Published: March 17th 2012March 17th 2012
Fumarole outside of geothermal plant in Mammoth Lakes.
After a brief hiatus, I'm on the flight home now and will post the rest. Hope you enjoy, I know we all sure did.
Day 6! 14 March 2012. As I said at the end of last night’s blog, there is nothing to report from last night because I spent an inordinate amount of time writing it, so I just went to bed. With so much geology in store, let’s get right into today, shall we? Our first stop was at a geothermal plant where we would encounter geothermal vents, or fumaroles, that are evidence of an existing magma chamber which could be used to generate electricity (photo 1048). Fumaroles escape from through fissures (cracks) within the earth (in this case, it is a crustal magma chamber somewhere on the order of 8-10km deep) An overly simplified chain for this process goes a little like this: Geothermal fluid runs up from an injection well. When it rises, it comes into contact with isobutene at a heat exchanger. Because isobutene has a boiling point at 11 degrees Fahrenheit, when the 320 degree geothermal fluid exchanges its heat, it turns into a high pressure steam (depending on perspective, of course.
U-shaped valleys and moraines visible in the Sierra Nevada from Panum Crater
It’s 450lb steam, submarine propulsion experts try not to scoff). So our steam (not sure why I just gave us proprietorship of the steam) eventually turns a turbine, which drives a gear wheel in a generator and ultimately produces enough electricity to power approximately 3500 homes, all in the Los Angeles area (photo 1048). I thought this stop was really cool because of the practical application of geology and science into a renewable energy source for humans through engineering. After a quick Q&A with Dan and the delivery of our pretty lame Columbia University chant, it was onto the next stop!
The next stop was at Panum Crater which provided some absolutely ridiculous hands on geology. Panum is a site of volcanic eruptions extending from 40,000 years ago to most recently just 650 years ago. This crater was the source of 18 out of 19 ash layers found in the Mono Basin sediment. On the crater itself, we were exposed to highly viscous (high levels of silica and quartz) rhyolitic rocks, namely pumice and obsidian (chemically identical rocks, but different in appearance and structure because of the rate at which they were cooled). Allow the record to show that
Adam sailing on top of a spire in Panum Crater
I was a much bigger fan of the pumice which were unbelievably light for their size….. oh, and the obsidian and its glassy edges cut me. The crater provided some unbelievable views of the Mono Basin. We were able to get a bird’s eye view of everything from the lake itself, to Black Point and the glacial carvings out of the Sierra Nevada (photo 1055, 1069). The basic geologic structure of what we were looking at (very, very, basic) was a rhyolitic volcano that erupted, spewed pumice ash, “breadcrust bombs” (which are pumice stones ejected from the volcano that develop and obsidian “crust” around its edges as it cools. You can see the distinct layering difference between the outside of the shell and its core. Photo 1062) As the viscous rhyolites began to cool, they cracked and allowed for magma to climb in between. This led to the “plug” feature being pushed up into spires, which eventually crumbled throughout the canyon allowing us the opportunity to see all of our rocks! (photo 1057) Other geologic features worth mentioning were teardrop lapilli which are pyroclastic debris that form as they are flying through the air. The “teardrop” shape is a result
"Teardrop" lapilli found in the crater.
of aerodynamics (photo 1061). There is a lot to say about this outcropping (it was definitely my favorite of the day), but the moment I will take away is the hike to the crater’s highest peak and the view out over the basin (Black Point, the source of ash 2 in the left center of the photo, its flat appearance is because of submergence during the time of eruption). Even though we all would’ve loved to stay for much longer, it was time to move on.
Next stop after lunch and some sightseeing in Mammoth was the South Tufas of Mono Lake. Tufa towers are precipitated calcium carbonate structures that climb and fossilize springs throughout the lake. The lake is a part of the larger, surrounding Long Valley Caldera (a caldera is essentially a sink hole left when a magma chamber erupts causing a void in the crust underneath. The mass above the chamber then sinks in to fill the void.) which is fed by springs that are heated by the magma chamber. This fresh water is rich in dissolved ions, most notably calcium. Because the lake is so saturated in carbonate (so saturated, in fact, the lake is
Breadcrust bomb from the crater
incredibly basic, nearly a 10 pH level.), when the calcium from the fresh water contacts the lake water it solidifies into the magnificent tufa structures that can be seen all around the lake. That makes for identifying past and current springs pretty easy! We were fortunate enough to be shown a video put together by the Mono Lake Committee explaining many of the geological and ecological features of the lake and its basin. The committee was put together after the future of the lake was put in serious peril by diversions of the streams that feed it to provide drinking water for Los Angeles. The reason why they pulled from the streams instead of the lake is because (and I’m not sure if I mentioned this before, but I don’t feel like reading over everything again) Mono Lake is terminal; meaning water doesn’t flow anywhere else after it enters. The evaporation process leaves behind the dissolved ions and minerals which are the ultimate cause of the salinity level being 2.5 times higher than normal sea water. Just to be sure, we were all encouraged to taste it. It was pretty salty and bitter! It is this same evaporative process that
View from the top overlooking Mono Lake
saturates the lake in carbonate. Armed with some background knowledge, it was time to head out into the field! We were accompanied by Bartshe Miller, the Education Director for the Mono Lake Committee, who provided us with a more in depth understanding of the basin. He also brought along some materials for us to make some tufa of our own! All it took was some lake water to be mixed with fresh water enriched with calcium and voila! Tufa. (photo 1074). Continuing on down the lake shore, we skipped a few rocks and went to see some tufa structures! They were incredible and actually, the pictures turned out really well! (Photos 1075, 1076, 1077) We even found a spot along the lake where tufa was currently forming at the lake’s edge, indicating the presence of an active spring nearby (photo 1080). From there, we walked a little ways down the trail to find an active hot spring! The water coming to the surface was around 95o
F. I took a moment to trudge through the mud and dip my finger in, it was worth it! Very cool (or hot). One last spot along the trail we wanted to hit was Navy
Hannah showing off her homemade tufa.
Beach. The beach got its name from its service to our country as an ordinance test site in the 60’s. What we found here was sand tufa. As it sounds, these were tufas with sand mixed in. This was the result of the lake level lowering, resulting in the spring being near the shoreline. As we know from sediment sorting, fine grain sands can be found along the shore. These tufas were much darker in appearance and much more brittle in structure (photo 1083).
Our final stop of the day, as decided by popular vote, was going to be the obsidian dome. This stop turned out to be more for playing in the snow and having some fun than any hardcore geology. While the 6 inches of snow may have been impressive for some without the exposure, to us Buffalonians, it’s only a dusting. None-the-less it was a cool stop to see a vast outcropping of obsidian that arrived there similarly to the way the obsidian at Panum Crater ended up there. It was highly viscous (remember high quartz and silica content making it very thick) and stacked in a dome fashion on top of its source. There were
Tufa in Mono Lake
some rocks with the polygonal cracks as well, which we all remember forms from the natural cooling process (photo 1086). Another day was in the books and we went back for dinner, blogging and a movie! See you tomorrow, bloggers!
There are more photos below