Mount-Meager-Massiv

Mount Meager, also called the Meager Group, Meager Mountain, Mount Meager Volcanic Complex or Meager Creek Volcanic Field (sometimes mistakenly spelled Meagre or Meagher), is a potentially active volcanic complex, located Vorlage:Unit km north of the city of Vancouver and Vorlage:Unit km northwest of Pemberton, British Columbia, Canada. It is the most unstable volcanic massif in Canada, dumping clay and rock into the Meager Creek and Devastation Creek valleys. The mountain and the surrounding area are part of Pacific Ranges of the Coast Mountains and Garibaldi Volcanic Belt which is a northern extension of the Cascade Volcanic Arc in the United States. Mount Meager is said to be the most promising site for geothermal power development in British Columbia, and the east flank of the volcano is staked out by BC Hydro for test drilling purposes. Plans surface now then for a "boutique" hotel and ski resort based around the two clusters of hot springs.

The volcano lies above the west flank of the Lillooet River and just south of the Lillooet Icecap. With at least eight vents, Mount Meager is generally considered the northernmost major volcanic center of the Cascade Volcanic Arc and Garibaldi Volcanic Belt. However, a few isolated volcanic centers northwest of Mount Meager, such as Mount Silverthrone, which is a circular Vorlage:Unit km wide, deeply dissected caldera complex, may also be the product of Cascadia subduction, but geologic investigations have been very limited in this region.

Mount Meager was named after J.B. Meager, who owned timber licenses on Meager Creek. Before its present name, it was known as the more fitting Cathedral Mountain.

Geology

Mount Meager is Pliocene-to-Holocene in age with glaciers on its slopes. It has produced basaltic to more evolved andesitic, dacitic and rhyolitic magmas. Andesite lava flows 500,000-1,000,000 years old are the most abundant rock type in the area, with a total flow thickness of over Vorlage:Unit km. The volcano consists of at least four overlapping composite dacite to rhyodacite volcanoes that become progressively younger from south to north, ranging in age from approximately 2 million years to around 2,490 years which have built a complex shape. It rests on a Vorlage:Unit m high ridge of nonvolcanic crystalline and metamorphic rock. Numerous feeder dikes to older units are exposed by deep erosion forming multiple eroded summit lava domes and volcanic necks. Quaternary basalts underlying the uppermost Vorlage:Unit km of the Elaho valley originated at the 1,375 metre level in the South Fork Meager River.

The Mount Meager volcanic complex in fall

Pumice deposits at Mount Meager are mined at several locations on its northeast flank. The pumice is hand picked at the volcano's vent, where it is naturally purest and is the only pumice mine produced in Canada. The deposit is 25 million cubic meters, which formed when Meager erupted 2350 years ago. It lies closer to a marine port than any other deposit in North America, providing the opportunity to export in bulk to the Pacific Rim. The pumice is 66% silica and 16% alumina.

Mount Meager is a member in the chain of volcanic peaks that run from southwestern British Columbia to northern California. The volcanoes formed over the past 35 million years as the Juan de Fuca Plate and the Explorer Plate to its west have been subducting under the North American Plate at the Cascadia subduction zone. As the oceanic crust of the Juan de Fuca and the Explorer Plate melts, it creates magma that penetrates the crust of the Cascade Range and southwestern Coast Mountains, causing periodic eruptions of the volcanoes.

Mount Meager lies within the Coast Plutonic Complex, which is the single largest contiguous granite outcropping in the world. The plutonic and metamorphic rocks extend approximately Vorlage:Unit km on the coast of British Columbia, southwestern Yukon and southeastern Alaska. In addition, Garibaldi, Meager, Cayley and Silverthrone areas are of recent volcanic origin.

Human history

The Mount Meager volcanic complex as seen northeast from Pemberton

Natives of the zone possibly visited the Meager area to hunt goats, and probably visited the Meager Creek Hot Springs. The first recorded ascents of the Mount Meager volcanic complex were made by the earliest Vancouver climbers Tom Fyles, Neal Carter, Alec Dalgliesh and Mills Winram in 1931. The crowd made contact with the Lillooet River floodplain on horseback, having been outfitted by a Mr. Perkins of Pemberton. The crowd climbed most of the major summits of Mount Meager with the exclusion of the impressive peak of Perkin's Pillar, and the unstable Mount Job, which is difficult to come near from the main summits of the volcanic complex.

Mount Meager suffered a long period of quiescence following the 1931 visit. It was not until the early 1970s, when logging roads came up to the volcanic complex, that a restitution of interest took place.

Mount Meager is hot under the surface. The surface water seeps under the volcano and becomes heated, then rises along fractures to reach the surface to form the Meager and Pebble Creek Hot Springs. The hot springs were originally used and revered by First Nations people. Water at the Meager Creek Hot Springs have been tested for a hot water plumbing system as a geothermal energy source. The hot springs are very popular and are under considerable pressure from heavy use from people and local developments. The springs are relatively easily accessible from Whistler and Vancouver, but the bridge into the recreation site was destroyed by flooding, effectively closing the site.

The Mount Meager volcanic complex

The springs located on Meager Creek are called Teiq in the language of the Lillooet River and were the farthest up the Lillooet River. The spirit-beings/wizards known as "the Transformers" reached during their journey into the Lillooet Country, and a "training" place for young First Nations men who would privite themselves at the springs to acquire power and knowledge. In this area, also, was found the blackstone chief's head pipe that is famous of Lillooet artifacts; found buried in volcanic ash, one supposes from the 2350 BP eruption of Mount Meager.

A few ski trips visited the area in the late 1980s when the road to the hot springs was regularly plowed. However, not much new was accomplished except for a few first ski ascents and descents. In the mid-to late 1990s, an old Hydro exploration road accessing the Affliction Glacier and north side of Plinth was partially reopened, a new bridge built above Keyhole Falls, and a pumice mine began operating below the north face of Plinth. This newly renovated access led to two new routes, in winter and summer, being climbed on the impressive north face of Plinth Peak, which rises Vorlage:Unit m from Lillooet River. The winter ascent also saw the massive face skied in an extreme descent. Finally, for the moment, Perkin's Pillar was climbed with the help of aid equipment in the summer of 2002, 70 years after it had first seen by Tom Fyles.

Skiing

Mount Meager is skiable over 2100 meters (7000 ft), but probably not skiable from summit.

Geological history

Keyhole Falls - all that grey is ash from the last time Mount Meager blew up 2350 years ago

Mount Meager is most noteworthy as the source of the Bridge River Ash, deposited during Meager's most recent volcanic eruption 2350 years ago. This eruption was similar in character to the 1980 eruption of Mount St. Helens, erupting from a vent on the north-east side of Plinth Peak. This activity produced a diverse sequence of volcanic deposits, well exposed in the bluffs along the Lillooet River, which is defined as the Pebble Creek Formation. It comprises airfall pumice, pyroclastic flows, welded breccias, lahars and an dacitic lava flow. The eruption was so great that thin, very fine grained, distal deposits of tephra have been identified in Alberta, Vorlage:Unit km east from the vent and sent an ash column at least Vorlage:Unit km high into the stratosphere. An unusual, thick apron of welded vitrophyric breccia may represent the explosive collapse of an early lava dome which deposited ash several meters in thickness near the vent area. Pyroclastic fall deposits up to Vorlage:Unit m thick from the eruption, covers slopes in the area of Mount Meager. About 1–5% of the pumice fragments are banded from white to dark grey. The eruption also blocked the Lillooet River to a height of at least Vorlage:Unit km, impounding a lake. The lake reached a maximum elevation of Vorlage:Unit m and thus was at least Vorlage:Unit m deep. The dam eventually eroded from water activity, causing a massive outburst flood that sent house-sized boulders down the valley for several kilometers, forming Keyhole Falls. The destructive floodwaters continued much further. In its final stages, the eruption produced a Vorlage:Unit km long glassy, porphyritic dacite lava flow that varies from 15 to 20 m thick. This volcanism is very recent in geological terms, suggesting that the volcano may yet have some ongoing volcanic activity.

Map of the Garibaldi Volcanic Belt centers, including the Mount Meager area.

In the past, Meager has dumped clay and rock several meters deep into the Pemberton Valley at least three times during the last 7,300 years. Two earlier debris flows, around 4,450 and 7,300 years ago, sent pyroclastic rock at least Vorlage:Unit km from the volcano into Meager Creek. Recently, the volcano has created smaller landslides about every ten years. Logging, mining, tourism and wilderness recreation on nearby slopes and valleys are vulnerable to the volcano’s excellent geomorphic activity. There is no sign of volcanic eruptions with these events, however they might have been triggered by the upwelling of magma to shallow depths within the volcano or by movement of earthquakes. The landslides may have also occurred without specific triggers following extended periods of long term weakening of the volcanic rocks. Geologists warn the volcano could release another massive debris flow over populated areas anytime without warning.

On the southwest side of the complex lies Devastator Peak, a massive leaning tower of rock which actually partially overlies the ice of the Devastator Glacier. As the glacier retreats, the rock becomes unsupported, and collapses. Massive rock avalanches result, which land on the glacier and partially melt its surface (surface temperatures in the rockfall, the result of friction from fragments colliding and rubbing on each other during the collapse, are high enough that the surface layers melt and then form an obsidian crust when cooling). The resultant landslide blocks Meager Creek at its confluence with Devastator, forming a temporary lake. When the lake grows to a large enough size, it overtops the landslide dam and produces a huge flood wave which roars down Meager Creek and Lillooet River for Vorlage:Unit km or more before subsiding into a large flood. Scientists believe a wave large enough to reach Pemberton could be created by a large enough initial rockfall. Historically, such landslide-flood events occurred in 1930 and on July 22, 1975. The latter event buried and killed a party of 4 BC Hydro geologists exploring the geothermal potential of the area.

Volcanic hazards

The far end of the Pemberton Meadows with the Mount Meager volcanic complex looming in the background

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Mount Meager is one of the top 11 Canadian volcanoes associated with seismic activity since 1985, the others include: Castle Rock, Mount Edziza, Mount Cayley, Hoodoo Mountain, Lava Fork Valley, Crow Lagoon, Mount Silverthrone, Wells Gray-Clearwater Volcanic Field, Mount Garibaldi and Nazko Cone. The hydrothermal activity at Mount Meager suggests that the volcano still contains living magma plumbing systems and may presence of a shallow magma chamber. Although the existing data do not allow a clear conclusion, these observations are further indications that some of Canada's volcanoes are potentially active, and that their associated hazards may be significant. It is noteworthy that the seismic activity correlates with some of Canada's most youthful volcanoes, and with long-lived volcanic centers with a history of significant explosive behavior, such as Mount Meager and other major volcanic centers in the Garibaldi Volcanic Belt. For this reason the Geological Survey of Canada are planning for developing hazard maps and emergency plains for Mount Cayley and Mount Meager volcanic complexes.

Past eruptions at Mount Meager were Plinian eruptions suggesting that this volcano poses a significant threat to long distances across southern British Columbia and southern Alberta. Lahars could easily travel as far as Pemberton, which is only Vorlage:Unit km from the volcano. Another Plinian style eruption from Mount Meager would have a significant impact on local mining, logging and air traffic. Meager has an explosive, eruptive history, including four episodes of activity, 1.9 to 2.2 million years, <1.9 and>0.5 million years, 1.0 and 0.5 million years and 0.15 to 0.002 million years ago. There haven't been any signs of renewed activity at Mount Meager, although it is a potentially active volcanic complex. The first signs of activity at Mount Meager would probably be abundant shallow earthquakes, which may be accompanied by changes in the temperature or the location of fumaroles and hotsprings. These signs generally occur well in advance of a potential eruption, although the volcanic hazard at this time is low.

Subsidiary peaks

The Mount Meager volcanic complex

The broad top of Mount Meager contains six named major summits. The highest is called Plinth Peak. The second highest summit is the main summit of Mount Meager, 2,646 metres (8,681 ft), the third highest summit is Capricorn Mountain, 2,569 metres (8,429 ft), which consists of a boomerang shaped ridge, with one summit on each end of the boomerang. The fourth highest summit is Mount Job, 2,493 metres (8,180 ft), which is a steep pile of rubble held together by volcanic ash and sand. The fifth highest summit is Pylon Peak, 2,473 metres (8,112 ft), at the southern edge, which overlooks Meager Creek Hot Springs. The lowest of the six summits is Devastator Peak, 2,327 metres (7,635 feet), this peak is seen as an impressive towering horn while from other angles it looks like a minor bump.

On the southernmost flank of Mount Meager are two pinnacled ridges that extend out from Pylon Peak and are named respectively the Pylons and the Marionettes on the Geological Survey of Canada special area map.

On the north side of Capricorn Mountain is a spectacular volcanic plug called Perkin's Pillar. The upper half of Perkin's Pillar broke sometime in June of 2005 and only a jagged sliver remains of the previously mighty summit.

The Mount Meager volcanic complex

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Provincial park

The western portion of Mount Meager lies in the Upper Lillooet Provincial Park, a 19,996 hecture park at the headwaters of the Lillooet River to protect valley bottom old growth forests, wetland habitat, high alpine ridges and glaciers.

Upper Lillooet Provincial Park has no developed trails or any other facilities, making access limited. The rough logging roads created in the early 1970s extend up Meager Creek towards the south end of, but not into, the park. Helicopter access has been fairly popular largely for accessing base camp areas in the alpine portions of the park.

See also

• Cascade Volcanoes
• Garibaldi Volcanic Belt
• Cascade Range
• Pacific Ranges
• Volcanism in Canada
• Geology of the Pacific Northwest
• Lillooet Icecap
• Geography of Canada
• List of volcanoes by elevation
• List of mountains by elevation

External links

Commons: Mount Meager – Album mit Bildern, Videos und Audiodateien

• CVO Website Canada Volcanoes and Volcanics
• Catalogue of Canadian volcanoes: Mount Meager
• Mount Meager in the Canadian Mountain Encyclopedia
• Mount Meager BC Fieldwork
• Pebble Creek Geothermal Prospect
• Volcanic landslide hazards at Mount Meager, British Columbia
• VolcanoDB.com: Mount Meager
• Meager Group in the Canadian Mountain Encyclopedia.
• Plinth Peak in the Canadian Mountain Encyclopedia.
• Mount Job in the Canadian Mountain Encyclopedia.
• Capricorn Mountain in the Canadian Mountain Encyclopedia.
• Devastator Peak in the Canadian Mountain Encyclopedia.
• Pylon Peak in the Canadian Mountain Encyclopedia.

Vorlage:Cascade volcanoes