Abstract

A large lake, measuring 600 m × 300 m and with a depth of nearly 5 m, was artificially drained on 13 August 1978. Observations on the formation, width, and depth of thermal contraction cracks for the first 7 years show that the crack profiles and ice wedge growth rates differ markedly from those of old ice wedges reported in the literature. The first winter's cracks had box-like profiles, with surface widths to 10 cm and depths to 2.5 m. Some cracks continued to widen and deepen, once opened in early winter, and then narrowed or even closed completely in summer. Mean growth rates for the ice wedges for the first few years have been as much as 3.5 cm/year. Temperature gradients at the time of first cracking have been in the range of 10–15 °C/m. The growth rate of young ice wedges is site specific and temperature dependent, varying with factors such as the temperature gradient, vegetation, and snow cover, so an estimate of the age of an ice wedge from its width will usually be impossible. A study of crack widths indicates that the apparent coefficient of linear expansion of frozen ground may be several times that of ice. Upward cracking has been proven.

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