It's been a while since my last post since I am currently on vacation! In the French school system, there is a two week vacation after every ten weeks of instruction. (It's great.)
I recently went on a camping trip with other teachers in the Amazon jungle, at Le Sentier Savane Roche Virginie, which roughly translates to the Virgin Savannah Rock Hike. (This will make sense in a few pictures.) It's about a two-hour drive from where I'm currently staying.
I started camping and hiking in a serious manner when I was in high school, and at age 17 I did my first solo-camping trip for five days and four nights in the White Mountains of New Hampshire. My love of the outdoors is a big reason why I decided to become a geologist. As a geologist, it feels amazing and empowering to be outside and understand what is going on around you.
But, back to the present - this was my first time hiking and camping in the Amazon Jungle, and boy it was hot. I don't think I've ever sweated so much during an hour-long hike before. The jungle floor is shaded and dark because all the plants are competing for every inch of sunlight they can get, but it's not much cooler in the shade. In fact, the heat and the humidity almost seem worse because you can't catch any passing winds.
But, there are all sorts of fascinating plants and animals to be found on the forest floor! Small pigs, pecarries, live in burrows and you can occasionally hear them sprinting away from you as you startle them along your path. Monkeys can be heard screeching as they swing from tree to tree. Cicadas give off their incessant, high-pitch whine. There are also plants of every kind - trees, mushrooms, ferns - and occasionally, rocks!
Large, allochthonous boulders can be seen as you near the top of mountain. Allochthonous just means that these rocks originated elsewhere before being moved by erosional forces (wind, water, ice, mud, etc.) to their current positions. Allochthonous boulders are normally indicative of incredible erosional forces - think of how much energy it takes to move that much mass! These rocks were granite, meaning that they crystallized slowly beneath the Earth's surface. And unlike the granite I've seen before, these rocks were weathered to the point where they were almost black. I almost mistook them for basalt at first, the rock type that Hawai'i is mainly composed of.
This extensive weathering becomes very clear once you reach the top of the mountain. There, plants have not yet been able to establish themselves on the rocks, so the expanse is bare and weathered. Because of this, it offers one of the best viewpoints for surveying the surrounding Amazon jungle, and this is likely why this spot was turned into a tourist attraction.
In addition, the shapes that the weathered rocks had taken on (their "geomorphology") were some of the wildest I have ever seen. It looked like lumpy waves of rocks cresting through the top of the Amazon jungle.
It reminded me of a Shel Silverstein poem about this guy who found out he has a wavy head instead of wavy hair. Walking up the mountain and peeling back the cover of the Amazon jungle revealed the fascinating, geologic surface that all these plants have grown on. It was a humbling reminder that before all these plants were here, this place was once barren rock. (These are the virgin rocks this place was named after!) But thanks to the work of tiny microbes eating away at the rock to create soil, climatic conditions, and the tenacity of plant life, here now exists the world's largest tropical rainforest.
But in addition to all the wonderful geology I saw, I also was able to share good fire-side meal with new friends & explore more of the wonders that French Guiana has to offer. Even if the rocks weren't there, my trip would have been worth it for that!
Thanks for reading, and until next time!
This past week I've been busy reading papers, applying to graduate schools, and studying for the GRE (Graduate Record Examination). Needless to say, I have been spending a lot of time hunched in front of my computer. However, (like a typical Californian) I still found time to go to the beach and (like a typical geologist) I had a lot of fun thinking about modern environments!
This Saturday, I went to the Leo Carillo State Park beach in Malibu. While my partner, Jan, went fishing, I wandered around, fascinated by the dynamism of the waves and its interactions with the shoreline. I watched as wave after wave sorted and tossed pebbles onto beach sands, and I found some great examples of how minerals can be preferentially sorted by density. Moving water (like incoming waves at a beach) will loft minerals and rock fragments, and then waning flow (in the form of a receding wave), will cause denser particles to fall out first because they require more energy to stay aloft. This process can create distinct patterns easily seen by the naked eye.
Magnetite is a dense, iron oxide mineral, and it offered great examples of preferential sorting at Leo Carillo. Fragments of it pooled into a shallow depression created by a rock, and traced the fine troughs of a delicate branching pattern carved by a receding wave. It was so interesting to watch this sorting happen in real time. (I would also like to apologize for committing a cardinal sin in all my geology photos this post, which is the lack of a scale!)
I like thinking about modern environments (read: I like going to the beach) because I like envisioning how these things will be preserved in the rock record. Over time, repeated motions and sortings caused by waves, like at Leo Carillo beach, can create the "stripes" that you sometimes see in sedimentary rocks. (Think of a layered cake with alternating black and white horizontal bands.) Many other processes can create this "striping" as well, and environmental forces create all sorts of interesting patterns that are later preserved in rocks. Sometimes, I wonder if future geologists will be able to identify the Anthropocene through a plastic-rich unit in the rock record.
Beaches are also places of incredible erosional forces, and this was on full display at Leo Carillo. California is heavily populated along the ocean, and these erosional forces are coming into conflict with homeowners and cities up and down the coast. (See this New York Times article on El Niño-enhanced erosion in Pacifica, CA.) Seeing this crumpled road at Leo Carillo was just a small reminder that we cannot escape the greater geologic forces surrounding us. I wonder what this beach will look like in the next ten or twenty years, and how much of this road will be left (if at all).