Imaging groundwater beneath a rugged proglacial moraine

Abstract

With the changing precipitation patterns and melting of mountain glaciers and permafrost that result from global warming, information on the distribution of groundwater in mountainous terrains is becoming increasingly important for developing prudent resource and hazard management strategies. Obtaining this information across topographically craggy and variably frozen ground in a cost-effective and nonintrusive manner is challenging. We introduce a modified 2D surface nuclear magnetic resonance (NMR) tomographic technique that allows us to account for substantial variations in surface topography in locating and quantifying groundwater occurrences in rugged mountains. Because contact with the ground is not necessary, it is a rare geophysical technique not affected by sensor-to-ground coupling problems common in high mountain environments. To demonstrate the efficacy of the tomographic imaging scheme, we invert a large multioffset surface NMR data set collected across a partially ice-cored proglacial terminal moraine in the Canadian Rocky Mountains. Our preferred model contains a 2- to 5-m-thick water layer, the top of which has practically the same elevation as the surface of a nearby lake and the bottom of which coincides with bedrock resolved in companion seismic and ground-penetrating radar studies.

Imaging in electrically conductive porous media without frequency encoding

“…(3) for water content m(r) using an Occam's type inversion routine [32,33] for all employed loop positions and pulse moments.…”

Magnetic resonance diffusion and relaxation characterization of water in the unfrozen vein network in polycrystalline ice and its response to microbial metabolic products

“…This work is a novel approach to characterization of ice structure as it relates to the habitat of microorganisms at sub-zero temperatures and demonstrates the potential for NMR techniques to characterize a broader range of low liquid fraction geophysical systems, from permafrost [27] to glacial ice [28] and snow, of interest to fields of oceanology, climatology, biology, and Earth science. More generally, these results are the first demonstration of NMR porous media techniques extended to extremely low porosity mediums ($2%).…”

Uncertainty estimates for surface nuclear magnetic resonance water content and relaxation time profiles from bootstrap statistics

“…the SNR (Müller-Petke et al, 2011) and the result of low SNR is increased uncertainty in the estimated aquifer properties. Other factors may contribute to uncertainty in surface NMR measurements such as geometrically imperfect loop shapes that are modeled using simple loop geometries (Lehmann-Horn et al, 2011b), poorly known background magnetic field (B 0 ) at a measurement site (Walbrecker et al, 2011) or instrument bias, however here we focus only on uncertainty attributed to signal quality (i.e. ambient electromagnetic noise) because we assume it is the most dominant and frequently encountered factor.…”