The low boom, like thunder, didn't startle Galden Sherpa at first. At Mt. Everest base camp, climbers often heard the loud rumble of ice fracturing as the first sunlight struck the mountainside above.
Then word came over the radio: A massive glacier had crashed down the mountain's west shoulder, burying 25 Nepalese sherpa guides under columns of ice the size of small houses. Galden, who had been mountaineering for nearly a decade, knew many of the men well.
The next morning, Galden descended from a helicopter and hiked a short distance to where a corpse lay half-submerged in the snow and ice. With a shovel and ax, he helped recover the body, his heart sinking when he recognized the sunburned face of a prominent sherpa union leader.
Thirteen bodies were recovered and nine men were rescued, but three sherpas, including Galden's close friend, Ash Bahadur Gurung, remained unaccounted for. With conditions worsening and the thin air making it dangerous for helicopters to fly, the search was called off.
Nearly a year later, as a new climbing season dawns on Everest, Galden should be preparing for another ascent. But his mother asked him — begged him — not to return to the job that has sustained his family.
"No more big mountains," she told her son, who has twice reached the Everest summit.
The 28-year-old didn't protest. The perils had become too obvious, the loss of friends too shocking to bear. One crisp afternoon in Katmandu, he sat at a rooftop cafe overlooking the giant white stupa of a famed Buddhist shrine and said he had reached a decision.
"I have no plans to climb Everest again," he said.
He held his head in his thick, weathered hands and cried.
The April 2014 avalanche was the deadliest recorded on the world's highest peak. All 16 who died were sherpas, the catch-all term for local mountain guides, porters and camp staff, a trade dominated by the ethnic Sherpa people who populate the Himalayan highlands.
In a show of respect and mourning, the sherpas refused to scale Everest for the rest of the year. Some, like Galden, say they won't return. But many others plan to ascend again when expeditions resume in April.
"Many families are shocked by the tragedy," said Tendi Sherpa, who has made 10 expeditions to the top of Everest. "But the sherpas themselves, they need the money. They feel obliged to climb. This is the only work they know."
A sherpa can earn as much as $6,000 for reaching the 29,029-foot summit, a princely sum in a country where the average annual salary is about $700. In the off-season, many supplement their income by guiding tours of lower peaks and studying English — the better to interact with wealthy Western clients.
Over several successful Everest expeditions, a sherpa can earn enough to build a concrete house for his family, put siblings through college, start a small business. For that, he will endure years of hauling clients' 80-pound loads in some of the most severe conditions on the planet.
"It's not an easy job. It's so painful," Tendi said. "You work hard so that the family who comes after you doesn't have to do it."
Galden has wide-set eyes, a thatch of black hair and a compact frame ideal for mountaineering. Yet it was necessity, not any natural affinity for high altitude, that drew him to climbing.
When his father died and his mother remarried, it fell to him to provide for three younger brothers and four step-siblings growing up near the Himalayan town of Lukla. At age 20, with a fifth-grade education, he got a job as a porter for low-altitude treks, then worked his way up to cook and assistant guide on bigger expeditions.
He reached the Everest summit for the first time in 2011, pocketing $4,000 — more than 10 times what he earned for the smaller peaks.
But in 2013, Galden watched his friend and mentor, Namgyal Sherpa, 36, collapse and die of heart failure at 27,000 feet before help could arrive. Months later, he and his expedition team were trapped without shelter in a 48-hour blizzard near the top of Nepal's 21,000-foot Mera Peak, but all of them survived.
Then came the avalanche.
Gurung, Galden's friend, was making his first Everest climb at the request of an American client, retired Los Angeles attorney Ed Marzec, who at 67 was trying to become the oldest man to reach the summit. On a previous trek, Marzec said, he slipped off a trail and could have fallen to his death had Gurung not been there to catch him.
"He went to earn money, but also to earn a name for himself," said Gurung's widow, Menuka. They had a 5-year-old girl and an infant boy, and Gurung was thinking about their future, she said.
"He thought if he climbed Everest, he would get the chance to go abroad and earn even more for us [as a climbing specialist]," she said. "He was fascinated by that idea. I really didn't know what it would be like for him. But he said not to worry — his relatives had climbed Everest and that he would come back."
Many believe that higher temperatures on Everest are melting the ice and making avalanches more common. But for years sherpas have also been complaining quietly — as is their custom — of tougher working conditions as the number of climbers grows.
Advanced gear and better weather forecasting have made Everest, the crown jewel in Nepal's $400-million tourism industry, seem more attainable than ever. According to the Himalayan Database, 658 people summitted Everest in 2013, a fivefold increase from 2000.
With clients willing to pay more than $60,000 for the climb, there is growing competition among tour companies to provide more comforts. High-end expeditions now offer sushi, espresso, fully stocked bars and makeshift Internet cafes as far up as 21,000 feet — all requiring more equipment and sherpas.
At the time of the avalanche, the climbers also included an American planning a BASE-jump from the summit, with a Discovery Channel crew along to record it, and a Google team collecting images for its maps application.
"There can be overcrowding," said Lhakpa Norpu Sherpa, an advisor to Mountain Spirit, an advocacy group. "We sense that a lot of these fatalities occur when you have too many people stuck at a dangerous place for too long."
Some say Nepal's government has failed to adequately regulate the industry or to invest in training for sherpas that could have reduced the death toll. After the avalanche, Nepalese officials raised the minimum insurance policy that expedition companies are required to carry for sherpa guides to $15,000 from $10,000. Mountaineering associations and foreign climbers also have contributed funds to educate the children of those who have died.
Authorities did pay each sherpa's family an additional $500 death benefit, but critics say that came in December, eight months after the disaster, and pales in comparison with the $11,000 the government charges each foreign climber for an Everest permit.
Tulsi Prasad Gautam, director of Nepal's tourism department, said the government was weighing whether to continue to allow film crews and stunts atop the mountain.
"We are very serious about making Everest safer. We have to try to minimize the incidents," Gautam said. "But deaths always happen in adventure sports. Even in Europe, in the Alps, this happens."
On the morning of April 18, while foreign climbers slept at base camp, the sherpas set off under a star-bright sky. They slowly hauled supplies across the treacherous Khumbu Icefall, a long maze of jagged glaciers and yawning crevasses that is traversed with shaky aluminum ladders.
As a team labored for more than half an hour to repair a broken ladder, a "traffic jam" developed, recalled Dawa Tashi, 23.
"That was when the ice came down," he said.
Tashi was near the end of the line, clipped to a rope harness. In the split-second before the snow hurtled into him, he turned to one side, trying to protect his spine from impact. He then fell unconscious.
When he awoke, ice had swallowed everyone around him. His own body was buried to his sternum, pain stabbing his chest. I'm going to die, he thought, crying.
Then, regaining his composure, he began screaming. Eventually, rescuers found him, digging him out with a shovel. His left shoulder, four ribs and nose were broken, and shards of ice had lodged in his face. It took months for the wounds to heal.
His wife, who gave birth to their first child two months after the avalanche, has urged him not to climb again. His doctors also say he shouldn't, at least not for a couple of years, while he regains his strength.
Tashi hasn't made a decision. But as the son of a climber, and the oldest of three brothers, he cannot shake a sense of duty.
"The whole family would be unhappy if I go back," he said. "But our profession is mountaineering. It will be difficult for me to do anything else. So, no, I can't say I'll never go up again."