Лëд и снег (Sep 2023)
Conditions on the Bedrock and Surface of the Vavilov Ice Cap (Severnaya Zemlya) During its Surge According To Airborne Radar Data
Abstract
The glacier surge at Vavilov Ice Cap, Severnaya Zemlya, Russia (79°18′ N, 94°40′ E) began as early as the mid-1960s with a slow advance of its margin in the western part. Since 2012, the advance switched to the phase of catastrophic movement, which reached its climax in 2016, when the glacier velocity reached 9.2 km a‒1. An ice fan with an area of about 140 km2 advanced into the Kara Sea water area 11 km from the shore, and a strongly crevassed ice stream was formed in the ice cap itself, which continues to move now with speeds of about 2 km a‒1. The dynamic instability of Vavilov Ice Cap can be triggered by changes in basal conditions, which are still poorly known. In this study, we used airborne radio-echo sounding data acquired in September 2014 over the ice cap to characterize its surface and bedrock conditions. Based on the delay time and reflection amplitudes, the power reflection coefficient (PRC) from glacier surface and bedrock was estimated. For its calibration, we used the amplitude of reflections from the sea surface registered from different altitudes. The bedrock PRC values were converted to dielectric permittivity and compared with the glacier surface velocities in 2014 obtained from Landsat-7 images. We found a high positive correlation between the bedrock PRCs and velocities in the area with glacier speed higher than 1000 m a-1. In this area, the PRC is 20 dB higher than in the neighboring slower moving areas. Such a difference may be because the ice stream advanced on marine loose sediments with higher dielectric permittivity and conductivity and a higher reflection coefficient. The range of estimated bedrock PRCs corresponds to bed materials with relative dielectric permittivity from 5 to 10 and electrical conductivity from 10–5 to 10–2 Sm m‒1.
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