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Cores are drilled with hand augers (for shallow holes) or powered drills; they can reach depths of over two miles (3.2 km), and contain ice up to 800,000 years old.
The physical properties of the ice and of material trapped in it can be used to reconstruct the climate over the age range of the core.
It can make some snow sublimate, leaving the top inch or so less dense.
When the sun approaches its lowest point in the sky, the temperature drops and hoar frost forms on the top layer.
Greenland ice cores contain layers of wind-blown dust that correlate with cold, dry periods in the past, when cold deserts were scoured by wind.The cuttings (chips of ice cut away by the drill) must be drawn up the hole and disposed of or they will reduce the cutting efficiency of the drill.The fluid must have a low kinematic viscosity to reduce tripping time (the time taken to pull the drilling equipment out of the hole and return it to the bottom of the hole).Ice cores are collected by cutting around a cylinder of ice in a way that enables it to be brought to the surface.Early cores were often collected with hand augers and they are still used for short holes.
Below this depth, electromechanical or thermal drills are used.