Because the summer season wraps up, additionally it is time to wrap up my tour of the Cascade Vary volcanoes as seen from area. The fashionable Cascades lengthen into Northern California and is the house of doubtless the most important volcano of the chain … however the Earth’s plates are plotting the tip of the Cascades, ranging from California.
The ocean plates that spawn the magma that varieties the Cascade volcanoes are younger and small. The Juan de Fuca plate is accountable for the volcanoes from Oregon to British Columbia (save for a sliver of the micro-micro Explorer Plate off Canada). Nonetheless, when you cross into California, one other micro-plate will get concerned: the Gordo Plate. Generally lumped into the Juan de Fuca plate, the Gordo Plate is discovered off the very southernmost coast of Oregon and continues all the way in which all the way down to space close to Mendocino in northern California.
Triple the Enjoyable
It’s off the coast of Mendocino the place one thing fairly distinctive exists: a triple junction. Right here, three tectonic plates come into contact: the Gordo Plate, the Pacific Plate and the North American Plate. This triple junction implies that south of Mendocino, subduction is not taking place anymore however as an alternative the 2 plates (Pacific and North American) are sliding aspect by aspect – a movement referred to as “strike-slip”. This remodel boundary is the rationale the San Andreas fault system exists.
The triple junction is not stationary, although. It’s slowly migrating northward relative to North America, which means subduction is being changed by remodel movement … and with that comes the tip of volcanism. The southernmost volcanism within the Cascades has been transferring north at a price of 15-20 kilometers per million years. Presently, the Lassen Volcanic Middle is the tip of the Cascade Vary.
So, because the triple junction crawls in direction of Oregon and Washington, the Cascade Vary will doubtless shut off till everything of the west coast of North America is one lengthy remodel boundary.
Fortunately for us volcanophiles, we bought a very long time to go earlier than that occurs. Let’s have a good time the volcanoes that we now have as we speak, protected within the data that they’re going to doubtless be round for a whole bunch of 1000’s to thousands and thousands of years extra.
Talking of which, after we cross the border from Oregon to California, the monitoring of the Cascade Vary modifications as effectively. As an alternative of the Vancouver (WA)-based Cascades Volcano Observatory expecting restlessness, it’s the comparatively new California Volcano Observatory (CalVO). Fashioned in 2012, CalVO has purview over the California Cascades, the Lengthy Valley Caldera space, the Salton Sea and Mojave volcanoes and anything that occurs within the Golden State.
Drugs Lake
Drugs Lake volcano seen by Sentinel-2 on October 4, 2023. Credit score: ESA.
Drugs Lake, like Newberry in Oregon, is a little bit of an oddball. It sits behind (additional east) the principle alignment of the Cascade Vary, nestled up towards the Basin & Vary province to west. The volcano is called for the lake that sits in the course of the 7 by 12 kilometer caldera at its summit.
In some ways, Drugs Lake is a twin of Newberry. It, too, is a broad defend volcano capped with rhyolite lava flows. The eruptions that fashioned Glass Mountain, named due to the glassy (obsidian) nature of the lava had been about 1,000 years in the past. It is a few hundred years earlier than Newberry’s Massive Obsidian Circulate. Glass Mountain, unsurprisingly, is a standard supply of obsidian in instruments throughout western North America.
And very similar to Newberry, Drugs Lake is surrounded by basaltic lava flows filled with lava tube caves. These eruptions that comprise a lot of Lava Beds Nationwide Monument had been made well-known within the late nineteenth century by Native Individuals that used them to cover throughout battles with American troopers.
There are some unsubstantiated stories that Drugs Lake may need seen some explosions round 1910, however there’s little to no bodily proof. Nonetheless, the panorama is pockmarked with small craters from the handfuls of eruptions which have occurred over the previous few hundred thousand years.
Shasta
Mount Shasta seen by Sentinel-2 on September 14, 2023. Credit score: ESA.
Mount Shasta is massive. The quantity of the volcano is over 350 cubic kilometers (~84 cubic miles). The truth is, Shasta is best stated to be a volcanic complicated quite than a single volcano. There may be the principle Shasta edifice (the Hotlum cone) after which smaller Shastina constructed on its aspect. We may even lump within the barely separate Black Butte.
Every part about Shasta is spectacular. It in direction of over the panorama of Northern California. When you have ever pushed down I-5 from Oregon to California, you’ve gotten pushed by way of one of many largest volcanic particles avalanche deposits recognized that destroyed the unique volcano. That avalanche from ~300,000-380,000 years in the past moved 45 cubic kilometers (10 cubic miles) of fabric, or 18 occasions greater than the avalanche from the Might 1980 eruption of Mount St. Helens!
Shastina fashioned round 9,500 years in the past with a sequence of explosive and dome-forming eruptions of andesite lava. Black Butte (west) is about the identical age however the lava erupted there are extra dacitic, which means they’re greater silica and had been doubtless extra silica wealthy. Each of those eruptions despatched pyroclastic flows down the valleys round Shasta.
It has been rather less than 800 years for the reason that final confirmed eruption of Shasta. If it had been to erupt once more, we would anticipate lava flows. They present up fairly effectively on the satellite tv for pc view of the volcano. We’d additionally anticipate pyroclastic flows and lahars (mudflows) which have travelled tens of miles from the volcano up to now. The geologic report at Shasta suggests an eruption each 600-800 years. This doesn’t imply we’re “due” for a brand new one, but it surely does make it one of many longer intervals of quiet at this large volcano.
Lassen
The Lassen Volcanic Middle seen by Sentinel-2 on September 24, 2023. Credit score: ESA.
Apart from Mount St. Helens, the Lassen Volcanic Middle is essentially the most lately energetic volcano in all of the Cascades. Lassen Peak erupted from 1914-17, creating what is known as the “Devastated Space” the place pyroclastic flows and lahars raced down the volcano. That eruption was fairly small, solely rating as a VEI 3 as a small dome of dacite fashioned on the summit of Lassen Peak.
A a lot larger occasion within the Lassen Volcanic Middle was the formation of Chaos Crags. These rhyodacite domes fashioned to the north of Lassen Peak solely about 1,100 years in the past. Doubtless these eruptions had been explosive in addition to producing the massive lava domes that stand there as we speak. There may be additionally a big avalanche deposit (Chaos Jumbles) that got here from the domes. You’ll be able to see it to the north of Chaos Crags within the higher left hand aspect of the picture.
In between these occasions was the eruption of Cinder Cone on the sting of the LVC in ~1666. You’ll be able to see Cinder Cone within the prime proper hand nook of the Sentinel-1 picture, with the darker lava flows standing out relative to the lighter floor that was scorched by fires just a few years in the past.
Due south of Lassen Peak close to the underside left nook of the picture is Bumpass Hell, an space of vigorous hydrothermal exercise. You’ll be able to stroll throughout Hell and odor the sulfur degassing and see mudpots and sizzling springs fed by superheated water. Near Bumpass Hell is the ominously named Chilly Boiling Lake the place plentiful carbon dioxide bubbles may be seen, once more coming from the degassing of magma far under the floor.
So, there you’ve gotten it, the Cascades from BC to California. If you wish to revisit wherever alongside the chain, listed here are the hyperlinks:
As all the time, if you wish to see these photos at greater decision, try my depository of Cascade volcanoes from area.
