By Max Cunningham
June 12, 2014
We continued to sample boulders in Valle de Las Morrenas, Valle Talari, where the hostel sits, and several places along Mount Chirripó’s ridgeline.
The view from the top of Mount Chirripó is spectacular. Looking out along the ridge I could see huge boulders of granodiorite produced by exfoliation, or the response of rock at the surface to the removal of ice.
The actual summit of Chirripó, however, is a very different kind of rock. I believe the peak is composed of a sedimentary rock that was melted and then fused back together as the magma that formed the granodiorite rocks moved toward the surface. This metamorphosed sandstone (meta-sandstone) is extremely hard, and resistant to weathering processes.
In the meta-sandstone near the summit of Mount Chirripó, I discovered glacial striations. These striations occur at 12,513 feet (the summit is 12,529 feet), which is a good 1,000 feet above the moraines in the upper portion of Valle de Las Morrenas.
By Max Cunningham
June 11, 2014
Mike and I hiked down 7,000 feet from Mount Chirripó to the Cloudbridge
Reserve early on the morning of June 10th to refuel and replenish supplies.
At this point, the Cloudbridge Reserve deserves a special mention. Tucked away in the forest above San Gerardo de Rivas, volunteers at the Cloudbridge Reserve work to transform old farmland into natural forest. After the cold ruggedness of the Mount Chirripó summit, the volunteers at Cloudbridge provided an exceptionally welcoming and engaging environment. Mike and I were extremely lucky to have such a supportive base camp.
I kept an eye out for interesting geomorphology as I walked along the trails of the Cloudbridge Reserve. The rivers here are particularly beautiful. The water is clear and blue, and channel beds are floored by bedrock and boulders (all granodioritic in composition, like many of the rocks atop Mount Chirripó). I was struck by the power of the local rivers; the erosional features carved into this hard, granodioritic rock were impressive.
After two days of rest and catching up on all we’d missed while isolated on Costa Rica’s highest peak, Mike and I headed back up to Mount Chirripó to continue sampling and to learn more about the processes shaping this landscape.
During our second journey, we hoped to extend our sampling range by venturing farther into glacial valleys and higher onto peaks. We targeted Valle de Las Morrenas, a valley that we knew well from our first sampling trip and that other researchers had discussed extensively.
Earlier, we sampled boulders from moraines adjacent to large lakes. This time, we targeted a steep drop-off (what we called a “lip) that occurs in the valley directly below the lakes. Looking at maps and satellite images, it appeared that the lower valley was actually a remnant cirque:
Our discovery of a large lateral moraine in the lower valley corroborated our hypothesis that a glacier produced the pronounced lip in Valle de Las Morrenas. The vegetative cover increased substantially as we moved lower in the valley, which made accessing the moraine a real challenge. After pushing through thick, woody bushes, we finally found ourselves on the crest of the moraine.
From the image it’s hard to tell, but this is actually a pretty big moraine, about 50-60 feet in height. Meandering rivers cut through cobbles along the moraine’s edge, analogous to what we saw in Sabana de los Leones, only here with water raging through the channel.
We quickly came to realize that the boulder selection on the crest of this lower moraine was a far cry from the beautiful, large, flat boulders we saw along moraines in the upper valley. Here, boulders seemed to be more deeply weathered, and more sparsely scattered.
While the lack of good boulders for sampling induced a bit of hand wringing (made worse by storm clouds quickly moving up the valley), the effectiveness of weathering on these boulders may add to the story of glaciation at Mount Chirripó. Deep weathering of boulders suggests that they have been sitting around, exposed to the atmosphere, for a long time. How long? Glaciologists have employed relative weathering techniques for centuries to estimate exposure age, but 10-Be dating will tell us for sure.
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.