Seeing Volcanoes Inside and Out: Exploring California's Volcanoes

Our just completed exploration of Northern California's Volcanoes was a fascinating journey through the interior and exterior of several volcanoes. How do you explore the innards of a volcano? On the one hand, you can do a Brendan Fraser and fall thousands of feet or miles into a volcano ("Journey to the Center of the Earth", a movie I appreciated mostly for the living trilobite in the opening scene). Or...you can wait for the volcano to go extinct, be uplifted and eroded for millions of years, and then be established as Castle Crags State Park, and go stand at the viewpoint at the end of the park road. We chose the latter.

The Castle Crags are an especially scenic part of the Klamath Mountains province, a region tucked between the Coast Ranges and the Cascades at the north end of the Great Valley (I've written about them previously, click here to see). Most of the Klamaths are composed of dark colored metamorphic rocks, many of them derived from the mantle, but at Castle Crags the rocks are different. The light colored cliffs are composed of granitic rock (mainly granodiorite, a plutonic rock containing lots of plagioclase feldspar), dating back to around 160 million years ago. The granodiorite was once molten, feeding volcanoes that would have existed several miles above where we were standing. Some of the magma remained in crust, cooling slowly and allowing for the growth of visible crystals. Standing among the granitic towers of Castle Crags is to be standing in the interior of a volcano.

The dramatic spires are the result of exposure at the Earth's surface, and the resulting release of pressure (remember that these rocks formed at a depth of three or four miles in the crust). As the pressure is released, the rock expands and fractures, sometimes in vertical cracks called joints. The joints are exploited by water and ice, leading to the erosion of the steep sharp cliffs.

Sometimes the expansion of the granitic rock is outwards, parallel to the surface of the cliff. This causes fractures that act to remove corners and edges, resulting in dome-like cliffs, much like those found in Yosemite and elsewhere in the Sierra Nevada. This process is called exfoliation.

Even as we stood at the viewpoint appreciating the underside of a volcano, we could turn to our right and see a rather astounding view of the outside of a volcano. A very big volcano. Mt. Shasta is the second tallest peak in the Cascades Range, exceeded only by Mt. Rainier, but it is the most voluminous stratovolcano in the Cascades, and perhaps even the world.

At 14,179 feet, it dominates the scenery from all directions in Northern California. A stratovolcano is composed of alternating layers of ash and lava, but the details of Shasta's structure contradict that description. It is actually the remnant of at least five different volcanoes which developed on more or less the same site. The term "composite cone" is perhaps a more accurate moniker.

Shasta was our next stop of the day. At over 14,000 feet, no roads approach the summit, but in years past a ski area had been constructed at the 8,000 foot level on the south side of the peak. The ski resort was removed long ago because of avalanche danger (a wide swath of fallen trees highlights the hazard), but the paved road remains.

We took the highway out of Mt. Shasta City and headed up the mountain...

So Much for the Green Flash...But is the Coast Toast?

So much for the green flash...the consensus seems to be that I didn't see one, although I stubbornly hope that I saw it but just didn't happen to photograph it...anyway, courtesy of wikipedia, here is what one type of a real green flash, a mock-mirage flash, looks like.

I'm thinking that seeking a green flash and failing like I did is a bit like those first few times panning for gold. You'll see pyrite (fool's gold) a dozen times and think it might be gold, but when you see a gold flake for the first time you'll never misdiagnose pyrite again. I shall keep searching for the green...

I enjoyed the sunset that night immensely. There were all kinds of things going on, in the sky and over the water. The optical effects of a setting sun are always interesting of course. The distortion almost looked like a bomb blast. Or a light bulb...

It was interesting to see the amount of damage that has been done by wave action. This used to be part of the parking lot at Leo Carrillo beach. This is a look at the future; rising sea level and declining supplies of sand can only mean that coastal erosion will be increasing in extent and intensity.

 The seas were calm on this late summer afternoon. The effect was hypnotic and peaceful.

There were dozens of pelicans flying west along the coast line.  I love how they glide just inches above the waves; they are such graceful fliers. The Brown Pelicans almost disappeared in the 1960s as they absorbed so much DDT in their diet that their eggshells weakened and broke. With the ending of the use of DDT as an insecticide in the 1970s their population rebounded strongly.

What a shame it would have been if they had disappeared entirely. Does anyone besides me and Steven Spielberg think that they look like resurrected pterodactyls?

The sun sank below the horizon and the clouds briefly turned orange and pink. We headed back to camp up in the canyon.

I glanced at one of the rocks on the beach that was being used as rip-rap (wave barriers). The holes made me wonder about something. Fifteen years ago a movie was released to a certain amount of derision among geologists: Volcano. Tommie Lee Jones played a gruff but lovable emergency services director, and Anne Hecht played the geologist with the heart of gold. The volcano sucked (literally it sucked: Anne's friend in the movie got sucked down a hole into the lava). There were earthquakes, there were exploding buildings, there were lost children, and melting people.

Obviously, the idea of a volcano erupting in downtown Los Angeles is preposterous. There must not be a volcano within hundreds of miles of the city. I mean, there aren't any volcanic mountain ranges in southern California...right? The faults are all strike-slip and thrusts. It just doesn't seem likely. So how to find out? Maybe, a look at the interactive geologic map of California from the California Geological Survey (clue: most of the volcanic rocks on the map are pink or orange...).

Is the coast really toast, or is it already toasted?

Geological Jealousy: Why don't I get to see this in California?

This spectacular image comes courtesy of Halldor Sigurdsson at Iceland banking crisis news and more, who has been providing some nice coverage of the ongoing eruption at Eyjafjallajokull (you may be sure that I didn't spell that from memory). More pictures and a nice aerial video can be found here. Note the cars parked at the edge of the lava flow. Yeah, I know most people run away from volcanic eruptions, but geologists and I guess Icelanders aren't most people! Erik at Eruptions has a nice rundown of recent activity.

Iceland is a volcanic wonderland, with the activity resulting from the country's location on the Mid-Atlantic Ridge (a divergent plate boundary), and possible location on top of a hot spot, perhaps similar to the one that underlies Hawaii. The precise nature of the conditions resulting in the volcanism is a concern of ongoing research.

So why can't we see this kind of thing in California? Well, actually we potentially could, but not for the same reasons. California does in part sit astride a divergent (or potentially divergent) boundary in a number of places. The Salton Sea and Imperial Valley area, for instance, sits in a deep trough caused by the rifting of Baja California. A few small volcanoes can be found near the lakeshore. The Basin and Range and Mojave Desert provinces in the eastern part of the state have also been rifted apart, and contain dozens of fairly recent cinder cones and lava flows. The northern Coast Ranges have a number of potentially active volcanoes in the Clear Lakes/Geysers region. And as I discussed in detail in the Other California series, the Cascades and Modoc Plateau provinces are both rich with recent volcanic activity due in part to the presence of the Cascadia subduction zone offshore to the west.

In short, our volcanoes don't erupt nearly as often as those in Iceland (39 times last century), but we do have lots of potential for future geological excitement. I would just love to see a modest eruption somewhere in the state, in one of remote spots anyway. Mt. Shasta and the Long Valley caldera are two places that I prefer would remain quiet...