page_title: Canadian Cascade Arc
section_title: Southern segment
hierarchical_section_title: Canadian Cascade Arc / Geology / Main-arc volcanism / Garibaldi Volcanic Belt / Southern segment
caption_attribution_description: English: Mount Garibaldi. Taken in Squamish, BC
context_page_description: The Canadian Cascade Arc, also called the Canadian Cascades, is the Canadian segment of the North American Cascade Volcanic Arc. Located entirely within the Canadian province of British Columbia, it extends from the Cascade Mountains in the south to the Coast Mountains in the north. Specifically, the southern end of the Canadian Cascades begin at the Canada–United States border. However, the specific boundaries of the northern end are not precisely known and the geology in this part of the volcanic arc is poorly understood. It is widely accepted by geologists that the Canadian Cascade Arc extends through the Pacific Ranges of the Coast Mountains. However, others have expressed concern that the volcanic arc possibly extends further north into the Kitimat Ranges, another subdivision of the Coast Mountains, and even as far north as Haida Gwaii.
  Over the last 29 million years, the Canadian Cascade Arc has been erupting a chain of volcanoes along the British Columbia Coast. At least four volcanic zones in British Columbia are related to Cascade Arc volcanism. This includes a large volcanic plateau in The Interior and three linear volcanic belts on The Coast.
context_section_description: Three principal volcanoes comprise the southern segment along with several smaller edifies. The largest and youngest principal volcano, Mount Garibaldi, is a dissected stratovolcano that began its formation 250,000 years ago. This eruptive period built a broad composite cone made of dacite and breccia. 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. Around where Columnar Peak and possibly Glacier Pikes are now located, a series of coalescing dacite lava domes were constructed. During the ensuing long period of dormancy, the Cheekye River cut a deep valley into the cone's western flank that was later filled with a glacier. After reaching its maximum extent the Cheekye Glacier and Cordilleran Ice Sheet were covered with volcanic ash and fragmental debris from Garibaldi. This period of growth began with the eruption of the Atwell Peak plug dome about 13,000 years ago from a ridge surrounded by the ice sheet. As the plug dome grew, massive sheets of broken lava crumbled as talus down its sides. Numerous Peléan pyroclastic flows accompanied these cooler avalanches, forming a 6.3 km³ (1.5 cu mi) fragmental cone and an overall slope of 12 to 15 degrees. Some of the glacial ice was melted by the eruptions, forming a small lake against Brohm Ridge's southern arm. The volcanic sandstones seen today atop Brohm Ridge were created by ash settling in this lake. Glacial overlap was most significant on the west and somewhat to the south. 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). Gaps left by melting ice caused minor to moderate cone distortion where the Cordilleran Ice Sheet was thin and major distortion where it was thick. The ice was thickest in and thus cone distortion was greatest over the buried Cheekye valley. Later volcanism occurred from Dalton Dome, which forms Garibaldi's western summit. Lava flows mantled the landslide headwall on Garibaldi's western flank. 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. 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.
  Mount Price, one of the three principal volcanoes in the southern segment, formed during three periods of eruptive activity. The first eruptive period 1.2 million years ago constructed a hornblende andesite stratovolcano on the floor of a cirque-like basin. During the Middle Pleistocene about 300,000 years ago, volcanism shifted westward and constructed the nearly symmetrical stratovolcano of Mount Price. Episodic eruptions produced andesite and dacite lavas, as well as pyroclastic flows from Peléan activity. Later, the volcano was overridden by the Cordilleran Ice Sheet. 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. Possibly contemporaneous volcanism occurred at Clinker Peak about 10,000 years ago with the eruption of two hornblende-biotite andesite lava flows. They are both over 250 m (820 ft) thick and 6 km (3.7 mi) long, extending to the northwest and southwest. The unusually large thickness of these lava flows is from them ponding and cooling against the Cordilleran Ice Sheet when it still filled valleys at lower elevations. This was the last eruptive activity at Mount Price.
  The Black Tusk, the oldest and most striking of the three principal volcanoes, is the glacially dissected remains of a stratovolcano that formed between 1.3  and 1.1 million years ago. Eruptions produced hornblende andesite lava flows and lithic tuffs. Pro
caption: Mount Garibaldi as seen from the town of Squamish
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