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Beach ridges constructed by pluvial Lake Clover in Elko County, Nevada during the Late Pleistocene were investigated with ground-penetrating radar (GPR). The primary objective was to document the internal architecture of these shorelines and to evaluate whether they were constructed during lake rise or fall. GPR data were collected with a ground-coupled 400-Mhz antenna and SIR-3000 controller. To constrain the morphology of the ridges, detailed topographic surveys were collected with a Topcon GTS-235W total station referenced to a second class 0 vertical survey point. GPR transects crossed the beach ridge built by Lake Clover at its highstand of 1725 m, along with seven other ridges down to the lowest beach at 1712 m. An average dielectric permittivity of 5.0, typical for dry sand and gravel, was calculated from GPR surveys in the vicinity of hand-excavations that encountered prominent stratigraphic discontinuities at known depths. Assuming this value, consistent radar signals were returned to a depth of ~3 m. Beach ridges are resolvable as ~90 to 150-cm thick stratified packages of gravelly sand overlying a prominent lakeward-dipping reflector, interpreted as the pre-lake land surface. Many ridges contain a package of sediment resembling a buried berm at their core, typically offset in a landward direction from the geomorphic crest of the beach ridge. Sequences of lakeward-dipping reflectors are resolvable beneath the beach face of all ridges. No evidence was observed to indicate that beach ridges were submerged by higher water levels after their formation. Instead, the GPR data are consistent with a model of sequential ridge formation during a monotonic lake regression.
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A framework for attenuation method selection evaluated with ice-penetrating radar data at South Pole Lake
Abstract All radar power interpretations require a correction for attenuative losses. Moreover, radar attenuation is a proxy for ice-column properties, such as temperature and chemistry. Prior studies use either paired thermodynamic and conductivity models or the radar data themselves to calculate attenuation, but there is no standard method to do so; and, before now, there has been no robust methodological comparison. Here, we develop a framework meant to guide the implementation of empirical attenuation methods based on survey design and regional glaciological conditions. We divide the methods into the three main groups: (1) those that infer attenuation from a single reflector across many traces; (2) those that infer attenuation from multiple reflectors within one trace; and (3) those that infer attenuation by contrasting the measured power from primary and secondary reflections. To assess our framework, we introduce a new ground-based radar survey from South Pole Lake, comparing selected empirical methods to the expected attenuation from a temperature- and chemistry-dependent Arrhenius model. Based on the small surveyed area, lack of a sufficient calibration surface and low reflector relief, the attenuation methods that use multiple reflectors are most suitable at South Pole Lake.
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- PAR ID:
- 10173843
- Date Published:
- Journal Name:
- Annals of Glaciology
- ISSN:
- 0260-3055
- Page Range / eLocation ID:
- 1 to 12
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1017/aog.2020.32
