Shoestring Glacier is a small valley glacier on Mount St. Helens in southwest Washington that descended from the volcano’s 8,364-foot summit. Formed from an ice and snow field near the mountain’s top, it helped shape the slope below, including a truncated spur. The glacier changed drastically in the 1980 eruption of Mount St. Helens, which removed about 75 percent of its volume. Meltwater and debris from the eruption fed deadly lahars rushing down the mountain, tying Shoestring Glacier to one of the most consequential volcanic eruptions in modern United States history.