Crater Glacier formed inside Mount St. Helens’s north-facing crater after the 1980 eruption destroyed the summit and created a deep crater around a central lava dome. Snow, avalanches, rockfalls, and persistent shade allowed this unusually young glacier to grow rapidly, with debris-covered ice helping preserve it. By 2001, despite all of its ice being younger than 1980, it had reached a large fraction of the mountain’s former glacial volume. Volcanic activity from 2004 to 2008 reshaped and pushed the glacier until it encircled the lava domes. It remains notable as North America’s youngest and fastest-growing glacier and a vivid example of ice and volcanism evolving together.