Mount Price (British Columbia)
Mount Price is a small stratovolcano in the Garibaldi Ranges of the Pacific Ranges in southwestern British Columbia, Canada. It has an elevation of and rises above the surrounding landscape on the western side of Garibaldi Lake in New Westminster Land District. The mountain contains a number of subfeatures, including Clinker Peak on its western flank, which was the source of two thick lava flows between 15,000 and 8,000 years ago that ponded against glacial ice. These lava flows are structurally unstable, having produced large landslides as recently as the 1850s. A large provincial park surrounds Mount Price and other volcanoes in its vicinity. It lies within an ecological region that surrounds much of the Pacific Ranges.
Mount Price is associated with a small group of volcanoes called the Garibaldi Lake volcanic field. This forms part of the larger Garibaldi Volcanic Belt, a north−south trending volcanic zone that represents a portion of the Canadian Cascade Arc. Mount Price began its formation 1.2million years ago and continued intermittently until sometime in the last 15,000 years. Although the mountain is not known to have been volcanically active for thousands of years, it could erupt again, which would potentially endanger the nearby populace. If this were to happen, relief efforts could be organized by teams such as the Interagency Volcanic Event Notification Plan who are prepared to notify people threatened by volcanic eruptions in Canada.
Geography
Mount Price is located south of Whistler on the western side of Garibaldi Lake in New Westminster Land District. It lies within the Pacific Ranges Ecoregion, a mountainous region of the southern Coast Mountains characterized by high, steep and rugged mountains made of granitic rocks. Much of this ecoregion encompasses the Pacific Ranges in southwestern British Columbia, although it also includes the northwesternmost portion of the Cascade Range in Washington state. Several coastal islands, channels and fjords occur along the western margin of the Pacific Ranges Ecoregion. The Pacific Ranges Ecoregion is part of the Coast and Mountains Ecoprovince which forms part of the Humid Maritime and Highlands Ecodivision.The Pacific Ranges Ecoregion is subdivided into seven ecosections, the Eastern Pacific Ranges Ecosection being the main ecosection at Mount Price. This ecosection is characterized by a rugged landscape of mountains that increase in elevation from south to north; the northern summits contain large icefields. A transitional climate between coastal maritime and interior continental climates dominates the Eastern Pacific Ranges Ecosection. It is characterized by little precipitation and mild temperatures due to Pacific air often passing over this area. During winter, cold Arctic air invades from the Central Interior, resulting in extreme cloud cover and snow. A number of other volcanoes are situated within the Eastern Pacific Ranges Ecosection. This includes Mount Meager, which lies near the headwaters of the Lillooet River, and Mount Garibaldi and Mount Cayley, which lie in the Squamish River watershed.
Several rivers flow through the Eastern Pacific Ranges Ecosection, including the Fraser and Coquihalla rivers on its eastern side, the Cheakamus, Squamish and Elaho rivers on its western side and the Lillooet River in the middle. Coastal western hemlock forests dominate nearly all the valleys and lower slopes of this ecosection, the upper slopes containing subalpine mountain hemlock forests and, to a lesser extent, Engelmann spruce and subalpine fir forests. Alpine vegetation lies just above the subalpine forests, which is normally overlain by barren rock. Wildlife such as grey jays, chipmunks, squirrels, flickers, deer, mountain goats, wolverines, cougars and grizzly and black bears are locally present. The communities of Whistler, Pemberton, Mount Currie, Hope and Yale are situated within the Eastern Pacific Ranges Ecosection, all of which are connected to the Lower Mainland by a network of highways.
Geology
Mount Price is one of the three principal volcanoes in the southern segment of the Garibaldi Volcanic Belt, the other two being Mount Garibaldi and The Black Tusk. Mount Price is also part of the Garibaldi Lake volcanic field. This consists of several volcanoes and lava flows that formed in the last 1.3million years; the oldest volcanic rocks are found at Mount Price and The Black Tusk. Several volcanic rocks with differing compositions are present in the Garibaldi Lake volcanic field. This includes andesite, dacite, basaltic andesite and basalt. It is unknown when the last eruption occurred but it may have been in the early Holocene. Although no hot springs are known in the Garibaldi area, there is evidence of anomalously high heat flow in Table Meadows just south of Mount Price and elsewhere.Like other volcanoes in the Garibaldi Volcanic Belt, Mount Price formed as a result of subduction zone volcanism. As the Juan de Fuca Plate thrusts under the North American Plate at the Cascadia subduction zone, it forms volcanoes and volcanic eruptions. Unlike most subduction zones worldwide, there is no deep oceanic trench along the continental margin of Cascadia. There is also very little seismic evidence that the Juan de Fuca Plate is actively subducting. The probable explanation lies in the rate of convergence between the Juan de Fuca and North American plates. These two tectonic plates currently converge at a rate of per year, only about half the rate of convergence from seven million years ago. This slowed convergence likely accounts for reduced seismicity and the lack of an oceanic trench. The best evidence for ongoing subduction is the existence of active volcanism in the Cascade Volcanic Arc.
Structure
Mount Price attains an elevation of and is one of several Garibaldi Belt volcanoes that have been volcanically active throughout the Quaternary. In contrast to most stratovolcanoes in Canada, Mount Price has a nearly symmetrical structure. Its western slope is flanked by Clinker Peak, a high parasitic stratovolcano containing a breached volcanic crater. Oxidation of Mount Price's volcanic rocks has given the mountain a red colour.Mount Price stands within a cirque-like basin cut into the plateau on the south side of the valley of Garibaldi Lake. This basin consists of a wall of granite, inclosing the volcano on its west and southwest sides. It is now almost completely filled up by Mount Price, but some small areas of its floor are exposed on the north side. The basin likely formed as a result of glacial action as its north side appears to have been almost certainly glaciated. It might otherwise have been attributed to explosive volcanism, but there are no fragmental materials around its margin which would confirm this.
Volcanic history
At least three phases of eruptive activity have been identified at Mount Price. The first eruptive phase 1.2million years ago deposited hornblende andesite lava and pyroclastic rocks on the floor of the cirque-like basin after an Early Pleistocene glacial event. During the Middle Pleistocene about 300,000 years ago, volcanism of the second phase shifted westward and constructed the nearly symmetrical stratovolcano of Mount Price. Episodic eruptions during this phase of activity produced andesite and dacite lavas, as well as pyroclastic flows from Peléan activity. Later, the volcano was overridden by the Cordilleran Ice Sheet, which covered a large portion of western North America during glacial periods of the Quaternary.After the Cordilleran Ice Sheet retreated from higher elevations less than 15,000 years ago, andesite eruptions of the third eruptive phase occurred from a satellite vent at Price Bay. These eruptions resulted in the creation of a small lava dome or scoria cone on Mount Price's northern flank with an elevation of. Possibly contemporaneous volcanism occurred at Clinker Peak with the eruption of two hornblende-biotite andesite lava flows. They are both at least thick and long, extending to the northwest and southwest. Their unusually large thickness is due to them ponding and cooling against the Cordilleran Ice Sheet when it still filled valleys at lower elevations. Age estimates for this final volcanic phase have varied from 15,000 years ago to as recently as 8,000 years ago.
A prominent feature of the Clinker Peak lava flows are the levees that demarcate the lava channels. The northwest lava flow forms a volcanic dam known as The Barrier. This retains the Garibaldi Lake system and has been the source of two large landslides in the past. The most recent major landslide in 1855–1856 resulted from failure along vertical rock fractures. It travelled down Rubble Creek to the Cheakamus River valley, depositing of rock. The southwest lava flow is in the upper reaches of the Culliton Creek valley. Both lava flows form steep cliffs; the current face of The Barrier is a result of the mid-19th century landslide.
Volcanic hazards
Mount Price is one of the four highest threat volcanoes in Canada adjacent to major populations with critical civil and economic infrastructure, the other three being Mount Meager, Mount Garibaldi and Mount Cayley. Although Plinian eruptions have not been identified at Mount Price, 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 Price. 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. Mount Price is also close to a major air traffic route; volcanic ash reduces visibility and can cause jet engine failure, as well as damage to other aircraft systems. These volcanic hazards become more serious as the Lower Mainland grows in population.Because andesite is the main type of lava erupted from Mount Price, lava flows are a low to moderate hazard. Andesite is intermediate in silica content, indicating that it has a higher viscosity than basaltic lava but is less viscous than dacite or rhyolite lava. As a result, andesite lava flows typically move slower than basaltic lava flows and are less likely to travel as far from their source. Dacite and rhyolite lavas are normally too viscous to flow away from a volcanic vent, resulting in the formation of lava domes. An exception is the long Ring Creek dacite lava flow from Opal Cone on the southeastern flank of Mount Garibaldi, a length that is normally attained by basaltic lava flows.
Concerns about The Barrier's instability due to volcanic, tectonic or heavy rainfall activity prompted the provincial government to declare the area immediately below it unsafe for human habitation in 1980. This led to the evacuation of the small resort village of Garibaldi nearby and the relocation of residents to new recreational subdivisions away from the hazard zone. The area below and adjacent to The Barrier has since been referred to as the Barrier Civil Defence Zone by BC Parks. Although landslides comparable in size to the one in 1855–1856 are unlikely to occur in the near future, warning signs are posted at the zone to make visitors aware of the potential danger and to minimize the chance of fatalities in the event of a slide. For safety reasons, BC Parks recommends visitors not to camp, stop or linger in the Barrier Civil Defence Zone.