As summer draws to a close, so does our journey of the Cascade volcanoes seen from space. The Cascades today stretch all the way to Northern California, and are probably home to the largest volcanoes in the range, but the Earth’s plates are orchestrating the end of the Cascades, starting in California.
The oceanic plates that produce the magma that forms the Cascadia volcanoes are young and small. Juan de Fucapitated For volcanoes from Oregon to British Columbia, this plate is widespread (except for a small portion of the Micromicro Explorer Plate off the coast of Canada), but once you get into California, another microplate comes into play: the Gordo Plate. The Gordo Plate, sometimes lumped together with the Juan de Fuca Plate, lies off the southernmost coast of Oregon and continues into northern California near Mendocino.
Three times the fun
There’s something very unique off the coast of Mendocino. Triple JunctionThree plates meet here: the Gordo Plate, the Pacific Plate, and the North American Plate. This triple junction means that south of Mendocino, subduction does not occur, but instead two plates (the Pacific Plate and the North American Plate) slide against each other. This motion is called “strike-slip.” This transform boundary is called San Andreas Fault System Yes it does.
But the Triple Junction is not stationary. It is slowly moving north relative to North America, meaning that subduction is being replaced by deformation, and volcanism will cease with it. The southernmost volcanism in the Cascades is moving north at a rate of 15-20 kilometers per million years. Today, Lassen Volcanic Center is at the edge of the Cascades.
Thus, as the triple junction slowly moves toward Oregon and Washington, the Cascades will likely be cut off and the entire west coast of North America will become one long transform boundary.
Luckily for us volcano lovers, we have a long way to go before that happens, and we can celebrate the volcanoes we have now, safe in the knowledge that they will continue to exist for hundreds of thousands, even millions, of years to come.
By the way, when you cross the border from Oregon to California, the monitoring of the Cascade Range also changes. Instead of the Cascade Volcano Observatory in Vancouver, Washington, monitoring volcanic activity, the relatively new California Volcano Observatory (CalVO)Founded in 2012, CalVO has jurisdiction over the California Cascade Range, the Long Valley Caldera region, the Salton Sea and Mojave Volcanoes, and all events occurring in the State of California.
Medicine Lake
Medicine Lake volcano as seen by Sentinel-2 on October 4, 2023. Courtesy of ESA.
Medicine Lakelike Newbury This Oregon volcano is a bit of an odd one, as it sits behind the main ridge of the Cascade Range and borders the Basin and Range Province on the west. It gets its name from the lake in the center of the 7 x 12 km caldera at its summit.
In many ways, Medicine Lake is the twin of Newberry Lake, also a broad shield volcano covered by rhyolite lava flows. Glass MountainNamed for the glassy (obsidian) lava it formed, the mountain is about 1,000 years old, several hundred years before the Great Newberry Obsidian Flow. Glass Mountain, not surprisingly, is a common source of obsidian, a material used for tools throughout western North America.
Like Newberry, Medicine Lake A basaltic lava flow with many lava tube caves. Lava Beds National Monument It gained fame in the late 19th century when it was used by Native Americans to hide during battles with American soldiers.
There have also been unsubstantiated reports of a possible explosion in Medicine Lake. Around 1910There is little physical evidence, however, although the landscape is dotted with small craters from dozens of eruptions over the past hundreds of thousands of years.
Shasta
Mount Shasta as imaged by Sentinel-2 on September 14, 2023. Courtesy of ESA.
Mount Shasta Shasta is big. The volcano has a volume of over 350 cubic kilometers (about 84 cubic miles). In fact, Shasta is more of a group of volcanoes than a single volcano. The main structure of Shasta ( Hot rum corn And next to it was built the little Shastina, and we can also include the almost detached Black Butte.
Everything about Shasta is impressive. It’s a landscape. Northern California. If you’ve ever driven I-5 from Oregon to California, One of the largest volcanic debris avalanche deposits The avalanche known to have destroyed the original volcano occurred about 300,000 to 380,000 years ago, displacing 45 cubic kilometers (10 cubic miles) of material, 18 times more than the avalanche caused by the May 1980 eruption of Mount St. Helens.
Shastina It was formed approximately 9,500 years ago by a series of explosive eruptions and dome formations of andesite lava. Black Butte (West) is about the same age, but the lavas that erupted there were more dacitic and had higher silica content, and were probably silica-rich. Both of these eruptions sent pyroclastic flows into the valleys around Mount Shasta.
It’s been just under 800 years since Shasta’s last confirmed eruption, and if it were to erupt again, we can expect lava flows, which are clearly visible on satellite images of the volcano, as well as pyroclastic flows and lahars, which have flowed dozens of miles from the volcano in the past. Shasta’s geological record shows that it erupts every 600 to 800 years.. this do not This means that a new eruption is “bound to happen,” but it will certainly be one of the longer periods of quiet for the giant volcano.
Lassen
Lassen Volcanic Center as seen by Sentinel-2 on September 24, 2023. Courtesy of ESA.
Besides Mount St. Helens, Lassen Volcanic Center It is the most recently active volcano in the Cascade Range. It erupted between 1914 and 1917.Pyroclastic flows and lahars flowed down the volcano creating an area known as the “disaster zone.” This eruption was fairly small and was rated VEI 3 because it formed a small dome of dacite on the summit of Mount Lassen.
The bigger event at Lassen Volcanic Center was Chaos CragsThese rhyolite domes formed just 1,100 years ago north of Lassen Peak. These eruptions were likely explosive and produced the large lava dome that stands there today. There is also a large avalanche deposit (Chaos Jumble) that came from the dome, which can be seen in the upper left of the image, north of Chaos Crags.
Between these events, Cinder Cone It was taken on the edge of the LVC around 1666. A cinder cone is visible in the upper right corner of the Sentinel 1 image, and the dark lava flow stands out against the lighter ground burned by a fire several years ago.
Directly south of Lassen Peak, near the bottom left corner of the image, Bumpass Hellis an area of intense hydrothermal activity. You can walk through the Hell, smell the sulfurous outgassing, and see the muddy pools and hot springs of superheated water. Near Bumpass Hell is the ominously named Cold boiling lake Here too, we see an abundance of carbon dioxide bubbles caused by outgassing from magma far below the surface.
So that’s the Cascade Mountain Range from British Columbia to California. If you want to revisit any of the areas along the range, here are some links:
As always, if you want to see these images in high resolution, check out my Cascade Volcano Archives seen from space.
