Geophysical Methods for Detecting Permafrost Discontinuities
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Date
2021-03-04
Authors
Salman, Max
Journal Title
Journal ISSN
Volume Title
Publisher
University of Waterloo
Abstract
Global climate change has sparked various concerns over the future of the Arctic. One of
the major concerns around the environmental and ecological health of the Arctic is directly
related to the deterioration of the permafrost. Permafrost is described as frozen soil below
0oC for at least two consecutive years, and is recognized by the World Meteorological
Organization (WMO) as an Essential Climate Variable (ECV). Geophysical methods have
been used to detect and measure the extent of the permafrost in various cold regions of
the Earth. Traditional methods such as electrical resistivity tomography (ERT), electro
magnetic induction (EMI), and seismic have all been used to characterize permafrost in the
subsurface. However, there are smaller scale features at the near surface requiring attention.
In this work, we used of a permafrost probe, an electrical resistivity tomography system,
and an electromagnetic induction system to measure the depth to the permafrost table
from the ground surface. The study was performed in the Sahtu Region of the Northwest
Territories, approximately 30 kilometers south of the Town of Norman Wells, Northwest
Territories.
Two sites were selected; one on a drill pad, one near a lake shore. The soils mainly
consisted of homogeneous organic-rich till. The permafrost probe measure a depth to
permafrost table of approximately 70 centimeters at the drill-pad site (MW04T) and approximately
30 centimeters at the lake shore site (Marg Lake). A Syscal Junior 48TM ERT
system was installed perpendicular to the topological features, such as the lake shore, and
the tree line. The electrode spacing was small due to the shallow nature of the permafrost,
and the dipole-dipole method was selected to collect measurements. The ERT data was
inverted using Res2DInvTM and the output data correlates well with the permafrost probe
measurements. A ground conductivity meter (GCM) was used to assess the capability of
using a non-ground-coupled geophysical methods in this terrain to detect permafrost discontinuity.
We deployed the Geonics EM-31TM and EM-34TM systems. The electrical data
was collected over the same permafrost probe and ERT survey lines and measurements
were plotted using MATLABTM. The data suggest that the GCM systems were able to
e ectively detect the change in permafrost table depth, correlative todirect measurement
of permafrost depth that were used concurrently. This study serves as a baseline analysis of
using small-scaled ground-based geophysical systems to detect permafrost discontinuities
in this region, and informs the future development of aerial-based systems and methods
to gather multiple strings of data to estimate permafrost table depth, and the integrity of
the permafrost.
Description
Keywords
geophysics, permafrost, electrical resistivity tomography, electromagnetic induction, Northern