A 15 year record of frontal glacier ablation rates estimated from seismic data

Köhler, Andreas; Nuth, C.; Kohler, Jack; Berthier, Étienne; Weidle, Christian; Schweitzer, Johannes

doi:10.1002/2016gl070589

Cited by 30 publications

(53 citation statements)

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“…The glacier front position undergoes seasonal oscillations, showing advance during the winter and spring followed by retreat in the summer and autumn. Since 2011, the summer retreat has outpaced the winter advance, with an overall net retreat of ∼ 2 km between 2011 and 2015 after a relatively stable period since the 1990s (Schellenberger et al, 2015;Luckman et al, 2015;Köhler et al, 2016). Velocities at the front can reach 5 m d −1 in the summer with large seasonal and annual variations associated with basal sliding velocity .…”

Section: Study Areamentioning

confidence: 99%

Effects of undercutting and sliding on calving: a global approach applied to Kronebreen, Svalbard

et al. 2018

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Abstract. In this paper, we study the effects of basal friction, sub-aqueous undercutting and glacier geometry on the calving process by combining six different models in an offlinecoupled workflow: a continuum-mechanical ice flow model (Elmer/Ice), a climatic mass balance model, a simple subglacial hydrology model, a plume model, an undercutting model and a discrete particle model to investigate fracture dynamics (Helsinki Discrete Element Model, HiDEM). We demonstrate the feasibility of reproducing the observed calving retreat at the front of Kronebreen, a tidewater glacier in Svalbard, during a melt season by using the output from the first five models as input to HiDEM. Basal sliding and glacier motion are addressed using Elmer/Ice, while calving is modelled by HiDEM. A hydrology model calculates subglacial drainage paths and indicates two main outlets with different discharges. Depending on the discharge, the plume model computes frontal melt rates, which are iteratively projected to the actual front of the glacier at subglacial discharge locations. This produces undercutting of different sizes, as melt is concentrated close to the surface for high discharge and is more diffuse for low discharge. By testing different configurations, we show that undercutting plays a key role in glacier retreat and is necessary to reproduce observed retreat in the vicinity of the discharge locations during the melting season. Calving rates are also influenced by basal friction, through its effects on near-terminus strain rates and ice velocity.

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Section: Study Areamentioning

confidence: 99%

Effects of undercutting and sliding on calving: a global approach applied to Kronebreen, Svalbard

et al. 2018

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“…Similar to most seismic stations (Bonnefoy-Claudet et al, 2006), the seismic noise wavefield measured on our network is mainly composed of ocean micro-seisms at low frequencies (<1 Hz) and a mixture of (here limited) cultural noise from the close settlement of Ny Ålesund and effects of local meteorological conditions (wind, ocean swell at local coastline) at high frequencies (>1 Hz). Frequent 10 calving activity at nearby tidewater glaciers during summer and autumn (Köhler et al, 2015(Köhler et al, , 2016 (Boike et al, 2018) at 1.6 km distance from BRA and 2.4 km from KBS.…”

Section: Datamentioning

confidence: 99%

“…Note that the temporary deployment was originally not designed as an active layer monitoring experiment, but for monitoring iceberg calving at nearby glaciers (Köhler et al, 2016). Similar to most seismic stations (Bonnefoy-Claudet et al, 2006), the seismic noise wavefield measured on our network is mainly composed of ocean micro-seisms at low frequencies (<1 Hz) and a mixture of (here limited) cultural noise from the close settlement of Ny Ålesund and effects of local meteorological conditions (wind, ocean swell at local coastline) at high frequencies (>1 Hz).…”

Section: Datamentioning

confidence: 99%

“…We use frequency-wavenumber analysis (FK, Kvaerna and Ringdal, 1986;Ohrnberger et al, 2004) and the spatial mapping by multi-array beamforming method (SMAB, in supplementary information in Köhler et al, 2016) to 25 locate the tremor source using the KBS and BRA array. Location accuracy is limited because of the resolution limit of array beamforming at these wavelengths (about 400 m).…”

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Potentials and pitfalls of permafrost active layer monitoring using the HVSR method: A case study in Svalbard

Köhler¹,

Weidle²

2018

Preprint

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Abstract. Time-lapse monitoring of the sub-surface using ambient seismic noise is a popular method in environmental seismology. We assess the reliability of the Horizontal-to-Vertical Spectral Ratio (HVSR) method for monitoring seasonal permafrost active layer variability in northwest Svalbard. We observe complex HVSR variability between 1 and 50 Hz in the record of a temporary seismic deployment covering frozen and thawn soil conditions between April and August 2016. While strong variations are due to changing noise conditions, mainly affected by wind speed and degrading coupling of instruments during 5 melt season, a seasonal trend is observed at some stations that has most likely a sub-surface structural cause. A HVSR peak emerges close to the Nyquist frequency (50 Hz) in beginning of June which is then gradually gliding down, reaching frequencies of about 15-25 Hz in the end of August. This observation is consistent with HVSR forward-modeling for a set of structural models that simulate different stages of active layer thawing. Our results reveal a number of potential pitfalls when interpreting HVSRs and suggest a careful analysis of temporal variations since HVSR seasonality is not necessarily related to changes in 10 the sub-surface. We compile a list of recommendations for future experiments, including comments on network layouts suitable for array beamforming and waveform correlation methods that can provide essential information on noise source variability. In addition, we investigate if effects of changing noise sources on HVSRs can be avoided by utilizing a directional, narrow-band (4.5 Hz) repeating seismic tremor which is observed at the permanent seismic broadband station KBS in the study area. A significant change of the radial component HVSR shape during summer months is observed for all tremors. We show that a 15 thawn active layer with very low seismic velocities would affect Rayleigh wave ellipticities in the tremor frequency band.

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“…Since 2011, the summer retreat has outpaced the winter advance, with an overall net retreat of ∼2 km between 2011 and 2015 after a relatively stable period since the 1990s (Schellenberger et al, 2015;Luckman et al, 2015;Köhler et al, 2016). Velocities at the front can reach 5 m d −1 in the summer with large seasonal and annual variations associated with basal sliding .…”

mentioning

confidence: 99%

Effects of undercutting and sliding on calving: a coupled approach applied to Kronebreen, Svalbard

Vallot¹,

Åström²,

Zwinger³

et al. 2017

Preprint

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Abstract.In this paper, we study the effects of basal friction, sub-aqueous undercutting and glacier geometry on the calving process with six different models: a continuum-mechanical ice flow model (Elmer/Ice), a climatic mass balance model, a simple subglacial hydrology model, a plume model, an undercut model and a discrete particle model to investigate fracture dynamics (Helsinki Discrete Element Model, HiDEM). We also demonstrate the feasibility of reproducing the observed calving retreat 5 at the front of Kronebreen, a tidewater glacier in Svalbard, during a melt season. Basal sliding and glacier motion is addressed using Elmer/Ice while calving is modelled by HiDEM. An hydrology model calculates subglacial drainage paths and indicates two main outlets at relatively different rates. Depending on the discharge, the plume model computes frontal melt rates, which are iteratively projected to the actual front of the glacier at subglacial discharge locations. This produces undercutting of different sizes, as melt is concentrated close to the surface for high discharge and is more diffuse for low discharge. By testing 10 different configurations, we show that the geometry (frontal position and topography) controls the calving location while basal sliding controls the calving rate. Undercutting plays a key role in glacier retreat and is necessary to reproduce observed retreat in the vicinity of the discharge location.

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A 15 year record of frontal glacier ablation rates estimated from seismic data

Cited by 30 publications

References 50 publications

Effects of undercutting and sliding on calving: a global approach applied to Kronebreen, Svalbard

Effects of undercutting and sliding on calving: a global approach applied to Kronebreen, Svalbard

Potentials and pitfalls of permafrost active layer monitoring using the HVSR method: A case study in Svalbard

Effects of undercutting and sliding on calving: a coupled approach applied to Kronebreen, Svalbard

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