Periglacial features developed on the exposed lake bottoms of seven lakes that drained rapidly after 1950, Tuktoyaktuk Peninsula area, western Arctic coast, Canada

A variety of periglacial features have been studied on the exposed bottoms of seven lakes that drained rapidly after 1950 in the Tuktoyaktuk Peninsula area, western Arctic coast, Canada. Ice-wedge growth commenced as early as the first winter following drainage. In most areas, ice-wedge growth cease within several decades, because of the growth and spread of vegetation which resulted in snow entrapment and increased ground temperatures. At sites where thermokarst lake enlargement had transgressed across terrain with ice-wedge polygons, reactivated polygon patterns developed rapidly in some pre-drainage shallow water areas, with the sites of former troughs becoming ridges. Excavations across the ridges exposed extensive differential frost heave, cryoturbations, and slickensided vertical shear planes. Many collapse pits developed because of differential frost heave between silts and sands, cavity formation beneath the frozen silts, and cavity infilling with adjacent sand in late summer. Other collapse pits developed, either subaqueously prior to drainage or subaerially after drainage. Underground flow has been observed, in early summer, where a near-surface layer of ice-rich silts was underlain by desiccated active layer sands at a temperature well below 0°C. At some sites where there has been underground flow some differential loading and water escape features appear to have developed during the thaw period. Copyright © 1999 John Wiley & Sons, Ltd. Un grand nombre de phenomenes periglaciaires divers ont ete etudies sur les fonds de sept lacs qui ont ete rapidement draines apres 1950 dans la peninsule de Tuktoyaktuk (delta du Mackenzie, Canada). La croissance de coins de glace a commence des le premier hiver qui a suivi le drainage. Dans la majorite des cas, la croissance des coins de glace a cesse en quelques decades a la suite de la croissance de la vegetation qui a eu pour effet de retenir la neige et d'augmenter la temperature du sol. Aux endroits ou l'elargissement du lac thermokarstique s'etait etendu sur des terrains contenant des polygones de coins de glace, des reseaux de polygones reactives se sont developpes rapidement la ou les eaux etaient peu profondes avant le drainage, et les fosses qui y correspondaient sont devenus des rides. Des excavations au travers de ces reliefs ont montre des soulevements differentiels extensifs, des cryoturbations et des plans verticaux de cisaillement. De nombreuses fosses d'effondrement se sont developpees a la suite de soulevements differentiels entre des silts et des sables, la formation de cavites sous des silts geles et le remplissage de ces vides par des sables voisins a la fin de l'ete. D'autres effondrements sont apparus, a la fois sous eau avant le drainage ou d'une facon subaerienne apres le drainage. Un ecoulement souterrain a ete observe au debut de l'ete a une temperature bien inferieure a 0°C, quand une couche de silts riche en glace et proche de la surface s'est trouvee sous des sables desseches de la couche active. En quelques sites ou il y a eu un ecoulement souterrain, quelques mouvements differentiels par densite ont eu lieu et des echappements d'eau se sont produits pendant le degel. Copyright © 1999 John Wiley & Sons, Ltd.

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