaving the weather station, we pause at a small lake filled with aquamarine water. As we fill our bottles, Stock points out the fine dust coating our boots – glacial flour, sign of an active glacier. The final push to the edge of the Lyell Glacier is a grueling climb over hillock after hillock of loose rock. The moraines once marked the edge of the glacier and are comprised of slabs the size of dinner tables, some of which shift unnervingly underfoot.
Once we arrive at the Lyell’s edge, Stock readies the laser rangefinder atop a large slab. Bob Anderson straps on his crampons and summons several volunteers to continue upward onto the ice. As we climb onto the glacier’s ashen skin the sound of flowing water becomes stereophonic. Small runoff channels feed larger ones and the icy water carried within eventually pours into vibrant blue chasms, disappearing with a guttural boom into the deep recesses of the glacier.
Our job is to find the stakes Stock affixed across the mountain during the last four seasons, including several we planted six feet deep in July. With the ferocious melting, the few stakes we find upright are barely anchored to the ice. Others are lost completely.
We set about reattaching the stakes and holding over them a prism, which Stock zeroes in on with the laser rangefinder. It doesn’t take lasers, however, to recognize the Lyell’s regression. There are no crevasses, deep fissures running through its surface, which are telltale signs of glacial action. Stock calls our attention to a barely discernible, 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 53 feet below point K. Stock’s measurements revealed the distance between K and the ice had grown to more than 120 feet. “I’m always reminded that these are not the same glaciers that Muir visited,” Stock tells me. 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.
Stock takes the last of his measurements, aiming his yellow rangefinder at the small specks of the team moving like dust motes against a vast canvas of white. After recording his final readings, Stock issues a shrill “whoop” and the team descends from the ice.
After removing his crampons, Anderson convenes with Stock to discuss the data, which subtly begins to convey the severity of the Lyell’s dissolution. My ears perk up when I hear Anderson utter the phrase, “death knell.”
“Four-hundred point two this versus four-hundred point three last month,” Stock says, flipping through his notebook. “One stake has shown a meter and a half movement per year.”
“And that’s, as you said, the anomaly,” Anderson says. “Everything else is not moving.”
“Everything else is zero,” Stock confirms.
By now the survey team has gathered to hear the grim news.
“Wow, folks,” says Anderson. “This thing is just a-melting away.”
At a presentation Stock and Pete Devine 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 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, we rise again and climb the steep spine of rock toward the met station. Instead of moving into the Lyell’s sun-drenched basin, we veer west, traversing the mountain’s flank, skirting Maclure Lake, a deep, arrowhead-shaped pool of azure water wedged between vertical walls.
The Maclure Glacier covers a much smaller area and has lost about 65 percent 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 and its environs is vastly different from that of the Lyell. Its basin is steeper and narrower, casting long shadows across the ice, which is cut through with dozens of deep crevasses.
There are many signs that the Maclure may still being a living glacier – but only the measurements will tell for sure.
The survey team ascends, repeating the procedures carried out on the Lyell. The work is more arduous on the Maclure’s steeper slopes and care must be taken to avoid the deep fissures that crisscross its surface. As Anderson leads the team to the markers, Stock surveys them and writes the data into his notebook. After a few hours, all the points have been collected.
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 exactly the same rate as John Muir measured in 1872 – one inch every twenty-four 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 at a fraction of its former rate. And yet, it continues apace. It’s a puzzle, but Anderson and Stock believe the physics of glacial motion may have shifted over 140 years. “You look at this thing and it looks like a solid. But in fact these objects are flowing,” Anderson says. “It can flow in one of two ways – by way of deformation or sliding.”
Deformation, Anderson explains, can be envisioned by thinking about a deck of cards. If you place the deck on the table and then run your hand over the top card, the layers underneath will “flow” in the direction you move your hand, with the uppermost cards moving farthest. Deformation is the mechanism by which the very large arctic glaciers move; the rate of movement is more or less constant and dependent on ice thickness rather than seasonal temperature shifts.
Now that the Maclure has been reduced to a thin sliver of ice, Stock believes sliding may have taken over. (To envision sliding, think of running your hand over a box of cards – the whole set moves across the table together.) The only way sliding is possible, Stock says, is if there is meltwater under the bed, which acts as a kind of lubricant allowing the movement of the entire ice sheet. As melting increases, so does the amount of water funneling through the crevasses to the bedrock below, in turn increasing the glacier’s downhill velocity. In this case, the glacier’s movement might be a symptom of weakness rather than vigor. “Sliding isn’t dependent on the thickness,” says Stock. “You can move even a thin carapace of ice if you’ve just got lubricant underneath it.”
But why has the Maclure continued to move while the Lyell has stopped? Turns out the Maclure’s steep, shaded topography may have played a key role in its “survival” to this point. Perhaps the Maclure and the nearby Dana Glacier – both of which are situated in steep, shaded basins – have been sheltered somewhat from warming temperatures. In contrast, the Lyell sprawls in its wide-open cirque exposed to the full brunt of the sun.
Just how long the Maclure 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.
Jeremy Miller’s writing has appeared in Harper’s, Orion, High Country News and Men’s Journal. Photojournalist Tim Palmer is author of the new book California Glaciers (Heyday Press).
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