Solving the Puzzle of the Labyrinth
Beneath a glacier in the Transantarctic Mountains some 12 million years ago, the downhill flow of a massive, growing reservoir of meltwater was restrained by walls of ice. As the reservoir grew, it became too heavy for the walls to hold. They gave way, releasing an explosive surge of water nearly 13 times the volume of water draining through the Amazon River.
As it ripped through the valley below, the water gushed into the bedrock, tearing away chunks of rock the size of refrigerators, hurling them miles down Antarctica’s Wright Valley. In its wake, the subglacial flash flood left a spectacular maze of channels, some hundreds of meters deep, incised into the stone, an intricate complex of meandering pathways called the Labyrinth.
It wasn’t easy to decode the history of this mysterious place. It may never have been understood were it not for the Channeled Scablands, a strikingly similar landscape in eastern Washington state, and a bit of meticulous sleuthing by geologist David Marchant and his graduate student, Adam Lewis.
A megaflood theory for the Scablands first appeared in the 1920s, but it wasn’t widely accepted until the 1970s, when geologist Victor Baker described the physical processes of major floods around the world. Features like giant gravel current ripples and displaced 65-foot-wide boulders in the Scablands could not be explained by changes in the nearby Columbia River, he wrote — the flow and volume of whatever water source formed them would have to be exponentially larger. In 2005, when Marchant and his team were exploring the Labyrinth, they noticed scouring patterns on the walls within the channels, hinting at a massive surge of water below a glacial surface. It was then they pieced the story together.
The subglacial megaflood, Marchant believes, occurred during the middle Miocene, a period 12 million to 16 million years ago. Antarctica cooled from a temperate climate with wet glaciers to the frigid climate and cold-based glaciers it has today. During the transition, ice sheets expanded, and meltwater accumulated below the ice at the edge of mountain divides, creating lakes below the glaciers. As the climate cooled, ice dams formed in mountain passes, including one above what is now the Labyrinth. As the lake beneath the glacier grew, pressure overcame the strength of the ice dam. Once the water broke through, nothing could stop its flow.
Smaller, so-called “proto-Labyrinths” exist elsewhere in Antarctica, suggesting catastrophic floods were probably not rare in the continent’s geologic history. Marchant suspects more of these landforms are buried under ice, which covers more than 98 percent of the continent.