A day at the beach

Hi everyone,

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! 

Jan Shi, taming the seas. (Sept. 2016) (Photo source: author)

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.

Bits of magnetite (black in color) pooling around a depression created by the interplay between an obstructing rock and incoming waves. Sorry for the lack of scale! (Sept 2016) (Photo source: author)

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!)   

Branching pattern in beach sand carved by receding waves. Magnetite (black in color) can be found in the bottom of each small trough. Sorry for the lack of scale! (Sept. 2016) (Photo source: author)

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. 

A crumbling former road at Leo Carillo State Park beach in Malibu, CA. Asphalt is about 6 feet / 1.8 meters above beach sands. Sorry for the lack of scale! (Sept. 2016) (Photo source: author)

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). 

​Renée