Day -2: Mono Lake

What an awesome way to start my trip!

I woke up bright and early this morning (without an alarm - Can you tell I'm excited?), and hit the road. I made great time, and before I knew it, I was coming over Echo Summit, just in time to see the sun rise over Lake Tahoe. After a brief stop - gotta have my morning Starbucks! - I drove on to my main stop for the day, Mono Lake.

A lot of people know about Mono Lake from the environmental issues in the 70s and 80s. I'm not really going to go into that, feel free to read up elsewhere on the web. It should suffice to say that Mono Lake is recovering nicely, and is an absolute must-see if you are anywhere near the Eastern Sierras.

My interest in Mono Lake, especially as it pertains to Spaceward Bound! is twofold. First is the formation of the tufa towers - those strange, white rocks in the middle of the lake. Since this is an Astrobiology blog, it should be natural to talk about the Carbon/Silicate Weathering Cycle. Atmospheric carbon dioxide reacts with water vapor to form a weak solution of carbonic acid. This acidic rainfall dissolves silicon-calcium rocks, forming SiO2 (the mineral in quartz) and calcium in solution. Normally, this calcium would flow to the ocean, where marine organisms would take it in, add some carbon dioxide, and make shells and bone out of it. The shells eventually settle to the bottom of the ocean, and over millions of years, eventually get recycled into the high pressure/temperature areas in the Earth's crust subduction zones. Those same high temperatures and pressures re-form the compressed shells (probably better known as limestone) into the original calcium/silicon rocks, and release the carbon dioxide, back into the atmosphere through volcanos.

Now, because Mono Lake has no outlet, it relies entirely on evaporation to maintain its level. Which also means that, while the water vapor will evaporate, any minerals that it brings with it stay behind. Mono Lake is extremely salty and alkaline - 2 1/2 times as salty as the ocean, and 80 times as alkaline. This unique chemical (im-)balance means that Mono Lake doesn't need marine organisms to precipitate out the dissolved calcium from rainwater. When underground springs, carrying the calcium flow out into Mono Lake, under the surface, the calcium immediately reacts with the bicarbonate in the water, forming the limestone towers. Although these can only be formed underwater, because Mono Lake's level has fluctuated (it's 25 feet below its 1941 level, and over 900 feet shallower than its peak depth after the last ice age), many of these tufa are now visible above the surface.

The second reason I wanted to visit Mono Lake is to see all the volcanic formations in and around it. The two major islands were both formed by underwater volcanic vents. Paoha Island remained underwater, after its eruption, and was partially covered in a layer of tufa. Negit Island (and Black Point - which was an island when the water level was about 400 feet deeper), rose above the surface of the lake before it could be covered in tufa, so it is much darker.

My real adventure for the day came when I stopped off for a hike around Panum Crater. About 650 years ago, Panum Crater was an active volcano. Today it lies dormant, and you are able to walk around the rim, into the crater, and onto the lava dome in the center.



This picture shows one side of the lava dome and you can just barely see the rim of the crater curving around behind the dome in the right of the picture. The crater is an amazing assortment of volcanic rocks. Around the outer rim is a mixture of crushed light pumice, obsidian flakes and an occasional small piece of Rhyolite. All three of these types of rocks have similar chemical composition, but vary vastly in appearance due to how they were formed. Obsidian is formed when volcanic lava, containing very little dissolved gasses (like the carbon dioxide from the carbon cycle above!) cools quickly. Pumice, the very light, porous rock, is formed when the same type of lava contains lots of dissolved gas and cools quickly, trapping the gas bubbles. Rhyolite is what forms when the same lava cools slowly. In this case, any dissolved gasses have time to escape. In addition, because the lava is cooling slowly, crystals of quartz (SiO2), plagioclase (combinations of NaAlSi3O8 and CaAl2Si2O8) and feldspar (combinations of KAlSi3O8, NaAlSi3O8 and CaAl2Si2O8) have time to form.

What made my day completely cool was a lucky stop by the Lee Vining Chamber of Commerce/Visitor's Center and a chance encounter with an Inyo State Forest Ranger. When I mentioned my interest in the geology of the region to the nice folks of the Chamber of Commerce, they suggested that I go to Obsidian Dome, where I would be able to collect some samples to share with my fellow Spaceward Bound! scientists. I thought that was a great idea, and headed off on another adventure. At the entrance to the Obsidian Dome road, I happened to meet up with a Ranger, and talked with him for a while. I wanted to make sure that it was ok to collect samples from this location. He said that it is ok, but only in small amounts, on the order of a gallon pail per person, which was fine by me. He also told me that the road to Obsidian Dome was still pretty soft (there was snow in several places), but told me where I could find a place with much more easily reachable volcanic rock samples. To make my long story short(er), I now have a bunch of samples of obsidian for some of my fellow scientists to take back to their classrooms after the expedition.

All-in-all, a perfect start to the week!