The Cascade Range is one of the most accessible spans of active volcanism on Earth. Running from southern British Columbia to northern California, many of the volcanoes are located within a day's drive from major cities like Seattle, Portland, Sacramento and San Francisco. If you've never visited a volcano, it is hard to describe what it is a like to see one in person. They're big. They are imposing. Many times they are covered with snow and ice. Sometimes they are just a big hole in the ground because they erupted so violently. Sometimes there are ancient lava flows that look as if they erupted yesterday. Visiting a volcano should be on everyone's life list.
Over the next few weeks, we'll be taking a tour of the modern Cascade Range volcanoes from north to south. Using some of the stunning imagery from the European Space Ageny's Copernicus program that utilizes the Sentinel-2 Earth-observing satellite to capture high resolution images of almost everywhere on the planet. These images span from visible light to infrared to surface moisture. The Copernicus browser for these images is possibly the ultimate rabbit hole for people who love Earth sciences. If you'd like to see the high resolution of the images below, you can check them out here.
The Cascade Range exists because the Juan de Fuca plate (and its broken brother, the Explorer Plate) are sliding down underneath North America in a process called subduction. As that oceanic plate goes down, it heats up and releases water that causes the mantle rock beneath North America to start to melt. This is magma and it rises through the North American crust to form volcanoes. Because this process mostly happens at the same depth as the Juan de Fuca plate goes down, the volcanoes occur as a line that is somewhat parallel to the edge of North America.
You can see that align in the map of the Cascades below (click here to see a higher resolution version). There are a few exceptions like Mount St. Helens that is closer to the coast than average and Newberry Volcano as well as Medicine Lake volcano that are further. This can mostly be explained here by "tectonics gets complicated" and we'll save that for another day.
One note: if you're read Rocky Planet for a while, you might remember I have advocated for the increased use of indigenous names for Cascade Range (indigenously known as Yamakiasham Yaina, or "Mountains of the Northern People") volcanoes. I won't rehash my arguments here, but I will be talking about these volcanoes with both the native names (as best as we can determine) and their Euroamerican names. You can see a map of the Cascades with both names above.
British Columbia's Volcanoes
Of any part of the Cascades, the volcanoes of British Columbia get the most forgotten. This is likely because they are remote, relatively quiet and quite beaten up by glaciers and the last Ice Age. However, they still present a hazard to North American air travel and the people who live in southern British Columbia. Many times the volcanoes are barely recognizable as such because of how much weathering and erosion has occurred over the past 10-20,000 years. However, eruptions have likely happened in British Columbia in the last few thousand years.
Silverthrone Caldera
The northernmost boundary of the Cascades is tricky to pinpoint. There are other volcanic fields in British Columbia, so pinpointing what is a volcano that is a Cascade Range one versus something else is definitely still in flux. Geologists like Dominique Weis at University of British Columbia put the boundary at the Nootka Fault. However, I am including Silverthrone Caldera because others have lumped it into the Cascades because there is evidence in the composition of the lava that it is formed by the same subduction processes as the other Cascade volcanoes.
You might look at the mess of glaciers, snow and ice and think "there is no way this is a potentially active volcano", but there is good evidence that eruptions have happened at Silverthrone in the past 12,500 years (and likely much more recently). Much of the volcano formed since 500,000 years ago and being a caldera (like Crater Lake), it may have been the site of some very large eruptions in its past.
We'll get into this more below, but Silverthrone Caldera is considered the 6th most dangerous volcano in Canada according to a new assessment that came out in 2024.
Lillooet (Bridge River Cones and the Salal Glacier Complex)
The Bridge River Cones are easy to miss. In the river valley just to the north of the Salal Glacier Complex are some ruddy cones and hills that erupted over the past ~1 million years. As we know, there have been multiple ice ages that have covered much of the BC Cascade Range with glaciers, so many of the features in this area formed as eruptions underneath the glacier (like we see today in Iceland). However, there are some lava flows that clearly are on top on the deposits from the most recent glaciation, meaning they are less than 10,000 years old and some have suggested they might be as young as ~1,500 years old. That being said, the Lillooet volcanics are seen as very low in terms of volcanic threat in Canada.
Qw̓elqw̓elústen (Mount Meager)
Mount Meager (known to the Líl'wat as Qw̓elqw̓elústen) might be the first of the more well known Canadian Cascade volcanoes. There is a long oral tradition about volcanism at Meager as far back as eruptions that happened ~2,360 years ago. That eruption is thought to have been VEI 5, meaning it was as large as the Mount St. Helens 1980 blast and the largest Holocene eruption (last 10,000 years) in Canada. Meager still has a vigorous hydrothermal system circulating hot water under the volcano and has even been proposed as a geothermal power site.
Meager is a good example of the lack of volcano monitoring currently in Canada. The 2024 assessment of the volcano threat it poses puts it at number two for the country, yet much like all Canadian volcanoes, it does not meet international monitoring standards. In fact, the Cascades as a whole are under-monitored compared to many active volcanic arcs around the world.
Sxel'tskwu'7 (Mount Cayley)
Likely not as recently active as its neighbors to the north (Meager) and south (Garibaldi), Mount Cayley (or Sxel'tskwu'7 to the local Squamish Nation) still ranks number 3 for potential volcanic threat in Canada. The edifice of the volcano has been heavily eroded by glaciers, but the most recent eruptions were likely since the glaciers receded (<12,000 years ago).
Most notably, Cayley has experienced a number of volcanic landslides in the past 10,000 years, likely thanks to the relatively weak construction of most volcanoes and the heavy weathering it has experienced. The most recent was in 1963 and was not associated with any volcanic activity. Even without more evidence of recent eruptions, the Cayley region is littered with hot springs and feels shallow earthquakes including at least 4 swarms since 1985.
Nch’Kay (Mount Garibaldi)
Our last stop in British Columbia is likely the most famous of the Canadian Cascades. Mount Garibaldi is just north of the border with Washington state. It has a long history of eruptions over the past 500,000 years, as well as possibly some major collapses due to partially forming on top of past glaciers. The most recent identified activity at Nch'Kay was ~8,000 BCE, but that doesn't stop it from being marked as the number one most potentially dangerous volcano in Canada.
This rank may be a combined effort between Nch'Kay and the adjacent Garibaldi Lake volcanic field that has been active over the last 1 million years. There is evidence there for multiple eruptions over the past 10,000 years. Lava flows from Cinder Cone can be seen stretching to the west of Garibaldi Lake in the Sentinel-2 image. Garibaldi Lake itself is held in by a lava dam known as "the Barrier" associated with activity from the Garibaldi Lake volcanoes and there is some concern that it could collapse due to the weak nature of the rock.
That's it for Canada. Next week, we'll look at the volcanoes in Washington state's Cascades.
