When the machinery mounted to the man-height pole announced “RTK initialized,” the scientists gave a cheer. It was late afternoon and the morning’s downpour had finally cleared. They were gathered in a sunny spot discussing what was still on the agenda for the day when the rover – the pole and its paramount differential GPS unit – announced its good news. Geologist Ronald Daanen grabbed the rover and raced to the toe of the lobe, hoping to get the measurement before the dense cluster of half-fallen trees or some other imperfect condition made the instrument lose its connection. He made it there in time to capture the data for yet another measurement point on the massive bulk of frozen debris lobe -A.
“As you drive up the highway to milepost 219 and look out your window, your passenger window to the east, you see this hill and it doesn’t look like much– I mean it really doesn’t look like much from the road. As you get out of your car and you walk up to the top of the toe – that’s the toe of the slide or the end of it – as you walk up to the toe and you look back to the highway you’d see that view and you’d say: ‘Wow, that’s not very far away.'” … “As you walk to the toe you’ll see signs of movement, evidence of movement. It’s like a big bulldozer; it pushes the organic mat up, rolls it up kind of like a carpet.” ~ Margaret Darrow
Studying frozen debris lobes is not at all a 9-5 job. That day the three scientists were up before dawn to forge uphill through thick wet brush. Even once they finished taking field measurements in the late evening they stayed up to communicate their science with us, to explain more, to film interviews, until the midnight hour. Once the long field-days are over and all the measurements are taken, the data will still need to be post-processed with software to ensure the highest level of accuracy.
These three devoted scientists are University of Alaska Fairbanks Mining and Geological Engineering Department associate professor Margaret M. Darrow, and Alaska Department of Natural Resources Division of Geological & Geophysical Surveys (Engineering Geology section) geologists Ronald P. Daanen and Trent D. Hubbard.
Frozen debris lobes (FDLs) are slow-moving landslides in permafrost. There are 23 FDLs identified looming upslope and less than a mile from Alaska’s Dalton Highway, the only road that connects interior Alaska to the North Slope. Besides the highway used by industry vehicles and oil tanker trucks, tourists and scientists, the Dalton Highway corridor also hosts the Trans Alaska Pipeline and the oil it transports south.
Darrow, Daanen and Hubbard were taking measurements at select FDLs because the lobes’ rate of motion has increased. FDL-A is the largest lobe, and also the closest to the road. It’s sliding downhill; its toe sits closer than 142 feet from the road.
Vivian & the base station
They used special instruments in their work. The rover, their pole-mounted Differential Global Positioning System, has been dubbed ‘Vivian’. “Vivian, the differential GPS, would come in and out of satellite coverage and she talks!” Darrow explained. The system is temperamental. “We started to talk back to her. We resented that she would tell us we couldn’t do what we wanted.” Darrow confessed: “Yeah, we have a love-hate relationship with our differential GPS.”
It’s a theme scribbled a few times with small variations in my notebook: ‘Vivian: RTK initialized.’ ‘Ronnie: Thank you.’ ‘Margaret: Yay!’
“We are measuring the position of the surface of these debris lobes as they come downhill and so the differential GPS gives us highly accurate readings of the surface and how it moves with time, depending on how many times we go out to take those readings. When it’s working, we get great data.” ~ Margaret Darrow
Great data: even in Alaska’s far north, within the Arctic Circle, the scientists could use Vivian to get centimeter-level accuracy – within 5 centimeters accurate. They measure many locations across the lobe by setting Vivian’s pole at the base of marked survey stakes at spots selected to measure the rate of movement of the surface of the frozen debris lobe. A small bubble inside a dome of liquid mounted to the pole helped the scientists hold the pole upright; meanwhile, the equipment did its work. Hubbard noted: “When the accuracy gets to the level it’s supposed to be, it will record the point.”
In order to attain that excellent accuracy the scientists set up a base station, a tripod holding equipment including an antenna and radio, directly over a benchmark, a spot with a precisely recorded location. While they hiked across the lobe and took measurements at marked locations, Vivian communicated with the base station. Both Vivian and the base station simultaneously tracked signals from satellites. Using a comparison of the data, Vivian’s precise location could be determined as long as she was within 20 kilometers of the base station.
“To get accurate measurements with a GPS system you need to have two points. One point is fixed and this is the base station, and the other point is the rover which we are going to use on the frozen debris lobe to actually measure markers. These two points both receive satellite signals but in order to know if centimeter level accuracy is reached we need to communicate between these two points and therefore we have put up this antenna. The antenna is going to send a signal from the base station to the rover so we can see on the screen in real time how accurate the point is that we are measuring.” ~ Ronald Daanen
“How do you pick the points?” I asked Margaret Darrow after a few hours pushing through wet alder thickets, sometimes only knowing my way because the scientists ahead (faster and more efficient, of course) were shouting to ward off bears. Darrow answered in jest “I think Ronnie was in a bad mood that day.” Then she explained a mixture of judgment and measurement. About 28 survey stakes with little flags atop them march across FDL-A. One row marches down the center of the lobe, while others stray left and right to span its bulk. No two stakes sit nearer than 100 meters apart. Sometimes a moose path helps connect them through the brush and drunken trees (growing sinuously as they partially topple in the shifting ground then try to recover).
Many of the survey stakes are accompanied by iButtons, a little disc like a fat dime. Daanen used a reader plugged into his laptop as he explained. “It measures the temperature every five hours, or whatever interval I want it to measure. It goes for about a year. And so every year we come here and we measure the movement rate of the stake, and the temperature with the iButton. So you press it in the computer and you can actually see the temperature on the screen.” Once the file is saved, the iButton could be reset to record the next year. The scientists kept them on moss if possible, not rocks or dark soil that heat up more intensely in the sun.
“I’m going to compare that to the air temperatures that we measure at the main weather station. And I’m going to see if there are trends of temperature along the lobe. Over many years maybe we’ll see what the temperature of the surface is and maybe we can correlate that with the temperature inside with a model and then see if it warms up or not. And if it does, determine what consequences that might have on the movement rate.” ~ Ronald Daanen
There’s a complete weather system installed on FDL-A. It’s solar-powered, with a battery to keep the machinery going through the winter. A data logger inside a big white box records the temperature, while lines to temperature sensors stray out along the ground’s surface and into the earth to measure the temperature of the permafrost at various depths. The box has its own grounded lightning rod. After the box was closed, Darrow listened to make sure it was running. “I can hear it: Brrrrrk. So that’s a good happy sound. When it’s taking all the readings on the multiplexer. You lock it and then you wait and you listen and you hear that Brrrrk. It means it’s working.”
That night in August 2014 the scientists learned that they wouldn’t be funded to continue frozen debris lobe research next season. They don’t have enough data yet to outline appropriate mitigation strategies, or to build a computational model that could show what might happen to the lobes under various conditions. I asked Daanen what he thought would happen when FDL-A reaches the road. “What will actually happen I think is that the lobe will just push the road out of the way. I don’t think there’s any force strong enough that is currently there that will stop it.” Daanen also brought up another lobe, FDL-D.
“FDL-D is one of these other lobes, you know, people don’t pay much attention to it because it’s further from the road. But it did move 150 feet in 1 year, 3 years in a row. If FDL-A starts moving at that rate it’ll be on the road in one year. So. Even if they move the road 400 feet, right, 3 years of 150 feet, that’s quickly covered. So, you know. They will have to find a solution. I don’t know what it is. They will probably ask us. And Margaret already said that: ‘No, we don’t know because we don’t have the research,’ so.” ~ Ronald Daanen
When asked for a takeaway message, Darrow said: “We need more drilling. Did I say that? I’ll say it again: We need more drilling. More geotechnical exploration, that’s really important.”
“Yeah we need more subsurface exploration. This is me coming from a geological engineering point of view, and that geotechnical data is so critical. We walk around them a lot and observe things on the surface and I always think, well, what’s underneath? Where is the bedrock? How could we describe this? Otherwise we’re just waving our hands. So I would really like to see more subsurface exploration and instrumentation because that hard fast data is so much better than handwaving.” ~ Margaret Darrow
Frontier Scientists: presenting scientific discovery in the Arctic and beyond
Frozen Debris Lobes project
- Interviews with the scientists during their field work season, 2014