<P> Although Mount St. Helens is in Skamania County, Washington, access routes to the mountain run through Cowlitz County to the west . State Route 504, locally known as the Spirit Lake Memorial Highway, connects with Interstate 5 at Exit 49, 34 miles (55 km) to the west of the mountain . That north--south highway skirts the low - lying cities of Castle Rock, Longview and Kelso along the Cowlitz River, and passes through the Vancouver, Washington--Portland, Oregon metropolitan area less than 50 miles (80 km) to the southwest . The community nearest the volcano is Cougar, Washington, in the Lewis River valley 11 miles (18 km) south - southwest of the peak . Gifford Pinchot National Forest surrounds Mount St. Helens . </P> <P> During the winter of 1980--1981, a new glacier appeared . Now officially named Crater Glacier, it was formerly known as the Tulutson Glacier . Shadowed by the crater walls and fed by heavy snowfall and repeated snow avalanches, it grew rapidly (14 feet (4.3 m) per year in thickness). By 2004, it covered about 0.36 square miles (0.93 km), and was divided by the dome into a western and eastern lobe . Typically, by late summer, the glacier looks dark from rockfall from the crater walls and ash from eruptions . As of 2006, the ice had an average thickness of 300 feet (100 m) and a maximum of 650 feet (200 m), nearly as deep as the much older and larger Carbon Glacier of Mount Rainier . The ice is all post--1980, making the glacier very young geologically . However, the volume of the new glacier is about the same as all the pre--1980 glaciers combined . </P> <P> With the recent volcanic activity starting in 2004, the glacier lobes were pushed aside and upward by the growth of new volcanic domes . The surface of the glacier, once mostly without crevasses, turned into a chaotic jumble of icefalls heavily criss - crossed with crevasses and seracs caused by movement of the crater floor . The new domes have almost separated the Crater Glacier into an eastern and western lobe . Despite the volcanic activity, the termini of the glacier have still advanced, with a slight advance on the western lobe and a more considerable advance on the more shaded eastern lobe . Due to the advance, two lobes of the glacier joined together in late May 2008 and thus the glacier completely surrounds the lava domes . In addition, since 2004, new glaciers have formed on the crater wall above Crater Glacier feeding rock and ice onto its surface below; there are two rock glaciers to the north of the eastern lobe of Crater Glacier . Crater Glacier is the only known advancing glacier in the contiguous United States . </P> <P> The early eruptive stages of Mount St. Helens are known as the "Ape Canyon Stage" (around 40,000--35,000 years ago), the "Cougar Stage" (ca . 20,000--18,000 years ago), and the "Swift Creek Stage" (roughly 13,000--8,000 years ago). The modern period, since about 2500 BCE, is called the "Spirit Lake Stage". Collectively, the pre--Spirit Lake stages are known as the "ancestral stages". The ancestral and modern stages differ primarily in the composition of the erupted lavas; ancestral lavas consisted of a characteristic mixture of dacite and andesite, while modern lava is very diverse (ranging from olivine basalt to andesite and dacite). </P>

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