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Reading the Arctic Landscape
DRI researchers link landscape evolution and soil strength to inform military needs in emerging regions
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When the U.S. military has questions about how environmental conditions impact its ability to protect troops, DRI’s Integrated Terrain Analysis Program (ITAP) gets to work problem-solving. For about 25 years, ITAP has been working to provide various U.S. Department of Defense agencies and laboratories with accurate, field-tested, science-based knowledge to help people and troops on the ground.
The ITAP team conducts field experiments for a range of defense needs, embracing the complexity faced under real-world conditions. At research sites set up not only around the country, but globally, the team uses analog plots that simulate conditions at mission-critical, but inaccessible, locations. Northern field sites in Alaska and Finland offer information that can be used in other polar environments around the globe, while deserts of the southwest U.S. provide insight for the Middle East. Using these and other U.S. analog locations, the research team can also offer insight into how information provided by satellites compares to conditions faced on the ground.
In an ongoing effort to prevent troops from getting trapped in dangerous situations, the ITAP team examines how geography and soil type influence ground strength and cross-country vehicle mobility. Our researchers are developing ways to estimate soil strength and correlate physical measurements with soil type and landforms. Particularly for emerging Arctic lands with complex permafrost thaw cycles, this information helps troops and their vehicles remain mobile – and safe.
DRI's science writer tagged along during fieldwork in Alaska for an inside look at the team's work. She joined Jennifer Kielhofer , Ph.D, and Nicholas Patton , Ph.D. -- two scientists with expertise in soil science and paleoclimatology -- to see how they use their knowledge of landscape evolution to depict and map the layers beneath our feet.
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Nicholas Patton holds silt pulled from a sampling hole.
From Satellites to Sand Grains
Before boarding their flights to Fairbanks, the researchers used satellite imagery to examine the region's landforms. In order to assess soil strength across Arctic and sub-Arctic regions, they needed data from all types of terrain, including wetlands, uplands, ephemeral water bodies, dunes, and floodplains. By looking at the region from above, they could follow the curves of braided rivers and differentiate the light, mottled green of their floodplains from the dark, textured green of upland forests. Each landform would have a different history, layered through time by the forces that shaped it. In Arctic regions like Alaska, much of the terrain is born from the movement of soil churned up and spit out by glaciers over time, evidenced by ribbons of silt carried along by the region's expansive rivers. A floodplain in Alaska would be an imperfect, but useful, proxy for a floodplain in the Nordic or Russian Arctic, but the team also examines parallel features at sites across Finland.
Above left: The team's map of landforms in a region near Fairbanks, Alaska, where they would conduct their fieldwork. Above right: While in the field, the researchers could reference the satellite imagery on their phones to pinpoint their location.
The Dirty Work
The ability to examine detailed views of far-flung locations is a scientific miracle, but it can't replace the information gathered from the ground. So, the team headed to Fairbanks and loaded a rented SUV filled with field equipment, lots of bug spray (Alaskans like to claim mosquitoes as the state bird), and a borrowed canister of bear spray from a kind and generous local.
Their first stop: a scenic lake dotted with lilies and ringed with cabins. Patton and Kielhofer follow the shoreline only briefly before finding their targeted landform: a "beach ridge," where rising waters from storms and snowmelt have formed a raised ridge. These can appear over the course of mere months, rather than years, but will look different with age. "The longer they persist, the more organized the structure is," Patton says.
Above left: A lake outside Delta Junction, Alaska. Above right: Patton digs into the beach ridge to get a profile of the soil.
The picturesque site, where the scientists work under dappled sunlight streaming through birch and spruce trees, is disturbed only by the constant hum of mosquitoes. Patton digs into the ridge and confirms what they both suspected: loess. Born from the German word for "loose," loess is light-colored, loosely-packed mineral dust that is easily picked up by winds. Here in Alaska, loess is the result of glacial movement, as the icy behemoths grind stone to dust and carry it in their melt waters. You can think of loess as "glacial flour," Kielhofer says.
Above left: Kielhofer inspecting the loess. Above right: A profile of the beach ridge, filled with plant roots and loess.
Above: Loess is carried around Alaska by glacial melt, and readily seen as minerals in heavily-silted rivers that sparkle in the sunlight. It deposits along the shoreline and builds up over time.
After inspecting the soil profile, Kielhofer pulls a small metal cylinder from her bag. She removes a plastic cap from one end of it, places the sharp end on top of the soil, and hammers it into the earth. Then she carefully scrapes the surrounding dirt away and pulls out the perfectly contained sample of the top few inches of soil. This will be taken back to the lab at DRI's Reno campus and used to assess how much water the soil can hold. Does it drain quickly, or become thick and clay-like?
Above left: Kielhofer carefully scrapes the soil sample from the earth. Above right: Patton blows excess dirt from the surface of the soil sample.
Next comes a range of equipment. First, the Dynamic Cone Penetrometer (DCP), a serious name for a long, heavy piece of metal that is used to determine the strength of soil at varying depths. Kielhofer places the tip on the ground, raises the built-in weight, and lets it drop with a bang. She does this about 10 times, with Patton reading the measurements of how many millimeters the tip moves with each hit. At sites like this, where the soil is soft, the researchers get through it quickly; at others where the permafrost lies just below the surface, the hard ice drags the process out. "Moisture, organic matter, gravel, and particle size can all impact soil strength," Patton says.
Above left and right: Kielhofer wields the DCP, while Patton notes the measurements on a datasheet.
Next, Patton places a bright red cylinder on top of the beach ridge. Known as a "clegg hammer," it drops a weight onto the earth to test compaction. Typically used on road construction projects, here it will help the scientists understand how soft the soils are, and how repeated compaction impacts it. "Some soils can get stronger with repeated passes or pressure, and others turn to mush," Patton says.
For the final measurement, Patton hammers a metal rod with four vanes into the soil. Then, he attaches a gauge to the top and rotates it, recording the torque required for the soil to fail. The same equipment has been used for decades to determine whether snowpacks are at risk of creating a slab avalanche.
Patton testing soil compaction and shear strength.
Kielhofer and Patton working beneath a birch tree canopy.
The Great Unconformity
The research team finds a sand dune lurking beneath this forest.
The following day, while investigating another field site, we stumble across a deep hole: remnants of researchers or surveyors past. Conveniently, it allows us to see a soil profile without the work of digging one ourselves. Patton rubs off the outer layer with a shovel to uncover the pristine coloration below. It confirms what the team suspected -- this area is the remnant of an ancient sand dune that is around 18 thousand years old. At some point, it was cut off from additional sand deposition when the river shifted directions, and now looks like a forest when you don't take a look at what lurks below the roots.
About one foot down, a distinct, dark red line crosses the entire soil profile -- contrasting sharply with the golden sand just above and below it. Kielhofer points it out excitedly, saying that she's seen the same distinct line at sand dunes all across Alaska while conducting the fieldwork for her Ph.D . Scientists are stumped by it, she says, leading Patton to jokingly refer to it as "the Great Unconformity of Alaska." He's referring to the gap in the geologic record that's clearly visible in the Grand Canyon, where more than 1.3 billion years of Earth's history were lost to erosion.
An 18,000 year old sand dune lurking just below the surface, with a mysterious dark red line indicating an unknown regional climate pattern preserved in the soil record.
Ankle-twisting Ground
After a week of fieldwork, the scientists and I all have aching muscles and more bug bites than we can count. But we still have one last site to visit, with what Kielhofer and Patton refer to as "patterned ground" -- what could more accurately be called "ankle-twisting ground." This is where bunch grasses called tussocks rise above the soil, roots and all, as if inside invisible planters -- with every step taken, it's easy to fall off of one into the hidden drops between each plant.
Tussocks between 2 and 3 feet tall obstruct the path to the field site.
Found across wide expanses of Arctic tundra, wetlands, and bogs, tussocks can live for more than 100 years. Most of them are not technically classified as grasses, but sedges called cottongrass for their white-tufted flowers. Despite their status as the nemesis of both Alaskan explorers and scientists conducting fieldwork, tussocks create valuable habitat for wildlife, providing food to caribou in the spring and serving as nesting spots for birds. They are also resilient, often recovering within a year of burning, which aids the landscape and its inhabitants in recovering after wildfires. Despite the abundant lakes, rivers, and wetlands of the region, lightning strikes from summer storms often spark wildfires here -- several are actively burning nearby as we complete our fieldwork. Unlike many of the infernos that burn throughout the American West, the fires we see here are on a smaller scale, burning patchily as they smolder through dense layers of low-lying vegetation.
Some of the tussocks are waist-high, and the mosquitoes are somehow even more plentiful at this boggy location. Everyone covers their face and heads with hats, hoods, and mosquito nets; Kielhofer uses earplugs to block out the maddening sound of their buzzing. "I read in some places they're so thick that they can kill animals," she says.
Kielhofer working near Fort Greely, Alaska, in winter of 2023.
Tussock tundra isn't just difficult to walk over, but considering that the scientists are here to gather data for informing vehicle mobility, we discuss what the difficult landscape means for roads. On our drive in, the road undulated beneath us, rising unexpectedly before dropping like a child's rollercoaster. This is due to the freeze-thaw cycles of the ground here, which quickly damages roads as the ground below swells and falls. A 2018 study by the Bureau of Land Management notes that oil companies often use ice roads in Arctic regions, using ice and snow from lakes to build up the base and spraying water on top to create elevated, stabilized surfaces. If these roads are used for a single season, the study found that the vegetation below can recover after about 20 years.
Because seasonal changes have dramatic impacts on the ability of vehicles to move through a landscape, Kielhofer and Patton have made repeated visits to their field sites. They were in this same stretch of Alaskan wilderness the previous winter, taking identical measurements under very different conditions.
Tussock Tundra in Alaska's National Parks
Endangered Ice
Once it's safe to do so, Kielhofer looks up from watching her step and notes the trees also growing at the site. "Black spruce is a great indicator for permafrost," she says, referring to ground that remains frozen year-round and which occurs in Arctic regions around the world.
Patton starts the DCP measurements and quickly hits resistance. "Feels like ice!," he says. When he pulls the metal tip from the ground, Kielhofer touches her hand to it. "Definitely cold," she says.
Patton begins twisting an auger into the soil until we all hear the sound of metal scraping on ice. "We've reached the permafrost!" he says. "It's like finding an endangered species." He pulls the auger from the ground and we all admire the ice crystals glittering in the sunlight. I hold some in my palm and watch as it melts in the warm August sun.
Above left: Soil sampling bags labeled with the essential data: date, location, and mosquito status. Above right: Ice crystals caked throughout the soil indicate that we found the permafrost.
The ground can remain frozen throughout the heat of summer because of the thick layer of vegetation insulating it. In some locations, the researchers pull out over a foot of dense, spongey vegetation and roots before they can even reach the soil beneath (what they call "duff"). This raises some interesting questions when they're taking measurements -- if the data is meant to reflect the status of the ground surface, where, exactly, does the ground start? Does this pillowy layer of organic matter count as the ground surface, or do they dig below it to measure the soil strength? The organic matter likely has more variation across the landscape than the soil below it, but the scientists agree that vehicles travel over whatever is on the ground, vegetation and all.
Patton's excitement about finding the permafrost is due to the increasingly precarious status of this hidden resource. As greenhouse gasses build up in Earth's atmosphere and air temperatures climb, ground temperatures are following. Scientists tracking 50-foot deep boreholes around Alaska have found that even at this seemingly untouchable depth, nearly all of them are warming . One study projects that if the climate stabilizes at 2°C above pre-industrial levels (an unfortunately likely scenario), Earth could lose more than 40% of the existing permafrost.
Above left: Patton removes more than a foot of thick vegetation to reach the soil beneath, a layer which helps insulate the permafrost below. Above right: Patton working amongst black spruce, which Kielhofer says are a good indicator for permafrost.
Thawing permafrost presents a number of challenges. Although most permafrost contains a top layer that undergoes a seasonal freeze-thaw cycle, an abnormal loss of ice that penetrates deeper can change the very structure of the ground, turning it to soft mud that can no longer support any infrastructure. When this happens, the ground surface collapses, creating what is known as a thermokarst -- essentially a deep sinkhole. More than 80% of Alaska sits on top of permafrost, making the state particularly vulnerable to collapsing roads and buildings as it thaws.
In fact, as we drive along the Richardson Highway south of Fairbanks to our field sites, we repeatedly cross paths with one piece of infrastructure that encapsulates the conundrum of climate change: the Trans-Alaska Pipeline. This 800-mile long pipeline stretches across the entire state, from the oil fields in far northern Alaska to the southern port in Valdez. Over 400 miles of the pipeline sit about 6-feet off the ground using supports that have built-in "thermo-syphons" to conduct heat away from the permafrost. But in 2020, for the first time since the pipeline was built in the mid 1970s, the Alaska Department of Natural Resources found that thawing permafrost is damaging some of these supports and threatening the pipeline's stability. A 2021 article for Inside Climate News notes the irony: "The state is heating up twice as fast as the global average , which is driving the thawing of permafrost that the oil industry must keep frozen to maintain the infrastructure that allows it to extract more of the fossil fuels that cause the warming."
Of course, another (and perhaps greater) concern that stems from thawing permafrost is the additional carbon dioxide and methane that it releases into the atmosphere -- what scientists refer to as a "positive feedback loop" that is part of the tricky accounting of just how much the global climate will change.
Above left: The Trans-Alaska Pipeline crosses more than 800 miles to carry oil from Prudhoe Bay in northern Alaska to the southern port in Valdez. Above right: Thermokarst lakes in Hudson Bay, Canada in 2008. Thermokarst lakes occur when permafrost thaws and the ground collapses, creating ponds when they fill with water. Photo By Steve Jurvetson - CC BY 2.0
A Landscape Carved by Glaciers
When we make it back to the perceived safety of the car, the mosquitoes follow us in, and the frantic swatting ends when the last one is smeared across the dashboard. “I’d like to take a minute in the car just to take a break and think about our choices,” Patton says. After a week of fighting them off and carrying heavy equipment over uneven ground, everyone is ready for some recovery time.
With fieldwork wrapped up early -- thanks to the efficient pace inspired by mosquitoes as well as the fires burning nearby -- the team has time for an afternoon detour to nearby Castner Glacier. When we pull up to the trailhead, tall mountains greet us for the first time. Our fieldwork had been centered in the Tanana River Valley southeast of Fairbanks, a lowland area with some of the oldest known archaeological sites in North America. In 2013, not far from the team's own field sites, researchers found the remains of an infant buried more than 11,000 years ago. The discovery helped strengthen the theory that humans first arrived to the continent by crossing the Bering Strait when it formed a land bridge between Alaska and Russia.
Kielhofer conducted her Ph.D. fieldwork in this region, using temperature records stored in ancient bacteria to show that temperatures in the Tanana Valley had remained fairly stable over time, conflicting theories that perhaps dramatic climate fluctuations had triggered early human migrations from the region.
The hike up to Castner Glacier, with a river born from glacial melt meandering through the landscape.
The hike to the glacier is brief, about a mile along a river born from glacial melt. Large boulders, fist-sized stones, and gravel line the river's edge, transported along by the glacier itself and by its meltwaters. We can see a distinct high water line, with a ridge of sediment pushed up along the river's banks. As we approach the glacier, I scan the rocks as I walk, turning up a long stone with parallel scrape marks, flattened on one edge. The stone is a "glacial tool," Patton says, meaning it had been trapped in the glacier's ice, the scrapings the mark of how it had helped the glacier to grind stones into loess.
It's difficult to fully visualize how glaciers can create and move such massive amounts of sediment, until I get a close-up look of one. A wall of ice with small rocks trapped inside, it is covered in dirt; water drips down from the top and flows over the surface, bringing rocks crashing down with it. The entire surrounding area is a boulder field, with small pools of glacier-blue water.
Above left: approaching the glacier, we cross sandy washes filled with rocks and pools of glacier-blue water. Above center: A wall of ice now stands on top of a boulder field, where a huge ice cave recently collapsed. Above right: Rinsing off the top layer of dirt shows the blue ice studded with stones beneath.
In a true testament to their changing nature, we had expected an altogether different sight. Photos of Castner Glacier from mere months ago show a large ice cave where we now stand upon a boulder field, the cave having recently collapsed in the strong summer sun. The wall of ice is actively melting as we examine it, and debris rains down from the top. Everywhere around us, there are stacks of rocks moved and altered by the shifting ice.
Above: Photos of Castner Glacier in November, 2022, with Patton (left) and Kielhofer (right) for scale. The ice cave had since collapsed, leaving a much smaller wall of ice behind. Photos by Jennifer Kielhofer (left) and Nicholas Patton (right).
We turn a bend and climb up a mound to see what's left of the glacier's caves. Now inaccessible, with a fast-moving river running through it, we admire it only briefly before the ice begins to groan and snap. The sounds are sudden and jolting, reverberating through our own chests. We take heed of our instincts and leave the glacier's side, aware of both our own precarious state and that of glaciers around the world . As we follow the river back to the trailhead, Patton talks about his experiences teaching, and how difficult it can be to get students excited about soil science. As someone who had rarely, if ever, thought much about soil before this trip, I can understand their disinterest. But after a week spent digging through the Alaskan earth and learning to link the icy mountain peaks to the sparkle of silty river water to the ground beneath our feet, I am embarrassed to admit it. It turns out that looking at dirt is really just an unglamorous way of reading the Earth's history, if you know what to look for.
Castner Glacier, with an ice cave draining into the river below. Photo by Nicholas Patton.