We’ve just published an exciting new paper in Science Advances which assess the transport of sediment in fine-grain river systems. The research is driven by Postdoctoral Researcher Hongbo Ma, who is the first author on the publication. I led the field survey and processed the Multibeam data of the Yellow River channel bed that you see in a few of the figures in the paper.
Hongbo has identified a physical explanation for why fine-grain rivers are able to move so much sediment. In short, it has to do with the organization of the channel bed, whereby dunes are wiped out at high Froude number flows with a small grain size on the bed. This reduces the form drag in the river and allows for more skin friction on sediment to bring into suspension. Hongbo continues to make strides in identifying a “phase transition” in sediment transporting systems that helps to explain the observations made in the Yellow River.
Yellow River at Hukou Waterfall. The river here is a bedrock-alluvial river, but this image provides a good demonstration of the comparatively massive volume of sediment transported by the Yellow River
You can get the paper here, or uploaded to my site as a pdf here.
There is a full article about the research with loads more information, including a video interview, from the Rice press department here. And an article from the National Science Foundation (funding organization) here. A Scientific American video explaining some of the research is available here.
For our research in China, I was charged with building a Vibracore system. The Vibracore works by utilizing a concrete vibrator to rapidly vibrate an upright thin-walled aluminium pipe into the sand/dirt/mud below. A tripod is then set up over the in-ground pipe to pull it up from the ground. The pipe (now called a core I suppose…) is then cut open with a saw and analyzed/sampled.
dimetric view of assembled tripod
This system is nothing we invented, although I’m not sure of its origin. I based the design for our tripod on an apparatus that our colleague John Anderson has in his collection of field equipment. Our only substantial modification to the design was to make the legs of our system separable so that instead of a solid 10′ pipes of aluminium, we have two 5′ pipes, joined by a coupler. This is quite useful for us, since we send our system to China each year, and it makes it much easier to handle for shipping.
I recently made some engineering drawings of our system for a colleague and figured I would share them here in case they may be helpful to others. You can find the plans as a .pdf file here, or explore the system in three dimensions in the software they were designed in (OnShape CAD) at this link.
example drawing: head assembly top plate
Rice crew Vibracoring the Yellow River delta
In the future, I hope that my colleague Brandee Carlson (who leads the research using the Vibracore) and I can write a bit of an updated guide to the system based on our experiences using the system in the field, but for now I’ll just leave you with a few references for the system design below.
Land-based Vibracoring and Vibracore analysis: Tips, Tricks, and Traps. Occasional Paper 58. Thompson, T. A., Miller, C. S., Doss, P. K., Thompson, L. D. P., and Baedke. 1991.
Collection and analysis techniques for paleoecological studies in coastal-deltaic settings — Robert A. Gastaldo
I’ll be departing soon for my second field campaign on the Yellow River, China. We traveled there around the same time last year to generate a dataset we could begin to explore and develop research ideas; now, a year later, we will return with a more focused plan to gather the data we need to address our research questions. We will bring with us a suite of sophisticated data collection equipment. Below is a terrible sketch I made to demonstrate most of the data we will collect at each of our stations located on the river.
Pretend that the grey thing floating on the water might look like a boat, viewed from the back. We aim to characterize the mechanisms for sediment transport within the Yellow River at various stages of a flood discharge curve. We use a point-integrating sediment sampler to collect numerous suspended sediment and water samples from various depths in the water column (yellow stars). In order to compare the compositions of suspended material to its source (i.e., the bed), we use a Shipek grab sampling device to collect sediment from the bed for our analysis. Deployed off the other side of the boat, we will can characterize the velocity structure of the water column through the use of an aDcp (acoustic velocity profiler) and a mechanical propeller driven velocimeter for near-bed measurements where the aDcp may lack resolution.
This setup represents only a portion of our survey plans, of course we’ll be there for six weeks that will generate a diverse and (hopefully!) comprehensive dataset for our future work.
I’ve recently returned from a trip to New Mexico for the field methods class of which I am a TA. It was an awesome trip and great experience for me in teaching, but that’s another story. The field area we work in is within the Jurrassic Morrison depositional basin (active roughly during the Kimmeridigan ~157-152 Ma). Within the Morrison Formation is the Brushy Basin member (abbreviated Jmb), renowned for the abundance of dinosaur fossils found within the rock unit. Jmb is found within our field area, so I told the students to keep an eye out for any good finds when walking with the unit.
Although Jmb has an abundance of fossils, we didn’t find any. BUT, the Morrison is also famous for its bounty of another paleontological tool, the gastrolith. Gastroliths are interpreted as stones that dinosaurs would ingest in order to aid with breaking down food and aiding in digestion. A gastrolith may be more generally defined as “a hard object of no caloric value (e.g., a stone, natural or pathological concretion) which is, or was, retained in the digestive tract of an animal” .
There are gastroliths all over within the Jmb, some small, and some larger. Below are three photos of the “best” gastrolith I found on our trip.
Gastroliths are often recognized by their very smoothed and polished appearance (some other examples here). I suppose that to be certain my rock is a gastrolith, and not simply a rock polished by water or wind, it should be found in association with the remains of the animal it was within. Regardless, I’m really glad to be able to add a rock with such an interesting back-story to my collection.
The 24th of August 2015 marks my one year anniversary of beginning graduate school. It has been an awesome year, filled with new science, great friends, and lots of travel. I kept a record of where I slept every night for the past year to see just how far I made it. I visited three continents (plus Central America), six states, and 32 different cities. I spent just over 30% of the year away from Houston (112 nights). I got to see some really amazing places on the planet. It puts into perspective for me how just how great of a gig being a grad student is — get paid to do cool science.
Below, I made some maps to show where I went. The color of a dot represents when I traveled there during the year (Aug 24 2014 to Aug 24 2015) according to traditional rainbow color order. The maps were made in GMT using this script.
Gulf Coast map
Cheers to what next year brings!
I’ve finally returned from China after a 6-week field campaign to get a first round look at my field location. We worked hard every single day after our gear was released by China Customs officials on the Yellow River Delta doing Vibracoring for Brandee Carlson’s research and doing Multibeam and river survey work for my work. Below you can see me running our Multibeam setup aboard our research vessel. More pictures and descriptions to come!
Well it’s been a while since I got back from Louisiana and our trip along the Mississippi River and delta so I figured I’d better post something. It’s been a busy few weeks getting ready for our summer campaign in China (international shipping of research equipment is an absolute nightmare I wouldn’t wish upon my worst enemies) so I got nostalgic for our time on the delta. Below is one of my favorite pictures of the group, showing us all sunk into our knees in mud just after we tried catching methane bubbles in a bucket to light them on fire. The photo was taken down on the distributary channels of Cubit’s Gap, a diversion on the Mississippi delta that was blasted ~100 years ago.
The group on the Mississippi delta trip, taken down one of the distributary channels of Cubit’s Gap.
I’m off to Louisiana for a week to spend some time on the Mississippi River and MR delta with my advisor (who spent a lot of time researching there) and some other colleagues. We’ll be spending a week, starting in St. Francisville, LA and driving down as far as Empire, LA where we’ll be for a few days. The Mississippi is a really cool system for so many reasons, and we’re going to be on the river during a moderate-to-high discharge, especially considering recent events across Louisiana (https://www.youtube.com/watch?v=CB-nBhsMiYc).
Below is a map showing roughly where we’ll be going. I’ll be sure to update with some pictures on the return.
Mississippi River trip map
I spent my spring break with an outstanding group of undergrads TAing a course in geological field methods taught by Helge Gonnerman and Monica Erdman at Rice. I had an absolute blast. We mapped the Tierra Amarilla Anticline [HERE] and the surrounding areas. It was really fun to get back in the field, since I spend most of my days behind a computer working with Matlab nowadays. I may digitize my field map a learning project in the next few weeks, so I’m not going to post that yet, but I will share a picture of the whole group (courtesy Jeffery Piccirillo).
The whole group in NM on our last field day…mapping till the sun went down.
I’ve just returned from an 8-day trip to the state of Washington to serve as a field assistant to my colleague Brian Demet and participate in a class field-trip to observe some really cool geomorphology. The field work was primarily on Whidbey Island, a glacial-sediment island northwest of Seattle that has isostatically rebounded about 300 m since LGM. We also worked elsewhere in Island County during our trip.
An outcrop that Brian and I scouted had a large exposure of megabreccias. A breccia is a broadly defined rock type and is essentially a rock that is comprised of smaller angular clasts bound by a fine matrix. Breccias form in a wide variety of high-energy environments that produce similar but distinctly different rocks; the key similarity is proximal and high-energy deposition. Below is an example of a common-looking breccia.
a common-looking breccia rock. Angular clasts (white) are bound by a fine matrix (gray).
The outcrop that I show below is the exposure of a megabreccia (mega- means large scale) within the glacially-derived sediment that the Whidbey Island bluffs are comprised of. Part of Brian’s thesis will be putting this outcrop into a broader context and story, to try and better understand grounding zone wedge deposits under the Antarctic ice sheet — but that’s another post for another time!
The outcrop here is approximately 60 m wide, and 15-20 m tall.
megabreccia deposit within glacially-derived sediment
post-processed image to highlight large angular clasts