Across a mixed landscape, Au. sediba plods
Sometimes on two feet, and sometimes on four,
Munching on fruits and leguminous pods,
Nuts and some seeds … C3 foods galore!
They did have a choice (so coprolites hint);
Lush grasses, fat grazers were also around,
But in these old ancestors (destined for flint?)
New clues, new stories have just now been found.
With lasers and microscopes, old dental plaque –
Tiny, stuck phytoliths show a rich diet!
Scratched-up enamel, it all brings us back
To lives of these creatures that have long been quiet.
What wonders are learned from plaque and from feces,
History bound in compounds beneath!
So, we should say to that wonderful species:
Thanks for not brushing your teeth!
Palaeoanthropology: The ancestral dinner table, Nature, 2012
The diet of Australopithecus sediba, Amanda G. Henry et al., Nature, 2012
This is one in a series of poems written by Katherine Allen, a researcher in geochemistry and paleoclimate at the Lamont-Doherty Earth Observatory.
Kristen de Graauw and Cari Leland
Cari and Kristen here, checking in from Mongolia. This year we were invited to be instructors for the Third National Dendroecological Fieldweek, May 23-29 in Udleg, Mongolia. We arrived to Ulaanbaatar on May 20th so we were fortunate enough to have a few days to recover from some pretty terrible jetlag before beginning the fieldweek marathon. Anyone who has ever attended a fieldweek anywhere in the world knows how challenging (and rewarding!) these events can be. Our first few days of the fieldweek were spent at the NUM (National University of Mongolia) research station near Udleg, a few hours north of UB. We were so happy to see the beautiful countryside for a few days. We got to ride there in this awesome Russian vehicle, which Cari nicknamed Herbie.
The research station was a complex of buildings for housing, a kitchen, and lecture rooms. We shared a cozy room for two and enjoyed beautiful views of the valley and mountains surrounding us.
After everyone settled in, we met for the opening ceremony. Baatar gave a nice introduction of the project and the history of the CEME collaboration. There were 8 students in total, and 7 of them were female (girl power!). There was a good mix of participants; from first year undergraduates to PhD students.
After the opening ceremony we went out to the field. Baatar gave us a guided tour of all the current research projects at the station (there were many!) and the potential sites for the fieldweek. Then we gave a quick lecture on the basics of dendrochronology and headed back towards the research station to discuss potential fieldweek projects.
Day 2 at the research station was field sampling day. Unfortunately we woke up to a cold and rainy day but that didn’t stop our groups from heading out into the forest. After a long discussion we decided Cari would teach the Climate group and Kristen would teach the Ecology group. Cari’s group headed up the mountain in search of old larch and pine trees to core while Kristen’s group went to a portion of the forest that had been logged. The goal for the climate group was to find moisture-stressed trees and look at the relationship between tree rings and climate. The ecology group’s goal was to determine logging dates and the effects on surviving trees.
After one of the coldest and rainiest field days we’ve ever experienced we headed back to the field station to thaw and dry ourselves and the cores.
While we waited for the cores to dry, the students practiced skeleton plotting.
The next day we mounted the cores with glue and taught the students how to sand. They quickly learned that a well sanded core took time, patience, and persistence. At the end of the day we headed back to UB to begin laboratory methods.
Back at the university we had to hit the ground running with lab methods. The students skeleton plotted the samples from the research station one day, learned how to do the list method and measure the next day, and finally on the last day they learned how to run COFECHA and read the output files. It was challenging but everyone worked their hardest. The final day was very busy. The students were working on their presentations until the very last minute. The groups did an outstanding job presenting their projects, which made us feel so grateful for being able to teach such a bright and dedicated group of students. During the closing ceremony Baatar gave us both a really nice Mongolian tree and shrub guide book and then presented each student with a certificate of achievement. The students then gave us the most thoughtful gifts of Mongolian art and script.
By Max Cunningham
June 10, 2014
Mike, Colin and I made meticulous plans for exploring Mount Chirripó before we left New York, but on the way to the summit Mike and I saw something that made us change direction: at about 9,500 feet, a mysterious grassland beckoned beneath jagged peaks. With just one day to go before our trip back to the Cloudbridge Reserve to refuel, we decided to make an early morning trek to this unusual valley to investigate why it is so flat and devoid of vegetation.
Over the course of a beautiful, sunny day Mike and I trekked over the rugged terrain from Crestones Base Camp before reaching a sudden transition from forest to grassland. A few things struck us. First, a thin river snakes through this entire shallow valley. Around bends in the river we noticed sharply cut banks where the stream has become more powerful and eroded away the banks.
Second, we were surprised to find the stream bed completely dry. From a distance, we had expected to find a powerful body of water. In another test of our geomorphology knowledge we discovered that this dry stream bed is paved mostly in cobble-sized rocks, the type you might find on a cobblestone street except these cobbles are sharp and angular instead of smooth and rounded. Mike and I spent the morning walking the Sabena de Leones valley and the more we looked, the more baffled we remained by the processes that shaped this landscape. Why is the river bed dry and its sediment load so large and angular? We hope to find more clues in the coming week.
In the early afternoon, Mike and I stumbled on a small marker along the river channel in Spanish dated 1956. Combining our Spanish skills, Mike and I deduced that the sign commemorated the unfortunate death of a man by mountain lion, and then I realized that Sabana de los Leones translates to “Savannah of the Lions.” That’s all we needed to know before skedaddling back to the Talari Valley and the security of the Crestones Base Camp.
By Max Cunningham
June 9, 2014
During the last decade, scientists have noticed an apparent rise in catastrophic events in mountain valleys as glaciers retreat and permafrost thaws. Some evidence suggests that thawing glacial valleys are responsible for enormous, fast-moving landslides that can destabilize river dams and cause other damage. Last July, my colleague Colin Stark and others at Lamont identified one such landslide in Alaska.
The idea that catastrophic processes may become more frequent as glacial valleys warm globally is a frightening one, but further information is needed to assess the threat. I came to Mount Chirripó hoping to find evidence of past landslides. Before flying here, Stark and I used high-resolution satellite images to identify potential landslide features on Mount Chirripó. On our second day in the field, Kaplan and I tried to locate them on foot.
We found our first landslide in Valle de los Conejos, a cirque valley carved into Mount Chirripó’s southern side. Apparently, we walked right by it on our previous day of fieldwork; the trees and bushes growing amid the fallen boulders provide an excellent disguise.The glacial debris blends in almost perfectly with the hillside. To highlight it, I have outlined the scarp in red where the failure occurred, but even this image, taken more than a half-mile away, is deceiving. Mike and I spent what felt like hours whacking through thick bushes to get there. You can just make out some of the large boulders in the background.
From a distance I thought we could scale the landslide, but the house-sized blocks were too big to scramble over. During the slide, boulders stacked up on each other and formed crevasses and caves that are now covered in treacherous mats of vegetation. I suspect that pumas may sleep in the caves by day if they are able to withstand the altitude.
Mike and I traipsed around the landslide, stopping at various scarps to enjoy the views. The run-out distance appears to be only about a tenth of a mile, and the boulders are densely packed. Looking down, I got the impression that the landslide created a crevasse somewhere between 60 to 100 feet in depth. When did this major failure happen in relation to deglaciation?
Mike and I decided to use our CRN dating tools to find out. We made our way to several boulders on the east side of the landslide, where the rock is sedimentary, unlike the granodiorite found in the Valle de las Morrenas. Once again, Mike and I found bits of fine-grained quartz in the rocks, indicating we can measure their Beryllium-10 levels to understand how long this landslide has been exposed to cosmic rays. Mike and I think that the extent of weathering on these boulders is a clue to the age of the landslide: For the surface of these boulders to undergo alteration, they probably sat in the same place for a long period of time. Perhaps this landslide is indeed paraglacial, a result of glacier retreat and permafrost thaw. We hope our efforts to measure CRN production here will inform us.
By Max Cunningham
Our expedition has two main goals: assess glacial erosion features on Mount Chirripó and search for clues of the summit’s age. Were the broad, flat landscapes on Mount Chirripó formed by glacial erosion or a change in tectonic forces pushing the Talamanca Range up about 2.5 million years ago?
A chemical dating technique called Cosmogenic Radionuclide (CRN) Dating may lead us to the answer. This technique will help tell us how long ago the valleys flanking Mount Chirripó eroded, and therefore, whether Mount Chirripó’s high elevation landscape is older than 2.5 million years or whether it eroded into its current shape as recently as 10,000 years ago.
Earth is being constantly bombarded by high-energy protons and neutrons from beyond our solar system, and CRN dating exploits this process. The collision of high-energy particles and atoms in the atmosphere and on rock at Earth’s surface produces new atoms of different mass, or isotopes. Fortunately for many Earth scientists, the impact of cosmic rays and oxygen produces an extremely rare isotope of the element Beryllium: Beryllium-10. Oxygen is abundant in Earth’s crust, and quartz (SiO2) is among the most common minerals found there. When cosmogenic rays react with quartz at the surface, about six atoms of Beryllium-10 are produced per gram of quartz per year.
Measuring concentrations of Berylium-10 at the surface can potentially tell us how long the rock has been exposed to the atmosphere, and quartz is a particularly convenient mineral for measuring Beryllium-10 concentrations. Mike and I sought out glacial features with quartz-bearing rocks at Mount Chirripó with the hope of understanding whether rocks here were exposed to the atmosphere after the recent retreat of ice.
Glacial features jumped out at us during our initial tour of Mount Chirripó. We saw broad cirque valleys, floored by large lakes likely filled during glacial retreat. We also saw striated rocks and moraine ridges scattered with cobbles and boulders. In one valley, Valle de Las Morrenas, we noticed several lakes above the boulder-strewn ridges. This fits in neatly with previous observations of lakes dammed by moraines.
Because moraines are abandoned when the ice retreats, measuring concentrations of Beryllium-10 in boulders on top of moraines may give us an idea of how long ago glacial erosion happened here. After locating boulders sitting on moraines, our next step was to see what the boulders are made of.
We discovered that many are granodioritic, an intrusive igneous rock composed of the minerals plagioclase, amphibole and our good friend quartz! Next we took samples to analyze their Beryllium-10 levels in the lab later. Collecting samples is a physically rigorous process, especially in the low-oxygen, rainy conditions at 10,000 feet on Mount Chirripó. With a hammer and a chisel, and a bandanna to protect our faces from shattering rock fragments, we chipped away at the surface of the boulder, hoping to come away with about two pounds of rock to analyze.
We collected samples from boulders on two moraine crests. After months of processing, we hope to be able to describe how long ago glacial ice retreated from different parts of the valley. Calling the day a success, we hiked back through the afternoon rain to Crestones Base Camp.
You may have heard the recent cries:
An asteroid towards us flies!
Apophis, a rocky mass,
Some years from now will closely pass,
Into the “keyhole,” if she falls,
The president will get some calls.
Chances that this fate arrive?
Apophis asteroid: Large space rock flies past Earth, BBC News, Jan. 9, 2013
This is one in a series of poems based on science news, written by Katherine Allen, a researcher in geochemistry and paleoclimate at the Lamont-Doherty Earth Observatory. “Lake Goo Clue” first appeared on Allen’s website on Jan. 11, 2013.
By Max Cunningham
After arriving in the town of San Gerrardo de Rivas, Mike Kaplan and I immediately started gearing up for our trek to Mount Chirripó.
Our arrival here was somewhat hectic. After landing in San Jose around 10:30 a.m., we hopped a bus to San Isidro de el General, a town just west of Chirripó National Park. Winding through the rugged mountains of the Talamanca Range, we were treated to spectacular views of central Costa Rica’s countryside.
Once in San Isidro de el General, we navigated our way to the local office of Ministerio de Ambiente y Energia de Costa Rica, the government agency that provides research permits for Chirripó National Park. Our contact, Marisol Rodríguez Pacheco, showed remarkable patience with our broken Spanish and helped us pull together some final requirements for the permit.
By 5 p.m., the two of us made base camp at the Cloudbridge Reserve, above the San Gerrardo de Rivas. Founded in 2002, the Cloudbridge Reserve supports researchers in Costa Rica and works towards sustainable forest management. Volunteers at the Cloudbridge Reserve provided us with a beautiful working space and a warm place to sleep.
The weather here can be erratic. During the early morning hours the sun is intense and the sky is blue; by 1 p.m. clouds roll in. You can anticipate heavy rain from 4 to 6 every day, and nights are cold.
After taking a day to gather food supplies and find porters to help us carry heavy packs up to Mount Chirripó, Mike and I set off around 4:30 a.m. to make our way to the top of Mount Chirripó before the afternoon rain.
Travelers and locals alike warned us that the hike would be strenuous, and indeed they were correct. The trail leading to Mount Chirripó is steep and rugged (although pristinely maintained), and we gained nearly 5,000 feet in elevation over nine miles of trail.
One especially difficult aspect of our climb was the dramatic change in climate with elevation. Below 10,000 feet, we trekked through a humid, dense rain forest, but once above about 9,500 feet, the vegetation became sparse and the temperature dropped. At the summit of Chirripó, we rarely experienced temperatures warmer than 60°F.
In terms of Earth surface processes, this dramatic change in environment invokes thoughts about difference in landscape evolution: How does change in altitude, and associated changes in climate, affect erosion processes in the long term? This is just one question we hope our research can eventually inform.
After an 8.5 hour hike, we finally reached Talari Valley, a lowland about 500 feet below Mount Chirripó. We made camp at the Crestones Base Camp, a meticulously maintained hostel in the Talari Valley, near Cerro Chirripó. The Crestones Base Camp is home to many travelers seeking the thrill of climbing Mount Chirripó. Impressively, many of the hikers we encountered wake up around 2:30 a.m. to hike the remaining 5,000 feet to the peak of Cerro Chirripo to watch the sunrise over this beautiful mountain. Mike and I made no such plans, and instead rested for a busy week of fieldwork.
By Max Cunningham
I’m a graduate student at the Lamont-Doherty Earth Observatory and work in Colin Stark’s Earth Surface Processes Group. My research focuses on the role that climate plays in molding Earth’s surface, and how we can use clues carved into landscapes to learn more about climate and climate change in the past.
Since arriving at Lamont-Doherty, I’ve focused my attention on glacial valleys responding to climate change. I want to learn more about erosion in landscapes undergoing a transition from cold, frozen conditions to warm conditions. Questions about the timing of glacial retreat in the past and the erosional processes that occur as landscapes unfreeze are particularly relevant today, as glaciers around the world shrink in response to a warming global climate.
Specifically, I want to learn about the history of glacial erosion in tropical mountains. Features on many tropical peaks around the world suggest that glaciers once persisted at low latitudes, but nearly all of these places are far too warm to sustain glaciers today.
Glaciers are a crucial link between climate and erosion: They form only under very specific climatic conditions and leave very distinctive marks after they retreat. During a glacier’s lifetime, snow accumulates at high elevation and compacts into hard ice that flows downslope; at lower elevations warmer temperatures melt away layers of snow, allowing ice deeper within the glacier to move toward the surface. The total effect of compacting ice above and disappearing ice below is a “scooping” motion, and rocks caught in this “ice scoop” wear away bedrock. A combination of this rock-on-rock wear and other processes produces features unique to glacial erosion, such as circular valleys called cirques. In map view glacially sculpted valleys look like thumbprints in clay.
A somewhat startling realization is that these glacial thumbprints can be found on mountains in hot, tropical places like Costa Rica, Uganda, Kenya and Papua New Guinea. Some major questions arise: How long ago did glaciers carve out valleys in the tropics? How far down mountainsides did glaciers persist in these perennially warm regions? To start honing in on these questions, I’ll be traveling to Costa Rica’s tallest peak, Mount Chirripó, in Chirripó National Park for the month of June.
On Mount Chirripó, which rises to 12,530 feet, glacial thumbprints are clustered a few hundred feet below the summit. River profiles have a distinctive shape, exiting U-shaped valleys along gentle gradients and then breaking suddenly into a steep slope at about 6,500 feet. Waterfalls, or more technically “knickpoints,” form at this steep slope change.
Scientists have studied the unusual glacial thumbprints and clustering of knickpoints at Mount Chirripó. In 2000, researchers at the University of Tennessee identified a series of lakes that formed as a result of glacial erosion. They extracted sediment cores from the lakes and noticed a sharp transition from granular, glacially-produced sediment to organic material with depth in the core. Using 14C radiometric dating, they found that the transition occurred between 12,000 and 9,800 years ago.
Why is that important? Between 20,000 and 10,000 years ago the world was thawing out of an ice age. The 14C dates imply that glaciers persisted at about 12,000 feet at Mount Chirripó as recently as 9,800 years ago. By comparison, North America’s Laurentide ice sheet, which once extended south of New York City, retreated into Canada well before 9,800 years ago.
A 2012 study looked at Mount Chirripó from a different lens. The collision of tectonic plates in the tropical Pacific Ocean pushed Mount Chirripó to its modern elevation, but the timing of this uplift remains unclear. The 2012 study suggested that the clustering of knickpoints could reveal when tectonic uplift began.
Rapid tectonic uplift provides rivers with potential energy that expresses itself in steep slopes that slowly creep up mountainsides, creating a “wave” of erosion that travels up hillslopes. By assuming a “vertical” erosion rate, these researchers estimate that knickpoints at 6,500 feet signify tectonic upheaval that began about 2 million years ago.
The conclusions reached by these independent studies present a major conflict. On the one hand, valleys atop Mount Chirripó may have been carved by glaciers. If this is the case, the landscape must be “young,” as glacial erosion would have occurred during the last 2.5 million years. On the other hand, the valleys at high elevations at Mount Chirripó may represent a landscape that existed before 2 million years ago and rode a pulse of uplift to 12,500 feet.
In other words, two competing hypotheses have emerged: Is Mount Chirripó a sculpture of glacial erosion, or an ancient landscape perched at high elevations by tectonic forces?
My colleague Mike Kaplan and I plan to analyze evidence of past glaciation on Mount Chirripó in an attempt to test these two competing hypotheses. Using a geochemical technique called surface exposure age dating, which will allow us to measure how long rocks at the summit of Mount Chirripó have been exposed to the atmosphere, we will attempt to test how “old” the landscape is—is it relatively young, around 9,800 years old? Or does it predate a massive shift in tectonic uplift that began 2 million years ago?
The lands of Africa’s Horn,
Great Valleys sliced by a Rift,
By drought and famine are torn …
What drives such a large rainfall shift?
Detectives of lake muck and goo,
Through models and efforts terrific,
Put forth a paleo-clue
From the Indian, not the Pacific.
Multidecadal variability in East African hydroclimate controlled by the Indian Ocean, Tierney et al. Nature 2013
This is one in a series of poems based on science news, written by Katherine Allen, a researcher in geochemistry and paleoclimate at the Lamont-Doherty Earth Observatory. “Lake Goo Clue” first appeared on Allen’s website on Jan. 18, 2013.