[5] The reason is that 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.

[1] The cessation of volcanism in the Pemberton Belt might have been caused by steepening of the subducted Juan de Fuca slab after the Explorer Plate formed about 6.0 million years ago.

[8] The first volcanic event 29 million years ago formed intrusive rocks of the large Chilliwack batholith, which extends south into the U.S. state of Washington.

Two younger plutons, consisting of nearly homogeneous leucocratic biotite quartz monzonite, are situated north of Chilliwack Lake and 3.2 km (2.0 mi) east of Slesse Mountain.

[10] Coquihalla Mountain, the highest summit of the Bedded Range with an elevation of 2,157 m (7,077 ft), is a major preserved stratovolcano and represents one of the few remaining Miocene volcanoes in southwestern British Columbia.

A 60 to 90 m (200 to 300 ft) wide dike, composed of granophyric hornblende plagioclase porphyry, is situated between quartz diorite of the Hope Plutonic Complex and Eocene conglomerate.

Volcanic activity during the Fraser Glaciation between 25,000 and 10,000 years ago interacted with glacial ice to form subglacial domes, tuyas and ice-marginal lava flows.

Parts of this "proto-Garibaldi" or ancestral volcano are exposed on Garibaldi's lower northern and eastern flanks and on the upper 240 m (790 ft) of Brohm Ridge.

Subsequent melting of the Cordilleran Ice Sheet and its component glaciers initiated a series of avalanches and mudflows on Garibaldi's western flank that moved nearly half of the original cone's volume into the Squamish Valley where it covers 26 km2 (10 sq mi) to a thickness of about 91 m (299 ft).

Around the same time, a voluminous dacite lava flow from Opal Cone travelled 20 km (12 mi) down Ring Creek on Garibaldi's southeastern flank without encountering any residual glacial ice.

[2] These latest eruptions of Mount Garibaldi occurred in the early Holocene shortly after remains of the Cordilleran Ice Sheet retreated in regional valleys between 10,700 and 9,300 years ago.

[2] After the ice sheet had retreated from higher elevations, andesite eruptions from a satellite vent created a small lava dome on Price's northern flank.

Renewed volcanism between 210,000 and 170,000 years ago produced hypersthene andesite lava flows, which locally terminate with precipitous 100 m (330 ft) thick ice-contact margins.

This latest eruptive activity culminated with extrusion of an endogenous dome and related lava which form the present 2,316 m (7,598 ft) high summit spire.

[2] The Table, a hornblende andesite tuya situated about 3 km (1.9 mi) southeast of Mount Price, rises precipitously 305 m (1,001 ft) above glaciated basement rocks.

Absence of glacial erratics on its summit and lack of erosional features attributable to glaciation indicates that The Table was formed by subglacial eruptions during the Early Holocene time, just prior to the disappearance of the ice sheet.

[19] A 9 km (5.6 mi) long lava flow, ranging from basalt to mugearite, issued from the base of the cone and travelled in a north-trending U-shaped valley on the eastern flank of The Black Tusk.

[2][19] The Monmouth Creek complex on the west side of the Squamish River mouth is a prominent and enigmatic edifice composed of basaltic andesite and dacite of unknown age.

It is the southernmost volcano in the Garibaldi Volcanic Belt, comprising about 0.02 km3 (0.0048 cu mi) of hornblende, pyroxene and sparsely porphyritic dacite lava and breccia.

This volcanic centre formed in a subglacial to englacial environment between 130,000 and 90,000 years ago, as shown by the existence of distinctive, radial columnar joint patterns, a glassy to fine-grained matrix and stratigraphic relationships to overlying glacial till.

One of these sequences, known as Tricouni Southwest, creates a cliff on the eastern side of a north–south trending channel with a depth of 200 m (660 ft) adjacent to the High Falls Creek mouth.

In 1958, Canadian volcanologist Bill Mathews suggested that the lava flows were erupted during periods of subglacial activity and traveled through trenches or tunnels melted in glacial ice of the Fraser Glaciation.

[27] The northern segment consists of one large volcanic complex, the Mount Meager massif, and a group of basaltic and andesitic volcanoes known as the Bridge River Cones.

It consists of dikes and subvolcanic intrusions overlain by tuffs, dacite breccia and eroded remains of a 450 m (1,480 ft) thick sequence of hornblende andesite lava flows.

[2] The third phase, less than 1,000 years ago, produced cinder cones, pyroclastic deposits and basaltic andesite lava flows that issued from vents on the rim of the caldera.

[2] The Milbanke Sound Group in the Kitimat Ranges consists of young lava flows and monogenetic cinder cones that were probably formed in the last 10,000 years.

[2] Helmet Peak, a steep-sided cinder cone on Lake Island with an elevation of 335 m (1,099 ft), consists of welded volcanic blocks and basaltic feeder dikes.

[31] This zone, known as the Chilcotin Group, formed as a result of back-arc basin volcanism behind the Canadian Cascade Arc, in response to ongoing Cascadia subduction.

It consists of several thin, flat-lying pāhoehoe lava flows that were erupted from a chain of low-profile shield volcanoes, which have since been eroded by Late Pleistocene glaciation to expose their gabbro-bearing volcanic plugs.

Most of the Alert Bay Belt volcanism corresponded with rapid changes in the geometry of Cascadia subduction and a hiatus in mainland Cascade Arc activity.