This weekend I decided to haul Rebecca out to Mono Lake and spend some time nerding out. The Eastern Sierra has some crazy geology and it was high time that I learned more about it. I was helped in this endeavor by a few sources, although I am particularly in love with Geology Underfoot in Yosemite National Park.
Mono Lake provides clues that give us a glimpse of what California’s climate looked like many years ago. The amount of water in the lake has fluctuated greatly over it’s long history. In these photos from Black Point you can see how much the lake has shrunk since it’s tributaries started being diverted to Los Angeles in 1941. They were taken from a spot that would have been near to the shore of the lake in 1941.
On the other side of the lake there is a string of mountains, which seem pretty tiny compared to the giant peaks only a few miles away, but that hold their own surprises. They’re the Mono Craters, and they are the remains of Volcanos that erupted only recently in the geologic sense of the word. (600-40,000 years ago.)
We hiked around, Panum Crater the smallest of the chain, and the easiest one to hike.
It begins with a short uphill hike as you climb over a ring of material that was blasted from the volcano during it’s eruption. (There’s a great aerial photo here if you’re having trouble picturing this.) As magma was rising through the earth’s crust it came in contact with ground water near the surface. This created steam, which built up a lot of pressure, causing the mixture of lava and steam to fountain upwards and outwards when it erupted. The lava/steam mixture cooled quickly creating pumice: one of the weirdest rocks I’ve ever encountered.
There was so much gas trapped in the lava when it cooled that it formed a rock that is unbelievably light. It’s feels more like holding a dried out sponge than rock. It’s also fairly brittle and creates a strange soft sand which makes climbing a giant pile of it loads of fun.
The inside of the crater did not disappoint either.
After the exploding fountain of lava had calmed down, magma continued to be pushed up towards the surface but at a slower pace. (The signs described it using the analogy of an oozing tube of toothpaste.) At Panum Crater it slowly formed a dome topped with these pillars.
Because the lava didn’t have much gas in it, but still cooled fairly quickly, most of the rock at the center is glass-like obsidian. (The darkest of the three rocks in the picture above.) Obsidian is important for the area because it was used by the Pauite for arrowheads and a number of other tools, and was traded across the Sierra Nevada. It’s also sharp and uncomfortable to sit on, but on the upside, it totally sparkles in the sun.
There are a ton of things to be explored around Mono Lake, you could probably keep an entire blog just about birding in the area. I’ve barely scratched the surface of geology in the Eastern Sierra, but it was fun to go out and adventure with this specific goal in mind.
This needs to happen again.