High on the Lyell Glacier in Yosemite National Park, a vein of water cut a narrow gouge as it streamed downslope from the melting ice.

Off to the right, you could see a thin, foot-wide current, also from melting ice, which flowed a quarter inch beneath the surface. At the foot of the glacier, drops of water from the glacier’s receding edge hit bare granite. Dozens of rivulets poured onto an exposed field of boulders, talus and a moraine that had been covered for thousands of years by snow and ice.

The Lyell Glacier, once estimated as a mile wide and Yosemite’s largest glacier when visited by John Muir in 1872, could melt and disappear in as soon as five years, according to park geologist Greg Stock, if warm temperatures at high elevations continue.

The glacier has lost about 90 percent of its volume and 80 percent of its surface area from 1883 to 2015, according to Stock and Peter Devine, a naturalist with the Yosemite Conservancy who has studied the Lyell Glacier for 30 years. Stock and a crew of geologists measured the perimeter of the glacier with a GPS in the last week of September.

“I’m getting the feeling I may be the last geologist to study these glaciers,” Stock said. “Pretty soon, there won’t be any ice here at all, just a rubble-strewn basin. I’m starting to think like a biologist, somebody who is studying an endangered species, something that can disappear.”

“It is disappearing right in front of our eyes,” Devine said on a recent trek to the glacier.

Seeing difference in a week

Josh Helling, a mountaineering guide and photographer who made trips to the Lyell Glacier in back-to-back weeks at the turn of the month with Stock and Devine, said he was stunned at how fast the glacier is melting.

“In just a week, you can see the difference,” he said.

The Lyell Glacier is located in the Yosemite Wilderness out of Tuolumne Meadows near Donohue Pass, nestled on the high flank of 13,120-foot Mount Lyell. To see it and the neighboring Maclure Glacier, The Chronicle joined an expedition at the end of September that involved a 30-mile trek with total climbs of 5,000 feet, and more than 10 miles hiked off trail across boulder fields, talus, scree and bedrock, and six hours of ice travel.

Miles above tree line, a harsh wind blew. A dark, cloud-lined ceiling painted the sky the color of blue steel. To trek up the glacier and measure its edges, hikers dug their spike-tipped boots, laced with crampons, into the ice, and steadied themselves with ice axes. It was the last of what remained of an open ice field.

“If we were standing here the day John Muir crossed the Lyell, we’d be under 150 feet of snow and ice,” Devine said.

Back to Gallery Glacier was once Yosemite’s largest; now it’s almost... 7 1 of 7 Photo: Tom Stienstra, The Chronicle 2 of 7 Photo: Tom Stienstra, The Chronicle 3 of 7 Photo: Braden Mayfield, Special to The Chronicle 4 of 7 Photo: Braden Mayfield, Special to The Chronicle 5 of 7 Photo: Tom Stienstra, The Chronicle 6 of 7 Photo: Tom Stienstra, The Chronicle 7 of 7 Photo: Josh Helling, Special to The Chronicle













“I think about John Muir a lot up there on the glacier,” Stock said. “I try to envision what it was like when Muir was here. It would have been so different. I think about what (Francois) Matthes (of the U.S. Geological Survey) said in 1935, about why we need to measure our glaciers, that glaciers are sensitive indicators of climate change.”

On the John Muir Trail

The expedition launched from Tuolumne Meadows in Yosemite National Park, with the first steps taken on the John Muir Trail, elevation 8,700 feet. It was the same route John Muir chose in the 1870s when he started measuring Yosemite’s glaciers.

The chosen path followed alongside the Lyell Fork of the Tuolumne River, the stream that is created from the first drops of the Lyell Glacier. The river then flows through Tuolumne Meadows, down the Sierra foothills and to the San Joaquin delta. It is the same water that millions drink when they turn on their faucets in San Francisco, the Peninsula and much of the Bay Area.

As the group hiked 8.5 miles to the head of Lyell Canyon, Devine talked about watching what he called “an aged companion,” the Lyell Glacier, recede in recent years at an alarming pace.

“Without the big snowpack in the High Sierra Nevada, what little snow we get melts off quickly in the spring,” Devine said. “Without a snow cover, the glaciers get exposed to sun and start melting. When an area melts off, the exposed rocks absorb the heat of the sun and then radiate it into the adjoining ice, and the glacier then melts even faster.”

The recession of glaciers has occurred worldwide as temperatures have warmed, Devine said. According to the California Department of Water Resources, snow provides 30 percent of the state’s reservoir capacity and, in some areas, much higher than that. On a global scale, glaciers hold more than 50 percent of the world’s freshwater, according to the National Geographic Society. In some areas, such as the Andes and Himalayas, the recession of glaciers is a long-term threat to water supply.

The recession of the Lyell Glacier and other glaciers isn’t from drought, according to many climatologists. Over the past 100 years, precipitation has remained steady, with occasional blips from droughts and floods, they say. What has changed, according to meteorologist Michael Pechner of Golden West Meteorology, is warmer temperatures and high snow levels.

‘Symbol of a changing world’

A weather station at Blue Canyon in the central Sierra, located at 5,280 feet near Nyack along Interstate 80, is a testament. Over the past 50 years, Blue Canyon has received an average of 252 inches of snow per year, according to the state Department of Water Resources. Last winter, it instead received 57 inches of rain. Many weather stations in the mountain country recorded similar numbers, according to DWR.

“The Lyell Glacier is a symbol of a changing world,” Devine said. The world we know is changing, he said, and at the same time, a new world where “we cannot fully measure or imagine what is to come” is arriving.

As the group neared its first night’s trail camp, the expedition reached a location near the head of Tuolumne Meadows where the Lyell Glacier first came in view.

“Look,” Devine said. One could see for miles across the barren country of the High Sierra, devoid of snow. The effects, with few glaciers and low winter snowpack, Devine explained, impact the state’s residents, agriculture, industry and fish and wildlife.

The ghosts of legends

From that first camp, the climbers rose 2,000 feet, including 2.5 miles off trail across boulders and bedrock. At dusk, they arrived at a sandy meadow in the greater Lyell Cirque, elevation 10,850 feet, to set up a base camp below the Lyell and Maclure glaciers. As dusk took hold, Mount Lyell and its glacier loomed above, and its peak poked a hole in the dimming sky.

“I’ve been coming up here for 30 years,” Devine said as he lit his tiny stove to boil water for a cup of tea. “Some years, I come up two, three times. I think a lot about John Muir, Joseph LeConte, Galen Clark. What they saw. What we’re seeing now. I think about how we are camping and walking in the same places, looking at the same things that the legends did.”

Stock made his first trip, guided by Devine, in 2006 to the Lyell Glacier, and on the shoulder of Lyell, the neighboring Maclure Glacier. This is where Muir conducted a velocity study to prove to California state geologist Josiah Whitney and others, such as LeConte of the University of California, that glaciers existed in California and were a primary force in carving out the deep canyons of Yosemite and the Sierra. A river of ice, as Muir called them, carved, pushed and ground up the rocks in their paths.

Climbers notice change

In recent years, high snow lines and receding glaciers have been apparent to many climbers without measured verification in the Yosemite high country, as well as at Mount Whitney, Mount Shasta and the Palisades in the central Sierra. In addition, at elevations above 10,000 feet, many have said that it just seemed warmer. In the past nine years, Stock, Devine and a team of geologists have worked together to monitor the Lyell Glacier in scientific terms. The Yosemite Conservancy funded the research for the National Park Service. In recent weeks, both made trips to observe the glacier.

“In September, I went to the toe of the Maclure Glacier and was looking for a survey point we established six years ago close to the edge of the glacier,” Stock said. “Looking for it, I walked far past that point before it hit me, that it was way back there. The glacier had receded so much from just the year before. I had to recalibrate in my mind what I was looking at.”

On The Chronicle’s recent trek, the group awoke early at our base camp above tree line and, as dawn took hold with temperature in the 20s, warmed up with hot cider and oatmeal. The team packed its crampons, ice axes and an outer layer, a combination of windbreaker and snow shells, along with water and trail food, and ventured out to climb 2,000 feet to the Lyell Glacier.

Hazardous trek to glacier

The trek started on a challenging boulder field, a massive jumble of rocks that ranged from the size of Volkswagens to bowling balls. On top, at a sub ridge, the group finally hit bedrock and, in another hour, topped another small ridge. The Lyell Glacier emerged into view. Gazing up at the expanse of ancient ice from a half mile away, one could see how a center strip of it was melting below the summit ridge.

Nearby was a small lake in a pocket, filled with glacial melt, edged by a loose boulder field and talus slope. Snow and ice can serve as a mortar that holds the glacial deposits, such as boulder fields, intact. With it melted, air pockets develop under the boulders that can lead to shifts, slides and collapses.

“This is extremely hazardous,” mountaineering guide Josh Helling said. “One step at a time. If the rock moves, it’s likely the one next to it is unstable, too.”

At one point, a reporter reached out to grab a 15-foot table rock for stability, and it felt like his right foot hit a trap door. Rocks gave way and the hiker’s foot plunged through a 4-foot hole. In a flashpoint, rocks caved in around the leg, trapping it in place.

Devine, who has seen this before, pounced. He grabbed and tossed rocks the size of softballs and bowling balls, and finally reached an oblong boulder, maybe 150 pounds, that had wedged over the top of my boot. There was no way to move anything, either the boulder, foot or leg.

Devine pulled out his pocketknife. “We’ll have to cut it off,” he said with a laugh.

Before the situation worsened, a boot was untied and the foot extracted.

“With the ice gone, and all these air pockets under the boulders, you can see how easy you can get into trouble out here,” Devine said. “At any moment, it all can give way.”

Helling also escaped injury when a loose scree-topped slope he was crossing collapsed. Helling looked as if he were dancing his way out of quicksand to reach a rock that held.

Crossing one last jumble of fallen boulders, including a 30-foot slot where truck-size rocks recently had given way downhill in a long cascade, the group reached the toe of the glacier at 12,000 feet. The hikers strapped on crampons, jammed ice axes into the surface, and took their first steps on the Lyell Glacier

The first thing one notices is the melting ice, with water streaming through a series of tiny gullies. The surface of the glacier was so soft that the crampon spikes punched through to the hilt. With an ice ax as a walking stick, it was a seamless effort to walk up the glacier, about a 30-degree slope.

A walk in time

After 50 yards, with an open exposure and free fall below, it was a bit eerie to look down the slope. You could see across a landscape of ice, rocks and water for miles, all the way down to the headwaters of the Lyell Fork Tuolumne, some 4,000 feet below.

Devine pointed at a mark high on the eastern wall of the upper cirque. “In the time of Muir, the glacier reached all the way up there,” he said. The point on the high wall was so high and far away that it seemed impossible.

Then Devine recalled what Muir wrote about the site: “The Lyell Glacier is about a mile wide and less than a mile long.” It is now the size of a several football fields, he said.

Up on that ice slope, the words of Muir from 1875 echoed in my thoughts. “It is the highest and most enduring remnant of the great Tuolumne Glacier, whose traces are still distinct 50 miles away, and whose influence on the landscape was so profound.”

The expedition members explored the glacier, its newly revealed edges and sublevel water flows. At one point, they dipped down and drank a scoopful of water, as sweet as any water in the world, yet much the same as the water, via the Tuolumne River downstream, that comes out of faucets in San Francisco.

Across the glacier surface, one could see a series of horizontal lines. “They are lines left behind with each snow year, like tree rings,” Devine said. “These are possibly from the time of Muir, about 140 years ago.”

In 1883, Israel Russell of the U.S. Geological Survey took a photo of the Lyell Glacier, and over the years, Stock and Devine have identified the sites where Russell and other geologists have captured images of the glacier. “We go to the same photo points Russell established and repeat those same photographs and compare them,” Stock said.

As the day became late and a hazardous descent awaited us, Devine took a seat at the foot of the glacier, and then scanned across what was left of the ice.

“In five years, this could be gone,” he said. “Even if we get a lot of snow with El Niño this winter, the long-term trend is unmistakable. The planet is warming up. It means higher snow levels. Glaciers are melting.”

The next morning, a harsh wind blew down from the Lyell Glacier. A few snowflakes fluttered down. In minutes, a cloud dropped down and smothered the cirque, and in turn, a 20-knot wind blasted snow across the terrain. A blizzard coated the landscape in minutes.

The group broke camp fast, then walked down slowly. Steep descents across boulders, talus and scree were dangerous enough. If coated by ice, or worse, buried by snow to create a moonscape, some mountaineers can slip between boulders, wedge an ankle or leg, and in the fall downhill, snap an ankle or tibia.

‘Goodbye to an old friend’

Small, iced flakes danced in the air as the group descended in a ravine, one boulder at a time. In less than two hours, the hikers reached flat ground, and soon after, the John Muir Trail. At 10,000 feet, just like in past years, the snow turned to rain. From there, it was 10 miles back to the trailhead.

At one point, Devine turned to get one last glimpse of the Lyell Glacier.

“It’s like saying goodbye to an old friend,” Devine said. “It’s hard to believe that the glacier that John Muir found and that I’ve loved for most of my life looks like it will be gone.”

Tom Stienstra is The San Francisco Chronicle’s outdoor writer. E-mail: tstienstra@sfchronicle.com Twitter: @StienstraTom

A moment

in time, 1935

“Why is it important that we should measure our glaciers? What need is there of going to all of this trouble, and what purpose will be served by the results? The answer is that glaciers are extremely sensitive to climatic fluctuations and register them more vividly than do streams, springs, lakes, or vegetation; and since we have so delicately, so daringly adjusted some of our great agricultural and engineering enterprises and their dependent industries to existing climatic conditions, it behooves us for the good of our complex American civilization to keep a close watch on climatic changes or fluctuations, however slight and transient, that may be taking place.”

— Francois Matthes,

U.S. Geological Survey, 1935

Trek itinerary

Day 1

Launch day: In Yosemite National Park, drive to Wilderness Center at Tuolumne Meadows, get Wilderness Permit, continue to trailhead at Dog Lake parking lot near Tuolumne Meadows Lodge, elevation 8,700 feet. Hike 8.5 miles on John Muir Trail, 300-foot elevation gain, up Lyell Fork Tuolumne River; set up camp near where Kuna Creek descends into Lyell Fork, elevation 8,980 feet, acclimate to high altitude. Synopsis: 8.5 miles, 300-foot gain, easy.

Day 2

Trek into cirque: From head of Lyell Canyon, hike John Muir Trail toward Donohue Pass, break off from trail, following a small watershed, and scramble and climb over mostly bedrock slabs into Lyell C irque for base camp at 10,850 feet, above tree line near small unnamed lake, Mount Lyell towering above. Synopsis: 3.6 miles, 1,970-foot climb, mostly off trail, challenging.

Day 3

Maclure Ice Field: From base camp (10,850 feet), climb challenging boulder field to sub ridge, then trek across steep glacier-polished bedrock and talus to Mount Maclure cirque and lake. With ice-climbing equipment, climb up Maclure G lacier and I ce F ield into glacier tunnel, 11,554 feet. Synopsis: 2.4 miles, no trails, 700-foot elevation gain, ice climb and return, hazardous.

Day 4

Lyell Glacier: From base camp (10,850 feet), climb boulder field to sub ridge, then trek up ridge across bedrock to small lake and across extremely hazardous loose boulder field and talus across moraine to Lyell Glacier (12,050 feet). With crampons and ice ax, climb up Lyell Glacier to shoulder of Lyell Peak (13,120 feet), open exposure. Synopsis: 3 miles, no trails, 2,000-foot climb, extremely hazardous.

Day 5

Snowbound exit: Blizzard blankets Mount Lyell and adjoining high country with 6 -inch snowfall in three hours. From base camp, canyoneer off-trail descent down drainage, over boulders and talus in snow, low visibility, ford stream, 2.5 miles to John Muir Trail. Descend to Lyell Fork/Tuolumne Meadows, hike out to trailhead in rain/snow. Drive to restaurant, The Mobil, better known as the Who a Nellie Deli, in Lee Vining for feast. Synopsis: 12 miles, 2,300-foot descent. Extremely hazardous.

Trek totals: 30 miles, 4,970 feet total climb, 10.4 miles off trail across boulder fields, talus, scree and bedrock, six hours ice travel.

Difficulty: The upper sections of the hike are off trail and involve steep, slippery rock scrambling, exposure above cliff bands, very unstable loose rock through the moraine, and slippery ice/glacier travel with crevasse and glacier tunnel navigation.

Disclaimer: “Everyone on the trip needs to assume personal responsibility of their own health and safety.” — Mountaineer Braden Mayfield.

If you want to go: A Wilderness Permit and park-approved bear-resistant food canister are required for overnight travel in the Yosemite Wilderness. Yosemite Conservancy leads Lyell Glacier treks for very fit backpackers each August. Info: www.YosemiteConservancy.org.

— Tom Stienstra