Internal structure and conditions of permafrost mounds at Umiujaq in Nunavik, Canada, inferred from field investigation and electrical resistivity tomography

Abstract

A systematic approach was used for the interpretation of the electrical resistivity tomography carried out on two permafrost mounds at Umiujaq in Nunavik, Canada, to assess their internal structure and conditions. Prior information under the form of a geocryologic model of the permafrost mounds was integrated in the inversion of the pseudo-section of apparent electrical resistivity. The geocryologic model was developed from the synthesis of previous field investigations, including shallow and deep sampling, temperature and electrical resistivity logging, and cone penetration tests performed in the permafrost mounds. Values of electrical resistivity were ascribed to the different layers making of the geocryologic model to define a synthetic resistivity model of the permafrost mounds used as a reference model to constrain the inversion. The constrained resistivity model clearly show the presence of ice-rich cores in the permafrost mounds underscored by high resistivity values in excess of 30 000 Ωm, while the unfrozen zones surrounding the permafrost mounds are characterized by resistivity values lower than 1000 Ωm. The spatial distribution of unfrozen water and ice contents in the permafrost mounds were also assessed according to empirical relationships between the electrical resistivity and water contents. The ice content is highly variable and can be as high as 80% in the ice-rich cores, while the unfrozen water content varies between 2% and 5%. The integration of prior information in the inversion process leads to a more realistic constrained resistivity model showing sharp resistivity contrasts expected at the boundaries such as the permafrost table and base.

Geomorphological processes and frozen ground conditions in Elephant Point (Livingston Island, South Shetland Islands, Antarctica)

“…The structure of the pronival ramparts is similar to that described in other areas (Ballantyne, 1987;Shakesby, 1997;Hedding and Sumner, 2013), with arcuate ridges and basal talus at their foot. Frost mounds are distributed on the ice-rich permafrost terrain of the moraine; although not found in an ice-core moraine, frost mounds may include up to 80% of ice content as observed in other permafrost environments (Fortier et al, 2008). Mudflow dynamics is very intense especially during periods with fairly positive temperatures and rainy events.…”

Geophysical mapping of palsa peatland permafrost

“…From these values a depth at which the surface data are no longer sensitive to the physical properties of the ground can be interpreted. The method has previously been applied in permafrost studies (e.g., Fortier et al, 2008;Marescot et al, 2003). To calculate the DOI-index we used a symmetrical two-sided difwww.the-cryosphere.net/9/465/2015/ The Cryosphere, 9, 465-478, 2015…”

Applicability of electrical resistivity tomography monitoring to coarse blocky and ice‐rich permafrost landforms

“…By this, interpretation methods can be tested under controlled circumstances to overcome the problem of only limited in-situ control (e.g. only by 1D boreholes) of the subsurface structures in a natural environment (Dahlin and Loke, 1998;Olayinka and Yaramanci, 2000;Fortier et al, 2008). Figure 1 illustrates the concept of forward/inverse modelling for an example from Murtèl rockglacier (which will be introduced in the following section).…”

“…The inverted synthetic model (Figure 1d) is compared to the inversion of the real data (Figure 1b), and, if necessary, the synthetic model is adapted and the forward-inverse cycle repeated until both synthetic and real data inversion produce similar results. According to this back-and-forth procedure (described by Fortier et al, 2008), we developed (2003) for permafrost studies. In this appraisal technique, two inversions of the same data sets are carried out using Equation (1), but with two different reference models with homogeneous resistivity values m 01 and m 02 .…”