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Hand augers can be rotated by a T handle or a brace handle, and some can be attached to handheld electric drills to power the rotation.With the aid of a tripod for lowering and raising the auger, cores up to 50 m deep can be retrieved, but the practical limit is about 30 m for engine-powered augers, and less for hand augers.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.Soviet ice drilling projects in Antarctica include decades of work at Vostok Station, with the deepest core reaching 3769 m.Numerous other deep cores in the Antarctic have been completed over the years, including the West Antarctic Ice Sheet project, and cores managed by the British Antarctic Survey and the International Trans-Antarctic Scientific Expedition.
Some volcanic events that were sufficiently powerful to send material around the globe have left a signature in many different cores that can be used to synchronise their time scales.
At Summit Camp in Greenland, the depth is 77 m and the ice is 230 years old; at Dome C in Antarctica the depth is 95 m and the age 2500 years.
As further layers build up, the pressure increases, and at about 1500 m the crystal structure of the ice changes from hexagonal to cubic, allowing air molecules to move into the cubic crystals and form a clathrate.
These data can be combined to find the climate model that best fits all the available data. Coastal areas are more likely to include material of marine origin, such as sea salt ions.
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.