Caractérisation du Pergélisol de Buttes Cryogènes à l'Aide de Diagraphies Électriques au Nunavik, Québec
Abstract Electrical loggings for permafrost characterization in cryogenic mounds in Nunavik, Québec. Geophysical methods are useful tools to improve the understanding of physical phenomena related to permafrost. Induced polarization logging has not been commonly used yet for permafrost studies. In t...
| Published in: | Permafrost and Periglacial Processes |
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| Main Authors: | , , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
Wiley
1991
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| Subjects: | |
| Online Access: | http://dx.doi.org/10.1002/ppp.3430020203 https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fppp.3430020203 https://onlinelibrary.wiley.com/doi/pdf/10.1002/ppp.3430020203 |
| Summary: | Abstract Electrical loggings for permafrost characterization in cryogenic mounds in Nunavik, Québec. Geophysical methods are useful tools to improve the understanding of physical phenomena related to permafrost. Induced polarization logging has not been commonly used yet for permafrost studies. In this study, electrical contact is insured through regularly spaced metallic electrodes vertically inserted in the ground along a multiconductor cable. Thermistors located at the same depths yield a temperature profile in the soil. Both apparent electrical resistivities and apparent electrical chargeabilities are logged. A dipole‐dipole configuration is used. The spacings between the electrodes of a dipole vary from 0.1 to 1 m. Two study areas (Kangiqsualujjuaq in Ungava Bay and Umiujaq in Hudson Bay) in northern Quebec are investigated; they are both located at the tree line and have a mean annual air temperature of about −5.6ºC. The base of permafrost is easily detected through the high contrasts in apparent electrical resistivity and apparent chargeability between frozen and unfrozen soils. Ice‐rich permafrost is characterized by high resistivity values and close to zero chargeability values, while ice‐poor permafrost is characterized by intermediate resistivity and low chargeability values. In unfrozen zones, low apparent resistivity and high apparent chargeability (positive or negative) values are encountered. These guidelines for the interpretation of the logs allow a categorization of different subhorizontal zones in permafrost. Ice‐rich zones do occur near the surface and at the base of permafrost. A low ice content zone is usually sandwiched between these two zones. In this central zone, the growth of ice lenses is limited due to the small intake of water which is damned by the icy zones above and below. |
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