Nocturnal Thermal Fracturing of a Himalayan Debris‐Covered Glacier Revealed by Ambient Seismic Noise

Podolskiy, Evgeny A.; Fujita, Koji; Sunako, Sojiro; Tsushima, Akane; Kayastha, Rijan Bhakta

doi:10.1029/2018gl079653

Cited by 29 publications

(41 citation statements)

References 39 publications

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“…A detailed explanation of the temporary observational network deployed across the glacier system can be found in Podolskiy et al (). A comprehensive description of the study area, highlighting the importance of glaciological monitoring in this rapidly changing region near Mount Everest, is also available in Podolskiy et al (, and references within). An overview map of the installed instruments is presented in Figure .…”

Section: Methodsmentioning

confidence: 99%

“…However, volumetric expansion may be spatially limited by the collective expansion of particles and therefore lead to the buildup of stresses at locked contacts that may break coseismically when some critical stress can no longer be opposed by friction. Such hypothesis stems from the observations showing minor pulses of seismicity during the local afternoon, most pronounced at the station C1 with the thickest debris mantle (Podolskiy et al, ). To our knowledge, indirect evidence of such behavior has already been investigated in granular materials.…”

Section: Thermal Stress Modelmentioning

confidence: 99%

“…The model output will be compared with a proxy for seismic activity, which is the continuous power spectral density of the relative displacements integrated over the 10‐ to 30‐Hz frequency range (after Podolskiy et al, ). For a visual comparison of stresses with the seismic noise, we show an average depth‐integrated stress,

\overset{τ}{true}

, within the upper centimeters of the layer under consideration, defined as

\overset{τ}{true} false(t false) \equiv \frac{\int_{d}^{d + l} τ_{+ false/ -} false(t, z false) normald z}{l},

where d is the starting depth of integration (i.e., d =0 corresponds to integration either from the debris surface or from the exposed ice surface), l is the layer thickness, and τ +/− is either positive or negative stress at a particular time step and depth.…”

Section: Thermal Stress Modelmentioning

confidence: 99%

“…The model output will be compared with a proxy for seismic activity, which is the continuous power spectral density of the relative displacements integrated over the 10-to 30-Hz frequency range (after Podolskiy et al, 2018b). For a visual comparison of stresses with the seismic noise, we show an average depth-integrated stress,̂, within the upper centimeters of the layer under consideration, defined aŝ…”

Section: Other General Considerationsmentioning

confidence: 99%

“…No focused analysis of the relationship between thermal stress and ice fracturing has been made on debris-covered glaciers to date, despite recent interest in the role of debris on the mass balance of glaciers and snow patches (e.g., Fujita & Sakai, 2014;Podolskiy et al, 2015). The main possible factors that lead to the processes observed by Podolskiy et al (2018b) are (1) the elastic response of the ice, (2) high diurnal temperature fluctuations, and (3) weak ice with high stress at heterogeneities.…”

Section: Introductionmentioning

confidence: 99%

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Viscoelastic Modeling of Nocturnal Thermal Fracturing in a Himalayan Debris‐Covered Glacier

et al. 2019

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Recent observations suggest that the nocturnal thermal fracturing of ice occurs at relatively warm temperatures (above −15 °C) at a high‐altitude Himalayan glacier system unless the ice is shielded by a debris mantle. Here we estimate the stresses induced by diurnal temperature variations using viscous, elastic, and two viscoelastic models, and various thicknesses of the debris mantle. Only the elastic and visco‐elastic models are in agreement with the observations. The timing and amplitudes of the stresses in the upper 15 cm of the glacier are different among the models despite the ability of each approach to predict a diurnal increase in tension exceeding the critical threshold proposed for crevasse formation. For example, the elastic stress is several times larger than the viscous stress at the ice surface (650 vs. 250 kPa) and reaches its peak up to 5–6 hr later in the night. The time lag is in line with the seismic records, suggesting that the viscous model is not appropriate. Furthermore, a debris layer of ≥50 cm in thickness suppresses the diurnal fluctuations in thermal stress and therefore protects the ice from mechanical damage. We suggest that high‐amplitude diurnal cooling and weak ice properties due to weathering are essential factors that influence thermal fracturing in the Himalayan environment. The ongoing expansion of seismic networks into cryospheric regions, which will be capable of detecting local thermal‐contraction‐induced cracks, in combination with the fact that such cracks can erode and weaken the ice, and thereby serve as meltwater and heat channels, warrants further research to better understand these near‐surface processes and to monitor ice properties.

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Section: Methodsmentioning

confidence: 99%

Section: Thermal Stress Modelmentioning

confidence: 99%

\overset{τ}{true}

, within the upper centimeters of the layer under consideration, defined as

\overset{τ}{true} false(t false) \equiv \frac{\int_{d}^{d + l} τ_{+ false/ -} false(t, z false) normald z}{l},

Section: Thermal Stress Modelmentioning

confidence: 99%

Section: Other General Considerationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Viscoelastic Modeling of Nocturnal Thermal Fracturing in a Himalayan Debris‐Covered Glacier

et al. 2019

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Glacier structure influence on Himalayan ice‐front morphology

Peacey

Reynolds

Holt

et al. 2023

Earth Surf Processes Landf

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We investigate the role of glacier structures in controlling ice-front morphology and dynamics of four Himalayan lake-terminating glaciers over a 20-year period.At Imja, Trakarding, Lumdin and Dang Pu glaciers, lake area was mapped between 2000 and 2020 using Landsat 5/7/8 and Sentinel-2 imagery. Discrete glacier flow units were identified, with glacier structures (e.g., open crevasses, transverse structures, longitudinal structures) digitised using the finest resolution panchromatic bands in each year (30, 15, or 10 m). Mapping revealed a distinct pattern of transverse structures towards the terminus of each glacier that influence ice-front position and morphology and are then exploited via iceberg calving events. Our structural analysis also illustrates the role of subsurface conduits in calving events.During subsurface conduit collapse, glacier recession is enhanced, leading to calving along adjacent transverse structures. Furthermore, our analysis shows that ice-front morphology influences the pattern of glacier recession. Ice fronts with distinct ice aprons undergo slower periods of recession than ice fronts with ice cliffs. We conclude that glacier structures are important in determining ice-front morphologies at lake-terminating Himalayan glaciers, and therefore, structural analysis is vital when assessing future ice-front positions and behaviour, as well as rates of glacier recession.

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Persistent shallow micro-seismicity at Llaima volcano, Chile, with implications for long-term monitoring

Lamb

Lees

Franco-Marin³

et al. 2022

Journal of Volcanology and Geothermal Research

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Nocturnal Thermal Fracturing of a Himalayan Debris‐Covered Glacier Revealed by Ambient Seismic Noise

Cited by 29 publications

References 39 publications

Viscoelastic Modeling of Nocturnal Thermal Fracturing in a Himalayan Debris‐Covered Glacier

Viscoelastic Modeling of Nocturnal Thermal Fracturing in a Himalayan Debris‐Covered Glacier

Glacier structure influence on Himalayan ice‐front morphology

Persistent shallow micro-seismicity at Llaima volcano, Chile, with implications for long-term monitoring

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