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Archive for September, 2010

While walking around Barcelona eating great food and contemplating the risks/rewards of piloting Vespas through the city traffic, I found myself the guide to a swift but exhilarating geologic tour.

Outside the Museo de Geologia (“Museum of Geology” for those of you who no habla espanol) are some displays of many rock types. Once we got to the exhibit my friends found themselves unwilling participants of an impromptu geology lecture. Here I am describing the contraction of basaltic lava while cooling that leads to the columnar jointing on display behind me. Look at those 120 degree angles! Also note the word “BASALTO” written on the side.

Speaking of lava flow, check out these samples of both pahoehoe and aa (great word for Scrabble). On my right is an example of pahoehoe lava flow which is recognized for its ropey texture caused from a very fluid lava underneath the thin cooling outer shell. On my left is the aa flow (pronounced “ah-ah”) which has a more blocky textured look. This particular flow carries fragments of lava called clinkers with it as it travels.

The aa sample is a local boy from Sant Feliu de Pallerols, Spain about an hour north from Barcelona.

Another great example of volcanic activity was seen in this volcanic bomb (“bomba volcanica” for those of you who DO habla espanol). These rocks are expelled high into the air during violent eruptions and fall to the earth as incandescent lava. I am pointing in the direction that the semi-molten bomb fell giving it this aerodynamic shape.

In this picture Kris, a native of Stockholm, Sweden, cozies up against a large piece of granodiorite. What’s the attraction? While it may be from a different part of Europe, this is the same type of rock seen all over Kris’ home.

Here is the same picture with some arrows to show the directions of maximum and minimum stress. The mineral grains in the rock which are subjected to stress during periods of metamorphism align in a direction perpendicular to the highest level of force (represented by sigma 1). Eventually the grains will all be aligned along a plane of foliation (probably seen on a counter top near you).

We had a unfortunate habit of showing up to every museum after it closed on this trip, so, this is where the tour ended.  Here is one last picture of the rocks. Check out the basalt column.

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Anybody who reads this blog needs to go check out my friend Sarah’s new blog Hydro-ecstatic! She is a George Mason alumni now working on her master’s in hydrology at New Mexico Tech.

Welcome to the party, Sarah, and thanks for giving me something else to read!

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Since I have been gone, at least from the blogging community, I have kept busy. I wrote a smattering of articles for Earth Magazine (now available in your local bookstore), school has started up again, and I traveled. In previous posts I mentioned how I made my way to Europe in mid-August, and was able to see one billion year old granitoids in Sweden, and paleontological sculptures in Barcelona. One place I did not mention, at least not in detail, was Norway, where I was able to spend a few visually stimulating days.

From Oslo, my traveling companions and I set off in a tiny car packed to the hilt for the small village of Geiranger conveniently located at the head of the Geirangerfjord. This particular fjord is 15 km long and located on the western side of Norway in the Sunnmøre region. It is a branch of Storfjord, which at its deepest is 679 m down while the surrounding mountains in Geiranger range up to 1500 m tall.

Geiranger is actually much sunnier than what Google Earth shows it to be.

Driving into the fjord was an awe-inspiring moment of monumental beauty where the U-shape of the fjord was on display with the sun barely splashing over the tops of the mountains. Unlike a river that cuts down into the valley where the over all shape is a V, fjords are created by glaciers dragging and scraping their way across the landscape as the ice sheets expand and retract. What they leave behind is a deep U-shaped basin with very high, almost vertical cliffs sandwiching the deep collection of meltwater from the mountain tops.

Below is a generic diagram of a fjord I drew on my white board at work (one of my favorite toys), and below an actual picture taken of Geirangerfjord.

The picture above was taken from a kayak about 4 km out from the village. Notice the contact of the cliff face and the water; there is no gradual flattening of the angle, the cliff dives straight in at 90º. While I enjoyed the cloud cover that day it made it difficult to display the mountaintop as we only see about halfway up in the picture. Car ferry for scale.

A closer look at the cliff face showed some high level of structural deformation including folding, shearing and boudinage, but that will be explained later.

Another feature seen on the outcrop were glacial scour marks, or grooves left in the rock as the ice passed by. It’s hard to see them in the original photo so I added some arrows.

The weather rind was inhibiting my ability to appreciate and get a good picture of the rocks at this point, and a lot of my attention and energy was focused on keeping myself upright in the kayak as well.

Here is one more picture of the fjord exhibiting the U-shape, just for good measure. This photo was taken ~200 meters up the cliff side after an interesting hike. Follow the link to get a better view, and please feel free to use this as your desktop background, I know you want to.

Cruise ship for scale.

Geirangerfjord as seen from ~200m up with a cruise ship for scale.

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