Tuesday, September 30, 2008

Class Project: East side of the Sierra

This semester I am taking an Advanced Volcanology class focusing on hydrovolcanism. A few weeks back I was preparing a talk for phreatomagmatic fragmentation and I was going to use photos I had taken on previous excursions to the eastern Sierra. Unfortunately, I did not have any photos of what I needed, so with my free weekend camping in Mammoth Lakes sounded great to me.

I stayed in the Twin Lakes campground and spent some time visiting different geologic sites in the area. The first picture was taken from my cot and is called the Dragon's Back, a ridge extending from Mammoth Mountain. The second photo is Twin Falls. If you have never been to the Mammoth Lakes area, the Lake Mary area is an awesome place to camp. There are 6 lakes with several different campground available and Twin Falls is located between Lake Mamie and Twin Lakes. With the activity of Mammoth Mountain in the 1980's, the highest elevation lake in the area, Horseshoe Lake, has been closed due to high levels of carbon dioxide at ground level. The area reminds me of a moon landscape because all plant life has been killed. The third photo is Twin Lake.

Traveling away from the Lake Mary area to the other side of the Mammoth Mountain is Minaret Summit, a place where you can see the Middle Fork of the San Joaquin River drainage, Ritter Range, and take a shuttle down to Devils Postpile National Monument during the summer time. The fourth photo is of the Ritter Range, the mountain peaks in the picture from left to right are Mt. Ritter, Mt. Davis, Rodgers Peak, and Mt. Lyell. The last photo is Mammoth Mountain, which is a major mountain biking and skiing resort destination for the Southern California area. The ski lift is visible at the top of the mountain.

More of the Mammoth Lakes area in the next blog.........

Thursday, September 25, 2008

Lassen Peak: May 1915 lavas

Once on top, we hiked across to get an aerial view of Chaos Crags considering I was suppose to be completing field work. The 1915 eruptions produced 4 different types of lavas 1) hybrid black dacite 2) andesitic enclaves 3) a banded pumice with dark andesite and light dacite and 4) unbanded light dacite (Clynne, 1999). Sorry, I didn't get extreme close ups of the lavas, I just realized this looking through my photos, darn I will have to hike the trail again. : o ) Instead, I took the artsy approach to photographing the lava.

The stay on top was very peaceful once we hiked away from the small crowd on top. Taking in the moment of hiking across lava on an active volcano, I thought of a story I had heard involving the early eruptions of Lassen Peak. The story is about three local guys who went to investigate Lassen Peak after one of it's small eruptions. Reaching the peak, they wanted to look down the vent, only to have the volcano produce another small steam eruption that sent tephra raining down on the guys. One man got hit in the head with a block and was knocked out, while his friends ran like hell. When the activity ceased, the two friends went back to check on the one friend, who they thought would be dead. Instead, they found was he was ok with just a bump on the head. I love this story because when I go on trips to very active geologic areas I secretly hope for a volcanic eruption, large earthquake or other natural disaster. But on the other hand, what good friends he had leaving him lying there in a dangerous moment. I have been lucky enough to witness small rockfalls and feel small earthquakes on various trips but nothing on the factor I am looking for.
The first three photos are the 1915 lavas at varying locations. I pretty much hiked though the entire lava field on top, because I thought it was the shorter way to get back to the main trail! The fourth photo is the aerial view of Chaos Crags. I left Melinda to rest and set out on an adventurous hike out to the furthest point possible without falling 1000 ft to my death. I think the small ridge could of been possible but I didn't want to chance it, I am still young and have a lot of life still to live. The last photo is from Lake Helen looking northeast to the grand peak.
Clynne, M.A., 1999, A Complex Magma Mixing Origin for Rocks Erupted in 1915, Lassen Peak, California; Journal of Petrology, v. 40, 105-132.

Wednesday, September 24, 2008

Made it to the top!

Well, we made it to the top! As I said in the last post, I completed the 2.5 miles in 1.5 hours. I love testing my body hiking. I am not in perfect shape, but I can hold my own. So all of today's pictures were taken along the trail at various locations. The trail starts out in pine trees, then the trees get smaller, and then there is no plant life at all. The first picture is the north facing barren slope of Lassen Peak. The barren slope is evidence from the 1915 eruptions that caused the Devastated Area (see previous post). Lenticular clouds are also very interesting and make great contrast for the picture.
The second picture was taken to the southwest and has a view of Brokeoff Mountain. Brokeoff Mountain is actually a remnant of Brokeoff volcano ( I have also heard it called Mt. Tehama) that started forming over 600,000 years ago. The volcano was estimated to be 12 km in radius, over 3350 m high, and have a reconstructed volume of 80 km3. The andesitic volcano has been eroded over time by volcanic processes and glaciers (Clynne, 1990).
The third picture exhibits prismatic jointing in the rock and is just interesting to me. The last picture is Me and Melinda on top. We are just two friends enjoying the experience!
Next blog, pictures of the May 19, 1915 lavas.
Clynne., M.A., 1990, Straitgraphic, Lithologic, and Major Element Geochemical Constraints on Magmatic Evolution at Lassen Volcanic Center, California; Journal of Geophysical Research, v. 95, 19651-19669.

Monday, September 22, 2008

Declaration of a National Park: Almost to the top!

So for my last day of my field work, I decided that I would not try to hike to Domes A, B and C, seeing I was tired from the previous two days and instead climb Lassen Peak to get an aerial view of the Chaos Crags. It is no means an easier hike, it is actually harder, and I know I can get aerial images from Google Earth, but the excitement is not as great as climbing one of the world's largest volcanic domes in 1 and half hours!

The view above is Lassen Peak from the Devastated Area (northeast of the volcano), named for the mud flow, avalanche, and pyroclastic flow that was released during explosive events on May 19 and 22, 1915. Luckily, no one was killed during these events, but several houses were destroyed along Hat Creek. From prolonged volcanic activity starting in 1914 and lasting to 1917 and the striking natural beauty of the area, Lassen Volcanic National Park was created in 1916.

The above picture is the black dacite lava flow that was erupted on May 19, 1915. This picture was a telephoto shot from the Devastated Area. The flow is more prominent on the southwest side of the volcano.

This feature located on the side of Lassen Peak is just interesting to me. It is called the Vuclan's Eye (this is for the Star Trek fans). I don't know the whole story on how it formed, it looks like some kind of prismatic jointing to me. Any guesses?

So we begin an epic journey up the 2.5 mile trail and over 2,000 ft of evelation gain. This was the second chance I had to hike the trail, but the first chance with amble time to do so. If you ever end up in Lassen Volcanic National Park, Lassen Peak is one of those must do hikes!

Wednesday, September 17, 2008

Second day of field work

On the second day of field work, we were going to get a real early start, of course that is if you get out of your sleeping bag. So we got a late start, but that was ok because it took only an hour reach Dome C (below picture).

We spent a good chunk of the day exploring Dome C, looking at enclaves and breaking rocks. Upon investigation, it was hard to tell what rocks were part Dome C and the Chaos Jumbles. It was also hard to find a fresh piece of the host dacite for Dome C, most of the rocks were highly altered. I did find all three types of enclaves, but the fine grained enclaves were not as abundant as the coarse grained and acicular enclaves. Then we headed east for Dome E (below picture).

Dome E was a fairly steep hike, but it was back in the tree line and did not have as many dangerous loose jagged blocks to hike over. There was still abundant enclaves, but many were smaller than a foot. Also this rock appeared harder, or maybe I was just tired from swinging my sledge hammer all afternoon. So we worked until late afternoon and started to head back, by then we over 4 challenging miles from the car. We had a decision to make, go back the way we came and have to climb up and over several large ridges to get back to the Chaos Lake Trail or make a straight line over the Chaos Jumbles and walk along road to get back to the car. So we opted for the last choice and that was still tiring.

This last photo was a beautiful sunset over Manzanita Lake, there was a bunch of people fishing, it was quiet and peaceful and it was a great way to end the day.

Heads up for the last day of field work, it involved the biggest elevation gain of the weekend!

Friday, September 12, 2008

More of the first day of field work

The loose blocks are part of the Chaos Jumbles with Dome C (straight back) and Dome D (peeking out over the trees). Hiking this area is difficult, as it is a bunch of loose blocks for miles and good balance is needed, because you will see why later.

In a previous post, I said the Chaos Jumbles were the result of Dome C collapsing around 300 years ago. When the dome collapsed it traveled down the north slope for several miles, ran up against Table Mountain on the other side of the valley, turned west and came to rest after several more miles. Manzanita Lake formed because the jumbles acted as a dam.

So back to the enclaves that are the key to my project. I really liked this enclave. It has both the medium and fine grained enclaves with host plagioclase. The size of enclaves for the Chaos Jumbles ranged from mm's to one I saw that was 2 ft, but it was the largest one I saw. Most where around a ft or smaller.

Tuesday, September 9, 2008

Field work

It has actually been awhile since I last posted a blog and I finally got to my field area. The above picture is after eating lunch in Anderson, CA at a Panda Express. I was laughing at the view, not many fast food joints have such a great view, so I figured the picture was a great way to start out the trip! If you want to know where Lassen Peak is look above my head. I was hoping that Lassen was not going to be busy and it wasn't. The weather was beautiful and the sky a wonderful blue color. So we set up camp and embarked on my reconnaissance trip of my field area.

So when we got there Wednesday afternoon, we didn't really have a plan, so we decided since I had not hiked the Chaos Jumbles in detail, that is what we would do first. A refresher, in case you forgot from previous posts, the Chaos Crags are six dacitic domes, named A-F, with Dome A, the oldest in age. The Chaos Jumbles were the result when Dome C collapsed somewhere around 300 years ago (Heiken and Eichelberger, 1980). For my field work, I am trying to figure out the magma mixing event or events. To do so, I need to look at the enclaves (blobs in the rock not of host origin) and distinguish if there are different types. So far there seems to be three different types present in each of the six domes, but I believe that there might be more variations. I think I will be able to determine this with more field work and Crystal Size Distributions (CSD).

The above picture is a fine-grained porphyritic enclave in the host dacite, as classified by Heiken and Eichelberger, 1980. The enclave is about 1 ft long, the larger crystals are resorbed plagioclase from the host dacite.

This is a medium grained porphyritic enclave also in the dacite host and once again the larger crystals are resorbed plagioclase. This enclave was smaller at around 8 in.

Heiken, G., and J.C. Eichelberger, 1980, Eruptions at Chaos Crags, Lassen Volcanic National Park, California; Journal of Volcanology and Geothermal Research, 7, 443-481.

There is still more from the first day, but you have to wait until the next post.