The thermal drilling methods are usually used in field conditions for the large ice formations research. The penetration rate depends on supplied heat rating and physical characteristics of ice. The computer records of penetration rate and water column (height) pressure in the borehole versus depth as well as their processing allow to obtain the information on the internal structure of ridges and stamukhas. In 2004 the new modification of electrothermal drill ETI-4 was made at AARI. In September, 2004, the field works aimed to research a geometry and internal structure of ridges using the thermal drilling method were held in the Central Arctic. During this work the electrothermal drill ETI-4 was tested. As result, the new in situ data on the ridge thickness including ridge sails and keels, location of voids, hard and porous ice, boundaries of refrozen layer were collected.
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