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This drill recovers a core several metres long and 10 cm (4 inches) in diameter.
Hydrochloric acid (HCl) and hydrofluoric acid (HF) are also produced in volcanoes and are measured in the cores as total acidity. GISP-2 cores have revealed more than 300 major eruptions over the past 9,000 years.
In areas of high accumulation, such as low-latitude mountain glaciers and the Greenland Ice Sheet, annual layers of ice representing tens of thousands of years can be seen and counted, often with the unaided eye.