Avalanche deaths tend to occur at the crossroads of science and human nature.Conditions are dictated mostly by snowpack, the danger often hidden far below the fresh powder — out of sight and, sometimes, out of mind. Humans are lured by the promise of fresh air and fluffy snow.This winter, though, an additional factor might be contributing to a sudden spike in fatalities: Covid-19.At least 14 people died in seven avalanches in the first week of February. It was the highest number of recreation-related fatalities in avalanches in the United States in at least a century, experts said.“The snowpack is the first-order reason — people are dying because it is very dangerous,” said Simon Trautman, an avalanche specialist for the U.S. Forest Service’s National Avalanche Center. “The question is the second-order or third-order effect. I don’t know, but what I do know is that there are more people out there this year because of Covid. There’s just no doubt about it.”Avalanche experts say this season would be a dangerous one without a pandemic. Early snow followed by a dry period across much of the West created a weak first layer of snow. Recent storms have dumped huge, heavy loads atop that weak layer — snow that entices people outdoors, but also threatens to shatter the support below it, sending it all downhill in a battle of physics between gravity and friction.A single misstep on a slope silently ready to give way can be the narrow line between thrill and tragedy.An average of about 25 people have died in avalanches in the United States each winter over the past decade. This season, through Sunday, 21 have died, according to reports compiled by the Colorado Avalanche Information Center.Deadly avalanches are almost always triggered by humans. The people captured in them are usually among those who inadvertently set the snow in motion.On Saturday, eight backcountry skiers were caught in an avalanche in Utah; four died. The same day, a group of snowmobilers in Montana were snared in a slide that killed one of them.Earlier last week, three Colorado skiers were killed in an avalanche. The next day, an avalanche killed three in Alaska. A day after that, two people in California were buried, and one died.Experts are parsing the anecdotal evidence, searching for answers beyond the scientific danger of this winter’s snowpack.“It’s hard to drive a direct connection to Covid, but I think we can drive an indirect connection,” Karl Birkeland, director of the National Avalanche Center, said. “Across the country, we’ve seen a continuation of what we saw this summer, which is more and more people going out onto our public lands. This winter we’ve seen more and more people going into the backcountry, whether on skis, snowshoes or snowmobiles. And with more people, you have a larger potential for people to get involved with avalanches.”Most victims have been experienced in the backcountry, experts said, shattering any presumptions that these are ill-equipped new adventurers desperate for socially distant outdoor activities. Most have been men in their 40s and 50s, though the victims in Utah on Saturday were all in their 20s and included two women. The victims have had the recommended safety equipment of beacons, probes and shovels, according to the avalanche investigations.Updated Feb. 9, 2021, 6:02 a.m. ETAll eight of Colorado’s victims this winter have been men older than 40. All but one had considerable backcountry experience, according to Ethan Greene, director of the Colorado Avalanche Information Center.And while a few accidents have occurred just outside ski areas, where chairlifts and loose boundaries provide quick access to tantalizing powder runs (called “sidecountry”), most have been in remote areas requiring hikes or climbs.That has led some experts to surmise that experienced backcountry skiers, looking to get away from this season’s unusual crowds, are pushing themselves deeper into unfamiliar terrain, all at a time of highly dangerous conditions.“It’s a lot of conjecture, but it’s really part of the discussion that we’re having around this stuff,” Birkeland said.There is speculation, too, that nearly a year’s worth of restrictions related to the coronavirus, which causes the disease Covid-19, might make people more apt to take chances. On Jan. 30, a 57-year-old expert skier died in an avalanche outside the boundary of Park City Mountain Resort.His skiing partner, who witnessed the slide and was unable to rescue him, said the coronavirus pandemic “had an impact.”“I realize now that I am exhausted from the 10+ months of near-constant stress Covid brings with worrying about my family, my friends, my work, etc.,” the partner, who was not identified, said in the accident report. “Plus financial stress, school closures, no physical contact with family members/friends, and so forth. As a result, my typical training, motivation, and mental reflection has been much less than in a normal fall/winter.”Such correlations are imprecise. In Europe, where an average of 100 people die in avalanches each winter, 56 have died this season. That is one more than all of last winter, but well short of the 128 who died in 2017-18.The head of the Swiss Mountain Guide Association told reporters last month that Covid may be dulling the decision-making process of backcountry skiers, who are perhaps overly eager to get outdoors and weary of free time constrained by virus rules.Greene, from the Colorado Avalanche Information Center, thinks there might be something to that, compounding what he calls the once-in-a-decade conditions of this year’s snowpack.“The environment that we’re all in, it is stressful,” Greene said. “That affects your interactions with people at the grocery store, and it also affects how you make decisions when you’re in avalanche terrain.”Mistakes in the backcountry do not have to be big to be fatal.In typical times, the difference from season to season is almost entirely built on the snowpack, which can alter greatly from one slope to another, depending on complex combinations of slope angle, sunlight, wind, temperature and other factors. (A common factor: Most avalanches occur on slopes with inclines between 30 and 45 degrees. Any steeper, and falling snow usually will not pile up in necessary quantities. Any shallower, and snow often will not move from forces of gravity.)Avalanche forecasting is done locally — by about 65 full-time forecasters, most of whom work for the U.S. Forest Service or the State of Colorado.Conditions in the Colorado Rockies might be completely different from, say, those in the Washington Cascades or California’s Sierra Nevada.But this season was unusual in that a huge swath of the West got a similar dump of early snow that was left exposed to the elements for weeks. That created, in general terms, a thin layer of fragile, sugarlike crystals.Like a house built on a bad foundation, the rest of this season’s snowpack sits precariously on top of that layer.The National Avalanche Center compiles the latest forecasts in an interactive map on its home page.“Last week was fascinating, because as the storms rolled through, you could just see the different parts of the country lighting up and going to red, or some cases even black, which is the highest danger rating,” Trautman said. “You can see that wave of instability and danger just roll the way up through the central portion of the West. It’s not that it doesn’t happen at other times, but the way this one happened was very dramatic.”And deadly. While the biggest storms have passed, for now, the weak layer in the snow is likely to last all season. That is the science.The human nature part of the equation is the variable that will determine how many more lives are lost.