Frost-Heaved Bedrock Features: A Valuable Permafrost Indicator
Frost-heaved bedrock features are periglacial forms produced by the vertical displacement of bedrock fragments. Blocks, frost-wedged from bare bedrock along joints, are raised above the general surface by heave. Although mentioned in the literature of the late 19th century, they have been described...
| Published in: | Géographie physique et Quaternaire |
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| Main Author: | |
| Format: | Text |
| Language: | English |
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Les Presses de l'Université de Montréal
1983
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| Subjects: | |
| Online Access: | http://id.erudit.org/iderudit/032521ar https://doi.org/10.7202/032521ar |
| Summary: | Frost-heaved bedrock features are periglacial forms produced by the vertical displacement of bedrock fragments. Blocks, frost-wedged from bare bedrock along joints, are raised above the general surface by heave. Although mentioned in the literature of the late 19th century, they have been described and studied in detail only recently. They are widespread in the northern hemisphere, notably in Canada, Greenland and Spitsbergen, where they develop in lithologies with well-developed systems of joints. Commonly, heaved blocks exhibit weathered and lichen-covered surfaces except at their base where freshly exposed rock indicates recent heaving. They result from frost processes, particularly from wedging and heaving due to pressure of the freezing of free-water in joints. Active and most non-active features are located in permafrost regions. The southermost occurrence in the northern hemisphere is the Groulx Mountains, in Québec (51°45'N, alt. 1000 m). The mean annual air temperature for the area of best-developed features ranges from -4° to -100C, with the number of days of frost ranging from 178 to 300. A thin snow cover is common to most sites. Based on climatic data and on the geographical distribution of frost-heaved bedrock features, it is suggested that permafrost occurrence is obvious. Relict features found outside the present-day permafrost zones should indicate former permafrost conditions. Les édifices rocheux d'éjection sont des formes périglaciaires résultant du déplacement vertical de fragments du substrat rocheux. Les fragments produits par gélifraction au droit des fissures et des diaclases sont poussés au-dessus de la surface environnante par l'action du froid. Signalés dès la fin du XIXe siècle, ils n'ont été décrits et étudiés convenablement que récemment. Ils sont fréquents dans l'hémisphère nord, en particulier au Canada, au Groenland et au Spitsberg. On les trouve dans les principaux types de roches affectés de réseaux de diaclases. Les blocs éjectés montrent souvent des parois altérées et ... |
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