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Columbia Bay near Valdez, Alaska. This is one of the old tributaries (West Branch) of the main Columbia trunk that filled the bay in the Chugach Mountains. The main trunk of the glacier is one of the fastest retreating glaciers in the world with an average retreat rate of 0.37 miles (0.6 km) per year since the 1980s. While climate change and atmospheric warming likely played a role in the initiation and extent of this retreat , this mechanical process is a natural cycle in tidewater glaciers [wiki]. Once the glacier recedes to near the shoreline, the retreat will slow, allowing it to begin building a moraine, or shoal of sediment that will slow the calving rate and insulate the ice from the warmer water so it can begin an advancing stage.