Science season in Antarctica begins in November, when noontime temperatures at McMurdo Station climb to a balmy 18 degrees Fahrenheit and the sun hangs in the sky all day and night. For a researcher traveling there from the United States, the route takes time as well as patience. The easiest way is to fly from Los Angeles to Christchurch, New Zealand—a journey of 17 hours, if you’re lucky—and then to McMurdo, a charmless cluster of buildings that houses most of the southern continent’s thousand or so seasonal residents and both of its ATMs. McMurdo isn’t the end of the line, though. Often it’s just a pass-through for scientists hopping small planes to penguin colonies or meteorological observatories farther afield.

Few places in Antarctica are more difficult to reach than Thwaites Glacier, a Florida-sized hunk of frozen water that meets the Amundsen Sea about 800 miles west of McMurdo. Until a decade ago, barely any scientists had ever set foot there, and the glacier’s remoteness, along with its reputation for bad weather, ensured that it remained poorly understood. Yet within the small community of people who study ice for a living, Thwaites has long been the subject of dark speculation. If this mysterious glacier were to “go bad”—glaciologist-­speak for the process by which a glacier breaks down into icebergs and eventually collapses into the ocean—it might be more than a scientific curiosity. Indeed, it might be the kind of event that changes the course of civilization.

January 2019. Subscribe to WIRED.

In December 2008, a Penn State scientist named Sridhar Anandakrishnan and five of his colleagues made the epic journey to Thwaites, two days from McMurdo by plane, tractor, and snowmobile. All glaciers flow, but satellites and airborne radar missions had revealed that something worrisome was happening on Thwaites: The glacier was destabilizing, dumping ever more ice into the sea. On color-coded maps of the region, its flow rate went from stable blue to raise-the-alarms red. As Anandakrishnan puts it, “Thwaites started to pop.”

The change wasn’t necessarily cause for alarm. Big glaciers can speed up or slow down for reasons that scientists still don’t completely grasp. But Anandakrishnan knew that Thwaites’ unusual characteristics—it is shaped like a wedge, with the thin front end facing the ocean—left it vulnerable to losing vast quantities of ice quickly. What’s more, its size was something to reckon with. Many glaciers resemble narrow rivers that thread through mountain valleys and move small icebergs leisurely into the sea, like a chute or slide. Thwaites, if it went bad, would behave nothing like that. “Thwaites is a terrifying glacier,” Anandakrishnan says simply. Its front end measures about 100 miles across, and its glacial basin—the thick part of the wedge, extending deep into the West Antarctic interior—runs anywhere from 3,000 to more than 4,000 feet deep. A few years before Anandakrishnan’s first expedition, scientists had begun asking whether warming waters at the front edge could be playing a part in the glacier’s sudden stirring. But he wanted to know what was going on deep below Thwaites, where its ice met the earth.

If the mysterious Thwaites Glacier were to “go bad,” it might change the course of civilization.

During that 2008 expedition and another a year later, Anandakrishnan’s team performed the geologic equivalent of an ultrasound on Thwaites. Each morning they’d wake up in their freezing tents, call McMurdo on the satellite phone to attest that they were still alive, eat a quick breakfast, and move out by snowmobile across the blankness of the ice sheet. At a prearranged point, they’d place an explosive charge at the bottom of a hole—usually between 70 and 100 feet deep—fill the hole with snow, and blow it up. The wave of energy would travel from the charge to the bed of the glacier and back to the surface, where it would be recorded by an array of geophones, exquisitely sensitive seismic instruments. By measuring the time it took for the waves to rebound, and by looking at alterations in the waves’ characteristics, Anandakrishnan’s team could gain clues about the depth and makeup of the glacier’s bed, thousands of feet below. They repeated the process again and again.