Mount St. Helens
Mount St. Helens National Volcanic Monument  is a United States National Monument in southwest Washington State that was the site of a massive volcanic eruption on May 18, 1980. It can be visited as a longish day trip from Seattle or Portland, or more conveniently as a side-trip while traveling between the two cities.
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.
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.
Flora and fauna
There are a lot of flying ants near Mt.St.Helens.BEWARE!
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.
Warning: As of August 2017, there are no gas/petrol stations past Toutle, about 10 miles from I-5 on Hwy 504. A Shell station in the Kid Valley (8 mi. east of Toutle) is closed as of August 2017, and a sign in Toutle warns that no further gas stations are available. The round trip distance to the end of the highway (Johnston Ridge) from Toutle is 84 mi (135 km). Cheaper gas is available at Castle Rock as you exit the I-5 freeway.
The most popular tourist route into the Mount St. Helens area is via Washington state route 504. It can be reached at Castle Rock (exit #49) off Interstate 5 in Washington, about one hour and 15 minutes north of Portland and two hours south of Seattle. If going north on the return route (Seattle/Tacoma), State Route 505 can be used as a short cut back to I-5 (turn right a few miles east of Toutle). This is not recommended for the initial trip up the mountain, as it bypasses the main visitor center near Castle Rock.
From the east, there are three main routes. If using GPS or computer routing, be sure it doesn't send you on unpaved, one-lane forest service roads unless that's what you want. From Spokane, all three take roughly the same amount of time.
There are NO public bus services to Mt St Helens. Closest is the Lewis Highway Mountain Transit (Tel: 360-496-5405)  which goes along US-12 between Centralia/Chehalis and Packwood (Senior Center), thrice daily.
Monument passes are sold for single-day admission to the visitor centers along Washington 504.
Golden Passports are honored at Mount St. Helens.
Golden Passports are available only to U.S. citizens or permanent residents online at http://www.natlforests.org, or at any U.S. Forest Service or National Park Service office.
Along Washington 504 are three visitor centers operated by Cowlitz County, the State of Washington, and the U.S. federal government. (Mount St. Helens and Spirit Lake are actually in Skamania County, but all the land near the mountain is federally owned.) A fourth center at Coldwater Ridge is semi-permanently closed now, and may be sold. The centers include video presentations, exhibits, and information desks:
In addition, there are also numerous viewpoints and turnoffs for taking photos along the highway.
As of 13 July 2006, the summit of St. Helens has been re-opened for climbing on a reservation/permit basis.
There is a food truck offering drinks, hot dogs and hamburgers at Johnson's Ridge Observatory. There are also options available outside of the park in the town of Toutle.
Water is available within the park. If getting water out of the rivers, streams or wells, be sure to filter & boil. Better to be safe than sorry!
There are no hotels located within the park, but the town of Toutle, located to the west of the park, offers numerous options.
Camping near I-5 exits to Mount St. Helens along Route 504 is available at Seaquest State Park or south of Hwy 12 at Lewis & Clark State Park. There are also National Forest Service campsites south of Randle (NE of MSH access forest road 99) and along the Lewis River east of Cougar.--18.104.22.168 13:54, 14 January 2014 (EST)
Volcano safety is, to put it mildly, a controversial subject; see the article on Volcanoes (and, particularly, its discussion page) for some of the issues. Compared to many other active volcanoes, Mount St. Helens has been studied extensively, and therefore has a relatively well-defined "safety envelope" that allows informed decision making as regards trail closures, etc. Even St. Helens, however, is prone to bouts of unexpectedly violent behavior, as for example on 8 March 2005 when an explosive event sent ash and steam to elevations above 35,000 feet (10 km) essentially without warning. The monument, therefore, has established a policy regarding road and trail closures that at first glance appears unnecessarily conservative -- but it is not. Believe it. The closures aren't there simply to inconvenience and irritate you. If a trail is closed due to eruptive hazard, stay off the trail.
Other than the volcanic activity, St. Helens poses basically the usual set of hazards associated with mountainous country -- changeable weather, potential for road closures due to snow in the winter, etc. One extra thing to be aware of is that much of the area on the north side of the mountain, particularly the northeast, does not yet have many travel services, even things as basic as gas stations. When leaving the main roads to head for the observatory, or particularly the Windy Ridge viewpoint and trailhead, it's wise to have a full gas tank.