Tropical mountain ranges erode quickly, as heavy year-round rains feed raging rivers and trigger huge, fast-moving landslides. Rapid erosion produces rugged terrain, with steep rivers running through deep valleys. However, in a number of tropical mountain ranges, landscapes with deep, steep valleys transition quickly into landscapes with low-sloping streams and gentle slopes at high elevations. This topographic contrast between high and low elevations poses a problem for geologists. Though heavy rains fall throughout the mountain range, erosion seems to sculpt parts of the mountain differently from others.
Mount Chirripó, Costa Rica’s highest peak, bears exactly this type of terrain, with flat valleys at high elevation capping rugged valleys below. The beveled summit of Mount Chirripó bears striking resemblance to summits as far away as Taiwan, Papua New Guinea and Uganda. Some geologists think that tectonic forces deep below earth’s surface pushed Chirripó into its flat-topped form about 2.5 million years ago. Others think glaciers did the work, sculpting the peak in over hundreds of thousands of years.
Max Cunningham, a graduate student at Columbia University’s Lamont-Doherty Earth Observatory, traveled to Chirripó this past summer to test the idea that mountain glaciers carved the summit we see today. Working with his adviser Colin Stark, a geomorphologist, and Michael Kaplan, a geochemist, both at Lamont-Doherty, Cunningham chiseled away samples of glacial debris to take home for analysis. The researchers hope to eventually pin down when the high-elevation valleys capping Mount Chirripó’s summit eroded into their current form. Read more about their work in the above slideshow.
Photos by Max Cunningham unless otherwise credited.
It was nearing time to launch the next expendable bathythermograph probe, or XBT. The software was readied and two scientists headed out of the lab, radio in hand. They donned lifejackets that had once been bright orange but were now closer to a dull rust color from long and dirty use on the deck and selected a T-5 probe from the box.
Out on the deck they were alone, perched partway up the stack of levels in the stern of the ship, the gun deck below them and the paravane deck above. It seemed that the others working the graveyard shift were all inside, perhaps wrestling with some mechanical puzzle or else simply keeping watch to make sure all was well, sipping strong coffee, playing cards to pass the time. The scientists snapped the probe into the gun-shaped launcher. They removed the plastic end cap from the black cylinder that housed the probe and its spool of fine copper wire.
“We’re in position.”
There was a pause, then the radio crackled back, “Launch probe.”
In a moment the probe was sliding down the long tube that extended out and downward from the starboard side. With a small splash it plunged from the end of the tube into the inky deep. Now to wait while it made its journey towards the bottom, more than 4000 meters below. Despite the very late (or very early, depending on your point of view) hour, it was warm. The air was muggy – not exactly a welcome change from the air-conditioned lab, although the tinge of diesel fumes was less out here in the relative open. There was little wind and the seas were calm. Standing on the moving island of light that was the ship the sea quickly disappeared into the surrounding void. What surface that could be seen appeared to rise disturbingly close up alongside them, like a churning wall of water. It was only visible at all by the few swirls of foam formed by the ship’s passage and a reflection here and there off the constantly moving face of the black oily-looking water. They waited for the go ahead to terminate the probe.
Down in the lab, there was a strange blip on the screen showing the multibeam bathymetry data, but no one noticed as they were too busy entering in location data for the XBT or scrutinizing the movement of the streamer birds that regulated the depth of the hydrophone streamer. There were, after all, 36 other monitor screens to watch.
Outside there was a louder than usual splash. The two scientists peered into the gloom.
“Dolphin?” one wondered out loud.
“While we’re shooting? I hope not,” the other replied, “We’ll end up having to interrupt the line.”
Was there something just under the water surface? A pale sinuous shape at the very edge of the ship’s halo of light? No, it must be a trick of the light and the weird perspective engendered by the lack of any sense of distance. Perhaps more coffee was in order when they got back inside.
The radio crackled again, “Terminate probe.”
The scientists broke the wire that was still spooling out to the probe that was now falling behind them. “Probe terminated,” they reported. They were just turning to leave when it emerged.
At first it looked like a whale back, though pale milky green in color rather than the expected grey. As it lifted free from the surface it became clear that it was much longer than an orca or even a grey whale, more like an ancient marble column turned soft and rubbery. It tapered as more of its length was exposed until the tip broke free of the clinging water. One side of the enormous snake-like shape was covered with round suckers the size of dinner plates in a poisonous green color. The cyclopean tentacle towered out of the water, waving gently with a sickening sort of grace ten meters or more above the uppermost deck. Here and there along its length were clots of a coppery tangled substance, almost like seaweed wrapped around it. “The XBT wire,” one of the scientists realized from the midst of her fascinated horror.
The tentacle hovered for another movement before swooping down with surprising swiftness. The two scientists were neatly plucked from the ship in the blink of an eye. With a clatter, the radio fell to the deck. They were held above the water for a long moment, crushed together so tightly they couldn’t speak and could barely draw breath. Then, slowly, the tentacle disappeared beneath the smoothly rolling waves.
Two hundred and sixty-seven shots until the next XBT.
-by Tanya Blacic aboard the R/V Langseth (with a wink to H. P. Lovecraft)
Our small ship is in a state of endless motion with pitch, roll, yaw, and heave. We continuously experience a feeling of fluctuating gravity at sea, as one minute we are several pounds heavier and the next we are several pounds less. We’re tossed about endlessly like riders at the fair. It’s a feeling that can turn the stomach of the saltiest of sailors, but more often disturbs the newbies the most. At sea there is also no such thing as silence. Out here the engines are always running, hydraulic pumps are always droning, and ships operations occur around the clock. From my bunk I can feel us lurch forward and lean into a turn to starboard, or port, and then they reverse the pitch of the propeller as if applying an emergency brake to slow the ships forward motion. This reverse pitch causes a shudder in the hull that shakes us like a cheap hotel vibrating bed and it chatters every moveable thing. From my bunk I can also hear the acoustic pings emanating from the hull-mounted transducers. Speaking to me in code, they tell me if OBS operations are going well. Based on the ping styles I can also discern the acoustic techniques used by WHOI and Scripps, so that I know which instrument type is being talked to. All of this information creates a movie in my mind that plays out until I fall asleep. Life on a ship is a constant immersion in all that is going on and for 30-days there will be no escape.
It’s been a week since we deployed all of our gear and started steaming along our lines, so now we have amassed a lot of data! Although we can only steam at very low speeds while towing the equipment (~4.5 nautical miles an hour or ~5 mph), each time we fire the air gun array, the 636 channels on the seismic streamer listen for returning sound waves for 18 seconds and record a total ~25 Mb of data. Repeat that every 30 seconds for 7 days, and it begins to add up! We now have 400 Gb of seismic data alone, not including all of the other types of data we collect while underway (bathymetry, magnetics, gravity). We are a data-collecting machine.
Matt, Jenna and Derek sit back and watch the data roll in from the Main Lab
Not only are we collecting data, we are also doing some preliminary data analysis to get a first look at the geology hidden below the ocean, which is always exciting.
Kara and Matt are entranced by velocity analysisAlthough we are only a week in, our data collection has already taken us through water depths as shallow as 20 m and as deep as 6000 m. At the edge of the continental shelf, water depths change rapidly from ~500 to ~3000 m over just 20 km – a slope of 10%. For perspective, that’s very similar in elevation change and slope to the course for the Pikes Peak marathon.
Perspective view of seafloor depth from MGDS across the continental slope overlain by a higher resolution swath of bathymetric data that we acquired along our transect, which is also shown projected onto the seafloor. We have also traveled over widely variable geology – from 35-km-thick continental crust to ~7-km-thick oceanic crust, and from sediment thicknesses of 5 m to over 7 km. Our data are also revealing cool structures in the sediments and crust – faults, sediment waves, and more. Below is a picture of a salt diapir that we imaged at the edge of the continental margin. The salt was probably first deposited at least 150 millions years ago in a flat layer, but as more sediments were deposited on top of it, it got squeezed up and out into dramatic diapirs.
Preliminary image of a salt diapir in seismic reflection data near the base of the continental slope. The y-axis shows the time it takes for a sound wave to travel down in the earth and back again. This images shows about ~5 km down into the earth below the seafloor. Donna Shillington aboard the R/V Langseth
(Originally posted on September 12)
Today was the first day of the onshore deployment of the RT130s through southern Virginia and North Carolina. My partner, Yanjun Hao, and I, were just one of five teams working to deploy instruments along the two survey lines. We deployed the first two instruments at West Harnett Middle School and South Hartnett Elementary School, both outside of Lillington, NC. In both case, the fifth and sixth graders were very interested in learning about what we were doing and eager to participate. I explained to them the basic concept of P and S-waves and then asked the children to jump so that we could test that each of the channels on the sensors was working correctly. They very much enjoyed getting to see on the clié exactly what the signal they generated looked like. At both schools, I was surprised how much the children, and the teachers, knew about earthquake seismology and the intelligent questions they asked. A teacher asked whether they would detect the explosives detonated at nearby Fort Bragg, and a sixth grader named Gauge blew me away when he asked if the sensors would be able to record the sound waves generated by the planes or nearby explosions! In total, we probably spoke to 100 kids about the project today. It was a very encouraging to see how excited and interested they all were in the science. When we first arrived and explained that we would be installing a seismometer, a 5th grade teacher looked at us with wide eyed and asked "Are you seismologists?!" I nodded yes and she was so excited she started jumping up and down. Despite some rain and GPS trouble later in the day, the excitement that the elementary and middle schoolers showed about seismology was enough to make it a great start to the deployment.
At South Hartnett Elementary School in Anderson Creek, NC. I am showing one fifth grade class what the seismic signal they just generated looks like on the clié.
From an academic prospective I learned about survey design, instrument deployment and the logistics. This provided a distinctly unique experience that is unavailable in the classroom environment. Beatrice and Dan were tremendously helpful and supportive. I learned a great deal about active seismic from my conversations with them. They’re passionate about nurturing future geophysicist. The GeoPRISMS is an altruistic endeavor for them. I am thankful to them for investing so much of their time and expertise into the project.
The GeoPRISMS experiment has been an overwhelmingly positive experience. I am grateful to have been given the opportunity to help with the deployment and look forward to my involvement in the recovery of the instruments! A future workshop will be held for processing the data and the inversions. This pre to post educational approach is invaluable to me as a future geophysicist.
Posted by Christopher Novitsky
Posted by Beatrice Magnani
Time series of the recovery after the OBS has been attached to the crane. Photo Credit: Ernie Aaron.
See ya'll later,
On skin, it’s barely a freckle I’d make,
But baby, en masse, we turn seas opaque!
Come darkness, come famine, come poison or flood,
My kind can flourish in any old crud.
I may be a tiny and brainless brown cell,
But my tactics are brilliant; I’m doing quite well.
So, “higher” life-forms, with deep-furrowed brow,
I’ve made my move … what will you do now?
Further reading (on what humans are doing now …):
De novo assembly of Aureococcus anophagefferens transcriptomes reveals diverse responses to the low nutrient and low light conditions present during blooms, Frischkorn et al., Frontiers in Microbiology
This is one in a series of poems written by Katherine Allen, a researcher in geochemistry and paleoclimate at the Lamont-Doherty Earth Observatory and the Institute of Marine and Coastal Sciences at Rutgers University.
For those of you following at home, it might be a bit confusing on which ship is doing what and where. I've made a little cartoon timeline that will hopefully illuminate our progress so far.
There are two ships currently in the Atlantic: the OBS deploying R/V Endeavor and the seismic shooting R/V Langseth. The R/V Endeavor has been putting OBS down and picking them back up again on lines 2, 3, and 4 while the R/V Langseth has shot seismic along line 2 and 3, and is going to head over to shoot on line 4 soon.
See you later,
Kate Volk aboard the R/V Endeavor
September 24, 2014
Well we have finished deploying OBS on line four and are now transiting back to the beginning of line 3 to start picking OBS back up again. At this point, we've all fallen into our jobs and are working like a well oiled machine. Each shift was able to deploy around 9 or 10 OBS in 12 hours time, moving smoothly from one site to the next. To celebrate our progress so far, I've got some group photos to share.
The science party from left to right: Gary, Dylan, Afshin, Harm, Brandon, Pamela, Jenny, and Kate (Photo credit: Dave DuBois, edited by Gary Linkevich)
The WHOI and SIO OBS technicians from left to right: Ernie, Peter, Mark, and Dave (Photo credit: Gary Linkevich)
The whole science group (Photo credit: Ethan, edited by Gary Linkevich)
The science group in the WHOI van with the WHOI OBS (photo credit: Dave DuBois)See you later,
Kate Volk aboard the R/V Endeavor
September 23, 2014
Good eats! We couldn’t do this cruise without our great Chief steward Mike. Mike keeps the morale up on the ship by preparing three fabulous meals a day, plus providing ample snacks and baked goods. I’ve especially enjoyed the coffee cake, macaroni and cheese and tomato soup, oh and pretty much every dessert he’s made. Mike is especially awesome at accommodating everyone on the ship and providing tons of variety for us. He includes meat dishes as well as vegetarian, whole wheat, and vegan options, all of them yummy!
The galley, Mike is preparing for dinner (Photo credit: Kate Volk)
Mike making dinner (Photo credit: Kate Volk) Mike in the Galley (Photo credit: Kate Volk)
Dessert (Photo credit: Kate Volk)Kate, Gary, Kurt, and Dylan enjoying a meal (Photo credit: Kate Volk)
See you later,
Kate Volk aboard the R/V Endeavor
September 23rd, 20141641
The last few days have been a bit rough, with intermittent rain, winds at 15 – 30 kts, and 6 – 10 foot seas, but that didn’t delay our progress at all. When I woke up for watch late yesterday morning, the sun was shining, the seas were calm, we successfully completed recovery of the OBSs that we had deployed on Line 2, and we were in transit to the beginning of Line 4 to begin our redeployment. Now, over the past 26 hours, we have deployed OBSs along the entirety of Line 4 (22 instruments) and begun our transit to the south end of Line 3 to begin recovery of those instruments.
Until next time,Dylan Meyer aboard the R/V Endeavor
September 22, 2014
Happy birthday Afshin! A member of the science team, Afshin from Oklahoma State University, celebrated a birthday on the ship. Our wonderful cook Mike baked a cake especially for him. Yum!
Afshin (Photo credit: Kate Volk)Mike's cake for Afshin (Photo credit: Kate Volk)
Afshin and Mike (Photo credit: Kate Volk)Afshin with the birthday hat (photo credit: Dave DuBois)