Internal structure of the Green Lake 5 rock glacier, Colorado Front Range, USA

Abstract

Information about the internal structure of rock glaciers is needed to understand their reaction to ongoing climate warming. Three different geophysical techniques—shallow seismic refraction, ground‐penetrating radar (GPR) and electrical resistivity tomography—were used to develop a detailed subsurface model of the Green Lake 5 rock glacier in the Colorado Front Range, USA. Below a thin zone of fine sediments and soils (0.7 – 1‐m thickness; 0 – 20 kΩm and 320 – 370 m s−1), a 1 – 3‐m thick zone with low p‐wave velocities (790 – 820 m s−1) and high electrical resistivity (20 – 100 kΩm) is interpreted as the ice‐free, blocky active layer with large void spaces. The data corroborate strong reflections of the GPR signals which travel at this depth at 0.11 m ns−1. A third layer that extends from depths of 1 – 3 m to about 5 m is characterised by lower electric resistivities (5 – 20 kΩm) and has lower electromagnetic wave velocities (0.65 m ns−1), representing unfrozen, finer and wetter sediments. At around 5‐m depth, the measured physical parameters change drastically (vp = 3200 – 3300 m s−1, 50 – 150 kΩm, vGPR = 0.15 m ns−1), showing an ice‐rich permafrost zone above the bedrock. This model of the internal structure was used to evaluate an existing hydrological flowpath model based on the hydrochemical properties of water outflow from the rock glacier. Copyright © 2011 John Wiley & Sons, Ltd.

Anatomy of terminal moraine segments and implied lake stability on Ngozumpa Glacier, Nepal, from electrical resistivity tomography (ERT)

“…The high resistivity values (>100 kΩ m) at Site A (Fig. 2) exceed those characteristic of regional geological materials (with the exception of bedrock) and, are consistent with values measured from Alpine rock glaciers and cold glacier ice5253555759.…”

Investigating groundwater flow components in an Alpine relict rock glacier (Austria) using a numerical model

“…Investigations of rock glaciers mainly focus on the distribution, movement and the inner structure of intact rock glaciers (e.g., Haeberli et al 2006;Jansen and Hergarten 2006;Leopold et al 2011;Monnier et al 2011). Monnier and Kinnard (2015) investigated the internal structure of an active rock glacier in the Dry Andes with ground penetrating radar.…”

Radar-bright Spot

“…Ice frozen in pore spaces will be stronger than the weathered debris aggregate (rockfill) itself and will not flow. These thermomechanical problems have been discussed elsewhere (Azizi and Whalley 1996;Azizi 1994, 2003;Leopold et al 2011). Note that the permafrost model in Fig.…”

“…Applying the traditional techniques of drill coring or excavating, it is difficult to determine where the ice is located inside the rock glacier; however, new geophysical techniques (e.g., ground-penetrating radar) are able to reveal the internal structure of rock glaciers (e.g., Musil et al 2006;Hausmann et al 2007Hausmann et al , 2012Degenhardt 2009;Leopold et al 2011). …”