The Mount Meager massif is a group of volcanic peaks in the Pacific Ranges of the Coast Mountains in southwestern British Columbia, Canada.

The Mount Meager massif lies in the Coast Mountains, which extend from Vancouver to the Alaskan Panhandle for 1,600 km (990 mi).

Wildlife such as wolves, wolverine, moose, raptors, black-tailed deer, mountain goats and waterfowl inhabit the area as well as grizzly and black bears.

[7][8][9][10] 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.

[8][15] 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.

[22] 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 Late Pleistocene also deposited large amounts of sediment into the trench.

[26] Numerous feeder dikes to older units, formed when magma intrudes into a crack then crystallizes as a sheet intrusion, are exposed by deep erosion.

[3] The geomorphology of the Mount Meager massif resembles that of Glacier Peak, another Cascade Arc volcano in the U.S. state of Washington.

[17] With a total volume of 20 km3 (4.8 cu mi), the massif is older than most volcanoes in the Cascade Arc, tracing its history back to 2,200,000 years ago.

[33] Plinth Peak was officially named on September 6, 1951 as identified in Carter's 1932 sketch map and article "Explorations in the Lillooet River Watershed".

[34] 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.

[17][40] 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 crustal weakness that are penetrated by rising magma batches.

[4] At the southwestern end of the massif, dacite with sparse phenocrysts (large and conspicuous crystals) of quartz, plagioclase and hornblende represents a 200 m (660 ft) thick remnant of subhorizontal lava flows.

Its western portion consists of roughly layered tephra while its eastern end represents the lava flows and subvolcanic intrusions of a partly preserved vent.

A thick sequence of andesite lava flows were erupted from the volcanic plug of Devastator Peak, creating the Pylon Assemblage.

[4][40] With a maximum thickness of more than 1 km (0.62 mi), the Pylon Assemblage is the largest rock unit comprising the Mount Meager massif.

A concentration of subvolcanic intrusions and coarse volcanic breccia clasts more than 100 m (330 ft) in length suggest that Devastator Peak is a major vent.

[4] The fourth and final eruptive period 150,000 to less than 3,000 years ago produced rhyodacite lava flows, domes, breccias and subvolcanic intrusions of the Plinth, Job and Capricorn assemblages.

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.

The fumarole field was considered unsafe to approach or enter due to the presence of hydrogen sulfide and potentially unstable ice crevasses.

[50] 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.

[51] Jack Souther, a leading authority on geothermal resources and volcanism in the Canadian Cordillera, expressed concern about the potential for another eruption: At present the volcanoes of the Garibaldi Belt are quiet, presumed dead but still not completely cold.

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.

[53][55] A significant structural collapse associated with loss of glacial buttressing might affect the magma plumbing system and lead to an eruption.

[56] More than 25 landslides have occurred there in the last 8,000 years,[26] and debris flows, mainly from the massif, have also filled Meager Creek valley to a depth of 250 m (820 ft).

Several tension cracks extend up to the summit, and as global warming causes glaciers to melt, the meltwater reaches deep into the massif.

As Pemberton continues to grow it will eventually extend into the surrounding mountains, creating a major hazard for people living there.

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.