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. 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.

Many different methods have been used since 1840, when the first scientific ice drilling expedition attempted to drill 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 began to be used; these drills melt the ice by heating the drill. Drills that use jets of hot water or steam to bore through ice soon followed. 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. 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.

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). Since then many other groups have succeeded in reaching bedrock through the two largest ice sheets, in Greenland and Antarctica. 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.

Goals of ice drilling:The below are the goals of drilling :

The first scientific ice drilling expeditions, led by Louis Agassiz from 1840 to 1842, had three goals: to prove that glaciers flowed,
[2] to measure the internal temperature of a glacier at different depths,
[3] and to measure the thickness of a glacier.
[4] Proof of glacier motion was achieved by placing stakes in holes drilled in a glacier and tracking their motion from the surrounding mountain.
[2] Drilling through glaciers to determine their thickness, and to test theories of glacier motion and structure, continued to be of interest for some time,
[5] but glacier thickness has been measured by seismographic techniques since the 1920s.
[6][7] 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.
[8][9] Temperature measurements continue to this day:
[3] modelling the behaviour of glaciers requires an understanding of their internal temperature,[3] and in ice sheets, the borehole temperature at different depths can provide information about past climates.
[10] Other instruments may be lowered into the borehole, such as piezometers, to measure pressure within the ice,
[11] or cameras, to allow a visual review of the stratigraphy.
[12] IceCube, a large astrophysical project, required numerous optical sensors to be placed in holes 2.5 km deep, drilled at the South Pole.
[13]

Borehole 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 as a "liner" to keep the hole open. 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.[14] 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.
A straightforward way to determine these effects across the surface of a glacier is to plant stakes (known as ablation stakes) in holes drilled in the glacier's surface, and monitor them over time to see if more snow is accumulating, burying the stake, or if more and more of the stake is visible as the snow around it disappears.
[15] The discovery of layers of aqueous water, and of more than a hundred subglacial lakes, beneath the Antarctic ice sheet, led to speculation about the existence of unique microbial environments that had been isolated from the rest of the biosphere, potentially for millions of years. These environments can be investigated by drilling.
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