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Arctic Coastal Erosion Modeling

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Abstract

An Arctic coastal erosion process or mechanism is distinct from a non-Arctic erosion process due to the importance of thermal processes in addition to mechanical ones. The Arctic contains permanently frozen soil (permafrost) as well as soil and sediments that freeze seasonally. Thawing of the coastal permafrost and seasonally frozen soils/sediments is a critical and distinctive feature of Arctic coastal erosion. Thus, the Arctic coastal erosion modeler must include both thermal and mechanical processes in their models, either implicitly or explicitly. Arctic coastal erosion modeling features the identification of particularly Arctic coastal configurations and the development of process-based and predictive Arctic coastal erosion models for those specific configurations. In this chapter, recent advances in Artic coastal erosion modeling are presented, with a particular focus on the work done in Arctic Alaska. In addition, suggestions for next steps are offered. Much of the Arctic coastal erosion modeling has focused on cross-shore processes and sediment transport. In the future, Arctic modelers will need to include longshore transport processes and account for their contribution to erosion and shoreline change. © 2018 by World Scientific Publishing Co. Pte. Ltd. All rights reserved.

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... Niche erosion/block collapse is the predominant erosion mechanism in settings where the coastal bluffs have high ice content (∼70%, Ping et al., 2011), and where the bluffs lack significant amounts of coarse material (sand and gravel). The lack of coarse material leads to a low elevation beach at the base of the bluff and frequent contact between the sea and the coastal bluffs (Ravens et al., 2011;Ravens and Peterson 2018). ...
... Bluff face thaw/slump is the predominant erosion mechanism in settings where significant amounts of coarse sediments are common (e.g., at Barter Island, Ravens et al., 2011;Ravens and Peterson 2018). With significant amounts of coarse sediments in the coastal bluffs, the elevation of the beach before the bluff is relatively high (1-2 m above mean sea level) and contact between the sea and the base of the bluff-and niche erosion-is infrequent. ...
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Two prominent arctic coastal erosion mechanisms affect the coastal bluffs along the North Slope of Alaska. These include the niche erosion/block collapse mechanism and the bluff face thaw/slump mechanism. The niche erosion/block collapse erosion mechanism is dominant where there are few coarse sediments in the coastal bluffs, the elevation of the beach below the bluff is low, and there is frequent contact between the sea and the base of the bluff. In contrast, the bluff face thaw/slump mechanism is dominant where significant amounts of coarse sediment are present, the elevation of the beach is high, and contact between the sea and the bluff is infrequent. We show that a single geologic parameter, coarse sediment areal density, is predictive of the dominant erosion mechanism and is somewhat predictive of coastal erosion rates. The coarse sediment areal density is the dry mass (g) of coarse sediment (sand and gravel) per horizontal area (cm ² ) in the coastal bluff. It accounts for bluff height and the density of coarse material in the bluff. When the areal density exceeds 120 g cm ⁻² , the bluff face thaw/slump mechanism is dominant. When the areal density is below 80 g cm ⁻² , niche erosion/block collapse is dominant. Coarse sediment areal density also controls the coastal erosion rate to some extent. For the sites studied and using erosion rates for the 1980–2000 period, when the sediment areal density exceeds 120 g cm ⁻² , the average erosion rate is low or 0.34 ± 0.92 m/yr. For sediment areal density values less than 80 g cm ⁻² , the average erosion rate is higher or 2.1 ± 1.5 m/yr.
... Accelerated erosion rates have been reported throughout the coastal regions of the Arctic corresponding to the broader spatial extent of open water, the longer open water period and the increased thawing rate of coastal permafrost [8]. Arctic coastal communities are highly affected by rapid coastline retreat, and valuable resources are at risk. ...
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Arctic coastal erosion demands more attention as the global climate continues to change. Unlike those along low-latitude and mid-latitude, sediments along Arctic coastlines are often frozen, even during summer. Thermal and mechanical factors must be considered together when analysing Arctic coastal erosion. Two major erosion mechanisms in the Arctic have been identified: thermodenudation and thermoabrasion. Field observations of Arctic coastal erosion are available in Baydaratskaya Bay in the Kara Sea. The objective of this study is to develop a probabilistic model of thermoabrasion to simulate the measured coastal erosion at two sites where observations suggest thermoabrasion is dominant. The model simulates two time periods: (a) the summer of 2013 (2012–2013) and (b) the summer of 2017 (2016–2017). A probabilistic analysis is performed to quantify the uncertainties in the model results. The input parameters are assumed to follow normal and lognormal distributions with a 10% coefficient of variation. Monte Carlo simulation is applied to determine the erosion rates for the two different cases. The simulation results agree reasonably well with the field observations. In addition, a sensitivity analysis is performed, revealing a very high sensitivity of the model to sea-level changes. The model indicates that the relation between sea-level rise and thermoabrasional erosion is exponential.
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