Melting glaciers can reroute entire rivers in one season
In just four days, a massive river that flowed north for centuries vanished, only to reappear on the opposite side of a mountain range heading south.
For over 300 years, the Slims River was a powerful force in the Yukon, carving a wide path toward the Bering Sea. But in the spring of 2016, the river effectively disappeared in a matter of days. As the Kaskawulsh Glacier retreated, it thinned so much that it exposed a new, lower-elevation path through the ice. Gravity took over, pulling the meltwater into a different valley and creating a phenomenon called river piracy. Instead of feeding the Slims, the water surged into the Alsek River, which flows toward the Pacific Ocean. This was the first time in modern history that geologists witnessed a river being stolen by another watershed in a single season.