When a hole in the ice is a big problem
When your airport runway is located at 72 degrees south latitude and more than 4000 kilometres from the nearest major city, it better be in tiptop shape. But in Antarctica, where most runways are made of snow or ice, holes can be a big problem.
Antarctica’s airstrips are like few others on the planet. Some select few need to be strong and solid enough to support repeated landings by giant cargo planes like the C-17 Globemaster and the C-130 Hercules, or passenger planes like a Boeing 757. And yet they are almost exclusively made of snow or ice.
Ice might seem to be a simple and elegant building solution in this frozen world. Why not build a runway out of the most common material in Antarctica? But ice is notoriously fickle stuff. Even in Antarctica, when sand and dust blown in from the surrounding mountains darken the ice, the sun can melt holes in a blue ice runway. You can always patch it, of course, but just how good are the patches?
Sven Lidström, Antarctica operations coordinator for the Norwegian Polar Institute’s Troll Research Station, has thought long and hard about this particular patching problem. His responsibilities include the Troll Airfield, a blue ice runway that was opened in 2005.
The runway is one of the few of its kind, and one of only five overall that can handle larger planes, Lidström said. That makes the holes in the runway more than just a vexing nuisance.
“They are the biggest problem we have,” Lidström said in an email from Troll station. A problem, it turns out, that is an ideal challenge for NTNU’s ice experts.
An important link in the network
Located in Queen Maud Land, 235 km from the Antarctic coast and 6.8 km from the Troll Research Station, the airfield is key not only in supplying the Norwegian research station, but as a part of DROMLAN, a coordinated shared transport project between the eleven countries that have bases in the region.
Under this arrangement, the Troll Airfield acts as a “hub”, with major supply flights from Cape Town International Airport, 4000 km away. Most of these supplies come on Airbus A-319s and Boeing 737s and 757s, but smaller jets are now starting to replace the normal Antarctic work horses, the C-130 Hercules and Ilyushin 76, Lidström says.
Feeder flights then supply other research stations from Belgium, Finland, Germany, India, Japan, the Netherlands, Russia, South Africa, Sweden and the UK.
Lidström says the shift to smaller, more “modern” jets is one reason why the Troll Airfield needs to be in tiptop shape.
“Modern aircraft are not as rugged or field-tested” as the older freighters, he said. “They need much better runways. But the modern aircraft are better, safer and much more fuel efficient.”
During the summer season, from November to March, Lidström says the runway is used for roughly 2-3 intercontinental flights per month and a couple of continental /domestic Antarctic flights per week.
Unlike other intercontinental runways in Antarctica, it can operate during the entire summer season, he says. Other intercontinental runways have to close during the warmest part of the summer because of melting. But that is also the peak season for air transport to and from the continent.
The runway is also “a very important part of our safety and emergency response,” he wrote. “It gives us the possibility to evacuate someone or bring expertise in if something serious would happen. Antarctica is still very remote and lacking much of the infrastructure and equipment available in the rest of world.”
Sand holes by another name
Lidström says the problem with holes in the ice runway began as soon as it was opened in 2005.
The surface of the runway can be damaged by cracks in the glacier and ice movement, but it is the sand holes that are the most common problem. The windblown dust, sand and microbes, collectively called “cryoconites”, are darker than the surrounding ice, and the sun heats up this debris where it collects. That allows the cryoconites to melt their way through the ice, creating a cavity or hole.
“Normally, some of the water freezes back above the sand, but that ice is thin and not as strong as the surrounding ice,” Lidström said. “It creates a risk that this ice would collapse if there is weight on top of it, creating a hole that aircraft tires could get stuck in. This could have catastrophic effects for an aircraft that is landing or taking off.”
Although Lidström and his colleagues can patch the holes with a slushy mix of water and ice, the patches aren’t the same colour as the hard blue ice of the runway. It’s likely their other properties are slightly different, too — but just how much isn’t really known. So Lidström decided he needed some solid research to learn more about the patches that pock the 3000-meter long airstrip.
He wrote that he decided to contact NTNU and UNIS, the University Centre in Svalbard, because he realized the question would be a perfect project for a master’s student.
“It’s a very special field, so it is hard to find someone with right competence and experience,” he wrote. “UNIS offers good courses preparing their students for the field, so it was natural for us to look for people with that background. In addition, we get access to expertise and the latest research in the field through NTNU and UNIS.”
Another, more long-term goal is to encourage other students to consider polar engineering, Lidström said.
“We have many areas where that type of expertise is needed, so we hope that the possibility to do your thesis or project work in Antarctica will encourage more students to choose this field,” he wrote.
A cold, but fun assignment
Maren Salte Kallelid, a master’s student at NTNU’s Sustainable Arctic Marine and Coastal Technology programme (SAMCoT) and at UNIS, was lucky enough to get the assignment.
“The subject is a little different than my education, as I am studying to be a geotechnical engineer,” she said. “But still, ice is just a building material with special properties. And the material is very close to its melting temperature, and its properties change a lot with small changes in temperatures.”
In February, she spent three weeks at Troll to conduct ice strength measurements on the runway. She tested both the runway ice itself and the ice that is used to patch the holes.
Custom-made NTNU equipment
Measuring ice strength out on an airstrip at the bottom of the world takes some ingenuity, however.
Kallelid and her NTNU supervisor, Torodd Nord, a postdoctoral fellow at SAMCoT and adjunct associate professor at UNIS, devised a lightweight borehole jack that Kallelid was able to take with her to Troll to do her measurements.
Nord and Kallelid field-tested the equipment in January at a frozen pond in Trondheim’s city forest called Bymarka. After 40 tests, the pair brought the borehole jack back to NTNU for a few adjustments, and then it —and Kallelid, also trained to work safely in a cold, remote place — were ready to do the tests in the Antarctic, Nord said.
Measuring ice strength in place
One of the advantages of the custom-made borehole jack is that it can measure the strength of the ice in place, instead of having to take it back to the laboratory.
“First I drill holes in the ice, and then lower the instrument to the depth I want,” Kallelid explained. “At the lower part of the steel cylinder there is a piston that is pushed into the ice. A data logger records the force this requires. The maximum value determines the strength.”
She also measured the strength of the ice with an instrument called a Russian Snow Penetrometer, abbreviated RSP. The instrument consists of a steel rod with a sharp tip and a “load hammer” that slides along the rod. The test is performed by dropping the load hammer from a specific height and measuring how deeply the steel rod penetrates the snow or ice.
The test involves calculating a strength index based on how many drops it takes for the penetrometer to sink to a certain depth in the surface being tested. The strength index is the standard used to decide if the runway or airstrip is strong enough to bear the weight of different aircraft.
“The values I have gotten at Troll are about three times higher than the minimum values,” Kallelid said.
Nevertheless, while the RSP is the standard test, its results “are difficult to relate to mechanical strength,” said Nord. That’s where the new borehole jack can help.
“I am sure that we can supply NPI with a better understanding of the mechanical properties of the Troll Airfield after this project,” he said. “At the end of the testing, the amounts of data were far beyond our expectations.”
Everything is different, every day of the year
The United States has some of the busiest runways on the Antarctic continent at McMurdo Station. Here, during the austral summer, the National Science Foundation’s Antarctic Program operates two airstrips to bring people and goods to McMurdo and onward to the South Pole Station and various field sites.
Margaret Knuth, Antarctic Operations Manager at the US National Science Foundation, says that a host of conditions combine to make managing ice runways a challenge. Knuth and Lidström have also talked informally about the challenges of maintaining an ice runway.
“Building and maintaining these snow and ice runways is complicated by the use of a non-traditional construction material – water,” Knuth said in an email. “Typical runway facilities are built using concrete or soils and are designed to have very little influence from temperature or radiation (sunlight). In the Antarctic, the times when we are interested in using the runways the most – the austral summer when research and logistics activities are high paced – these two issues are also most likely to be present.”
Even though average temperatures are relatively cold in Antarctica, she says, it can still climb to above freezing temperatures. And even if temperatures are below freezing, if the runway is covered with dust or grit, it will be more likely to absorb incoming sunlight.
The ultimate challenge is that everything changes all the time, she said.
“The temperature and radiation impacts are different every day of every year and outside of our control,” she said. “So what worked for you last year, may not work for this one. The average temperature of the summer is the same as last, but the above 0 days all came in a row, or the temperature is above average but clouds block portions of the incoming radiation. What is important is minimizing the impacts and finding tools to predict when failure may be imminent.”
The next steps
Kallelid is back in Norway now, but she brought an unusual package with her when she flew home via Cape Town: A box full of ice samples.
Although her ice strength testing on the Troll Airfield is critical to her results, she also wants to study the ice structure in greater detail. One way to do this is to make thin sections from the ice she’s sampled and to look at the structure using polarized light.
“By milling the ice to a thickness of less than 1 mm, the colours of the ice (when looked at through the polarized light) reveals information about the structure,” she said. “You can also measure the grain size. This is important when comparing the results with previous results, and also for the further use of the data.”
“But to do this I need a lot of equipment,” she said. “So instead of bringing all that to Troll, we decided to bring the ice back to NTNU.”
This required some serious logistics: She contacted the hotel where she stayed in Cape Town so she could keep the samples in their freezer during her stay there.
The last step to Norway also required some logistical arrangements, but nothing quite as formidable as asking a South African hotel to clear out a spot in their restaurant freezer for a box full of ice.
“I told my mother to make room in her freezer, too,” Kallelid said.