Climate
Most viewpoints on the Monument's north, east, and south sides can be reached from Memorial Day until snow closes the roads, usually in late October. Trails are generally open from June through October, although some lower elevation trails can be hiked all year. The Mount St. Helens Visitor Center Highway 504 milepost 5 now operated by Washington State Parks is open during the winter, except winter holidays.
Landscape
Mount St. Helens is a typical "stratovolcano," the volcanic form most familiar from photographs of their typically conical profiles. The great 1980 eruption destroyed most of the volcanic cone, leaving a huge amphitheater on the north side that is well seen from the Johnston Ridge observatory/visitor center. Current 2004-5 volcanic activity is building a new lava dome within this amphitheater, visible from the "VolcanoCam" at the observatory but not yet large enough to replace the destroyed cone.
St. Helens is still glaciated to some extent, despite its reduced altitude. One unexpected and remarkable bit of landscape on the mountain is the astonishing Loowit Falls, a waterfall that emerges directly from the amphitheater bearing meltwater from a glacier within the crater. This falls can be seen use binoculars from the observatory, but to get the best feeling for the incongruity of the falls -- it seems to emerge as though from the surface of the moon -- requires a hike on a trail that is closed as of 2005 owing to the volcanic activity.
History
On March 20, 1980, Mount St. Helens awakened from over 100 years of dormancy with a magnitude 4.1 earthquake which began a series of events leading to eruption. Steam and ash eruption started on March 27, and over the next two months the north side of the mountain started bulging at the rate of about 5 to 6 feet a day.
Then on May 18, 1980, at 8:32 a.m., a magnitude 5.1 earthquake caused the bulging north face to collapse in one of the largest landslides in recorded history. The highly pressurized magma burst forth in an explosive eruption, sending super-heated volcanic gas and ash across a large portion of the United States, destroying hundreds of square miles of forest, and killing 57 people in what was the most destructive volcanic eruption in the United States.
Today, over a quarter century later, life is starting to return to the barren landscape surrounding the mountain. However, as the recent steam eruptions starting in October 2004 have illustrated, the danger of another catastrophic eruption is ever present. Visiting Mount St. Helens National Volcanic Monument is to simultaneously witness the result of catastrophic destruction and see the result of rebirth.