Erosion and sedimentation in Surtsey island quantified from new DEMs

We present data from a photogrammetric study on Surtsey island that generated three new DEMs and orthoimages, two from scanned aerial images from 1967 and 1974 and one from high-resolution closerange images from a survey in 2019. DEM differencing allowed for quantification of the erosion and the sedimentation in the island since 1967. Of the subaerial volcanics, about 45% of the lava fields have eroded away but only about 16% of the tuff cones. The prevailing SW coastal wave erosion is evident from the erosive pattern in Surtsey, and the cumulative loss of the coastal margins amounts to 28±0.9x106 m3 since 1967, with the current average erosion rate of 0.4±0.02x106 m3 /yr. Wind deflation and runoff erode the tuff cones and the sediments at the flanks of the cones, with the total volume loss amounting to 1.6±0.2x106 m3 and the current erosion rate of 0.03±0.004x106 m3 /yr. A rapid decline in erosion rates characterized the first years post-eruption, and the coastal erosion rate during the winter of 1967–68 was about 5–6 times higher than the current erosion rate due to the thinner and less cohesive nature of the lava apron at the edge of the shelf. The cones eroded at a rate about 2–3 times higher during the first years due to the uncompacted and unconsolidated nature of the cones at that time. The 2019 area of 1.2 km2 and an extrapolation of the current erosion rate fits well with the projected erosion curve of Jakobsson et al. (2000) with the island becoming a tuff crag after approximately 100 years.

Improving geomorphological process understanding of complex glacier surfaces using aerial robotics

<p>In the last decade or so, improvements in unpiloted aerial systems (UAS) technology and the emergence of low-cost digital photogrammetry have democratised access to accurate, high-resolution topographic data products, particularly in remote, glacial environments. One such application of these tools has been for advancing understanding of debris-covered glaciers (DCG) which are an important component of the high-mountain cryosphere, but also where detailed, ground-based process analysis is challenging. In this work, we seek to improve meso-scale (<km) geomorphological understanding of DCG surface evolution over multi-annual timescales by quantifying how debris moves around on the surface of these glaciers, and how debris transport is reconciled with wider patterns and mechanisms of ice mass loss. We applied annual UAS-photogrammetry and DEM differencing alongside debris thickness and debris stability modelling to unravel the evolution of a 0.2 km<sup>2</sup> sub-region of the debris-covered Miage Glacier, Italy, between June 2015 and July 2018. Following corrections for glacier flow, DEM differencing revealed widespread surface lowering (mean 4.1 ± 1.0 m a<sup>-1</sup>; maximum 13.3 m a<sup>-1</sup>). We combined DEMs of difference with local meteorological data and a sub-debris melt model to produce high resolution (metre-scale) maps of debris thickness. Median debris thicknesses ranged from 0.12 – 0.17 m and were highly spatially variable. Debris thickness differencing revealed localised debris thinning across ice cliff faces, except those which were decaying, where debris thickened, as well as ingestion of debris by a newly exposed englacial conduit. Debris stability mapping showed that 18.2 - 26.4% of the survey area was theoretically subject to debris remobilisation in a given year. By linking changes in stability to changes in debris thickness, we observed a net debris thinning signal across slopes which become newly unstable, and a net thickening signal across those which stabilise between years. Finally, we linked morphometric descriptors of the glacier surface with debris thickness change data to derive empirical relationships which describe observed rates of downslope debris thickening as a function of slope-distance and slope angle. These UAS-enabled data provide new insight into mechanisms and rates of debris redistribution on glacier surfaces over sub-decadal timescales, and open avenues for future research to explore patterns of debris remobilisation and the morphological evolution of glacier surfaces at much larger spatiotemporal scales.</p>

Synergistic Use of Single-Pass Interferometry and Radar Altimetry to Measure Mass Loss of NEGIS Outlet Glaciers between 2011 and 2014

Mass balances of individual glaciers on ice sheets have been previously reported by forming a mass budget of discharged ice and modelled ice sheet surface mass balance or a complementary method which measures volume changes over the glaciated area that are subsequently converted to glacier mass change. On ice sheets, volume changes have been measured predominantly with radar and laser altimeters but InSAR DEM differencing has also been applied on smaller ice bodies. Here, we report for the first time on the synergistic use of volumetric measurements from the CryoSat-2 radar altimetry mission together with TanDEM-X DEM differencing and calculate the mass balance of the two major outlet glaciers of the Northeast Greenland Ice Stream: Zachariæ Isstrøm and Nioghalvfjerdsfjorden (79North). The glaciers lost 3.59 ± 1.15 G t a − 1 and 1.01 ± 0.95 G t a − 1 , respectively, between January 2011 and January 2014. Additionally, there has been substantial sub-aqueous mass loss on Zachariæ Isstrøm of more than 11 G t a − 1 . We attribute the mass changes on both glaciers to dynamic downwasting. The presented methodology now permits using TanDEM-X bistatic InSAR data in the context of geodetic mass balance investigations for large ice sheet outlet glaciers. In the future, this will allow monitoring the mass changes of dynamic outlet glaciers with high spatial resolution while the superior vertical accuracy of CryoSat-2 can be used for the vast accumulation zones in the ice sheet interior.

Interannual surface evolution of an Antarctic blue-ice moraine using multi-temporal DEMs

Multi-temporal and fine-resolution topographic data products are increasingly used to quantify surface elevation change in glacial environments. In this study, we employ 3-D digital elevation model (DEM) differencing to quantify the topographic evolution of a blue-ice moraine complex in front of Patriot Hills, Heritage Range, Antarctica. Terrestrial laser scanning (TLS) was used to acquire multiple topographic datasets of the moraine surface at the beginning and end of the austral summer season in 2012/2013 and during a resurvey field campaign in 2014. A complementary topographic dataset was acquired at the end of season 1 through the application of structure from motion with multi-view stereo (SfM-MVS) photogrammetry to a set of aerial photographs acquired from an unmanned aerial vehicle (UAV). Three-dimensional cloud-to-cloud differencing was undertaken using the Multiscale Model to Model Cloud Comparison (M3C2) algorithm. DEM differencing revealed net uplift and lateral movement of the moraine crests within season 1 (mean uplift ~ 0.10 m) and surface lowering of a similar magnitude in some inter-moraine depressions and close to the current ice margin, although we are unable to validate the latter. Our results indicate net uplift across the site between seasons 1 and 2 (mean 0.07 m). This research demonstrates that it is possible to detect dynamic surface topographical change across glacial moraines over short (annual to intra-annual) timescales through the acquisition and differencing of fine-resolution topographic datasets. Such data offer new opportunities to understand the process linkages between surface ablation, ice flow and debris supply within moraine ice.

Inter-annual surface evolution of an Antarctic blue-ice moraine using multi-temporal DEMs

Multi-temporal and fine resolution topographic data products are being increasingly used to quantify surface elevation change in glacial environments. In this study, we employ 3-D digital elevation model (DEM) differencing to quantify the topographic evolution of a blue-ice moraine complex in front of Patriot Hills, Heritage Range, Antarctica. Terrestrial laser scanning (TLS) was used to acquire multiple topographic datasets of the moraine surface at the beginning and end of the austral summer season in 2012/2013 and during a resurvey field campaign in 2014. A complementary topographic dataset was acquired at the end of season 1 through the application of Structure-from-Motion (SfM) photogrammetry to a set of aerial photographs taken from an unmanned aerial vehicle (UAV). Three-dimensional cloud-to-cloud differencing was undertaken using the Multiscale Model to Model Cloud Comparison (M3C2) algorithm. DEM differencing revealed net uplift and lateral movement of the moraine crests within season 1 (mean uplift ∼ 0.10 m), with lowering of a similar magnitude in some inter-moraine depressions and close to the current ice margin. Our results indicate net uplift across the site between seasons 1 and 2 (mean 0.07 m). This research demonstrates that it is possible to detect dynamic surface topographical change across glacial moraines over short (annual to intra-annual) timescales through the acquisition and differencing of fine-resolution topographic datasets. Such data offer new opportunities to understand the process linkages between surface ablation, ice flow, and debris supply within moraine ice.

Balanced conditions or slight mass gain of glaciers in the Lahaul and Spiti region (northern India, Himalaya) during the nineties preceded recent mass loss

The volume change of the Chhota Shigri Glacier (India, 32° 20 N, 77° 30' E) between 1988 and 2010 has been determined using in situ geodetic measurements. This glacier has experienced only a slight mass loss between 1988 and 2010 (−3.8 ± 2.0 m w.e. (water equivalent) corresponding to −0.17 ± 0.09 m w.e. yr−1). Using satellite digital elevation models (DEM) differencing and field measurements, we measure a negative mass balance (MB) between 1999 and 2010 (−4.8 ± 1.8 m w.e. corresponding to −0.44 ± 0.16 m w.e. yr−1). Thus, we deduce a slightly positive or near-zero MB between 1988 and 1999 (+1.0 ± 2.7 m w.e. corresponding to +0.09 ± 0.24 m w.e. yr−1). Furthermore, satellite DEM differencing reveals that the MB of the Chhota Shigri Glacier (−0.39 ± 0.15 m w.e. yr−1) has been only slightly less negative than the MB of a 2110 km2 glaciarized area in the Lahaul and Spiti region (−0.44 ± 0.09 m w.e. yr−1) during 1999−2011. Hence, we conclude that the ice wastage is probably moderate in this region over the last 22 yr, with near equilibrium conditions during the nineties, and an ice mass loss after. The turning point from balanced to negative mass budget is not known but lies probably in the late nineties and at the latest in 1999. This positive or near-zero MB for Chhota Shigri Glacier (and probably for the surrounding glaciers of the Lahaul and Spiti region) during at least part of the 1990s contrasts with a recent compilation of MB data in the Himalayan range that indicated ice wastage since 1975. However, in agreement with this compilation, we confirm more negative balances since the beginning of the 21st century.