Abstract
<strong class="journal-contentHeaderColor">Abstract.</strong> In addition to ice and water, glaciers expel sediment. As a result, changing glacier dynamics and melt will result in changes to glacier erosion and sediment discharge, which can impact the landscape surrounding retreating glaciers, as well as communities and ecosystems downstream. To date, the available models of subglacial sediment transport on the sub-hourly to decadal-scale exist in one dimension, usually along a glacier's flow line. Such models have proven useful in describing the formation of landforms, the impact of sediment transport on glacier dynamics, the interactions between climate, glacier dynamics, and erosion. However, because of the large role of sediment connectivity in determining sediment discharge, the geoscience community needs modeling frameworks that describe subglacial sediment discharge in two spatial dimensions over time. Here, we present SUGSET_2D, a numerical model that evolves a two-dimensional subglacial till layer in response to the erosion of bedrock and changing sediment transport conditions below the glacier. Experiments employed on test cases of synthetic ice sheets and alpine glaciers demonstrate the heterogeneity in sediment transport across a glacier's bed. Furthermore, the experiments show the non-linear increase in sediment discharge following increased glacier melt. Lastly, we apply the model to Griesgletscher in the Swiss Alps where we use a parameter search to test model outputs against annual observations of sediment discharge measured from the glacier. The model captures the glacier's inter-annual variability and quantities of sediment discharge. Furthermore, the model's capacity to represent the data depends greatly on the grain size of sediment. Smaller sediment sizes allow sediment transport to occur in regions of the bed with reduced water flow and channel size, effectively increasing sediment connectivity into the main channels. Model outputs from the three test-cases together show the importance of considering heterogeneities in water discharge and sediment availability in two dimensions.
Highlights
As a result, changing glacier dynamics and melt will result in changes to glacier erosion and sediment discharge, which can impact the landscape surrounding retreating glaciers, as well as communities and ecosystems downstream
We apply the model to Griesgletscher in the Swiss Alps where we use a parameter search to test model outputs against annual observations of sediment discharge measured from the glacier
We identify some drivers of subglacial sediment discharge from these simulations
Summary
Increasing glacier ablation will change the ways that glaciers erode bedrock and supply sediment to downstream sources (e.g. 20 Church and Ryder, 1972; Lane et al, 2017; Milner et al, 2017). Implementation of the model to existing glacier hydrology, topography, and sediment discharge datasets from the Griesgletscher helps to understand some subglacial sediment transport processes at this site that could be generalizable to other situations. SUGSET_2D requires a hydraulics model as a means to route sediment and water through the subglacial environment and to evaluate the sediment transport capacity of this water, based upon the hydraulic gradient, channel size and water flux (Table 1, Section 2.2; e.g. Walder and Fowler, 1994; Alley et al, 1997). 100 equipped with Dh, we insert the instantaneous value of Qw into Equation 1 to evaluate the instantaneous hydraulic gradient Ψ In this formulation, we assume that the timescales over which the channel size responds (days) are different than the those of instantaneous water discharge (minutes or hours). We note that to prevent unreasonable water pressures when Q∗w rapidly increases and Dh is small, the model limits the 105 minimal cross-sectional area of Dh to 0.3 m2
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
