The area of Crater Glacier is approximately one fifth the area of glaciated terrain that existed on Mount St. Helens prior to the catastrophic eruption of May 18, 1980. Crater Glacier is approximately 0.33 square miles, which is twice the area of White River Glacier on the south side of Oregon's Mount Hood. Crater Glacier is the newest glacier to form in North America. It is one of the most rapidly advancing and one of the lowest glaciers in the lower 48 states.
At the present, the growing lava dome is squeezing the glacier against the crater walls, causing the ice to thicken and flow more quickly out of the crater. The two arms are moving generally northward, but obliquely towards one another, and their termini, in early September, were approximately 180 feet apart. On April 20, 2007, the termini were approximately 400 feet apart. Between now and then, the glacier termini have advanced towards one another at the rate of approximately 0.7 feet a day.
Information provided by USGS