Mount Garibaldi is one of the three principal volcanoes in the southern segment of the
Garibaldi Volcanic Belt, the other two being
Mount Price and
The Black Tusk. This
volcanic field consists of at least twelve eruptive centres that are in the form of stratovolcanoes,
lava domes,
cinder cones and
subglacial volcanoes. These include Mount Price, The Black Tusk,
The Table,
Cinder Cone and
Round Mountain, all of which formed in the last 1.3 million years.
Structure Mount Garibaldi is a moderately eroded stratovolcano overlooking the town of Squamish at the head of
Howe Sound north of Vancouver. It is one of the three Cascade Arc volcanoes made exclusively of dacite, the other two being
Glacier Peak and Mount Cayley.
Rhyodacite is also a common volcanic rock at Mount Garibaldi and Mount Cayley, although high-
silica rhyolite is uniquely present at Mount Garibaldi. Subordinate
andesite erupted at all three volcanoes relatively early in their histories. At Mount Garibaldi, the total volume of volcanic rocks amount to and represent many episodes of activity spanning from about 670,000 years ago to the
Holocene. Andesite-dacite lavas and their
pyroclastic accompaniments from several vents initially filled
paleovalleys glacially incised into the
Coast Plutonic Complex basement. Several dacitic domes and derivative pyroclastic material then built the main volcanic edifice starting about 260,000 years ago. Much of the volcano was rebuilt in the last 50,000 years by a series of violent eruptions similar in character to the
1902 eruption of Mount Pelée. The modern volcanic edifice is a
supraglacial volcano, having been partially constructed over glacial ice during the
Pleistocene epoch. At the time of its formation, the Cheekye Fan extended across Howe Sound, resulting in the impoundment of a freshwater lake upstream of the fan. The Squamish River subsequently built a
delta into this lake during the Holocene. It then filled in the lake with sediment over the last 3,300 years to create the Squamish River
floodplain. Extending from the southern flank of Mount Garibaldi is the unusually long Ring Creek lava flow. It is dacitic in composition, attains a length of approximately and contains well-defined levees along its margins. The western slopes of Mount Garibaldi are underlain by
sheared and altered
quartz diorite, which has undergone stream and glacial erosion to form rugged
topography with relief up to . The initial Cheekye stage took place between 260,000 and 220,000 years ago with the eruption of dacite and breccia, resulting in the formation of a broad
composite cone. Parts of this "proto-Garibaldi" or ancestral volcano are exposed on Mount Garibaldi's lower northern and eastern flanks and on the upper of Brohm Ridge. Around where Columnar Peak and possibly Glacier Pikes are now located, several coalescing dacitic domes were constructed. This catastrophic collapse produced the Cheekye Fan and the scarp exposing the internal structure of Mount Garibaldi. Soon before or after the buried ice had melted away, the Dalton Dome stage commenced with the eruption of dacite lava down Mount Garibaldi's north and northeastern flanks. At least two debris flows in the order of occurred at Mount Garibaldi in the 1930s and 1950s, both of which swept down the Cheekye River. The 1950s debris flow was caused by heavy rains and reached the Cheakamus River where it formed a temporary
landslide dam. This is the latest debris flow to reach the Cheakamus River from the Cheekye basin. In contrast to Mount Cayley and Mount Meager, no
hot springs are known in the Garibaldi area. However, there is evidence of anomalously high heat flow in Table Meadows and elsewhere. At least three seismic events have occurred at Mount Garibaldi since 1985, indicating that the volcano is potentially active and poses a significant hazard to the area.
Volcanic hazards Mount Garibaldi is one of two volcanoes in Canada classified as a very high threat by
Natural Resources Canada, the other volcano being Mount Meager to the northwest. Although
Plinian eruptions have not been identified at Mount Garibaldi, Peléan eruptions can also produce large amounts of volcanic ash that could significantly affect the nearby communities of Whistler and Squamish. Peléan eruptions might cause short and long term water supply problems for the city of Vancouver and most of the Lower Mainland. The catchment area for the
Greater Vancouver watershed is downwind from Mount Garibaldi. An eruption producing floods and
lahars could destroy parts of
Highway 99, threaten communities such as
Brackendale and endanger water supplies from
Pitt Lake. Fisheries on the Pitt River would also be at risk. These volcanic hazards become more serious as the Lower Mainland grows in population. As a result, the Cheekye linears pose potential landslide hazards to Brackendale and several
Squamish Nation villages nearby. The danger of catastrophic landslides from Mount Garibaldi has restricted development on the Cheekye Fan. This high percentage in silica content increases the viscosity of dacitic melts relative to that of andesite or
basalt, generally resulting in the formation of steep-sided lava domes and stubby lava flows. An exception is the Ring Creek dacite flow from Opal Cone, a length that is normally attained by basaltic lava flows. If Mount Garibaldi were to erupt, mechanisms exist to orchestrate relief efforts. The Interagency Volcanic Event Notification Plan 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. ==Human history==