As an Earth scientist who studies surface processes I’m fascinated by channels. Channels are found all over the Earth’s surface, on land and in the deep sea, and we have mapped ancient and active channels on the surface of other planets/moons. As a sedimentary geologist I typically ponder the types of channels that shape landscapes and seascapes, move sediment across the surface, and serve as long-term repositories of deposited sediment.
This week’s photo is indeed a channel but instead of moving sediment it moved molten rock across the surface of the Big Island in Hawaii. It’s now frozen in time, an abandoned channel, perhaps it will be reoccupied by younger lava flows someday. I don’t know the first thing about lava channels, but it seems that it must solidify from the edges inward, resulting in the down ‘stream’ texture (?).
This photo and more from the Big Island on my Flickr page.
My first post about using R back in January focused on creating custom plots and led to some interaction with other R users in the comment thread and this post from R expert Gavin Simpson in which he kindly offered a solution (and code) to what I was trying to do. I ended up using a slightly modified version of that code to make a bunch of plots for a paper I’m working on. (In fact, I should be working on that paper right now … yep.)
Anyway, for this post I want to briefly summarize another aspect of R (or most programming languages for that matter) that is quite powerful: automating data processing and/or computational tasks that need to be done for multiple files. This funny graphic* below was going around some months ago and very nicely illustrates what I’m talking about.
Just a bit of background before I get on to the R code. I’m starting some research that will take me and my current/future students at least a few years, perhaps more, to accomplish simply because of the huge number of samples. I have a literal boatload of deep-sea sediment samples from IODP Expedition 342 (see this post for context) that will be used to better understand the history of deep ocean circulation in response to past climate change. Specifically, we’ll be measuring the variability in grain size of the terrigenous (land-derived, non-biogenic) sediment through time. To the naked eye, all this sediment is mud. But, subtle differences in the mean size of the silt fraction over time can tell us about the relative intensity of long-lived abyssal currents that transported the sediment. (If you want to know more about this approach, including all the assumptions, limitations, and caveats, this is a nice review.)
It’s been two years since we moved from California to Virginia, time flies! We really love where we live now, but there are times where I do miss California. I especially miss exploring the outcrops along the coast. Many of these wave-washed bluffs have gorgeous exposures of bed-scale sedimentary geology, a real delight for those who like sedimentary structures.
The above photo shows some Paleocene turbidites along beach cliffs in the town of Gualala, a few hours north of the Bay Area.
This photo is from the past field season in Patagonia. We wanted to get to these rocks on the other side of the river. My student eventually got there … by going ~30 km downstream to where there was a proper bridge and then driving on some gnarly roads for a couple hours. If only we had jet packs. Drones are all the rage these days … drones shmones, I want jet packs!
Summer is in full swing and this summer is all about lab work. An undergraduate researcher and I are in the midst of extracting the terrigenous (land-derived) sediment from marine sediment. We are interested in the grain-size and compositional characteristics of the terrigenous component to better understand the history of a long-lived oceanic current that transported the sediment. Isolating the terrigenous material means we have to get rid of the other components, namely the biogenic (marine microfossils made of carbonate and opal) and authigenic (metalliferous oxyhydroxides that formed in place) material. We are using this method with some tweaks from a helpful collaborator.
I have >1,000 samples from IODP Expedition 342 (see this post for more about that expedition) that will eventually be processed in this way. But, because we have not done this before and are still getting the lab fully equipped, we are currently using ‘practice’ sediment (a chunk from one of the core catchers) to fine-tune the methodology. That is, when we make a mistake — which is inevitable when learning something new — we won’t be sacrificing a ‘real’ sample. This training will pay off in a couple weeks as we ramp up and start processing samples in batches.
While we work on that two of my graduate students are busy crushing, grinding, sawing, drilling, etc. rock samples for their respective Ph.D. projects. We’ve got mineral separation underway for bedrock thermochronology, sample preparation for stable isotope measurement of carbonate rocks, and thin sections being made.
Here’s a shot of the sand dunes not far from Stovepipe Wells in Death Valley National Park from this past March. Check out this Flickr set for a whole bunch more. Happy Friday!
This week’s photo is from the deck of the JOIDES Resolution drill ship last summer. Before IODP Expedition 342 I had spent only a few days at sea, and even then it wasn’t more than ~20-30 km from land. Being out in the open ocean — several hundred km from land — was an experience I didn’t think about or appreciate before I did it.
I never grew tired of watching the sea during that two months. The interaction of swells of different sizes and forms moving in different directions resulted in unique displays of nature. And it’s quite different than watching the sea near the coast. Watching the water pile up into ‘mountains’ and ‘ridges’, creating a constantly changing topography, was actually quite therapeutic during an incredibly busy expedition.
See this photo and many more from IODP Expedition 342 on my Flickr page.