{{Short description|Group of volcanoes in British Columbia, Canada}} {{Infobox mountain | name=Mount Meager massif | other_name= | image=MountMeagerPlinthCapricorn.jpg | image_caption = The Mount Meager massif as seen from the east near [[Pemberton, British Columbia|Pemberton]]. Summits left to right are [[Capricorn Mountain]], [[Mount Meager (British Columbia)|Mount Meager]] and [[Plinth Peak]]. | image_alt = A large lightly glaciated mountain rising over a forested valley. | country=Canada<ref name="gvp">{{cite gvp|vn=320180|title=Meager|access-date=2011-07-14}}</ref> | region_type=[[Provinces and territories of Canada|Province]] | region=[[British Columbia]]<ref name="gvp"/> | district=[[Lillooet Land District]]<ref name="QQQK">{{BCGNIS|id=34788|name=Mount Meager|access-date=2011-07-06}}</ref> | parent=[[Pacific Ranges]] | borders_on= | topo_maker=[[National Topographic System|NTS]] | topo_map={{Canada NTS Map Sheet|92|J|12}}<ref name="QQQK"/> | formed_by=[[Complex volcano]]<ref name="gvp"/> | orogeny= | age= | geology= | length_km=13 | length_orientation= | length_ref=<ref name="GDK">{{cite book|last=Hildreth|first=Wes|title=Quaternary Magmatism in the Cascades—Geologic Perspectives|publisher=[[United States Geological Survey]]|pages=7, 11|year=2007|isbn=978-1-4113-1945-5}}</ref> | width_km=9 | width_orientation=<ref name="GDK"/> | volume_km3=20 | volume_ref=<ref name="GDK"/> | highest=[[Plinth Peak]]<ref name="gvp"/> | elevation_m=2680 | elevation_ref =<ref name="gvp"/> | coordinates = {{coord|50|40|0|N|123|31|0|W|type:mountain_region:CA_scale:200000|format=dms|display=inline}} | coordinates_ref = <ref name="gvp"/> | range_coordinates = {{coord|50.63|N|123.05|W|type:mountain_region:CA_scale:200000|format=dms|display=inline,title}} | range_coordinates_ref= <ref name="gvp"/> | map=Canada British Columbia | map_caption=Location map of the Mount Meager massif | volcanic_arc = [[Canadian Cascade Arc]] | volcanic_belt = [[Garibaldi Volcanic Belt]] | last_eruption = 410 BCE ± 200 years<ref name="gvp"/> }} The '''Mount Meager massif''' is a group of volcanic peaks in the {{nobr|[[Pacific Ranges]]}} of the [[Coast Mountains]] in southwestern [[British Columbia]], Canada. Part of the [[Cascade Volcanoes|Cascade Volcanic Arc]] of western North America, it is located {{nowrap|{{Convert|150|km|mi|abbr=on}}}} north of [[Vancouver]] at the northern end of the [[Pemberton Valley]] and reaches a maximum elevation of {{nowrap|{{Convert|2680|m|ft|abbr=on}}}}. The massif is capped by several eroded volcanic edifices, including {{nobr|[[lava dome]]s}}, [[volcanic plug]]s and overlapping piles of lava flows; these form at least six major [[summit (topography)|summits]] including Mount Meager which is the second highest of the massif.

The [[Garibaldi Volcanic Belt]] (GVB) has a long history of eruptions and poses a threat to the surrounding region. Any [[volcanic hazard]] ranging from [[landslide]]s to eruptions could pose a significant risk to humans and wildlife. Although the massif has not erupted for more than 2,000&nbsp;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]] (IVENP) 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&nbsp;years. About 2,400&nbsp;years ago, an [[explosive eruption]] formed a [[volcanic crater]] on its northeastern flank and sent avalanches of hot ash, rock fragments and [[volcanic gas]]es down the northern flank of the volcano. Evidence for more recent volcanic activity has been documented at the volcano, such as [[hot spring]]s and [[earthquake]]s. The Mount Meager massif has also been the source of several large landslides in the past, including a massive [[debris flow]] in [[2010 Mount Meager landslide|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&nbsp;Panhandle]] for {{nowrap|{{Convert|1600|km|mi|abbr=on}}}}.<ref name="ALG"/><ref name="AAL">{{BCGNIS|id=21188|name=Coast Mountains|access-date=2011-07-02}}</ref> It is about {{nowrap|{{Convert|300|km|mi|abbr=on}}}} wide, cut by [[fjord]]s, 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.<ref name="AAL"/>

Valleys surrounding the massif contain [[old-growth forest]]s. The area also features [[wetland]] habitats, plants of the {{nobr|[[Populus trichocarpa|cottonwood]]-[[willow]]-[[thimbleberry]] association}} and [[epilobium glaberrimum|glaucous willowherb]]s. Wildlife such as [[gray wolf|wolves]], [[wolverine]], [[moose]], [[bird of prey|raptors]], [[black-tailed deer]], {{nobr|[[mountain goat]]s}} and [[waterfowl]] inhabit the area as well as [[grizzly bear|grizzly]] and [[American black bear|black]] [[bear]]s.<ref>{{cite web|title=Upper Lillooet Provincial Park|url=http://www.env.gov.bc.ca/bcparks/explore/parkpgs/up_lillooet/|publisher=[[BC Parks]]|access-date=2011-07-20}}</ref>

===Regional geomorphology===

====Garibaldi Volcanic Belt==== [[File:Cascadia subduction zone USGS.png|thumb|left|alt=Map of the Cascadia subduction zone and location of nearby volcanoes along coastal United States and Canada.|Area of the [[Cascadia subduction zone]], with the Mount Meager massif being the northernmost red triangle in the [[Cascade Volcanoes|Cascade Volcanic Arc]]]] The Mount Meager massif is part of the [[Garibaldi Volcanic Belt]] (GVB), the northernmost segment of the {{nobr|[[Cascade Volcanic Arc]]}}. This [[volcanic belt]] includes [[cinder cone]]s, [[caldera]]s, [[stratovolcano]]es and [[subglacial volcano]]es (volcanoes under glaciers or [[ice sheet]]s) that have been active in the last 10,000&nbsp;years.<ref>{{cite web|publisher=[[Natural Resources Canada]]|url=http://gsc.nrcan.gc.ca/volcanoes/cat/volcano_e.php?id=gvb_ocn_007|archive-url=https://web.archive.org/web/20110604152239/http://gsc.nrcan.gc.ca/volcanoes/cat/volcano_e.php?id=gvb_ocn_007|archive-date=2011-06-04|title=Opal Cone|work=Catalogue of Canadian volcanoes|date=2009-03-10|access-date=2010-07-06}}</ref><ref name="QN">{{cite web|publisher=[[Natural Resources Canada]]|url=http://gsc.nrcan.gc.ca/volcanoes/cat/volcano_e.php?id=gvb_scl_044|archive-url=https://web.archive.org/web/20110604152752/http://gsc.nrcan.gc.ca/volcanoes/cat/volcano_e.php?id=gvb_scl_044|archive-date=2011-06-04|title=Silverthrone Caldera|work=Catalogue of Canadian volcanoes|date=2009-03-10|access-date=2010-07-06}}</ref><ref>{{cite web|publisher=[[Natural Resources Canada]]|url=http://gsc.nrcan.gc.ca/volcanoes/cat/volcano_e.php?id=gvb_mpc_009|archive-url=https://web.archive.org/web/20110629141852/http://gsc.nrcan.gc.ca/volcanoes/cat/volcano_e.php?id=gvb_mpc_009|archive-date=2011-06-29|title=Mount Price|work=Catalogue of Canadian volcanoes|date=2009-03-10|access-date=2010-07-06}}</ref><ref>{{cite web|publisher=[[Natural Resources Canada]]|url=http://gsc.nrcan.gc.ca/volcanoes/cat/volcano_e.php?id=gvb_cdm_023|archive-url=https://web.archive.org/web/20110604162809/http://gsc.nrcan.gc.ca/volcanoes/cat/volcano_e.php?id=gvb_cdm_023|archive-date=2011-06-04|title=Cauldron Dome|work=Catalogue of Canadian volcanoes|date=2009-03-10|access-date=2010-07-06}}</ref> The latest [[explosive eruption]] in the Garibaldi Volcanic Belt occurred at a crater on the northeastern slope of the massif about 2,400&nbsp;years ago, which forms a clearly defined depression.<ref name="LLP"/><ref name="AAN"/>

The GVB extends north from the [[Watts Point volcanic centre|Watts Point volcano]] to at least as far as the Meager massif.<ref name="JQ">{{cite web|publisher=[[Natural Resources Canada]]|url=http://gsc.nrcan.gc.ca/volcanoes/cat/belt_garibaldi_e.php|archive-url=https://web.archive.org/web/20110604155110/http://gsc.nrcan.gc.ca/volcanoes/cat/belt_garibaldi_e.php|archive-date=2011-06-04|title=Garibaldi volcanic belt|work=Catalogue of Canadian volcanoes|date=2009-04-02|access-date=2010-07-06}}</ref><ref>{{cite web|publisher=[[Natural Resources Canada]]|url=http://gsc.nrcan.gc.ca/volcanoes/map/map_e.php?id=gvb|archive-url=https://web.archive.org/web/20110514005621/http://gsc.nrcan.gc.ca/volcanoes/map/map_e.php?id=gvb|archive-date=2011-05-14|title=Garibaldi Volcanic Belt|work=Map of Canadian volcanoes|date=2005-08-20|access-date=2010-07-06}}</ref> Because little is known about the volcanoes north of the massif, such as the [[Silverthrone Caldera|Silverthrone]] and {{nobr|[[Franklin Glacier Complex|Franklin Glacier volcanic complexes]]}}, experts disagree about their nature.<ref name="QN"/><ref name="BL">{{cite web|publisher=[[Natural Resources Canada]]|url=http://gsc.nrcan.gc.ca/volcanoes/cat/volcano_e.php?id=gvb_fgl_006|archive-url=https://web.archive.org/web/20110604151750/http://gsc.nrcan.gc.ca/volcanoes/cat/volcano_e.php?id=gvb_fgl_006|archive-date=2011-06-04|title=Flanklin Glacier|work=Catalogue of Canadian volcanoes|date=2009-03-10|access-date=2011-11-04}}</ref> 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.<ref name="DFI"/><ref name="HLK"/> It is also unclear whether the [[Milbanke Sound Cones]] are part of the Garibaldi Belt or formed by different tectonic processes.<ref>{{cite web|publisher=[[Natural Resources Canada]]|url=http://gsc.nrcan.gc.ca/volcanoes/cat/feature_milbanke_e.php|archive-url=https://web.archive.org/web/20110604145310/http://gsc.nrcan.gc.ca/volcanoes/cat/feature_milbanke_e.php|archive-date=2011-06-04|title=Anahim Volcanic Belt: Milbanke Sound cones|work=Catalogue of Canadian volcanoes|date=2009-04-14|access-date=2011-11-04}}</ref> However, there is evidence the Silverthrone and {{nobr|Franklin Glacier}} 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 [[rhyolite]]s, [[dacite]]s, [[andesite]]s and [[basaltic andesite]]s. Such rock types are produced by subduction zone volcanism indicating volcanism at Silverthrone and {{nobr|Franklin Glacier}} is probably related to [[subduction]]. If these two volcanoes are true Cascade Arc volcanoes, the {{nobr|Mount Meager}} massif is not the northernmost volcano of the Garibaldi Belt or the Cascade Arc.<ref>{{cite book|last1=Blakes|first1=Stephen|last2=Argles|first2=Tom|page=55|title=Growth and Destruction: Continental evolution at subduction zones|year=2003|publisher=[[The Open University]]|location=[[Milton Keynes]], [[United Kingdom]]|isbn=0-7492-5666-4}}</ref>

====Cascade Volcanic Arc==== [[Volcanism]] in the Cascade Volcanic Arc is caused by subduction of the [[Juan de Fuca Plate]] under the [[North American Plate]] at the {{nobr|Cascadia subduction zone}}.<ref>{{cite book|last1=Gillespie|first1=Alan R.|last2=Porter|first2=Stephen C.|last3=Atwater|first3=Brian F.|title=The Quaternary period in the United States|publisher=[[Elsevier]]|location=[[Amsterdam]], [[Netherlands]]|page=351|year=2004|isbn=0-444-51471-6 |url=https://books.google.com/books?id=ys2keOYC5AoC&q=The+Quaternary+period+in+the+United+States |access-date=2014-02-27}}</ref> This is a {{nowrap|{{Convert|1094|km|mi|abbr=on}}}} long [[fault zone]] lying {{nowrap|{{Convert|80|km|mi|abbr=on}}}} off the {{nobr|[[Pacific Northwest]]}} from [[Northern California]] to southwestern British Columbia. The plates move at a relative rate of more than {{nowrap|{{Convert|10|mm|in|abbr=on}}}} per year at an [[Angle#Types of angles|oblique angle]] to the subduction zone. Because of the huge fault area, the Cascadia subduction zone can produce large earthquakes of [[Moment magnitude scale|magnitude]] 7.0&nbsp;or greater. The interface between the Juan de Fuca and North American plates remains locked for periods of roughly 500&nbsp;years. During these periods, [[Stress (mechanics)|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&nbsp;years of stored energy in a massive earthquake.<ref name="ZEQ"/>

Unlike most subduction zones worldwide, there is no deep [[oceanic trench]] present along the [[continental margin]] in Cascadia.<ref name="CLI">{{cite web|url=http://www.nature.nps.gov/geology/usgsnps/province/cascade2.html|title=Pacific Mountain System&nbsp;– Cascades volcanoes|publisher=[[United States Geological Survey]]|date=2000-10-10|access-date=2010-03-05|archive-date=2011-12-11|archive-url=https://web.archive.org/web/20111211154105/http://www.nature.nps.gov/geology/usgsnps/province/cascade2.html|url-status=dead}}</ref> 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 (geology)|depression]], or area of sunken land. Massive floods from prehistoric [[Glacial Lake Missoula]] during the {{nowrap|[[Late Pleistocene]]}} also deposited large amounts of [[sediment]] into the trench.<ref name="ZZL">{{cite web|title=Cascade Ranges Volcanoes Compared |url=http://www.uwsp.edu/geo/projects/geoweb/participants/dutch/VTrips/CascadesComp.HTM |last=Dutch |first=Steven |date=2003-04-07 |access-date=2010-05-21 |url-status=dead |archive-url=https://web.archive.org/web/20120318021653/http://www4.uwsp.edu/geo/projects/geoweb/participants/dutch/VTrips/CascadesComp.HTM |archive-date=2012-03-18 }}</ref> However, as with other subduction zones the outer margin is slowly being compressed like a giant spring.<ref name="ZEQ">{{cite web|publisher=[[Natural Resources Canada]]|url=http://www.nrcan.gc.ca/earth-sciences/energy-mineral/geology/geodynamics/earthquake-processes/9141|archive-url=https://web.archive.org/web/20131122083619/http://www.nrcan.gc.ca/earth-sciences/energy-mineral/geology/geodynamics/earthquake-processes/9141|archive-date=2013-11-22|title=Cascadia Subduction Zone|date=2008-01-15|access-date=2010-03-06}}</ref> 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&nbsp;[[1700 Cascadia earthquake|Cascadia earthquake of January 26, 1700]].<ref name="LXI">{{cite web|url=http://www.earthquakescanada.nrcan.gc.ca/historic-historique/events/17000126-en.php|title=The M9 Cascadia Megathrust Earthquake of January 26, 1700|publisher=[[Natural Resources Canada]]|date=2010-03-03|access-date=2010-03-06}}</ref> 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 [[convergent boundary|convergence]] between the Juan de Fuca and North American plates, which converge at {{nowrap|{{Convert|3|cm|in|abbr=on}}}} to {{nowrap|{{Convert|4|cm|in|abbr=on}}}} per year, about half the rate of convergence from seven million years ago.<ref name="CLI"/>

===Local geography===

[[File:Garibaldi Volcanic Belt-en.svg|thumb|right|alt=Map showing the location of a zone with related volcanoes.|The location and extent of the [[Garibaldi Volcanic Belt]], showing its isolated volcanoes and related volcanic features]]

Six main summits constitute the Mount Meager massif. The highest and northernmost summit is {{nobr|[[Plinth Peak]]}} with an elevation of {{nowrap|{{Convert|2680|m|ft|abbr=on}}}}.<ref name="gvp"/><ref name="GSC"/> Mount Meager itself is {{nowrap|{{Convert|2650|m|ft|abbr=on}}}} in elevation.<ref name="GSC"/> [[Capricorn Mountain]] west of Mount Meager rises with an elevation of {{nowrap|{{Convert|2570|m|ft|abbr=on}}}}. Just west of Capricorn Mountain lies [[Mount Job]], {{nowrap|{{Convert|2493|m|ft|abbr=on}}}} in elevation.<ref name="gvp"/><ref name="GSC"/> [[Pylon Peak (Canada)|Pylon Peak]] with an elevation of {{nowrap|{{Convert|2481|m|ft|abbr=on}}}} is south of Capricorn Mountain and Mount Meager.<ref name="GSC"/> [[Devastator Peak]], also known as ''The Devastator''<!--As a name, "The Devastator" is entirely capitalized, as shown on BC Geographical Names.-->, has an elevation of {{nowrap|{{Convert|2315|m|ft|abbr=on}}}} and is the lowest and southernmost summit of the massif.<ref name="gvp"/><ref name="GSC"/>

Streams and glaciers have played a significant role in dissecting the massif, and its upper slopes are covered with snow and ice.<ref name="XH"/> Numerous feeder [[dike (geology)|dikes]] to older units, formed when magma intrudes into a crack then crystallizes as a [[sheet intrusion]], are exposed by deep erosion.<ref name="HLK"/> [[Perkin's Pillar]], a vertical tower of [[breccia]]ted lava, represented an erosional remnant of the massif until its collapse in June 2005.<ref name="LLP"/> More than 10&nbsp;streams drain [[meltwater]] from the Mount Meager massif, including {{nobr|Capricorn Creek}}, Job Creek, No Good Creek, Angel Creek, Devastation Creek, Canyon Creek and {{nobr|Affliction Creek}}.<ref name="XH"/> The massif is located within one of British Columbia's many territorial divisions known as the [[Lillooet Land District]].<ref name="QQQK"/>

===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 (state)|Washington]].<ref name="LLP">{{cite book|last=Monger|first=J.W.H.|chapter=Character of volcanism, volcanic hazards, and risk, northern end of the Cascade magmatic arc, British Columbia and Washington State|pages=231, 241, 242|title=Geology and Geological Hazards of the Vancouver Region, Southwestern British Columbia|year=1994|publisher=[[Natural Resources Canada]]|location=[[Ottawa]], [[Ontario]]|isbn=0-660-15784-5}}</ref> It consists of at least four overlapping stratovolcanoes that are younger from south to north.<ref name="HLK"/> With a total volume of {{nowrap|{{Convert|20|km3|mi3|abbr=on}}}}, the massif is older than most volcanoes in the Cascade Arc, tracing its history back to 2,200,000&nbsp;years ago.<ref name="LLP"/><ref name="HLK"/> In the [[Cascade Range]], the oldest volcanoes are generally no more than a million years old.<ref name="AB">{{cite book|title=Climbing the Cascade Volcanoes|last=Smoot|first=Jeff|publisher=[[Globe Pequot Press]]|location=[[Guilford, Connecticut]]|page=9|year=1999|isbn=1-56044-889-X}}</ref> This includes [[Mount Rainier]] (500,000&nbsp;years&nbsp;old),<ref>{{cite book|title=Mountains|last=Aleshire|first=Peter|publisher=[[Infobase Publishing]]|location=[[New York City]], [[New York (state)|New York]]|page=[https://archive.org/details/mountains0000ales/page/97 97]|year=2008|isbn=978-0-8160-5918-8|url-access=registration|url=https://archive.org/details/mountains0000ales/page/97}}</ref> [[Lassen Peak]] (25,000&nbsp;years old),<ref name="HLK"/> [[Mount Jefferson (Oregon)|Mount Jefferson]] (290,000&nbsp;years old)<ref name="HLK"/> and [[Mount St. Helens]] (50,000&nbsp;years old).<ref name="HLK"/> However, portions of the massif formed in the last million years.<ref name="ALG"/> The volcano is made of [[volcanic rock]]s ranging from [[rhyodacite]] to [[basalt]]. Rhyodacite forms a series of eroded [[volcanic plug]]s which form the highest peaks. Their slopes are covered with their eruptive products and serve as the surface expressions of [[intrusion]]s. As a result, they provide a unique opportunity to study the relationships between [[magma chamber]]s and their lavas. The [[mafic]] (rich in [[magnesium]] and [[iron]]), [[intermediate composition|intermediate]] (between mafic and felsic) and [[felsic]] (rich in [[feldspar]] and [[quartz]]) volcanic rocks of the massif were erupted from at least eight volcanic vents.<ref name="HLK"/>

===Bridge River Vent=== {{Main|Bridge River Vent}} [[File:Bridge River Vent ice and debris.jpg|thumb|right|alt=A glaciated mountain rising over a forested valley.|The glaciated northeastern flank of Plinth Peak. Also shown is the inconspicuous ice and debris-covered [[Bridge River Vent]] in the middle of the photo.]] The Bridge River Vent is a relatively young volcanic crater that formed during an eruption about 2,400&nbsp;years ago.<ref name="XH"/><ref>{{cite web|publisher=[[Natural Resources Canada]]|url=http://gsc.nrcan.gc.ca/volcanoes/cat/volcano_e.php?id=gvb_brv_033|archive-url=https://web.archive.org/web/20090608031656/http://gsc.nrcan.gc.ca/volcanoes/cat/volcano_e.php?id=gvb_brv_033|archive-date=2009-06-08|title=Bridge River Vent|work=Catalogue of Canadian volcanoes|date=2009-03-10|access-date=2011-10-09}}</ref> This eruption ranged in character from explosive to effusive and involved [[lava dome]] extrusion, [[pyroclastic flow]]s, [[lahar]]s and lava flows.<ref name="gvp"/> Eastward migration of the {{nobr|[[eruption column]]}} spread material across [[Western Canada]] to deposit the [[Bridge River Ash]]. In the {{nobr|[[Bridge River]]}} and Lillooet River area the ash occurs as a coarse-textured deposit with blocks of [[pumice]] up to {{nowrap|{{Convert|10|cm|in|abbr=on}}}} in diameter. The texture rapidly becomes finer eastward from the Bridge River. At Big Bar on the [[Fraser River]] pellets are up to {{nowrap|{{Convert|3|mm|in|abbr=on}}}} in diameter while pellets in the Messiter area have a maximum diameter of {{nowrap|{{Convert|0.7|mm|in|abbr=on}}}}.<ref>{{cite journal|last1=Nasmith|first1=H.|last2=Mathews|first2=W. H.|last3=Rouse|first3=G. E.|journal=[[Canadian Journal of Earth Sciences]]|title=Bridge River Ash and Some Other Recent Ash Beds in British Columbia|publisher=[[NRC Research Press]]|location=[[Ottawa]], [[Ontario]]|volume=4|issue=1|pages=163–170|year=1967|issn=0008-4077|doi=10.1139/e67-007|bibcode=1967CaJES...4..163N}}</ref>

Situated on the northeastern flank of Plinth Peak, the Bridge River Vent has an elevation of {{nowrap|{{Convert|1524|m|ft|abbr=on}}}}.<ref name="gvp"/> It has oversteepened walls covered with ice and debris from volcanic activity and slope collapses.<ref name="ALG"/><ref name="gvp"/> The crater is roughly bowl-shaped, although it is breached on the northern side.<ref name="gvp"/> 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 (flowing laterally rather than vertically toward the surface) of magma from a reservoir to produce such eruptions.<ref>{{cite journal |last1=Acocella |first1=V. |last2=Neri |first2=M. |title=What makes flank eruptions? The 2001 Etna eruption and its possible triggering mechanisms |publisher=[[Springer-Verlag]] |location=[[Berlin]], [[Germany]] |page=518 |year=2003 |bibcode=2003BVol...65..517A |volume=65 |journal=Bulletin of Volcanology |doi=10.1007/s00445-003-0280-3 |issue=7|s2cid=16202578 }}</ref>

==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 {{nobr|Mount Meager}}. According to a [[BC&nbsp;Geographical&nbsp;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.<ref name="QQQK"/> Despite its official name, Mount Meager is sometimes mistakenly spelled ''Mount Meagre'' or {{nobr|''Mount Meagher''}}.<ref>{{cite book|last1=Halstead|last2=E.C.|title=Ground water supply&nbsp;– Fraser Lowland, British Columbia|page=60|year=1986|publisher=National Hydrology Research Institute|location=[[Saskatoon]], [[Saskatchewan]]|isbn=0-662-15086-4}}</ref>

[[File:Meager Group3.jpg|thumb|left|alt=A multi-peak mountain raising above trees and a paved road|The Mount Meager massif on February 11, 2006]] The massif's peak names were submitted by Canadian mountaineer [[Neal Carter (mountaineer)|Neal M. Carter]], who was a member of the [[British&nbsp;Columbia&nbsp;Mountaineering&nbsp;Club]]. Devastator Peak was officially named on {{nobr|August 3, 1977}} in association with Devastation Glacier.<ref>{{BCGNIS|id=14555|name=Devastator Peak|access-date=2011-07-06}}</ref> Plinth Peak was officially named on {{nobr|September 6, 1951}} as identified in Carter's 1932 sketch map and article "Explorations in the Lillooet River Watershed".<ref>{{BCGNIS|id=16912|name=Plinth Peak|access-date=2011-07-06}}</ref> 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.<ref>{{BCGNIS|id=26264|name=Mount Job|access-date=2011-07-06}}</ref><ref>{{BCGNIS|id=21386|name=Pylon Peak|access-date=2011-07-06}}</ref> 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 [Perkins] to the stream which drains the Capricorn glacier at its base". Subsequently, the peak was renamed to {{nobr|Capricorn Mountain}} on June 22, 1967.<ref>{{BCGNIS|id=11155|name=Capricorn Mountain|access-date=2011-07-06}}</ref>

===Mining and geothermal energy=== A large pumice [[outcrop]] more than {{nowrap|{{Convert|2000|m|ft|abbr=on}}}} long and {{nowrap|{{Convert|1000|m|ft|abbr=on}}}} wide has been the subject of [[mining]] operations since at least the 1970s. The deposit was first held by J. MacIsaac. In the mid-1970s the second owner W. H. Willes investigated and mined the pumice. It was crushed, removed and stored close to the village of [[Pemberton, British Columbia|Pemberton]]. Later the bridge that was used to access the pumice deposit was washed out and mining operations were not renewed. Mining resumed in 1988 when the deposit was staked by L. B. Bustin. In 1990 the pumice outcrop was bought by D. R. Carefoot from the owners B. Chore and M. Beaupre. In a program from 1991 to 1992 workers evaluated the deposit for its properties as a construction material and as an absorber for oil and [[stone washing|stonewash]]. About {{nowrap|{{Convert|7500|m3|ft3|abbr=on}}}} of pumice was mined in 1998 by the {{nowrap|Great Pacific Pumice Incorporation}}.<ref>{{cite web|url=http://minfile.gov.bc.ca/Summary.aspx?minfilno=092JW+040|publisher=[[Government of British Columbia]]|work=MINFILE Mineral Inventory|title=Mount Meager, Lillooet River Pumice, Pum, Great Pacific, Mt. Meager Pumice|date=1998-12-04|access-date=2010-03-16}}</ref>

The Mount Meager massif has been investigated as a potential [[geothermal energy]] resource. At least 16&nbsp;geothermal sites have been identified in {{nobr|British Columbia}}, the Mount Meager area being one of the five areas most capable of commercial development. At Meager Creek, there is potential for commercial development of a 100–200&nbsp;[[megawatt]] [[power station]]. Nearby {{nowrap|Pebble Creek}} also has "very good" potential for a 200&nbsp;megawatt plant.<ref name="AAP">{{cite web|url=http://www.bchydro.com/etc/medialib/internet/documents/environment/pdf/green_energy_study.Par.0001.File.greenenergystudy-summary.pdf |archive-url=https://web.archive.org/web/20110611224244/http://www.bchydro.com/etc/medialib/internet/documents/environment/pdf/green_energy_study.Par.0001.File.greenenergystudy-summary.pdf |archive-date=2011-06-11 |title=BC Hydro Green & Alternative Energy Division |publisher=[[BC Hydro]] |year=2002 |page=20 |access-date=2011-07-20 |url-status=dead }}</ref> Because the two creeks offer the greatest potential for commercial development, the Mount Meager area is the most promising site for [[geothermal power]] development in British Columbia.<ref name="gvp"/><ref name="AAP"/>

==Volcanic history== [[File:Eruptive history of the Mount Meager Volcanic Complex.png|thumb|right|350px|alt=A graph showing the eruptive history of a volcano.|Diagrammatic representation of eruptive activity at the Mount Meager massif in millions of years (Ma). Height of the [[histogram]] gives a very crude indication of the size of the event. The latest event about 2,400&nbsp;years ago (shown in the histograph as the latest eruption) was similar to the [[1980 eruption of Mount St. Helens]]. Eruptive events marked with question marks are those with uncertain identity.]] At least 54&nbsp;eruptions have occurred at the massif in the last 2,600,000&nbsp;years, ranging in character from [[Effusive eruption|effusive]] to explosive.<ref name="LLP"/><ref name="AAN">{{cite web|publisher=[[Natural Resources Canada]]|url=http://gsc.nrcan.gc.ca/volcanoes/cat/feature_meager_e.php|archive-url=https://web.archive.org/web/20090606072234/http://gsc.nrcan.gc.ca/volcanoes/cat/feature_meager_e.php|archive-date=2009-06-06|title=Garibaldi volcano belt: Mount Meager volcanic field|work=Catalogue of Canadian volcanoes|date=2009-04-01|access-date=2010-07-06}}</ref><ref name="ZL"/> Four primary eruptive periods have been identified, with individual eruptions separated by thousands of years.<ref name="HLK">{{cite book|last1=Wood|first1=Charles A.|author2=Kienle, Jürgen|pages=113, 141, 149, 161, 177, 218 |title=Volcanoes of North America: United States and Canada|year=1990|publisher=[[Cambridge University Press]]|location=[[Cambridge]], [[England]]|isbn=0-521-43811-X}}</ref><ref name="ZL"/> Large northwest–southeast trending structures paralleling [[Harrison Lake]] and the [[Pemberton Valley]] may control volcanic activity at the volcano or at least create zones of [[crust (geology)|crustal]] weakness that are penetrated by rising magma batches.<ref name="LLP"/>

===First record of activity=== During the first eruptive period between 2,200,000&nbsp;and 1,900,000&nbsp;years ago, eruption of intermediate to felsic pyroclastic rocks occurred at the southern end of the massif.<ref name="DFI">{{cite book|last1=Stelling|first1=Pete|last2=Tucker|first2=David S.|pages=2, 14, 15|title=Floods, Faults, and Fire: Geological Field Trips in Washington State and Southwest British Columbia|year=2007|publisher=[[Geological Society of America]]|location=[[Boulder, Colorado]]|isbn=978-0-8137-0009-0}}</ref><ref name="HLK"/> Basal breccia, perhaps from an exhumed vent, underlies andesite and [[tuff]]s, flows, lava domes and breccia of Devastator Peak.<ref name="DFI"/> It has a maximum thickness of {{nowrap|{{Convert|300|m|ft|abbr=on}}}} and overlies a {{nowrap|{{Convert|400|m|ft|abbr=on}}}} high ridge of [[bedrock]] that formed between 251,000,000&nbsp;and 65,500,000&nbsp;years ago during the [[Mesozoic]] era.<ref name="ALG"/>

At the southwestern end of the massif, dacite with sparse [[phenocryst]]s (large and conspicuous crystals) of [[quartz]], [[plagioclase]] and [[hornblende]] represents a {{nowrap|{{Convert|200|m|ft|abbr=on}}}} thick remnant of subhorizontal lava flows.<ref name="ALG"/> Although the first eruptive period is generally estimated to have started about 2,200,000&nbsp;years ago, two andesite eruptions may have occurred about 2,400,000&nbsp;and 2,600,000&nbsp;years ago. The first might have produced lava flows and breccia, whereas the latter may have erupted mainly breccia.<ref name="ZL"/>

===The Devastator and Pylon assemblage eruptive periods=== The second eruptive period between 1,600,000&nbsp;and 1,400,000&nbsp;years ago produced rhyodacite tuff, breccia, lavas and domes of {{nobr|[[The Devastator Assemblage]]}}.<ref name="DFI"/><ref name="ZL"/> This {{nowrap|{{Convert|500|m|ft|abbr=on}}}} thick geological formation lies on the south and west flanks of Pylon Peak and Devastator Peak. Its western portion consists of roughly layered [[tephra]] while its eastern end represents the lava flows and [[subvolcanic rock|subvolcanic]] intrusions of a partly preserved vent. Here, The Devastator Assemblage is massive and steeply truncates basal breccia from the first eruptive period.<ref name="ALG"/>

Volcanic activity of the third eruptive period occurred between 1,100,000&nbsp;and 200,000&nbsp;years ago. A thick sequence of andesite lava flows were erupted from the [[volcanic plug]] of Devastator Peak, creating the [[Pylon Assemblage]].<ref name="ALG"/><ref name="ZL"/> With a maximum thickness of more than {{nowrap|{{Convert|1|km|mi|abbr=on}}}}, the Pylon Assemblage is the largest rock unit comprising the Mount Meager massif.<ref name="AAN"/><ref name="DFI"/> The lava flows are layered, separated by a thin layer of [[lapilli tuff]] and reddened breccia. A concentration of subvolcanic intrusions and coarse volcanic breccia clasts more than {{nowrap|{{Convert|100|m|ft|abbr=on}}}} in length suggest that Devastator Peak is a major vent.<ref name="ALG"/>

===Formation of the Plinth, Job, Capricorn and Mosaic assemblages=== The fourth and final eruptive period 150,000&nbsp;to less than 3,000 years ago produced rhyodacite lava flows, domes, breccias and subvolcanic intrusions of the Plinth, Job and Capricorn assemblages.<ref name="DFI"/><ref name="HLK"/> Around Mount Job, [[porphyritic]] hornblende, [[biotite]] and quartz rhyodacite lava flows of the [[Job Assemblage]] were erupted. They are prominently layered and locally [[columnar jointing|columnar jointed]]. On the east side of Affliction Glacier, they overlie porphyritic andesite lava flows of the Pylon Assemblage. Later, rhyodacite lava flows of the [[Capricorn Assemblage]] were erupted and flowed over biotite rhyodacite of the Job Assemblage. The upper {{nowrap|{{Convert|600|m|ft|abbr=on}}}} of Capricorn Mountain and Mount Job are formed by these lava flows.<ref name="ALG"/>

[[File:Meager ash-fall and pyroclastic flow deposits.jpg|thumb|left|alt=A rocky cliff with a person at its base.|A geologist next to a tree trunk that was buried by [[pyroclastic fall|ash-fall]] deposits and then overrun by a [[pyroclastic flow]] from the Bridge River Vent eruption about 2,400&nbsp;years ago]] Another sequence of rhyodacite lava flows were subsequently erupted and form the [[Plinth Assemblage]]. Mount Meager, a massive lava dome or volcanic plug, consists of steeply inclined flow layering and was the southern source of Plinth Assemblage lava flows and breccias. Plinth Peak was also formed during the Plinth Assemblage eruptive stage and is mostly composed of prominent columnar or partly jointed lava flows. Its north ridge and flat-topped summit contain three areas of steep flow layering and subhorizontally-oriented columnar jointing. These areas are possibly the remains of volcanic plugs or lava domes that were the northern source of Plinth Assemblage lava flows.<ref name="ALG"/> The [[Mosaic Assemblage]], a sparsely porphyritic plagioclase-[[augite]]-[[olivine]] basalt and [[trachybasalt]] formation, also formed during the fourth eruptive period. It is the remains of [[scoria]]ceous lava flows, breccias, [[volcanic bomb]]s and {{nobr|[[pillow lava]]s}}.<ref name="ALG">{{cite journal|last1=Read|first1=Peter B.|year=1990|title=Mount Meager Complex, Garibaldi Belt, Southwestern British Columbia|journal=Articles|volume=17|issue=3|pages=167, 168, 169, 170|publisher=[[St. John's, Newfoundland]]|issn=1911-4850}}</ref><ref name="DFI"/>

The best known and most documented eruption of the Mount Meager massif is a [[Bridge River Vent#400s BC eruption|large explosive eruption]] that occurred about 2,400&nbsp;years ago.<ref name="XH"/> This eruption, which likely reached 5&nbsp;on the {{nobr|[[Volcanic Explosivity Index]] (VEI)}}, was similar to the [[1980 eruption of Mount St. Helens]].<ref name="gvp"/><ref>{{cite web|url=http://gsc.nrcan.gc.ca/volcanoes/map/index_e.php|archive-url=https://web.archive.org/web/20110514004904/http://gsc.nrcan.gc.ca/volcanoes/map/index_e.php|archive-date=2011-05-14|title=Map of Canadian volcanoes|work=Volcanoes of Canada|publisher=[[Natural Resources Canada]]|date=2008-02-13|access-date=2011-07-14}}</ref> It sent a massive [[Plinian eruption|Plinian column]] at least {{nowrap|{{Convert|20|km|mi|abbr=on}}}} high into the [[atmosphere of Earth|atmosphere]]. [[Westerlies|Prevailing westerly winds]] carried [[volcanic ash]] from this explosion eastwards to as far as [[Alberta]]. Nearby areas were devastated by heavy [[pyroclastic fall]] when parts of the Plinian column collapsed. Later, a series of [[pyroclastic flow]]s were erupted and travelled {{nowrap|{{Convert|7|km|mi|abbr=on}}}} downstream. After this, a lava flow was erupted that repeatedly collapsed on the steep slopes of Plinth Peak, creating a thick, welded breccia deposit that blocked the Lillooet River. This created a lake just upstream which later collapsed to produce a massive {{nobr|[[outburst flood]]}}. Large boulders were carried downstream for more than {{nowrap|{{Convert|2|km|mi|abbr=on}}}}, but the destructive floodwaters continued further. Later, a small dacite lava flow was erupted, which cooled into well-preserved columnar joints.<ref name="AAN"/> The entire eruption cycle originated from the Bridge River Vent on the northeastern flank of Plinth Peak. This is the latest known eruption of the Mount Meager massif, as well as the largest known Holocene explosive eruption in Canada. However, it is unknown when this eruption ended.<ref name="gvp"/>

In 1977, J. A. Westgate of the [[University of Toronto]] suggested that a smaller eruption may have occurred at the Bridge River Vent after the eruption 2,400&nbsp;years ago, sending tephra southeast. A tephra deposit overlying the Bridge River Ash at Otter Creek shows strong genetic relationships with the Bridge River Ash, differing only by its absence of biotite. In earlier publications, this tephra is classified as part of the Bridge River Ash. However, it has been dated to be about 2,000&nbsp;[[radiocarbon year]]s old, indicating that this tephra is a few hundred years younger than the Bridge River Ash. Apparent absence of biotite and occurrence well south of the Bridge River Ash likewise favour a separate identity.<ref>{{cite journal|title=Identification and significance of late Holocene tephra from Otter Creek, southern British Columbia, and localities in west-central Alberta|journal=Canadian Journal of Earth Sciences|publisher=[[NRC Research Press]]|location=[[Ottawa]], [[Ontario]]|year=1977|volume=14|page=2595|issn=0008-4077|bibcode=1977CaJES..14.2593W|last1=Westgate|first1=J. A.|doi=10.1139/e77-224|issue=11}}</ref> Large-volume, fine-grained debris flows north of the volcano might have been caused by volcanic activity. If this is correct, the knowledge of eruptions at the Mount Meager massif in the last 10,000&nbsp;years is insufficient.<ref name="LLP"/>

===Recent activity=== [[File:Meager hot spring.jpg|thumb|right|alt=Steaming pool of water surrounded by a group of rocks.|A [[hot spring]] near [[Meager Creek]] related to [[volcanism]] at the massif]] Two small hot spring clusters are found at the Mount Meager massif, indicating magmatic heat is still present.<ref name="AAN"/> These two clusters of hot springs, known as the Meager Creek Hot Springs and {{nobr|Pebble Creek Hot Springs}}, are most likely related to recent volcanic activity at the massif.<ref name="gvp"/><ref name="GSC"/> The {{nowrap|Meager Creek Hot Springs}}, the largest in British Columbia, remain free of snow for most of the year.<ref name="GSC">{{Cite journal|title=Geological Survey of Canada, Open File 5906|last=Jessop|first=A.|publisher=[[Natural Resources Canada]]|location=[[Ottawa]], [[Ontario]]|year=2008|pages=33, 35}}</ref><ref>{{cite book|last=Gardner|first=Matthew|title=Western Canada|publisher=Footprint Handbooks Ltd|location=[[Bath, England]]|page=[https://archive.org/details/westerncanada0000gard/page/157 157]|year=2008|isbn=978-1-906098-26-1 |url=https://archive.org/details/westerncanada0000gard |url-access=registration|access-date=2014-02-27}}</ref> The springs at the Mount Meager massif might be evidence of a shallow magma chamber beneath the surface.<ref>{{cite journal|last=Woodsworth|first=Glenn J.|publisher=Gold Commissioner's Office|location=[[Vancouver]], [[British Columbia]]|title=Geology and Geothermal Potential of the AWA Claim Group, Squamish, British Columbia|page=10|date=April 2003}}</ref>

Between 1970 and 2005 more than 20&nbsp;small earthquakes were recorded at the volcano. The [[Surface wave magnitude|magnitudes]] of these events were generally no higher than 2.0&nbsp;on the [[Richter magnitude scale]] and they originated {{nowrap|{{Convert|20|km|mi|abbr=on}}}} to less than {{nowrap|{{Convert|1|km|mi|abbr=on}}}} below the surface.<ref name="XH">{{cite journal|title=Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards|journal=Hazard and Risk from Large Landslides from Mount Meager Volcano, British Columbia, Canada |last1=Friele |first1=Pierre |last2=Jakob |first2=Matthias |last3=Clague |first3=John |publisher=[[Taylor & Francis]]|location=[[United Kingdom]]|pages=48, 49, 50, 56 |volume=2 |issue=1|issn=1749-9518 |year=2008 |oclc=123714937 |doi=10.1080/17499510801958711 |s2cid=15157361 }}</ref> Other volcanoes in the {{nobr|Garibaldi Volcanic Belt}} with recorded [[seismicity]] include [[Mount Garibaldi]], [[Mount Cayley]] and {{nobr|Silverthrone Caldera}}.<ref name="ZBR">{{cite book|last1=Etkin|first1=David|author2=Haque, C.E. and Brooks, Gregory R.|title=An Assessment of Natural Hazards and Disasters in Canada|publisher=[[Springer Science+Business Media]]|location=[[Berlin]], [[Germany]]|date=2003-04-30|pages=569, 582, 583|isbn=978-1-4020-1179-5 |url=https://books.google.com/books?id=kaJz_SNNuKMC&q=An+Assessment+of+Natural+Hazards+and+Disasters+in+Canada&pg=PR7 |access-date=2014-02-27}}</ref> Seismic data suggest that these volcanoes still contain active magma chambers, indicating that some Garibaldi Belt volcanoes are probably active with significant potential hazards.<ref name="ZBR"/><ref name="AK">{{cite web|publisher=[[Natural Resources Canada]] |url=http://198.103.48.70/volcanoes/gscvol_e.php |title=Volcanology in the Geological Survey of Canada |work=Volcanoes of Canada |date=2007-10-10 |access-date=2010-07-06 |url-status=bot: unknown |archive-url=https://web.archive.org/web/20110412214415/http://198.103.48.70/volcanoes/gscvol_e.php |archive-date=2011-04-12 }}</ref> The seismic activity corresponds with some of Canada's recently formed volcanoes and with persistent volcanoes that have had major explosive activity throughout their history such as Mount Garibaldi and the Mount Cayley and Mount Meager massifs.<ref name="ZBR"/>

[[Fumarolic]] activity and [[sulfur]] smells were detected at the massif in 2016, with a fumarole field discovered on the Job Glacier.<ref name="CBC">{{cite web|title=Dormant B.C. volcano sparks with activity|url=http://www.cbc.ca/news/canada/british-columbia/meager-mountain-volcanic-explosion-1.3792808|publisher=[[CBC News]]|date=2016-10-05|access-date=2017-12-08}}</ref><ref>{{cite document|last1=Roberti|first1=G.|last2=Ward|first2=B.|last3=van Wyk de Vries|first3=B.|last4=Falorni|first4=G.|last5=Menounos|first5=B.|last6=Friele|first6=P.|last7=Williams-Jones|first7=G.|last8=Clague|first8=J. J.|last9=Perotti|first9=G.|last10=Giardino|first10=M.|last11=Baldeon|first11=G.|last12=Freschi|first12=S.|title=Landslides and glacier retreat at Mt. Meager volcano: hazard and rish challenges|publisher=[[Simon Fraser University]]|page=7|year=2018}}</ref> This was followed by [[prediction of volcanic activity|monitoring]] of the mountain by [[Natural Resources Canada]] [[volcanologist]]s, the results of which did not detect much seismicity. The fumarole field was considered unsafe to approach or enter due to the presence of [[hydrogen sulfide]] and potentially unstable ice crevasses.<ref name="CBC"/>

==Threats and preparedness==

===Eruptions=== The Mount Meager massif remains a major volcanic hazard, capable of producing highly explosive eruptions. A full-scale eruption would threaten many populated areas throughout southern British Columbia and Alberta. [[Pemberton, British Columbia|Pemberton]], a community {{nowrap|{{Convert|50|km|mi|abbr=on}}}} downstream from the massif, faces high risk.<ref name="AAN"/> If the volcano were to erupt violently, it would disrupt the Lillooet River fishery as well as nearby [[mining]] and [[logging]] activity.<ref name="AAN"/> In addition, the Mount Meager massif lies in the immediate proximity of a major [[airway (aviation)|air traffic route]].<ref>{{cite web|url=http://198.103.48.70/volcanoes/haz_e.php |title=Volcanic hazards |work=Volcanoes of Canada |publisher=[[Natural Resources Canada]] |date=2009-04-02 |access-date=2011-07-23 |url-status=bot: unknown |archive-url=https://web.archive.org/web/20110410173636/http://198.103.48.70/volcanoes/haz_e.php |archive-date=2011-04-10 }}</ref> Volcanic ash reduces visibility and can cause jet engine failure, as well as damage to flight control systems.<ref>{{cite web|last1=Neal|first1=Christina A. |author-link1=Christina Neal |last2=Casadevall|first2=Thomas J.|last3=Miller|first3=Thomas P.|last4=Hendley II|first4=James W.|last5=Stauffer|first5=Peter H.|title=Volcanic Ash–Danger to Aircraft in the North Pacific|publisher=[[United States Geological Survey]]|date=2004-10-14|url=https://pubs.usgs.gov/fs/fs030-97/|access-date=2011-07-23}}</ref> Even a minor eruption from the volcano could cause massive devastation by rapidly melting glacial ice to produce large debris flows. An example of such an event is the 1985 [[Armero tragedy]] in [[Colombia]], which resulted from a small eruption under the summit ice cap of [[Nevado del Ruiz]].<ref name="QKF">{{cite web|url=https://www.sfu.ca/volcanology/pdfs/Roberti_Geohaz%2718.pdf|last1=Roberti|first1=G.|last2=B.|first2=Ward|last3=van Wyk de Vries|first3=B.|last4=Falomi|first4=G.|last5=Menounos|first5=B.|last6=Friele|first6=P.|last7=Williams-Jones|first7=G.|last8=J. Clague|first8=J.|last9=Perotti|first9=G.|last10=Giardino|first10=M.|last11=Baldeon|first11=G.|last12=Freschi|first12=S.|title=Landslides and glacier retreat at Mt. Meager volcano: hazard and rish challenges|publisher=[[Simon Fraser University]]|year=2018|access-date=2018-11-05|archive-date=2021-07-17|archive-url=https://web.archive.org/web/20210717085644/https://www.sfu.ca/volcanology/pdfs/Roberti_Geohaz%2718.pdf|url-status=dead}}</ref>

[[File:Bridge River Vent pyroclastic flow.jpg|thumb|left|alt=A valley-engulfed forest rising above a rocky cliff.|This pyroclastic flow deposit forms the foreground canyon wall on the [[Lillooet River]]. It erupted from the Bridge River Vent on the northeastern flank of Plinth Peak.]] [[Jack Souther]], a leading authority on geothermal resources and volcanism in the Canadian Cordillera, expressed concern about the potential for another eruption: <blockquote>At present the volcanoes of the Garibaldi Belt are quiet, presumed dead but still not completely cold. But the flare-up of Meager Mountain 2,500&nbsp;years ago raises the question, "Could it happen again?" Was the explosive eruption of Meager Mountain the last gasp of the Garibaldi Volcanic Belt or only the most recent event in its on-going life? The short answer is nobody really knows for sure. So just in case I sometimes do a quick check of the old hot-spots when I get off the Peak Chair.<ref>{{cite web|url=http://www.cangea.ca/images/uploads/Jack_Souther_Biography.pdf |archive-url=https://www.webcitation.org/5tfQWFYBa?url=http://www.cangea.ca/images/uploads/Jack_Souther_Biography.pdf |archive-date=2010-10-22 |title=CanGEA {{Sic|?|nolink=y|Honou|rary|expected=Honorary}} Member 2008 Dr. Jack Souther |publisher=Canadian Geothermal Energy Association |access-date=2010-03-04 |url-status=dead }}</ref></blockquote>

Because of concerns about potential eruptions and danger to communities in the area, the {{nobr|[[Geological Survey of Canada]]}} plans to create [[hazard map]]s and emergency plans for the Mount Meager massif as well as Mount Cayley to the south.<ref name="AK"/> Although very few eruptions in Canada have been witnessed by people, it remains nonetheless an area of intense volcanic activity. According to the Geologic Hazards '91 Workshop, "priority should be given to eruption impact studies of the two recently active volcanic centres closest to urban areas, Mount Baker and Mount Meager. The former case will require a combined US-Canada-Washington State-B.C. effort".<ref name="ZL">{{cite journal |title=Geologic Hazards in British Columbia |journal=Volcanic Hazards |last1=Bobrowsky |first1=Peter |publisher=Geologic Hazards '91 Workshop |location=[[Victoria, British Columbia]]|pages=5, 41, 54|issn=0835-3530|year=1992|oclc=14209458 }}</ref>

The Mount Meager massif is not monitored closely enough by the {{nobr|Geological Survey of Canada}} to ascertain how active its magma system is. The [[Canadian National Seismograph Network]] has been established to monitor earthquakes throughout Canada, but it is too far away to provide an accurate indication of activity under the mountain. It may sense an increase in seismic activity if the massif becomes highly restless, but this may only provide a warning for a large eruption; the system might detect activity only once the volcano has started erupting.<ref name="ALP">{{cite web|url=http://gsc.nrcan.gc.ca/volcanoes/mon_e.php|archive-url=https://web.archive.org/web/20110514011941/http://gsc.nrcan.gc.ca/volcanoes/mon_e.php|archive-date=2011-05-14|title=Monitoring volcanoes|work=Volcanoes of Canada|publisher=[[Natural Resources Canada]]|date=2009-02-26|access-date=2011-06-15}}</ref> If the Mount Meager massif were to erupt, mechanisms exist to orchestrate relief efforts. The Interagency Volcanic Event Notification Plan (IVENP) was created to outline the notification procedure of some of the main agencies that would respond to an erupting volcano in Canada, an eruption close to the [[Canada–United States border]] or any eruption that would affect Canada.<ref>{{cite web|url=http://gsc.nrcan.gc.ca/volcanoes/ivenp_e.php|archive-url=https://web.archive.org/web/20100221035040/http://gsc.nrcan.gc.ca/volcanoes/ivenp_e.php|archive-date=2010-02-21|title=Interagency Volcanic Event Notification Plan (IVENP)|work=Volcanoes of Canada|publisher=[[Natural Resources Canada]]|date=2008-06-04|access-date=2011-06-15}}</ref>

Although the Mount Meager massif is a potentially active volcano, as of 2016 there was no evidence of an imminent eruption.<ref name="AXE">{{cite journal|title=Preliminary drilling results from the Pemberton Valley, British Columbia|journal=Current Research |last1=Simpson|first1=K.A.|last2=Stasiuk|first2=M.V.|last3=Clague|first3=J.J.|last4=Evans|first4=S.G.|last5=Friele|first5=P.|publisher=[[Geological Survey of Canada]]|location=[[Ottawa]], [[Ontario]]|year=2003|page=6|issn=1701-4387}}</ref><ref name="CBC"/> Many shallow earthquakes normally occur before a volcano erupts. As magma rises to the surface over time, it will probably create much more vigour and heat at the regional hot springs, as well as the formation of new springs or [[fumarole]]s.<ref name="AXE"/> These signs generally occur for weeks, months or years before a potential eruption, although the possibility of an eruption occurring in the near future remains low.<ref name="ALP"/><ref name="AXE"/> A significant structural collapse associated with loss of glacial buttressing might affect the magma plumbing system and lead to an eruption.<ref name="QKF"/>

===Landslides=== Scientists have argued that the Mount Meager massif, made of altered volcanic rock which breaks apart easily, is the most unstable mountain massif in Canada<ref name="XH"/> and may also be its most active landslide area.<ref>{{cite book|title=Periglacial and Paraglacial Processes and Environments|page=229|publisher=[[Geological Society of London]] |location=[[London]], [[United Kingdom]] |last1=Knight |first1=J. |last2=Harrison |first2=S. |year=2009 |isbn=978-1-86239-281-6 |url=https://books.google.com/books?id=gdiaf4ZiTCUC&q=Periglacial+and+Paraglacial+Processes+and+Environments |access-date=2014-02-27}}</ref> More than 25&nbsp;landslides have occurred there in the last 8,000&nbsp;years,<ref name="XH"/> and debris flows, mainly from the massif, have also filled Meager Creek valley to a depth of {{nowrap|{{Convert|250|m|ft|abbr=on}}}}.<ref name="ALG"/>

Large volcano-associated debris flows known as lahars pose a threat to populated areas downstream from glaciated volcanoes.<ref name="ALC">{{cite web|url=https://pubs.usgs.gov/fs/fs002-97/|title=What Are Volcano Hazards?|publisher=[[United States Geological Survey]]|date=2010-08-24|access-date=2011-08-18}}</ref> Although lahars are typically associated with the effects of volcanic eruptions, they can occur whenever conditions allow collapse and movement of mud originating from existing [[volcanic ash]] deposits. Melting snow and ice, intense rainfall or the breakout of a summit [[Volcanic crater lake|crater lake]] can all generate lahars. Landslides at the Mount Meager massif may also be indirectly related to [[climate change]]. Several tension cracks extend up to the summit, and as [[global warming]] causes glaciers to melt, the meltwater reaches deep into the massif. It then flows along the ruptured surfaces creating landslide zones.<ref name="AF"/>

Because the Mount Meager massif is capable of producing large landslides, Meager Creek valley is probably the most dangerous valley in the {{nobr|[[Canadian Cordillera]]}}.<ref name="ALG"/> Rapidly growing communities down the Lillooet River valley, such as Pemberton,<ref name="AAN"/> are vulnerable despite their distance from the massif. As Pemberton continues to grow it will eventually extend into the surrounding mountains, creating a major hazard for people living there.<ref name="AF"/>

The landslide risk is somewhat mitigated by the Lillooet River Early Warning System which was established in 2014 to alert the Pemberton Valley of landslides. Monitoring is done by measuring the Lillooet River water level using two sensors: one on the Hurley River Forestry Bridge and the other in the river.<ref>{{cite web|last=Noel|first=Alyssa|title=Risk rising: Receding glaciers are making Pemberton-area volcano Mount Meager less stable than ever before|url=https://www.piquenewsmagazine.com/whistler/risk-rising/Content?oid=10617939|year=2018|access-date=2018-11-06}}</ref> Damming of the Lillooet River by a landslide would be indicated by the lowering of the water level while the release of a [[landslide dam]] would be followed by water level rise.<ref>{{cite web|url=https://www.pvdd.ca/files/2015NewsletterFinal.pdf|title=2015 Update|publisher=Pemberton Valley Dyking District|year=2015|access-date=2018-11-07}}</ref>

====Prehistoric==== {| class="wikitable sortable" |- ! scope="col" | Event ! scope="col" | Source ! scope="col" | Years before present ! scope="col" | Volume ! scope="col" | Reference<ref name="XH"/> |- | Rock avalanche/debris flow || Pylon Peak || 7900 || {{nowrap|450,000,000 m<sup>3</sup> (16,000,000,000 cu ft)}} || Friele and Clague (2004) |- | Rock avalanche/debris flow || Job Creek || 6250 || {{nowrap|500,000,000 m<sup>3</sup> (18,000,000,000 cu ft)}} || Friele ''et al.'' (2005) |- | Rock avalanche/debris flow || Capricorn Creek || 5250 || {{nowrap|{{Convert|5000000|m3|ft3|abbr=on}}}} || McNeely and McCuaig (1991) |- | Rock avalanche/debris flow/[[hyperconcentrated flow]] || Pylon Peak || 4400 || {{nowrap|200,000,000 m<sup>3</sup> (7,100,000,000 cu ft)}} || Friele and Clague (2004); Friele ''et al.'' (2005) |- | Rock avalanche/debris flow || Job Creek, eruption precursor || 2600 || {{nowrap|500,000,000 m<sup>3</sup> (18,000,000,000 cu ft)}} || Friele ''et al.'' (2005); Simpson ''et al.'' (2006) |- | Pyroclastic flow || Syn-eruptive || 2400 || {{nowrap|440,000,000 m<sup>3</sup> (16,000,000,000 cu ft)}} || Stasiuk ''et al.'' (1996); Stewart (2002) |- | Rock avalanche/outburst flood/debris flow/hyperconcentrated flow || Syn-eruptive || 2400 || {{nowrap|200,000,000 m<sup>3</sup> (7,100,000,000 cu ft)}} || Stasiuk ''et al.'' (1996); Stewart (2002) |- | Rock avalanche || Syn- to post-eruptive || 2400 || {{nowrap|44,000,000 m<sup>3</sup> (1,600,000,000 cu ft)}} || Stasiuk ''et al.'' (1996); Stewart (2002) |- | Debris flow || Job Creek || 2240 || {{nowrap|{{Convert|1,000,000|m3|ft3|abbr=on}}}} || Pierre, Jakob and Clague (2008) |- | Debris flow || Devastation Creek || 2170 || {{nowrap|{{Convert|12,000,000|m3|ft3|abbr=on}}}} || McNeely and McCuaig (1991) |- | Debris flow || Angel Creek || 1920 || {{nowrap|{{Convert|500000|m3|ft3|abbr=on}}}} || McNeely and McCuaig (1991) |- | Debris flow || Job Creek || 1860 || {{nowrap|{{Convert|1000000|m3|ft3|abbr=on}}}} || McNeely and McCuaig (1991) |- | Debris flow || Job Creek || 870 || {{nowrap|{{Convert|9000000|m3|ft3|abbr=on}}}} || Jordan (1994) |- | Debris flow || No Good Creek || 800 || {{nowrap|{{Convert|100000|m3|ft3|abbr=on}}}} || McNeely and McCuaig (1991) |- | Debris flow || Job Creek || 630 || {{nowrap|{{Convert|1000000|m3|ft3|abbr=on}}}} || Pierre, Jakob and Clague (2008) |- | Debris flow || No Good Creek || 370 || {{nowrap|{{Convert|5000000|m3|ft3|abbr=on}}}} || McNeely and McCuaig (1991) |- | Debris flow || Angel Creek || 210 || {{nowrap|{{Convert|100000|m3|ft3|abbr=on}}}} || McNeely and McCuaig (1991) |}

====Historic==== {| class="wikitable sortable" |- ! scope="col" | Event ! scope="col" | Source ! scope="col" | Year ! scope="col" | Volume ! scope="col" | Reference<ref name="XH"/><ref>{{Cite journal |last1=Guthrie |first1=R. H. |last2=Friele |first2=P. |last3=Allstadt |first3=K. |author-link3=Kate Allstadt |last4=Roberts |first4=N. |last5=Evans |first5=S. G. |last6=Delaney |first6=K. B. |last7=Roche |first7=D. |last8=Clague |first8=J. J. |last9=Jakob |first9=M. |date=2012-05-04 |title=The 6 August 2010 Mount Meager rock slide-debris flow, Coast Mountains, British Columbia: characteristics, dynamics, and implications for hazard and risk assessment |url=https://volcanoes.usgs.gov/vsc/file_mngr/file-87/nhess-12-1277-2012-Meagerlandslide.pdf |journal=Natural Hazards and Earth System Sciences |language=English |volume=12 |issue=5 |pages=1277–1294 |bibcode=2012NHESS..12.1277G |doi=10.5194/nhess-12-1277-2012 |issn=1561-8633 |s2cid=55793271 |id={{Researchgatepub|258685686}} |doi-access=free }}</ref>{{Rp|page=1280}} |- | Debris flow || Capricorn Creek || 1850 || {{nowrap|{{Convert|1300000|m3|ft3|abbr=on}}}} || Jakob (1996); McNeely and McCuaig (1991) |- | Debris flow || Capricorn Creek || 1903 || {{nowrap|30,000,000 m<sup>3</sup> (1,100,000,000 cu ft)}} || Jakob (1996) |- | Debris flow || Devastation Creek || 1931 || {{nowrap|{{Convert|3000000|m3|ft3|abbr=on}}}} || Carter (1931); Decker ''et al.'' (1977); Jordan (1994) |- | Rock avalanche || Capricorn Creek || 1933 || {{nowrap|{{Convert|500000|m3|ft3|abbr=on}}}} || Croft (1983) |- | Rock avalanche || Devastation Creek || 1947 || {{nowrap|{{Convert|3000000|m3|ft3|abbr=on}}}} || Read (1978) |- | Debris flow || Capricorn Creek || 1972 || {{nowrap|{{Convert|200000|m3|ft3|abbr=on}}}} || Jordan (1994) |- | [[1975 Devastation Glacier landslide|Rock avalanche]] || Devastation Creek || 1975 || {{nowrap|{{Convert|12000000|m3|ft3|abbr=on}}}} || Mokievsky-Zubot (1977); Evans (2001) |- | Debris flow || Affliction Creek || 1984 || {{nowrap|{{Convert|200000|m3|ft3|abbr=on}}}} || Jordan (1994) |- | Rock avalanche || Mount Meager || 1986 || {{nowrap|{{Convert|500000|m3|ft3|abbr=on}}}} || Evans (1987) |- | Debris flow || Capricorn Creek || 1998 || {{nowrap|{{Convert|1300000|m3|ft3|abbr=on}}}} || Bovis and Jakob (2000) |- | Debris flow || Capricorn Creek || 2009 || {{nowrap|{{Convert|500000|m3|ft3|abbr=on}}}} || Friele (unpublished data) |- | Rock slide/debris flow || Capricorn Creek || 2010 || {{nowrap|48,500,000 m<sup>3</sup> (1,710,000,000 cu ft)}} || Guthrie ''et al.'' (2012) |}

=====1975 landslide===== [[File:2010 Meager debris flow.jpg|thumb|right|alt=Two images showing the landscape of a large landslide.|These river valleys are filled with debris from the 2010 landslide of Mount Meager. Photo A is the collapsed debris dam near the intersection of Capricorn Creek and [[Meager Creek]]. Photo B is the debris flow at the junction of Meager Creek and the [[Lillooet River]].]] {{Main|1975 Devastation Glacier landslide}} A massive rock avalanche occurred at the massif on July 22, 1975. With a volume of {{nowrap|{{Convert|13000000|m3|ft3|abbr=on}}}}, it buried and killed a group of four geologists at the confluence of Devastation Creek and Meager Creek.<ref name="KKV">{{cite journal|title=The geomorphic impact of catastrophic glacier ice loss in mountain regions|last=Evans|first=S.G.|year=2006|page=1247|bibcode=2006AGUFM.H11B1247E|volume=11|journal=AGU Fall Meeting Abstracts}}</ref><ref>{{cite journal |last1=Simpson |first1=K.A. |last2=Stasiuk |first2=M. |last3=Shimamura |first3=K. |last4=Clague |first4=J.J. |last5=Friele |first5=P. |journal=[[Canadian Journal of Earth Sciences]]|title=Evidence for catastrophic volcanic debris flows in Pemberton Valley, British Columbia |publisher=[[NRC Research Press]] |location=[[Ottawa]], [[Ontario]] |page=688 |volume=43 |year=2006 |issn=0008-4077 |bibcode=2006CaJES..43..679S |doi=10.1139/E06-026 |issue=6}}</ref> The landslide originated on the western flank of Pylon Peak and flowed down Devastation Creek for {{nowrap|{{Convert|7|km|mi|abbr=on}}}}. Geologic studies have shown that the landslide was the result of a complex history of glacial erosion, loading and unloading of the toe (a protrusion at the front of the slide mass) caused by the [[Little Ice Age]] advance and subsequent retreat of Devastation Glacier due to global warming.<ref name="KKV"/>

=====2010 landslide===== {{Main|2010 Mount Meager landslide}} On August 6, 2010, a massive debris flow cascaded down from Capricorn Glacier at a speed of {{nowrap|{{Convert|30|m|ft|abbr=on}}}} per second.<ref name="AF">{{cite news|title=Flooding averted after landslide blocked Meager Creek|newspaper=[[The Vancouver Sun]]|location=[[Vancouver]], [[British Columbia]]|last1=Luk|first1=Vivian|date=2010-08-09|pages=1, 2|issn=0832-1299}}</ref> Experts initially estimated that the volume of debris totaled {{nowrap|{{Convert|40000000|m3|ft3|abbr=on}}}}, which would make it the second largest landslide on record in Canadian history, behind the {{nobr|1965 [[Hope Slide]]}} that removed {{nowrap|{{Convert|47000000|m3|ft3|abbr=on}}}} of rock from Johnson Peak, a mountain in the [[Nicolum River|Nicolum Valley]] near Hope, British Columbia.<ref name="AF"/><ref>{{cite web|url=http://atlas.nrcan.gc.ca/auth/english/maps/environment/naturalhazards/landslides/fig_12_land_hope_slide.jpg/image_view |title=Photograph of Hope Slide |publisher=[[Natural Resources Canada]] |date=2007-03-27 |access-date=2011-07-06 |url-status=bot: unknown |archive-url=https://web.archive.org/web/20101203213643/http://atlas.nrcan.gc.ca/auth/english/maps/environment/naturalhazards/landslides/fig_12_land_hope_slide.jpg/image_view |archive-date=2010-12-03 }}</ref> However, the landslide was later estimated to be more than {{nowrap|{{Convert|48500000|m3|ft3|abbr=on}}}}, which would make it the largest of all time in Canada.<ref name="AF"/>

The 2010 landslide was {{nowrap|{{Convert|300|m|ft|abbr=on}}}} wide and {{nowrap|{{Convert|2|km|mi|abbr=on}}}} long, creating a dam across Meager Creek and the Lillooet River. This created a lake just upstream. Early concerns that the dam might collapse and flood the Lillooet River valley ended a day later, when part of the dam ruptured and slowly released the accumulated water. An evacuation alert was rescinded, and nearly 1,500&nbsp;residents were allowed to return to their homes on the weekend after the landslide occurred. No injuries were reported.<ref name="AF"/>

==See also== {{Portal|Volcanoes|Mountains}} *[[List of Cascade volcanoes]] *[[List of volcanoes in Canada]] *[[Salal Glacier volcanic complex]] *[[Sham Hill]] *[[Tuber Hill]] *[[Volcanology of Western Canada]]

==References== {{USGS}} {{Reflist|30em}}

==External links== {{Commons category|Mount Meager massif}} *{{cite bivouac|id=957|name=Capricorn Mountain|access-date=2011-07-03}} *{{cite cgndb|id=JATUN|title=Capricorn Mountain|access-date= 2011-08-16}} *{{cite bivouac|id=956|name=Devastator Peak|access-date=2011-07-03}} *{{cite cgndb|id=JBAAF|title=Devastator Peak|access-date= 2011-08-16}} *{{cite bivouac|id=958|name=Mount Job|access-date=2011-07-03}} *{{cite cgndb|id=JBUVQ|title=Mount Job|access-date= 2011-08-16}} *{{cite bivouac|id=953|name=Mount Meager|access-date=2011-07-03}} *{{cite cgndb|id=JCJGT|title=Mount Meager|access-date= 2011-08-16}} *{{cite bivouac|id=6102|name=Perkin's Pillar|access-date=2011-07-03}} *{{cite bivouac|id=952|name=Plinth Peak|access-date=2011-07-03}} *{{cite cgndb|id=JBEDD|title=Plinth Peak|access-date= 2011-08-16}} *{{cite bivouac|id=955|name=Pylon Peak|access-date=2011-07-03}} *{{cite cgndb|id=JBMCJ|title=Pylon Peak|access-date= 2011-08-16}}

{{Pacific Ranges}} {{Garibaldi Volcanic Belt}} {{Cascade volcanoes}} {{Authority control}}

{{DEFAULTSORT:Meager, Mount}} [[Category:Mount Meager massif| ]] [[Category:Volcanic plugs of British Columbia]] [[Category:Stratovolcanoes of Canada]] [[Category:Active volcanoes]] [[Category:VEI-5 volcanoes]] [[Category:Subduction volcanoes]] [[Category:Pleistocene lava domes]] [[Category:Complex volcanoes]] [[Category:Natural disasters in British Columbia]] [[Category:Hot springs of British Columbia]] [[Category:Pacific Ranges]] [[Category:Pleistocene stratovolcanoes]] [[Category:Polygenetic volcanoes]] [[Category:Landslides in Canada]] [[Category:Two-thousanders of British Columbia]] [[Category:Lava domes of British Columbia]]