Ancient Sediment — Lakes and Fens in Colorado
September 21-25, 2019. Colorado, USA. Michael Erb
Field work is essential to the study of past climate. By providing scientists with real data about climate of the ancient past, field work is a complement to running climate models. This is why scientists set off to all corners of the world—from icy Antarctica to vast oceans to deep caves—to take measurements and collect samples. Most of my research centers on modeling and data analysis, but last September I had the opportunity to join some colleagues in the field. Field work can take many forms, but read along to hear (and see) my experiences in the mountains of Colorado.
Day 1. A long drive (plus, building a raft)
Shortly before five in the morning, on September 21st, Nick McKay's rental truck arrived outside my apartment. I'd woken an hour earlier and, walking under the stars, I hopped inside the truck. Steph was already inside and we picked up Sela on our way out of town. I don't normally get up this early, but we planned to meet some colleagues from the University of Texas at noon in Durango, Colorado, which is a five-hour drive from Flagstaff (with an additional hour lost to time zones). Yesterday, we packed our bags and got our equipment ready. Now, with the truck bed full, we drove northeast toward Colorado as the sun crested over a dry landscape.
Today was our first day of field work.
Nick McKay, driving the truck, is a professor at Northern Arizona University, as am I, and Steph and Sela are both graduate students. I'd wanted to do field work in the past, but most of my research doesn't require it, so this was my first opportunity to join a trip. Our goal was to travel to high-elevation lakes and fens in Colorado and collect long sediment cores from the ground. Sediment accumulates year after year in these places, so taking long cores is a good way to get a record of the past. The sediment is affected by climate, so a long sediment core isn't just mud—it's a transcription of past climate.
In Durango, we met up with our colleagues from the University of Texas, who'd driven there from Austin over the past day and a half. Tim Shanahan led the Texas group. I'd met him a few years prior when I worked in Austin as a postdoc. Along with him were Natasha and C.J., two of his graduate students. With our group together, our first task was to travel north from Durango and build a raft. The raft would have to be large enough to carry several people, stable enough to work as a platform, and light enough that it could be broken down and carried in separate backpacks up a mountain. We wanted to test out the raft today at a lake we could drive to, since we'd be hiking up a mountain with gear on our backs tomorrow.
Andrews Lake, north of Durango, provided a good place to test our raft. After a bit of planning, we settled on the design you see below. It's made of two large pontoons in the shape of a V, two ladders attached crosswise, and two boards on top for sitting. Everything was strapped together or bolted down. The four graduate students took it for a spin.
Shortly before five in the morning, on September 21st, Nick McKay's rental truck arrived outside my apartment. I'd woken an hour earlier and, walking under the stars, I hopped inside the truck. Steph was already inside and we picked up Sela on our way out of town. I don't normally get up this early, but we planned to meet some colleagues from the University of Texas at noon in Durango, Colorado, which is a five-hour drive from Flagstaff (with an additional hour lost to time zones). Yesterday, we packed our bags and got our equipment ready. Now, with the truck bed full, we drove northeast toward Colorado as the sun crested over a dry landscape.
Today was our first day of field work.
Nick McKay, driving the truck, is a professor at Northern Arizona University, as am I, and Steph and Sela are both graduate students. I'd wanted to do field work in the past, but most of my research doesn't require it, so this was my first opportunity to join a trip. Our goal was to travel to high-elevation lakes and fens in Colorado and collect long sediment cores from the ground. Sediment accumulates year after year in these places, so taking long cores is a good way to get a record of the past. The sediment is affected by climate, so a long sediment core isn't just mud—it's a transcription of past climate.
In Durango, we met up with our colleagues from the University of Texas, who'd driven there from Austin over the past day and a half. Tim Shanahan led the Texas group. I'd met him a few years prior when I worked in Austin as a postdoc. Along with him were Natasha and C.J., two of his graduate students. With our group together, our first task was to travel north from Durango and build a raft. The raft would have to be large enough to carry several people, stable enough to work as a platform, and light enough that it could be broken down and carried in separate backpacks up a mountain. We wanted to test out the raft today at a lake we could drive to, since we'd be hiking up a mountain with gear on our backs tomorrow.
Andrews Lake, north of Durango, provided a good place to test our raft. After a bit of planning, we settled on the design you see below. It's made of two large pontoons in the shape of a V, two ladders attached crosswise, and two boards on top for sitting. Everything was strapped together or bolted down. The four graduate students took it for a spin.
With our raft successfully tested, we disassembled it and drove to South Mineral Campground, which sat near the trail we'd be hiking up the following day. There, eating fresh-cooked vegetarian chili under the stars, we made camp.
Day 2: Ice Lake
We woke before sunrise and, grabbing our gear, drove to the trailhead. Our backpacks, packed the night before, contained the parts of our raft as well as coring equipment we'd use to collect sediment from the bottom of the lake. With headlamps shining the way, we started our hike up the mountain toward Ice Lake.
The first part of the trail had been washed out, and all that remained was a narrow strip of slanted dirt on the edge of a sheer drop. We carefully navigated this in the dark. It was dangerous, and this was the only part of our trip I didn't like. If I had to do it again, I would have suggested we find another way. Field work is important, but not worth risking lives over. Be safe out there.
The rest of the hike was better. As the sun rose, we wound our way through trees up a valley. Tim Shanahan told me that the shape of the valley, which had a U-shaped rather than V-shaped bottom, meant it had once been dug out by the advance of a glacier. You can see it in the second picture below, stretching out behind me. I enjoyed conversations like this. Being out in the field, where you can see the impact of past climate on the landscape, is engaging.
Day 2: Ice Lake
We woke before sunrise and, grabbing our gear, drove to the trailhead. Our backpacks, packed the night before, contained the parts of our raft as well as coring equipment we'd use to collect sediment from the bottom of the lake. With headlamps shining the way, we started our hike up the mountain toward Ice Lake.
The first part of the trail had been washed out, and all that remained was a narrow strip of slanted dirt on the edge of a sheer drop. We carefully navigated this in the dark. It was dangerous, and this was the only part of our trip I didn't like. If I had to do it again, I would have suggested we find another way. Field work is important, but not worth risking lives over. Be safe out there.
The rest of the hike was better. As the sun rose, we wound our way through trees up a valley. Tim Shanahan told me that the shape of the valley, which had a U-shaped rather than V-shaped bottom, meant it had once been dug out by the advance of a glacier. You can see it in the second picture below, stretching out behind me. I enjoyed conversations like this. Being out in the field, where you can see the impact of past climate on the landscape, is engaging.
The hike passed through woods, across plains, and up the valley for about three and a half miles. The final part of the hike—the last ascent toward Ice Lake—tested our stamina. In the thin air above 11,000 feet, I had to take frequent breaks to catch my breath.
Ice Lake is a beautifully blue lake at 11,400 feet. After a quick breather, we began constructing our raft. Nick, Natasha, and Steph soon departed onto the lake and Sela manned a separate support boat, which could ferry supplies between the raft and the shore as necessary.
The process of coring a lake is neat. After rowing out to a good location, three anchor stones are dropped at different locations. The lines connected to these anchor stones provide opposing forces to keep the raft stationary. A stable raft is key for getting a good core, so anchors must be well-placed. A long tube with a coring device attached to the top is then lowered into the water. A hole in the middle of the raft, which was part of our raft design, made this easier. Two lines are fixed to the coring device: one is attached to the main part of the device and the second is attached to a sliding weight at the top which can be raised and dropped. This whole device, along with the long plastic tube attached to the bottom of it, is lowered to the bottom of the lake. When the tube reaches the bottom, it's held there, upright. The second line is then raised and dropped multiple times. Since this line is attached to the sliding weight, the weight slowly hammers the tube into the sediment.
All of this is done by feel, since the whole device is sight at the bottom of the lake. All that can be seen are the two lines gradually disappearing into the depths. As the line is raised and lowered, the metal clanking of the weight resonates up to the surface. Later, after the tube is estimated to be full, the whole thing is pulled toward the surface, with suction holding the sediment in place as long as the bottom of the tube is submerged. As a final step, someone reaches their hand under the water to put on a cap.
This whole process can take some time. As Nick and the others worked on the core, Tim, C.J., and I stayed on the shore. We kept an emergency blanket and the car keys handy, which might be necessary if anyone fell into the cold water. Ice Lake is a popular hiking spot, and several groups of people came by to ask what was going on during this time. They all seem interested and polite, and we told them how things worked.
But why do this at all? Why hike up a mountain to gather mud from the bottom of a lake? Well, lakes are great collectors of sediment. Year after year, sediment washes into the lake and settles to the bottom. It builds up very slowly, with newer sediment layers accumulating on top of old ones. This means that, by taking a core, you gather sediment that's been building up for a long time, perhaps thousands of years. Climate affects multiple aspects of the sediment, so the core provides information about past local changes. This, fundamentally, is what paleoclimate scientists do in the field—they collect physical samples that tell us what the climate has been doing in the past. And that's what, at the moment, our colleagues were doing out on the lake.
During this time, I took a short walk to see other ponds in the area, but the other ponds looked smaller and less interesting. Once the crew on the raft returned to shore, we saw what they recovered. The coring tube wasn't full, but they managed to gather about a meter of sediment. We removed the tube from the coring device, cut the empty part of the tube off, capped the top, and taped up the whole thing. This preserved the sediment so it could be measured in a lab at a later date.
The process of coring a lake is neat. After rowing out to a good location, three anchor stones are dropped at different locations. The lines connected to these anchor stones provide opposing forces to keep the raft stationary. A stable raft is key for getting a good core, so anchors must be well-placed. A long tube with a coring device attached to the top is then lowered into the water. A hole in the middle of the raft, which was part of our raft design, made this easier. Two lines are fixed to the coring device: one is attached to the main part of the device and the second is attached to a sliding weight at the top which can be raised and dropped. This whole device, along with the long plastic tube attached to the bottom of it, is lowered to the bottom of the lake. When the tube reaches the bottom, it's held there, upright. The second line is then raised and dropped multiple times. Since this line is attached to the sliding weight, the weight slowly hammers the tube into the sediment.
All of this is done by feel, since the whole device is sight at the bottom of the lake. All that can be seen are the two lines gradually disappearing into the depths. As the line is raised and lowered, the metal clanking of the weight resonates up to the surface. Later, after the tube is estimated to be full, the whole thing is pulled toward the surface, with suction holding the sediment in place as long as the bottom of the tube is submerged. As a final step, someone reaches their hand under the water to put on a cap.
This whole process can take some time. As Nick and the others worked on the core, Tim, C.J., and I stayed on the shore. We kept an emergency blanket and the car keys handy, which might be necessary if anyone fell into the cold water. Ice Lake is a popular hiking spot, and several groups of people came by to ask what was going on during this time. They all seem interested and polite, and we told them how things worked.
But why do this at all? Why hike up a mountain to gather mud from the bottom of a lake? Well, lakes are great collectors of sediment. Year after year, sediment washes into the lake and settles to the bottom. It builds up very slowly, with newer sediment layers accumulating on top of old ones. This means that, by taking a core, you gather sediment that's been building up for a long time, perhaps thousands of years. Climate affects multiple aspects of the sediment, so the core provides information about past local changes. This, fundamentally, is what paleoclimate scientists do in the field—they collect physical samples that tell us what the climate has been doing in the past. And that's what, at the moment, our colleagues were doing out on the lake.
During this time, I took a short walk to see other ponds in the area, but the other ponds looked smaller and less interesting. Once the crew on the raft returned to shore, we saw what they recovered. The coring tube wasn't full, but they managed to gather about a meter of sediment. We removed the tube from the coring device, cut the empty part of the tube off, capped the top, and taped up the whole thing. This preserved the sediment so it could be measured in a lab at a later date.
After lunch, we launched the raft again. This time, I manned the support boat while Nick, Tim, and C.J. worked on the main raft. From out on the water, the lake looked remarkable. Blue and vibrant. Sitting out here, we spent a while trying to collect another sediment core but had trouble. Possibly our anchor stones weren't keeping us stable enough. After a few unsuccessful attempts, the afternoon started to grow long and we decided to pack it up. We dissembled the raft, packed our heavy backpacks, and eventually started the long hike down the mountain.
Below, you can see our group holding the sediment core. This core will eventually be analyzed back in the lab in Flagstaff. You can see our unwieldy backpacks too. I got off easy. I was carrying the Uwitec coring device, so while my pack was heavy, at least it wasn't as bulky as some others. Tim and I chatted some more on the way down. Dinner that night was hamburgers and leftover chili. Conversation followed, then stargazing and bed.
Below, you can see our group holding the sediment core. This core will eventually be analyzed back in the lab in Flagstaff. You can see our unwieldy backpacks too. I got off easy. I was carrying the Uwitec coring device, so while my pack was heavy, at least it wasn't as bulky as some others. Tim and I chatted some more on the way down. Dinner that night was hamburgers and leftover chili. Conversation followed, then stargazing and bed.
Day 3: Coring a fen
For our third day in the field, we had a change of plans. Instead of heading for another mountain lake and another long hike, we decided to do something simpler. We'd go back to Andrews Lake and split into two groups. The Texas group would go out on the lake where Tim would give his graduate students more experience coring from the raft. Meanwhile, the rest of us would hike behind the lake to a grassy fen (which is a kind of wetland, like a bog), where we'd take more sediment cores. We didn't expect Andrews Lake to yield interesting sediment cores, but experience like this, in an easily reachable spot, is important.
This new plan meant that we could sleep in. After two early morning, I was thankful.
Once at Andrews Lake, Nick, Steph, Sela, and I left the Texas group and made the short hike to the fen, just out of sight of the lake itself. We walked across wet ground in muck boots and found a nice spot to take sediment cores. For this task, we carried a Russian corer, which you can see below.
For our third day in the field, we had a change of plans. Instead of heading for another mountain lake and another long hike, we decided to do something simpler. We'd go back to Andrews Lake and split into two groups. The Texas group would go out on the lake where Tim would give his graduate students more experience coring from the raft. Meanwhile, the rest of us would hike behind the lake to a grassy fen (which is a kind of wetland, like a bog), where we'd take more sediment cores. We didn't expect Andrews Lake to yield interesting sediment cores, but experience like this, in an easily reachable spot, is important.
This new plan meant that we could sleep in. After two early morning, I was thankful.
Once at Andrews Lake, Nick, Steph, Sela, and I left the Texas group and made the short hike to the fen, just out of sight of the lake itself. We walked across wet ground in muck boots and found a nice spot to take sediment cores. For this task, we carried a Russian corer, which you can see below.
The Russian corer is completely mechanical and hand-powered, like the coring device we used on the lake the day before. It has a flat metal fin that sticks out to one side and a rotating half-cylinder compartment attached to a long bar with a crossbar handle. The device is pushed into the ground and, once it's been driven to the right depth, the handle is rotated. The flat fin remains stationary, held in place by the ground, while the half-cylinder rotates around, trapping a half-cylinder of mud in a compartment. With the mud trapped, the entire device is pulled out.
The process takes a lot of force. Pushing the device into the ground, rotating it, and pulling it back out required the combined efforts of all four of us. And it's not just done once. The device takes a half-meter of sediment at a time, but we wanted as many meters as we could get. So, after getting the first half meter, we put the device back into the same hole and repeated the process. Extra pieces of handle let us get several meters down. Eventually we struck something we couldn't pierce, which may have been an ancient lakebed, so we stopped. We then started a new hole and took cores offset by half a meter to get overlapping segments.
This process had some mishaps and mistakes, but we eventually got quite a lot of sediment from the ground. Packing up, we regrouped with Tim, Natasha, and C.J. at the lake. The lake hadn't been good for sediment cores, as we expected, but they got useful experience out of the process.
The process takes a lot of force. Pushing the device into the ground, rotating it, and pulling it back out required the combined efforts of all four of us. And it's not just done once. The device takes a half-meter of sediment at a time, but we wanted as many meters as we could get. So, after getting the first half meter, we put the device back into the same hole and repeated the process. Extra pieces of handle let us get several meters down. Eventually we struck something we couldn't pierce, which may have been an ancient lakebed, so we stopped. We then started a new hole and took cores offset by half a meter to get overlapping segments.
This process had some mishaps and mistakes, but we eventually got quite a lot of sediment from the ground. Packing up, we regrouped with Tim, Natasha, and C.J. at the lake. The lake hadn't been good for sediment cores, as we expected, but they got useful experience out of the process.
After going back to Durango for some general supplies, we went east toward our next destination. It had grown late so, instead of camping, we stopped at a hotel in Pagosa Springs. Before stopping for the night, though, we sat down for dinner at a Mexican restaurant in Bayfield. There, surrounding huge plates of food, we shared stories, ate, and laughed. Sometimes, when on a trip, it's these little moments that are the most satisfying.
Day 4: Another fen and a bumpy drive
As the sun rose the next day, we left our hotel. A winding road took us up into the mountains near a little place called Elwood Cabin, where we scouted for another fen to core. Fens, like lakes, preserve sediment, and taking a core can reveal the local climate history. Mountain locations are good because they're more remote from development, which can obscure climate signals with human activity. That's why so many of our locations are remote.
Settling on another fen, we got to work. This time, all seven of us worked together. As before, it took an awful lot of force to get the corer into the ground or to pull it back out.
Day 4: Another fen and a bumpy drive
As the sun rose the next day, we left our hotel. A winding road took us up into the mountains near a little place called Elwood Cabin, where we scouted for another fen to core. Fens, like lakes, preserve sediment, and taking a core can reveal the local climate history. Mountain locations are good because they're more remote from development, which can obscure climate signals with human activity. That's why so many of our locations are remote.
Settling on another fen, we got to work. This time, all seven of us worked together. As before, it took an awful lot of force to get the corer into the ground or to pull it back out.
We took a set of cores from one location, then drove to a nearby location and repeated the process. People took field notes about our location and the depths of each segment of core, and the foil-wrapped cores were labeled and stored in boxes. Eventually, like the day before, we reached something that we couldn't pierce through. We gave it one last go and managed to break the corer, which was a material failure, not user error, I think. So we called it a day. We'd retrieved quite a lot of sediment from this fen, and hopefully it will reveal something interesting back in the lab.
With our Russian corer broken, we made for our next destination: Kerr Lake. The drive became increasingly bumpy as we neared the lake, and the final two miles went over steep hills, puddles, and large roots—the sort of off-roading you see in commercials for large trucks. Our rental tossed and bucked, but we made it to the remote mountain lake. Nick, driving our truck, seemed to relish the experience, and Natasha, driving the truck behind, did admirably. We set up our raft beside the lake.
The plan here was similar to that at Ice Lake, minus the long hike. Nick, C.J., and Sela went out on the raft to retrieve sediment cores while Steph paddled around the lake in the support boat, this time gathering bathymetry data with a depth sounder. Tim, Natasha, and I, after some trouble finding the right parts, started getting dinner ready on the gas camping stove, cooking Andouille sausage, mushrooms, diced tomatoes, peppers, and pasta. At the end of the day, our colleagues returned from the water with two one-meter long cores. Success!
That night we sat around the fire and ate. Between us, embers rose like fireflies into the starry sky. Talking with everyone, with faces illuminated by the faint red glow of the fire, was very nice. This was my favorite night of the trip.
The plan here was similar to that at Ice Lake, minus the long hike. Nick, C.J., and Sela went out on the raft to retrieve sediment cores while Steph paddled around the lake in the support boat, this time gathering bathymetry data with a depth sounder. Tim, Natasha, and I, after some trouble finding the right parts, started getting dinner ready on the gas camping stove, cooking Andouille sausage, mushrooms, diced tomatoes, peppers, and pasta. At the end of the day, our colleagues returned from the water with two one-meter long cores. Success!
That night we sat around the fire and ate. Between us, embers rose like fireflies into the starry sky. Talking with everyone, with faces illuminated by the faint red glow of the fire, was very nice. This was my favorite night of the trip.
Day 5: A few final cores, then a long drive home
Over the course of our trip, the temperature got remarkably cold each night. Even bundled in multiple layers, plus gloves, coat, hat, thick socks, and a 15-degree sleeping bag, I still got chilly. Despite this (and especially looking back at it now, back in Flagstaff), it was great to camp and do field work. I slept relatively well each night and the work was challenging but never unreasonable.
The next day, which was the final day of our trip, I went out on the lake with Tim and Natasha to take a core. The first coring attempt was mine, so with the two lines in my hands, I slowly lowered the corer and tube. The friction of the lines warmed my gloved hands. The core tube disappeared from sight in the lake depths, so finding the bottom, as well as knowing how far to hammer, had to be done by feeling changes in weight and observing the rope. We hammered for a while, then pulled the heavy tube back out of the water.
The first attempt didn't recover much sediment, so we released it and tried again. Natasha took charge this time and we had better success, recovering a meter-long core. We then moved to a new location and tried again, using a longer tube this time. Taking turns, we hammered until we estimated that the tube had been completely submerged. We probably hammered it too deeply, but that should be alright. Pulling the whole apparatus out of the water, we found the core tube completely filled with sediment. A job well done, we went back to shore.
Tim, Natasha, and I made tacos for lunch. The others went onto the lake to recover a three-meter core. They ate lunch on the raft, receiving their tacos wrapped in tin foil, delivered on the support boat. Later, with cores collected, we packed up the rental trucks and said our goodbyes.
For the Flagstaff group, this was the end of our field work. We started our drive back to Flagstaff while the Texas group traveled toward Santa Fe, where they would be scoping out Stuart Bog the following day. We traveled as a caravan as far as the town of Chama. Then, waving farewell from our windows, we turned west as they continued south.
Over the course of our trip, the temperature got remarkably cold each night. Even bundled in multiple layers, plus gloves, coat, hat, thick socks, and a 15-degree sleeping bag, I still got chilly. Despite this (and especially looking back at it now, back in Flagstaff), it was great to camp and do field work. I slept relatively well each night and the work was challenging but never unreasonable.
The next day, which was the final day of our trip, I went out on the lake with Tim and Natasha to take a core. The first coring attempt was mine, so with the two lines in my hands, I slowly lowered the corer and tube. The friction of the lines warmed my gloved hands. The core tube disappeared from sight in the lake depths, so finding the bottom, as well as knowing how far to hammer, had to be done by feeling changes in weight and observing the rope. We hammered for a while, then pulled the heavy tube back out of the water.
The first attempt didn't recover much sediment, so we released it and tried again. Natasha took charge this time and we had better success, recovering a meter-long core. We then moved to a new location and tried again, using a longer tube this time. Taking turns, we hammered until we estimated that the tube had been completely submerged. We probably hammered it too deeply, but that should be alright. Pulling the whole apparatus out of the water, we found the core tube completely filled with sediment. A job well done, we went back to shore.
Tim, Natasha, and I made tacos for lunch. The others went onto the lake to recover a three-meter core. They ate lunch on the raft, receiving their tacos wrapped in tin foil, delivered on the support boat. Later, with cores collected, we packed up the rental trucks and said our goodbyes.
For the Flagstaff group, this was the end of our field work. We started our drive back to Flagstaff while the Texas group traveled toward Santa Fe, where they would be scoping out Stuart Bog the following day. We traveled as a caravan as far as the town of Chama. Then, waving farewell from our windows, we turned west as they continued south.
All in all, it was fun to be involved in field work. It was satisfying to help collect physical samples and work with colleagues, both old and new, in novel places. Hopefully, when analyzed back in the lab, the sediments will reveal interesting records of past change.
And who knows, maybe I'll find myself on another trip like this in the future. It was hard work, but rewarding too.
And who knows, maybe I'll find myself on another trip like this in the future. It was hard work, but rewarding too.