Mount St. Helens (known as Lawetlat'la to the Indigenous Cowlitz people, and Loowit or Louwala-Clough to the Klickitat) is an active stratovolcano located in Skamania County, Washington, in the Pacific Northwest region of the United States.
It is 83 km northeast of Portland, Oregon, and 158 km south of Seattle. Mount St. Helens takes its English name from the British diplomat Lord St Helens, a friend of explorer George Vancouver who made a survey of the area in the late 18th century.
The volcano is located in the Cascade Range and is part of the Cascade Volcanic Arc, a segment of the Pacific Ring of Fire.
Mount St. Helens is most famous for its major eruption on May 18, 1980, the deadliest and most economically destructive volcanic event in U.S. history. Fifty-seven people were killed; 200 homes, 47 bridges, 24 km of railways, and 298 km of highway were destroyed. A massive debris avalanche, triggered by an earthquake of magnitude 5.1, caused a lateral eruption that reduced the elevation of the mountain's summit from 2,950 m to 2,549 m, leaving 1.6 km wide horseshoe-shaped crater. The debris avalanche was 2.5 km3 in volume.
Ever since its main eruption, it had continuous volcanic activity until 2008. Despite this, geologists predict that future eruptions will be more destructive, since the configuration of the lava domes there require more pressure to erupt. Despite the dangers, Mount St Helens is a popular hiking spot, and is climbed year round.
More information: USGS
Mount St. Helens is 55 km west of Mount Adams, in the western part of the Cascade Range. Considered brother and sister mountains, the two volcanoes are approximately 80 km from Mount Rainier, the highest of the Cascade volcanoes. Mount Hood, the nearest major volcanic peak in Oregon, is 100 km southeast of Mount St. Helens.
Mount St. Helens is geologically young compared with the other major Cascade volcanoes.
It formed only within the past 40,000 years, and the summit cone present before its 1980 eruption began rising about 2,200 years ago. The volcano is considered the most active in the Cascades within the Holocene epoch, which encompasses roughly the last 10,000 years.
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 (4.3 m) per year in thickness.
Mount St. Helens is part of the Cascades Volcanic Province, an arc-shaped band extending from southwestern British Columbia to Northern California, roughly parallel to the Pacific coastline. Beneath the Cascade Volcanic Province, a dense oceanic plate sinks beneath the North American Plate; a process known as subduction (geology). As the oceanic slab sinks deep into the Earth's interior beneath the continental plate, high temperatures and pressures allow water molecules locked in the minerals of solid rock to escape. The water vapour rises into the pliable mantle above the subducting plate, causing some mantle to melt. This newly formed magma ascends upward through the crust along a path of the least resistance, both by way of fractures and faults as well as by melting wall rocks. The addition of melted crust changes the geochemical composition. Some melt rises toward the Earth's surface to erupt, forming the Cascade Volcanic Arc above the subduction zone.
Future eruptions of Mount St. Helens will likely be even larger than the 1980 eruption.
The current configuration of lava domes in the crater means that much more pressure will be required for the next eruption, and hence the level of destruction will be higher. Significant ashfall may spread over 100,000 km2, disrupting transportation. A large lahar flow is likely on branches of the Toutle River, possibly causing destruction in inhabited areas along the I-5 corridor.
More information: The Spokesman-Review
Native American lore contains numerous stories to explain the eruptions of Mount St. Helens and other Cascade volcanoes. The most famous of these is the Bridge of the Gods story told by the Klickitat people.
The mountain is also of sacred importance to the Cowlitz and Yakama tribes that also live in the area. They find the area above its tree line to be of exceptional spiritual significance, and the mountain (which they call Lawetlat'la, roughly translated as the smoker) features prominently in their creation story, and in some of their songs and rituals. In recognition of its cultural significance, over 4,900 ha of the mountain, roughly bounded by the Loowit Trail, have been listed on the National Register of Historic Places.
Other area tribal names for the mountain include nšh´ák´ (water coming out) from the Upper Chehalis, and aka akn (snow mountain), a Kiksht term.
In 1982, President Ronald Reagan and the U.S. Congress established the Mount St. Helens National Volcanic Monument, a 45,000 ha area around the mountain and within the Gifford Pinchot National Forest.
Following the 1980 eruption, the area was left to gradually return to its natural state.
In 1987, the U.S. Forest Service reopened the mountain to climbing. It remained open until 2004 when renewed activity caused the closure of the area around the mountain.
Most notable was the closure of the Monitor Ridge trail, which previously let up to 100 permitted hikers per day climb to the summit.
On July 21, 2006, the mountain was again opened to climbers.
More information: Scientific American
over to the south of me is covered.
It's gonna get me, too. I can't get out of here...
Gerry Martin, HAM radio operator
No comments:
Post a Comment