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Insights from the Field: Meet the Researcher Studying 2,000-Year-Old Dirt From the Bottom of a Lake In Nepal

Mary Hubbard, Geology Team co-lead for the National Geographic and Rolex Perpetual Planet Everest Expedition, provides a behind the scenes glimpse into the work she and her team conducted in the Gokyo Valley lakes. The team, whose work was recently featured in the December 2019 issue of National Geographic magazine, will be integral to analyzing environmental conditions impacting the region.

What is the importance of the lakes in the Gokyo Valley?

The Gokyo lakes, located near Mt. Everest, are interesting because there are six of them lined up and down the Gokyo Valley. Their locations give scientists an opportunity to draw comparisons between the lakes to reconstruct past environmental conditions at a range of elevations. The lakes in Gokyo Valley sit below the Ngozumpa glacier and are bordered by side valleys that were likely filled with ice during the last Ice Age, ~18,000 years ago.

Why did you decide to do research at the two lakes you studied?

We chose the two lowest lakes because we were doing our work early in the season and the higher lakes still had too much ice for us to break through to safely reach the bottom and collect a sediment core.

What is the purpose of taking lake cores? Why are they important?

Lakes are dynamic systems with water inputs and typically an outlet. Along with water, the incoming streams bring sediment from their source areas and that sediment settles out in the lake bottom. Also, settling to the bottom of the lake are relics of living organisms, mostly microscopic in size. This material also includes fossilized pollen from nearby vegetation that has been carried by the wind and deposited in the lake. Over time, layers of sediment accumulate. These layers are representative of the environmental conditions at the time they are deposited. By coring the lake’s sediments, we can retrieve a section of these layers, which we examine and analyze to determine how old the layers are and what environmental conditions were present at the time the were deposited.

What is the process for taking a lake core?

We used two inflatable rafts that were tethered together — like a catamaran. The catamaran-esque set-up was necessary because it allowed us to safely work between the boats to lower the coring device into the lake. The coring device consisted of a clear plastic tube about one-meter long that was attached to a weight along a one-meter-long rod, attached to a separate rope. After we lowered the whole instrument to the bottom of the lake and gently rested it on the lake bed, we repeatedly raised the weight about 30 cm and let it drop along the rod, which essentially acted like a hammer to drive the tube into the sediment.

It’s interesting because you’re using your senses while getting the cores. When we no longer felt the tube penetrating the lake bottom any deeper, we’d pull the whole device back up to our boats.

What did you do with the lake cores?

We sealed the ends of the lake cores once we had them on land, and we tried to keep them refrigerated until we get them to the laboratory. At each lake, we collected two neighboring cores. One core from each lake stayed at the Tribhuvan University in Nepal for our Nepali team members to analyze. The other cores came to the U.S. When they were in the lab, we cut the cores lengthwise in half. One half was archived and the other half was photographed and scanned to determine differences in the amount of magnetic grains in each layer and other optical properties. We then scooped samples from several layers of the core to determine the age of any organic material found in them We also examined each layer of the core for the types of clay minerals, species of pollen, and other fossil organisms that might be present. We are working with very experienced collaborators in these very specialized methods to help us to do the analyses.

Are there any results from the cores that you can share?

So far, we learned that one of our cores was likely from a steep slope on the lake bottom, and some of the sediment slumped or slid to form a fold in the layering. Preliminary work tells us that the deepest part of our cores are around 2,000 years old.

What is it like doing research on these remote lakes? What were the weather conditions while you were in the field?

These lakes are at quite high altitude (around 15,400 feet), so carrying the equipment is extra difficult. We had porters who helped us with most of the carrying so that we could focus on the science. There was still ice on parts of even the lower lakes, so it was quite cold. One of the days was too windy to core and one of the days that we did core, it was snowing on us. The coring device got quite muddy, so eventually our boats were muddy and so were we!

Why is it important to cultivate relationships with local researchers and communities? Are there any anecdotes or examples you can provide that shows the important impact these relationships have on conducting research?

It is essential to cultivate relationships with local researchers and with local communities and these are typically two very different groups.

When you are doing research in another country it’s important to recognize and respect that the land belongs to the local people. The knowledge we gain through our research will have direct relevance to communities where we worked. Through our partnership with Tribhuvan University in Nepal and Dr. Ananta Gajurel, we provided an opportunity for seven Nepali graduate students to participate in our efforts in order to provide training that they will need to build their careers. The students learned new scientific methods that will allow them to better research their local environment. We also engaged with local faculty members and researchers who will continue to educate these students and remain engaged in scientific questions and solutions that are relevant to the region.

In addition to involving local scientists in research like this, it is also critical that people who live at and around the research site are involved and consulted. Their input about the questions they have about their environment is vital, and it is equally important for scientists to share why we are interested in research in their region and what benefit this research might provide.

One thing we learned was that both mountains and lakes in the high Himalayas are considered by the local people to be sacred sites. The third lake in the Gokyo Valley, by Gokyo village, is particularly sacred, and thus we were sure to not disturb that lake in any way.

The team's work on glacial lakes was recently featured in the December 2019 issue of National Geographic magazine. Learn more about the National Geographic and Rolex Perpetual Planet Expedition by visiting

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