Dilation of subglacial sediment governs incipient surge motion in glaciers with deformable beds

Minchew, Brent; Meyer, Colin R.

doi:10.1098/rspa.2020.0033

Cited by 39 publications

(45 citation statements)

References 119 publications

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“…Under these conditions, rate‐and‐state friction theory predicts that driving at velocities above these speeds in a less‐stiff apparatus should produce stick‐slips. The generation of stress drops when the velocity enters the rate‐weakening velocity zone is in agreement with predictions for unstable slip via rate‐and‐state friction (Scholz, 1998) and supports conditional use of rate‐and‐state friction laws for describing glacier slip, as others have done (see Lipovsky & Dunham, 2016; Minchew & Meyer, 2020). The a , b , and D c parameters measured for use in rate‐and‐state friction depend on in situ slip conditions and are therefore not simply material constants (Scholz, 1998).…”

Section: Discussionsupporting

confidence: 86%

Application of Constitutive Friction Laws to Glacier Seismicity

Zoet

Ikari

Alley

et al. 2020

Geophysical Research Letters

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While analysis of glacial seismicity continues to be a widely used method for interpreting glacial processes, the underlying mechanics controlling glacial stick-slip seismicity remain speculative. Here, we report on laboratory shear experiments of debris-laden ice slid over a bedrock asperity under carefully controlled conditions. By modifying the elastic loading stiffness, we generated the first laboratory icequakes. Our work represents the first comprehensive lab observations of unstable ice-slip events and replicates several seismological field observations of glacier slip, such as slip velocity, stress drop, and the relationship between stress drop and recurrence interval. We also observe that stick-slips initiate above a critical driving velocity and that stress drop magnitude decreases with further increases in velocity, consistent with friction theory and rock-on-rock friction laboratory experiments. Our results demonstrate that glacier slip behavior can be accurately predicted by the constitutive rate-and-state friction laws that were developed for rock friction. Plain Language Summary Glacier beds and tectonic faults may at first appear to be quite different, but they share important characteristics. In both cases, motion may be smooth (aseismic creep) or earthquake-producing "stick-slip." A powerful physical constitutive relationship called rate-and-state friction has been developed to understand earthquakes and smooth slip on tectonic faults. Laboratory experiments reported here simulate glacier-bed motion by sliding debris-bearing ice over a rock plate under conditions that are typical for glacier beds. They produce the first laboratory icequakes. Transitions between steady and stick-slip motions are generated by controlling shearing velocity and other conditions, as predicted by rate-and-state friction theory. Future studies can thus apply this physical framework to glacier slip, helping to understand ice motion and its potential to accelerate sea level rise in a warming world. Furthermore, because motion at the glacier bed is often much easier to study than tectonic faults, additional observations of glaciers may provide useful insights into earthquake behavior.

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Section: Discussionsupporting

confidence: 86%

Application of Constitutive Friction Laws to Glacier Seismicity

Zoet

Ikari

Alley

et al. 2020

Geophysical Research Letters

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“…In some cases it may be desirable to enforce spatial coherency when solving form to reduce the influence of data noise onm (Hetland et al, 2012;Riel et al, 2014;Minchew et al, 2015). Examples of such cases involve low-amplitude signals with spatial wavelengths longer than a single data pixel and, more generally, cases where the data have low SNR values.…”

Section: Time Series Analysis Methodsmentioning

confidence: 99%

Observing traveling waves in glaciers with remote sensing: new flexible time series methods and application to Sermeq Kujalleq (Jakobshavn Isbræ), Greenland

2021

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Abstract. The recent influx of remote sensing data provides new opportunities for quantifying spatiotemporal variations in glacier surface velocity and elevation fields. Here, we introduce a flexible time series reconstruction and decomposition technique for forming continuous, time-dependent surface velocity and elevation fields from discontinuous data and partitioning these time series into short- and long-term variations. The time series reconstruction consists of a sparsity-regularized least-squares regression for modeling time series as a linear combination of generic basis functions of multiple temporal scales, allowing us to capture complex variations in the data using simple functions. We apply this method to the multitemporal evolution of Sermeq Kujalleq (Jakobshavn Isbræ), Greenland. Using 555 ice velocity maps generated by the Greenland Ice Mapping Project and covering the period 2009–2019, we show that the amplification in seasonal velocity variations in 2012–2016 was coincident with a longer-term speedup initiating in 2012. Similarly, the reduction in post-2017 seasonal velocity variations was coincident with a longer-term slowdown initiating around 2017. To understand how these perturbations propagate through the glacier, we introduce an approach for quantifying the spatially varying and frequency-dependent phase velocities and attenuation length scales of the resulting traveling waves. We hypothesize that these traveling waves are predominantly kinematic waves based on their long periods, coincident changes in surface velocity and elevation, and connection with variations in the terminus position. This ability to quantify wave propagation enables an entirely new framework for studying glacier dynamics using remote sensing data.

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“…Clarke and others, 1984;Truffer and others, 2000;Woodward and others, 2003) and theoretical studies (e.g. Clarke, 1987b;Minchew and Meyer, 2020) suggest…”

Section: Probable Surge Mechanismmentioning

confidence: 98%

Kinematics of the exceptionally-short surge cycles of Sít’ Kusá (Turner Glacier), Alaska, from 1983 to 2013

et al. 2021

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Glacier surges are periodic episodes of mass redistribution characterized by dramatic increases in ice flow velocity and, sometimes, terminus advance. We use optical satellite imagery to document five previously unexamined surge events of Sít’ Kusá (Turner Glacier) in the St. Elias Mountains of Alaska from 1983 to 2013. Surge events had an average recurrence interval of ~5 years, making it the shortest known regular recurrence interval in the world. Surge events appear to initiate in the winter, with speeds reaching up to ~25 m d−1. The surges propagate down-glacier over ~2 years, resulting in maximum thinning of ~100 m in the reservoir zone and comparable thickening at the terminus. Collectively, the rapid recurrence interval, winter initiation and down-glacier propagation suggest Sít’ Kusá's surges are driven by periodic changes in subglacial hydrology and glacier sliding. Elevation change observations from the northern tributary show a kinematic disconnect above and below an icefall located 23 km from the terminus. We suggest the kinematic disconnect inhibits drawdown from the accumulation zone above the icefall, which leads to a steady flux of ice into the reservoir zone, and contributes to the glacier's exceptionally short recurrence interval.

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Dilation of subglacial sediment governs incipient surge motion in glaciers with deformable beds

Cited by 39 publications

References 119 publications

Application of Constitutive Friction Laws to Glacier Seismicity

Application of Constitutive Friction Laws to Glacier Seismicity

Observing traveling waves in glaciers with remote sensing: new flexible time series methods and application to Sermeq Kujalleq (Jakobshavn Isbræ), Greenland

Kinematics of the exceptionally-short surge cycles of Sít’ Kusá (Turner Glacier), Alaska, from 1983 to 2013

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