To understand whether a glacier is shrinking or growing, its mass balance must be measured: this is the net effect of gains from fresh snow, minus losses from melting and sublimation. This allows the three-dimensional position of the borehole to be mapped periodically, revealing the movement of the glacier, not only at the surface, but throughout its thickness. īorehole inclination, and the change in inclination over time, can be measured in a cased hole, a hole in which a hollow pipe has been placed to keep the hole open. IceCube, a large astrophysical project, required numerous optical sensors to be placed in holes 2.5 km deep, drilled at the South Pole. Other instruments may be lowered into the borehole, such as piezometers, to measure pressure within the ice, or cameras, to allow a visual review of the stratigraphy. Temperature measurements continue to this day: modelling the behaviour of glaciers requires an understanding of their internal temperature, and in ice sheets, the borehole temperature at different depths can provide information about past climates. Although it is no longer necessary to drill through a glacier to determine its thickness, scientists still drill shot holes in ice for these seismic studies. Drilling through glaciers to determine their thickness, and to test theories of glacier motion and structure, continued to be of interest for some time, but glacier thickness has been measured by seismographic techniques since the 1920s. Proof of glacier motion was achieved by placing stakes in holes drilled in a glacier and tracking their motion from the surrounding mountain. The first scientific ice drilling expeditions, led by Louis Agassiz from 1840 to 1842, had three goals: to prove that glaciers flowed, to measure the internal temperature of a glacier at different depths, and to measure the thickness of a glacier. Recent projects have focused on finding drilling locations that will give scientists access to very old undisturbed ice at the bottom of the borehole, since an undisturbed stratigraphic sequence is required to accurately date the information obtained from the ice. Since then many other groups have succeeded in reaching bedrock through the two largest ice sheets, in Greenland and Antarctica. In 1966, a US team successfully drilled through the Greenland ice sheet at Camp Century, at a depth of 1,387 metres (4,551 ft). For obtaining ice cores from deep holes, most investigators use cable-suspended electromechanical drills, which use an armoured cable to carry electrical power to a mechanical drill at the bottom of the borehole. A growing interest in ice cores, used for palaeoclimatological research, led to ice coring drills being developed in the 1950s and 1960s, and there are now many different coring drills in use. Drills that use jets of hot water or steam to bore through ice soon followed. In the 1940s, thermal drills began to be used these drills melt the ice by heating the drill. 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. Many different methods have been used since 1840, when the first scientific ice drilling expedition attempted to drill through the Unteraargletscher in the Alps. Instruments can be placed in the drilled holes to record temperature, pressure, speed, direction of movement, and for other scientific research, such as neutrino detection. Ice drilling allows scientists studying glaciers and ice sheets to gain access to what is beneath the ice, to take measurements along the interior of the ice, and to retrieve samples. 9 Cable-suspended electromechanical drills.4.5 Power, torque, antitorque, and heat.4.4 Borehole stability and permeability.4.1 Ice removal method and project logistics.Thomas Shafee contact Reviewers: ( comments) This is an open access article distributed under the Creative Commons Attribution ShareAlike License, which permits unrestricted use, distribution, and reproduction, provided the original author and source are credited. Content has also subsequently been used to update that same Wikipedia article Wikipedia: This work is adapted from the Wikipedia article Ice drilling ( CC BY-SA). Post-publication review comments or direct edits can be left at the version as it appears on Wikipedia. It was adapted from the Wikipedia page Ice_drilling and contains some or all of that page's content licensed under a CC BY-SA license. This article has been through public peer review.
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