Abstract
Crevasses are formed by glacier movement and the stresses within glacier ice. Knowledge of the crevasses’ distribution is critical for understanding the glacier and ice shelf stability. In this study, we propose an automated crevasse extraction framework based on Sentinel-1 SAR imagery and an improved U-Net network. The spatial distribution of crevasses on Antarctic ice shelves in 2020 was mapped with a spatial resolution of ~40 m, and the characteristics of crevasses on the Nickerson Ice Shelf, Jelbart Ice Shelf, Amery Ice Shelf, Thwaites Glacier, and Shackleton Ice Shelf were analyzed. The results indicated the extraction accuracy of our method was 84.2% and the F1 score was 72.5%. Compared with previous published studies, the identification of the crevasse areas had good visual consistency. However, in some scenes, the recall rate was relatively lower due to the quality of the SAR image, terrain surrounding the crevasses, and observation geometry. The crevasses on different ice shelves had different characteristics in terms of length, density, type, and spatial pattern, implying the different stress structures of ice shelves. The Thwaites Glacier and the Nickerson Ice Shelf in the West Antarctica Ice Sheet (WAIS) had shorter ice crevasses, whereas the lengths of ice crevasses on the Jelbart Ice Shelf and the Amery Ice Shelf in the East Antarctica Ice Sheet (EAIS) were relatively long. Nevertheless, there are more closely spaced crevasses on the ice shelf in WAIS compared to that in the EAIS. For the distribution of crevasse types, the Nickerson Ice Shelf and the Shackleton Ice Shelf had various forms of crevasses. There were mainly transverse crevasses developed on the Jelbart Ice Shelf and the Amery Ice Shelf. This study provides a helpful reference and guidance for automated crevasse extraction. The method proposed by this study manifests great application potential and the efficacy of producing a time-series crevasse data set with higher spatial resolution and larger coverage. In the future, more Sentinel-1 SAR imagery will be applied and the effect of temporal and spatial variations in crevasses on the stability of ice shelves will be investigated, which will contribute to project the ice shelf stability and explore the sea level rise implications of recent and future cryosphere changes.
Highlights
We focused on five classical glaciers and ice shelves: Jelbart Ice Shelf, Thwaites Glacier, Nickerson Ice Shelf, Amery Ice Shelf, and Shackleton Ice Shelf (Figure 1)
Regular and more closely spaced transverse crevasses developed on the edge of the Borchgrevinkisen Ice Shelf (Figure 8a), Jelbart Ice Shelf (Figure 8b), Getz Ice Shelf (Figure 8c), and Shirase Ice Shelf (Figure 8d)
Crevasses of different shapes reflect the movement characteristics of different glaciers
Summary
Crevasses have developed on almost all glaciers and ice shelves and are the direct result of glacier movement, reflecting the characteristics of glacier development and stresses [1,2]. The crevasses contribute to the glacier mass balance through impacting the processes of meltwater transportation on the ice surface [3,4,5]. When sufficient surface meltwater infuses into crevasses, hydrofracturing may be induced, resulting in ice shelf instability; crevasses are essential factors for assessing the stability of glaciers and ice shelves [6]. Antarctic scientific research expeditions are closely associated with crevasses because the rapid appearance of crevasses may herald the disintegration of the ice shelf and pose a serious safety hazard to field researchers [7,8].
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