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Ice drilling allows scientists studying glaciers and ice sheets to gain access beneath the ice, to take measurements along its interior, and to retrieve samples. Instruments in the bored holes can record temperature, pressure, speed, and direction of ice movement. Many different methods have been used since 1840, when the first scientific ice drilling expedition attempted to bore through the Unteraargletscher in the Alps. Two early methods were percussion, in which the ice is fractured and pulverized, and rotary drilling, a method often used in mineral exploration for rock drilling. In the 1940s, thermal drills that melt ice were developed, and jets of hot water or steam to bore through ice soon followed. A growing interest in ice cores, used for paleoclimatological research, led to the development of ice coring drills in the 1950s and 1960s, and there are now many different coring drills in use. (Full article...)