Régime thermique des sols et rôle du gel dans la dynamique des versants d’un milieu subéquatorial d’altitude : les Andes centrales du Pérou
Frost and frost action are studied here in a subequatorial high mountain environment. Frost occurs every day but minimum temperatures under shelter at 5 000 m generally do not exceed -6° C. In the ground at 10 cm depth, -2° C is the minimum that was measured and depth of freezing is less than 10-15...
| Published in: | Géographie physique et Quaternaire |
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| Main Author: | |
| Format: | Text |
| Language: | French |
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Les Presses de l'Université de Montréal
1989
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| Subjects: | |
| Online Access: | https://doi.org/10.7202/032757ar http://id.erudit.org/iderudit/032757ar |
| Summary: | Frost and frost action are studied here in a subequatorial high mountain environment. Frost occurs every day but minimum temperatures under shelter at 5 000 m generally do not exceed -6° C. In the ground at 10 cm depth, -2° C is the minimum that was measured and depth of freezing is less than 10-15 cm. Frost penetration is deeper in sandy and silty soils than in openwork gravels, except when they are saturated. In the rockfaces, frost is shallow and limited to a few hours. Present day conditions do not allow the formation of permafrost in the ground and in the rockfaces below 5 200 m. With such characteristics, and in spite of its frequency frost cannot presently trigger efficient rock splitting except in the very porous rocks which yield many small particles. In the ground surficial movement of particles is induced by needle ice but also by frost creep. Sorted patterned ground is very common on the slopes. Sorting is due to frost action and slope washing. Talus slope and stone banked lobes in this environment often are stratified deposits. In a paleoclimatic view analysis of inactive forms allows us to assume that frost cycle did not always take the same characteristics since the end of the last glaciation. In one or several periods severe climatic conditions caused more intensive and prolonged frosts. Le gel et son action sont étudiés ici dans le milieu de la haute montagne subéquatoriale. La fréquence du gel est journalière et son intensité mesurée sous abri à 5 000 m ne descend guère au-delà de - 6° C. Dans le sol, les températures relevées à 10 cm ne dépassent pas - 2° C et le gel est atteint moins de 50 jours par an. L'épaisseur de la couche du sol parcourue par le front de gel est limitée à 10-15 cm. Le gel pénètre mieux dans les sols fins (sables silteux) et bien drainés. Dans les parois rocheuses, le gel est « pelliculaire » et limité à quelques heures jusqu'à 5 200 m. Dans les conditions actuelles, la formation d'un pergélisol dans le sol ou dans la roche n'est pas possible en dessous de 5 200 m. En ... |
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