page_title: Ice drilling
section_title: Cuttings and meltwater
hierarchical_section_title: Ice drilling / Drilling design considerations / Cuttings and meltwater
caption_attribution_description: English: An ice core drill lies on a table revealing the scoop cutters and collet (the metal ring just inside the drill). Both features are new to ice core drilling and were tested at WAIS this summer. Dec. 6, 2006
context_page_description: 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.
context_section_description: Mechanical drilling produces pieces of ice, either as cuttings, or as granular fragments, which must be removed from the bottom of the hole to prevent them from interfering with the cutting or percussing action of the drill.  An auger used as the cutting tool will naturally move ice cuttings up its helical flights. If the drill's action leaves the ice chips on top of the drill, they can be removed by simply raising the drill to the surface periodically.  If not, they can be brought to the surface by lowering a tool to scoop them up, or the hole can be kept full of water, in which case the cuttings will naturally float to the top of the hole.  If the chips are not removed, they must be compacted into the walls of the borehole, and into the core if a core is being retrieved.
  Cuttings can also be moved to the surface by circulating compressed air through the hole, either by pumping the air through the drillpipe and out at the drillhead, forcing the chips up in the space between the drill string and the borehole wall, or by reverse air circulation, in which the air flows up through the drill string.  Compressed air will be heated by the compression, and it must be cooled before being pumped downhole, or it will cause melting of the borehole walls and the core.  If the air is circulated by creating a vacuum, rather than pumping air in, ambient air carries the cuttings, so no cooling is needed.
  A fluid can be used to circulate the cuttings away from the bit, or the fluid may be able to dissolve the cuttings.  Rotary mineral drilling (through rock) typically circulates fluid through the entire hole, and separates solids from the fluid at the surface before pumping the fluid back down.  In deep ice drilling it is usual to circulate the fluid only at the bottom of the hole, collecting cuttings in a chamber that is part of the downhole assembly.  For a coring drill, the cuttings chamber can be emptied each time the drill is brought to the surface to retrieve a core.
  Thermal drills will produce water, so there are no cuttings to dispose of, but the drill must be capable of working while submerged in water, or else the drill must have a method of removing and storing the meltwater while drilling.
caption: Mechanical ice auger, showing cutting teeth, helical flights used to transport ice cuttings up away from the cutting region, and a central void for the core itself.
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