History of ice drilling

Scientific ice drilling began in 1840, when Louis Agassiz attempted to drill through the Unteraargletscher in the Alps. Rotary drills were first used to drill in ice in the 1890s, and thermal drilling, with a heated drillhead, began to be used in the 1940s. Ice coring began in the 1950s, with the International Geophysical Year at the end of the decade bringing increased ice drilling activity. In 1966, the Greenland ice sheet was penetrated for the first time with a 1,388 m hole reaching bedrock, using a combination of thermal and electromechanical drilling. Major projects over the following decades brought cores from deep holes in the Greenland and Antarctic ice sheets. Hand drilling, using ice augers to retrieve small cores, or small drills using steam or hot water to install ablation stakes, is also common.

History

Agassiz

The earliest attempt to drill through ice for scientific reasons was made by Louis Agassiz in 1840, on the Unteraargletscher in the Alps. It was not clear to the scientific community of the day that glaciers flowed, and when Franz Josef Hugi demonstrated that a large boulder on the Unteraargletscher had moved 1315 m between 1827 and 1836, sceptics argued that the boulder might have slid down the glacier. Agassiz visited the glacier in 1839, and returned in the summer of 1840. He planned to make temperature observations on the glacier's interior, and brought an iron drilling rod, 25 feet (7.6 m) long, for that purpose. The first attempt at drilling, in early August, made only 6 inches (15 cm) of progress after several hours work. After heavy rain overnight, the drilling became much faster: a foot (30 cm) of progress was made in less than fifteen minutes, and the hole eventually reached a depth of 20 feet (6.1 m). Another hole drilled nearby reached 8 feet (2.4 m), and more were drilled to place six flow markers in a line across the glacier, which Agassiz hoped would have moved by the following year, demonstrating the flow of the glacier. He believed in the dilatation theory of glacier flow, which argued that the refreezing of meltwater caused glaciers to progressively lengthen; this theory implied that the flow rate should be greatest where the water input was greatest. Agassiz returned to the Unteraargletscher in August 1841, this time equipped with a drill consisting of 10 iron rods, each 15 feet (4.6 m) long, of the kind used to drill for wells; a longer drill could not have been used by hand, and would have required a scaffold, which would have been too expensive. He was hoping to drill deeply enough to ascertain the thickness of the glacier. Once it was realized that drilling went faster when the holes were full of water, the holes were positioned so that they could be supplied with water by one of the many small streams on the glacier. This had the additional benefit of simplifying the removal of the chips of ice from the bottom of the hole, as they rose to the surface and were carried away by the current. When the first hole reached 70 feet (21 m) the drilling rods became too heavy for the men to use, so a tripod was constructed and a pulley set up so the drill could be raised and lowered by a cable. The tripod took several days to complete, and when the men attempted to begin drilling again they were surprised to discovered the drill would no longer go into the hole, which had closed up to only half an inch across, forcing them to start a new hole. The deepest hole achieved in 1841 was 140 feet (43 m). The flow markers placed in 1840 were located in 1841 but proved to be uninformative; so much snow had melted that they were all lying flat on the glacier, which made them useless for proving the movement of the ice they had been embedded in. However, a stake set eighteen feet deep in the ice was still embedded, with seven feet projecting above the surface, and ten feet showing by the start of September 1841. Agassiz drilled deeper holes, and planted six stakes in a straight line across the glacier, taking measurements with reference to identifiable points on the surrounding mountains to ensure that he would be able to tell if they had moved. These flow markers were still in place in July 1842 when Agassiz returned to the Unteraargletscher, and now formed a crescent shape; it was apparent that the ice flowed much faster in the centre of the glacier than at the edges. Drilling began again on 25 July, again using the cable tool approach. Some problems were encountered: the equipment broke at one point and had to be repaired; and on one occasion it was discovered that the borehole had become distorted overnight, and had to be redrilled. As the hole became deeper, the increasing weight of the drilling equipment forced Agassiz to increase the number of men pulling on the cable to eight; even so they only were able to gain three or four metres a day. While the drilling continued, soundings were taken of moulins and depths of 232 m and nearly 150 m were found. Although Agassiz understood that these measurements were not rigorous, because unseen obstacles might be distorting the readings, he became convinced that it would be impossible for his team to drill to the base of the glacier, and it was decided not to drill below 200 feet (61 m). Additional holes were subsequently drilled to 32.5 m and 16 m to be used for temperature measurements.

Late 19th century

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