Subglacial Bedrock Sampler

Currently the under-ice geology has to be inferred from the few locations where the rock rises through the ice, as well as some gravity and magnetometer measurements taken from aircraft. We could learn much more if we had actual samples. Rays from space age the surface of exposed rocks, and measurements of this aging can indicate how long that rock has been exposed to daylight. This method, cosmogenic dating, can be used on the samples to determine when they were last exposed to radiation, and therefore reveal how long the rock has been covered by ice. Provided samples can be obtained across a wide area, it would be possible to chart the growth and withdrawal of the ice sheets in earlier climate epochs. That knowledge helps us to understand how the ice sheets will change in the future, which is very important as we try to understand the processes of climate change and sea level rise. Obtaining these samples is not easy. The ice is many hundreds of metres thick, and stretches across extremely remote areas. Drilling through it has been possible, using heavy drilling rigs powered from the surface, but there are still a number of very major problems. Firstly, a drill which can cut through ice is not necessarily suited to drilling through rock, and vice versa. The teeth used to plane through ice will not penetrate rock, while rock grinding teeth can glaze over if an attempt is made to force them through ice. Furthermore a huge drilling rig, mechanically powered from the surface, cannot easily be transported across the large areas we need to sample. A smaller system, which can be transported by aeroplane, is needed. This type of system is called a wireline drill. The drill unit is lowered into a hole by a cable, and it uses its own weight to recover a few metres’ worth of ice using an auger. The drill is then winched out, emptied, and lowered back in again. Repeating this process allows the hole to be dug out, deeper and deeper, until the drill hits the rock boundary. The problem comes when we reach the rock boundary. It is very hard to drill into the hard rock and extract the samples using the small weight of the wireline device, and so we have turned to technologies developed to drill through rock in other situations where force available to push the drill into the rock is limited. In space, planetary rovers must drill through rock to obtain samples even though gravity is very low. That means that they cannot force their way through very easily, but yet percussive tools can still operate. We are therefore going to assess two different types of percussive drill, both of which have been suggested for Mars exploration: the cam-hammer and the ultrasonic-percussive device. They both generate high impulse forces by moving small hammer masses against a drilling bit, and they have been tested in icy conditions. Most importantly, this hammering motion does not result in large external forces that need to be supplied by the wireline. In fact, the external forces can be around 100 times smaller than the hammering forces, if the shocks are properly damped. This project will determine if these devices can be fitted to a wireline drill, and then evaluate how well each type works before choosing one for development. That technology will then be designed into a new wireline device that could be lowered downhole to obtain rock samples, instead of just ice. And with the rock samples, we can start to ununravel the history of the ice sheets above.