In 1942, at the height of the Second World War, treacherous weather and low fuel forced six US fighter jets and two bombers to make an emergency landing on a Greenland glacier. Within days, a rescue operation was staged, and all 25 members of the party were successfully evacuated. The planes, however, remained in place and were largely forgotten until 50 years later, when a salvage team set out to recover them. The history is fascinating, and there have been books and documentaries made on the subject; I myself can hardly do it justice.
What happens when you leave a plane on a glacier with a sign on the windshield that says: “Gone for lunch, be back in 50 (years)?” I’ll give you a hint – 50 years later, you won’t find it where you left it. In fact, the squadron moved a mile towards the sea and 270 feet (82 meters) downwards into the ice – the height of a 25-story building! The science here is incredibly exciting; the engineering required to extract the planes – even more so. The fundamental principle that we don’t immediately consider is that, like rivers, glaciers flow. Recently, a Greenland glacier set the speed record, travelling an average of 150 feet (46 meters) per day, although most glaciers are much slower.
There are two components to glacial flow – basal slip and internal deformation. Basal slip is the motion that results as the glacier slides along its bed. Imagine an ice cube on a smooth, slightly inclined plastic surface. If the surface is cold, the ice won’t melt on contact and friction will hold it in place. On a warmer surface, the ice will begin to melt at the interface with the plastic and gradually start to slide downwards. The temperature of the surface and the resulting lubrication by water is very important in determining flow. Beneath the giant mass of a glacier, the pressure is enough to melt ice even at temperatures below freezing. The second component, internal deformation, is the motion of ice within the glacier. This is also caused by pressure and can be compared to thick honey flowing down the same plastic surface. A little bit of honey might resist motion, but add several spoons, and it will begin to flow under the resulting pressure. Once the mass of honey has flowed to the bottom, you’ll see that a layer of honey is left behind, ‘stuck’ to the surface (and difficult to wash off). This layer never moved (ie. no basal slip) while the rest of the mass flowed over it by internal deformation.
After extensive analysis of historic photos, studies of ice flow, and subsurface mapping with ground penetrating radar, the salvage operation was ready to go. Drilling through the overlying ice involved a machine resembling a giant spinning hot iron, affectionately termed the Super Gopher. A generator heated water and pumped it through copper tubing, melting the ice on contact. The glacial water was pumped out of the shaft as the machine was gradually lowered. Even so, the rate of drilling was slow – an average of 2 feet (.6 meters) per hour. After a month of drilling, the shaft was ready. Workers labored beneath the ground to widen the cavern, disassemble the plane, and hoist them to the surface. Once the four month operation was complete, a remarkably well-preserved jet had been recovered. Nicknamed Glacier Girl, it has since been fully reassembled and restored.
Super Gopher (photos from P-38 National Association)
Glacier Girl (green) at an airshow (photo from militaryaircrafthistorian.com)
Be warned: you may have just sustained a lethal dose of mostly harmless science.
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Cover photo courtesy of Andy Lederer, Flickr Creative Commons. All uncredited images from Wikimedia Commons.