Mount Meager massif
The Mount Meager massif is a group of volcanic peaks in the of the Coast Mountains in southwestern British Columbia, Canada. Part of the Cascade Volcanic Arc of western North America, it is located north of Vancouver at the northern end of the Pemberton Valley and reaches a maximum elevation of. The massif is capped by several eroded volcanic edifices, including, volcanic plugs and overlapping piles of lava flows; these form at least six major summits including Mount Meager which is the second highest of the massif.
The Garibaldi Volcanic Belt has a long history of eruptions and poses a threat to the surrounding region. Any volcanic hazard ranging from landslides to eruptions could pose a significant risk to humans and wildlife. Although the massif has not erupted for more than 2,000 years, it could produce a major eruption; if this were to happen, relief efforts would be quickly organized. Teams such as the Interagency Volcanic Event Notification Plan are prepared to notify people threatened by volcanic eruptions in Canada.
The Mount Meager massif produced the largest volcanic eruption in Canada in the last 10,000 years. About 2,400 years ago, an explosive eruption formed a volcanic crater on its northeastern flank and sent avalanches of hot ash, rock fragments and volcanic gases down the northern flank of the volcano. Evidence for more recent volcanic activity has been documented at the volcano, such as hot springs and earthquakes. The Mount Meager massif has also been the source of several large landslides in the past, including a massive debris flow in 2010 that swept down Meager Creek and the Lillooet River.
Geography and geology
Regional geography
The Mount Meager massif lies in the Coast Mountains, which extend from Vancouver to the Alaskan Panhandle for. It is about wide, cut by fjords, narrow inlets with steep cliffs created by glacial erosion. The Coast Mountains have a profound effect on British Columbia's climate. Lying just east of the Pacific Ocean, they shear off moisture-laden air coming off the ocean, causing heavy rainfall on their western slopes. This precipitation is among the most extreme in North America, feeding lush forests on the mountain range's western slopes.Valleys surrounding the massif contain old-growth forests. The area also features wetland habitats, plants of the and glaucous willowherbs. Wildlife such as wolves, wolverine, moose, raptors, black-tailed deer, and waterfowl inhabit the area as well as grizzly and black bears.
Regional geomorphology
Garibaldi Volcanic Belt
The Mount Meager massif is part of the Garibaldi Volcanic Belt, the northernmost segment of the. This volcanic belt includes cinder cones, calderas, stratovolcanoes and subglacial volcanoes that have been active in the last 10,000 years. The latest explosive eruption in the Garibaldi Volcanic Belt occurred at a crater on the northeastern slope of the massif about 2,400 years ago, which forms a clearly defined depression.The GVB extends north from the Watts Point volcano to at least as far as the Meager massif. Because little is known about the volcanoes north of the massif, such as the Silverthrone and, experts disagree about their nature. Some scientists regard the Silverthrone Caldera as the northernmost volcano of the Garibaldi Volcanic Belt, while others contend that the geology of the massif more closely matches that of the GVB. It is also unclear whether the Milbanke Sound Cones are part of the Garibaldi Belt or formed by different tectonic processes. However, there is evidence the Silverthrone and complexes are related to activity at the Cascadia subduction zone. Geologically these two volcanoes contain the same rock types as those found elsewhere in the Cascade Arc, including rhyolites, dacites, andesites and basaltic andesites. Such rock types are produced by subduction zone volcanism indicating volcanism at Silverthrone and is probably related to subduction. If these two volcanoes are true Cascade Arc volcanoes, the massif is not the northernmost volcano of the Garibaldi Belt or the Cascade Arc.
Cascade Volcanic Arc
in the Cascade Volcanic Arc is caused by subduction of the Juan de Fuca Plate under the North American Plate at the. This is a long fault zone lying off the from Northern California to southwestern British Columbia. The plates move at a relative rate of more than per year at an oblique angle to the subduction zone. Because of the huge fault area, the Cascadia subduction zone can produce large earthquakes of magnitude 7.0 or greater. The interface between the Juan de Fuca and North American plates remains locked for periods of roughly 500 years. During these periods, stress builds up on the interface between the plates and causes tectonic uplift of the North American margin. When the plate finally slips, it releases 500 years of stored energy in a massive earthquake.Unlike most subduction zones worldwide, there is no deep oceanic trench present along the continental margin in Cascadia. The mouth of the Columbia River empties directly into the subduction zone and deposits silt at the bottom of the Pacific Ocean, burying this large depression, or area of sunken land. Massive floods from prehistoric Glacial Lake Missoula during the also deposited large amounts of sediment into the trench. However, as with other subduction zones the outer margin is slowly being compressed like a giant spring. When the stored energy is suddenly released by slippage across the fault at irregular intervals, the Cascadia subduction zone can create enormous earthquakes such as the magnitude 9.0 Cascadia earthquake of January 26, 1700. However earthquakes along the Cascadia subduction zone are uncommon, and there is evidence of a decline in volcanic activity over the last few million years. The probable explanation lies in the rate of convergence between the Juan de Fuca and North American plates, which converge at to per year, about half the rate of convergence from seven million years ago.
Local geography
Six main summits constitute the Mount Meager massif. The highest and northernmost summit is with an elevation of. Mount Meager itself is in elevation. Capricorn Mountain west of Mount Meager rises with an elevation of. Just west of Capricorn Mountain lies Mount Job, in elevation. Pylon Peak with an elevation of is south of Capricorn Mountain and Mount Meager. Devastator Peak, also known as The Devastator, has an elevation of and is the lowest and southernmost summit of the massif.Streams and glaciers have played a significant role in dissecting the massif, and its upper slopes are covered with snow and ice. Numerous feeder dikes to older units, formed when magma intrudes into a crack then crystallizes as a sheet intrusion, are exposed by deep erosion. Perkin's Pillar, a vertical tower of brecciated lava, represented an erosional remnant of the massif until its collapse in June 2005. More than 10 streams drain meltwater from the Mount Meager massif, including, Job Creek, No Good Creek, Angel Creek, Devastation Creek, Canyon Creek and. The massif is located within one of British Columbia's many territorial divisions known as the Lillooet Land District.
Local geomorphology
The geomorphology of the Mount Meager massif resembles that of Glacier Peak, another Cascade Arc volcano in the U.S. state of Washington. It consists of at least four overlapping stratovolcanoes that are younger from south to north. With a total volume of, the massif is older than most volcanoes in the Cascade Arc, tracing its history back to 2,200,000 years ago. In the Cascade Range, the oldest volcanoes are generally no more than a million years old. This includes Mount Rainier, Lassen Peak, Mount Jefferson and Mount St. Helens. However, portions of the massif formed in the last million years. The volcano is made of volcanic rocks ranging from rhyodacite to basalt. Rhyodacite forms a series of eroded volcanic plugs which form the highest peaks. Their slopes are covered with their eruptive products and serve as the surface expressions of intrusions. As a result, they provide a unique opportunity to study the relationships between magma chambers and their lavas. The mafic, intermediate and felsic volcanic rocks of the massif were erupted from at least eight volcanic vents.Bridge River Vent
The Bridge River Vent is a relatively young volcanic crater that formed during an eruption about 2,400 years ago. This eruption ranged in character from explosive to effusive and involved lava dome extrusion, pyroclastic flows, lahars and lava flows. Eastward migration of the spread material across Western Canada to deposit the Bridge River Ash. In the and Lillooet River area the ash occurs as a coarse-textured deposit with blocks of pumice up to in diameter. The texture rapidly becomes finer eastward from the Bridge River. At Big Bar on the Fraser River pellets are up to in diameter while pellets in the Messiter area have a maximum diameter of.Situated on the northeastern flank of Plinth Peak, the Bridge River Vent has an elevation of. It has oversteepened walls covered with ice and debris from volcanic activity and slope collapses. The crater is roughly bowl-shaped, although it is breached on the northern side. Because the Bridge River Vent is located on the northern slope of the Mount Meager massif, it represents a satellite vent. The eruption that formed the Bridge River Vent was probably fed through a conduit from the magma chamber below the massif. A stress field controlled by regional tectonics has been commonly invoked to explain the dynamics of lateral flow of magma from a reservoir to produce such eruptions.
Human history
Naming
The name Meager Mountain was adopted on May 6, 1924, as labelled on a 1923 British Columbia map. In 1966 the volcano was renamed. According to a BC Geographical Names letter written in March 1983, "the local name, Cathedral, was duplicated elsewhere, so the mountain was renamed Meager after the creek of that name which lies to the south of it". Meager Creek is named after J. B. Meager who owned timber licences on the creek. Despite its official name, Mount Meager is sometimes mistakenly spelled Mount Meagre or.The massif's peak names were submitted by Canadian mountaineer Neal M. Carter, who was a member of the British Columbia Mountaineering Club. Devastator Peak was officially named on in association with Devastation Glacier. Plinth Peak was officially named on as identified in Carter's 1932 sketch map and article "Explorations in the Lillooet River Watershed". Mount Job and Pylon Peak were both officially named on January 17, 1957, from their labels on Carter's 1954 sketch map of the Lillooet River. Capricorn Mountain was originally identified as Mount Capricorn in the 1932 Canadian Alpine Journal, Vol XXI. According to the journal, "the name chosen for the 8440-foot mountain was Mt. Capricorn, a variation of the all-too-common appellation "Goat Mountain", applied by Bert to the stream which drains the Capricorn glacier at its base". Subsequently, the peak was renamed to on June 22, 1967.