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Clear Lake Volcano More Active Than Previously Thought

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Dormant volcano Mount Konocti rises from the western shores of Clear Lake, California. By Flickr user @leoville

In June I wrote about the threat to San Francisco posed by Mount Konocti, specifically the Clear Lake Volcanic Field. People seem to have forgotten the volcano, I lamented. Our earthquakes, landslides, and wildfires tend to overshadow California’s windows to the furnace churning beneath our feet. Scientists previously estimated the field last produced an eruption some 11,000 years ago. 

Now they’re saying it might be more active than we thought.

Volcanoes? In My Backyard?

That we have an active volcano a short drive from the city still takes many by surprise. Geologically, the field relates to the complex stretching and warping of the crust along the San Andreas Fault Zone. The Mendocino Triple Junction, host of December’s deadly M6.4 quake, once lay parallel to the Bay Area. It drifted to the north-northwest, spawning new sites of volcanism and snuffing out others as it zipped up the plate boundary. A volcano in the Berkeley Hills was active for around 1.2 million years.

Roughly ninety miles north of San Francisco, Clear Lake is the northernmost eruptive center in a chain of activity. It boasts the largest magma chamber of any California volcano. Not even Long Valley, a supervolcano which excavated a caldera twenty miles long and eleven miles wide, surpasses its 240-cubic-mile volume. Magma lies just 3,300 feet below ground at some points. The lakeside Mount Konocti, a lava dome not unlike Lassen Peak, rises to 4,305 feet.

Also like the Lassen Peak complex, Clear Lake contains a variety of volcanic features. Alongside Mount Konocti the area holds geothermal springs, maars and tuff rings, overlapping lava and pyroclastic flows. Eruptions range from relatively localized cinder cone formation to unpredictable steam explosions to superheated blasts of incinerating ash and gasses. Some eruptions left deposits of pulverized rock up to six feet thick. Today, around ten thousand people live on top of them.

On hazardous ground

Figure 2, J. Ball, 2022.

Let’s say a violent, energetic eruption occurs without warning. Ideally when volcanoes reawaken, they tell you through months of precursory activity like poisonous gas emissions and earthquake swarms. My unconfirmed fear is, with molten rock already so close to the surface, ‘stirring’ may quickly lead to ‘exploding.’ Destructive eruptions of steam and ash called phreatic bursts often catch people off-guard. Can ten thousand residents leave town with only a moment’s notice? 

Now let’s say the vent is not on Mt. Konocti proper but at or in Clear Lake itself. In certain eruptions, water can act like gunpowder, as seen at Hunga Tonga–Hunga Ha’apai in January 2022. It didn’t just amplify the undersea explosion to yield the most powerful volcanic blast since 1991. It also triggered a tsunami with an initial height of ninety meters, “roughly the height of the Statue of Liberty.” A string of waves emanated from the South Pacific, tearing boats from a Santa Cruz harbor 5,200 miles away.

A similar setup, albeit on a much smaller scale, exists at Clear Lake. A steam-fueled explosion through the interaction of lakewater and rising magma can inundate shoreline communities with tsunami-like waves. Evidence of blasts from the past lies on the lake’s cratered floor and around its scalloped outline. Ashfall could stall engines, ground planes, and bury homes before people have a chance to get out. The next eruption may play out this way, but let’s talk Worst-Case Scenario. 

Fire and Water

We’ve had a lot of rain lately. Except for the flood victims, most Californians are pretty happy with this. The trees and hills of the Bay Area will remain green for that much longer. It could even signal the end of our terrible drought. 

But if one of these atmospheric rivers we’ve been getting coincides with an eruption at Clear Lake? An incredible disaster could unfold. Near the volcano, torrential rains would mix with freshly fallen ash and create a slurry the consistency of wet concrete. Massive mudslides known as lahars could suffocate creeks and streams running off and around Mount Konocti. The battering force of a fast-moving lahar demolishes any obstruction with ease: bridges, houses, entire groves of forest.

The 1980 eruption of Mt. St. Helens resulted in several lahars, one of which tore loose and carried this bridge over a quarter-mile downstream. Public domain.

In the Bay Area and beyond, rainfall would capture ash particles suspended high aloft and drag them back to Earth. The result is a slick, blinding mud that falls in fat drops, clogging drainages and sanding paint off anything left outside. The FAA would’ve halted all regional air traffic. Nothing in or out of our three major airports—hot jet engines quickly choke on melted ash. Under a microscope, volcanic ash looks like jagged shards of glass.

Local governments will issue shelter-in-place order for residents. Ash is hazardous to the lungs. Breathe too much and it’ll thicken the fluids naturally present in your alveoli. Drivers will wipe out on ashy, wet roads whether or not it rains. Accidents would dot northern Highway 101, if by a miracle it doesn’t get shut down. 101 runs less than thirty miles from the summit of Mount Konocti. 

A hazy future

After the eruption subsides, Northern Californians will find ash in their sills, cars, and gutters for years to come. Black and grey streaks will accumulate on the windows of highrises following every shower. It turns out this could happen sooner than later. Dr. Jessica Ball published a study in September detailing her findings at Clear Lake. She located traces of six untallied eruptions that occurred between nine and thirteen thousand years ago, earlier than originally thought.

Given the populous flanks of the volcano, the United States Geological Survey designated Clear Lake a high threat. It might be difficult to picture the awesome violence that shaped the gorgeous forest and chaparral-covered hills. Here’s hoping that image will belong only to our imaginations. If a volcano has erupted since the last Ice Age ended around 11,500 years ago, geologists consider it active. 

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Jake Warren

Jake Warren

A Potawatomi nonfiction writer and Tenderloin resident possessing an Indigenous perspective on sexuality and a fascination with etymological nuance. Queer decolonial leftist, cannabis industry affiliate, seasoned raver, and unofficial earthquake authority.


  1. January 4, 2023 at 8:03 pm — Reply

    Wrong: Scientists previously estimated the field last produced an eruption some 11,000 years ago.

    Now they’re saying it might be more active than we thought.

    In fact it’s most dormant and erupted some 800,000 years ago. Although dormant volcanoes have been known to erupt violently, Clearlake has not and liquefaction movement is normal; specifically around the geysers.

    Other earthquakes seemingly nearby, are actually due to plate tectonic movements that are not generally related to volcanic zones.

    How did I do to explain this?

    -broke too, but oh well.

  2. Jake Warren
    January 10, 2023 at 2:03 am — Reply

    Hi! Please refer to the paper by Dr. Jessica Ball (mentioned in the second-to-last paragraph), from which gathered most of the details for this article. Thanks for reading!

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