Major Volcanic Areas

Volcanoes do not seem to be part of the Canadian reality today. However, there are many volcanoes in western Canada. The entire western Cordillera (British Columbia and Yukon) remains geologically active. The possibility of an eruption, even a large explosive one, cannot be ruled out. Quiet as they are, the West Coast volcanoes are part of the "Pacific ring of fire".

In fact, in southwestern British Columbia and adjacent parts of the United States, an offshore tectonic plate is forced under the edge of the continental plate, causing molten rock to rise to the surface and form volcanoes. Volcanoes in the northern end of Cascade chain include among others Mount Garibaldi and Mount Meager, both north of Vancouver, and Mount St. Helens, Mount Baker and Mount Rainier, all in Washington State.

West of Vancouver Island, there is also an undersea ridge called the Juan de Fuca Ridge, where the earth's crust is being stretched and pulled apart, and where new magma wells up forming new oceanic crust.

Distribution of the Main Volcanic Complexes in Canada and the World

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Figure 1. Map of the Distribution of Main Volcanic Complexes in the World

On this map, the red areas represent the location of volcanoes in the world, and the yellow areas, the edges of crustal plates. The circle of volcanoes that surrounds the Pacific Ocean is called the Pacific Ring of Fire of which British Columbia is part. In the Western Cordillera of British Columbia, there are numerous volcanoes that have been active within the last two million years. The most recent volcanic eruption in Canada was Lava Forks volcano, about 150 years ago. Tseax volcano erupted about 400 years ago and led to many fatalities among the Nisga'a people.

How do volcanoes work?

Volcanoes erupt, in part, because of pressure from dissolved gas with the liquid rock called magma. Magma rises through cracks and channels in the earth's crust and pools in magma chambers below the volcano. When ready to erupt, it moves upward into and out of the volcano through a vent. If the magma is fairly fluid, gases can escape readily and the eruption will be in the form of a lava flow. However, if the magma is more viscous (meaning that it flows more slowly), the lava can impede the gradual escape of the gases and an explosive eruption might occur, depositing volcanic ash over a wide area.

Recent Examples of Volcanic Activity in Canada

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Photograph of Mount St. Helens, Washington, United States

Mount St. Helens erupted violently in 1980. Mount St. Helens is 300 kilometres south of Canada.

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Photograph of Mount Baker

Closer to Canada, Mount Baker, which is cooling from a minor eruption in the early 1800's, still lets off steam near its top.

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Photograph of Mount Meager, British Columbia

Some 2400 years ago (not long ago in geological time), Mount Meager, 180 kilometres north of Vancouver, erupted in a huge explosion that dumped volcanic ash as far away as southern Alberta.

What are the dangers?

Although southwestern British Columbia and the Yukon have not experienced a major volcanic eruption for more than 1000 years, the potential for future activity remains. A volcano may sleep for many centuries while gas pressure slowly builds in its subterranean magma chambers. However, before an eruption the increasing pressure creates many small earthquakes which are detected at seismograph stations and warn of the eruption to come.

Lava flows and burning hot projectiles are hazards only in the immediate vicinity of a volcano. Mudflows and clouds of volcanic ash are also dangerous. When a large volcano erupts, the snow and ice on its slopes can melt rapidly and sweep down the mountain in a slurry of meltwater and debris. These mudflows can follow valleys and river beds for hundreds of kilometres, carrying away anything in their path. When Mount St. Helens erupted, its mudflows followed the Toutle and Cowlitz rivers as far south as the Columbia River, 120 kilometres downstream.

In an explosive eruption, volcanic ash may be hurled high enough into the atmosphere to be carried with the prevailing winds. The city of Yakima, Washington, 130 kilometres northeast of Mount St. Helens, received 30 centimetres of ash over it after the May 18, 1980 eruption of Mount St. Helens.

On Canadian territory, large zones are covered by tephra. Tephra means anything thrown out by an erupting volcano such as volcanic ash. The map below (Figure 2) shows the distribution of tephras deposited during the Holocene period i.e. since about 12 000 years ago. Those deposits occured during the seven following events:

• 1 - St. Helens, 508 years ago
• 2 - White River, 1200 years ago
• 3 - White River, 1500 to 1900 years ago
• 4 - Bridge River, 2400 years ago
• 5 - St. Helens, 3400 years ago
• 6 - Mazama, 6800 years ago
• 7 - Glacier Peak, 11 200 years ago

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Figure 2. Map of the Tephra Deposition, Holocene Period

Volcanoes and Lava Flows Seen from Canada

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Photograph of Mount Baker, United States

Mount Baker, in the United States, can be seen from many places in the Lower Mainland and in southern Vancouver Island. This mountain is 25 kilometres south of the border.

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Photograph of Mount Garibaldi, British Columbia

Just north of Vancouver, Mount Garibaldi can be viewed from the road leading to the resort municipality of Whistler. From the viewpoint on Highway 99, five kilometres south of Squamish, the volcano's prominent twin peaks are easily recognized.

Lava flows, recognizable by their well-defined columnar jointing, can be spotted from several places along the roads to Whistler. In Brandywine Falls Provincial Park, just south of Whistler, Brandywine Creek has carved a canyon through lava flows 35 000 years old forming a spectacular waterfall at the head of the canyon.

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