Localised thickening and grounding of an Antarctic ice shelf from tidal triggering and sizing of cryoseismicity

Pirli, Myrto; Hainzl, Sebastian; Schweitzer, Johannes; Köhler, Andreas; Dahm, Torsten

doi:10.1016/j.epsl.2018.09.024

Cited by 8 publications

(19 citation statements)

References 38 publications

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“…Hammer and others (2015) and Lombardi and others (2016) observed hybrid events and attributed their source triggering mechanisms to basal cracking and subsequent seawater filling that was analogous to the infiltration of meltwater under Alpine glaciers (West and others, 2010). Pirli and others (2018) observed seismic signals at a similar frequency, but they attributed the source mechanism to basal stick–slip motion between the ice shelf and a sub-shelf pinning point. Our GNSS observations demonstrated that the vertical ice motion was in phase with the tidal variation (Fig.…”

Section: Discussionmentioning

confidence: 97%

“…Compared with other PSD-PDFs, only the falling tides produce this relatively narrow, localized peak. There are two possible source mechanisms: i) basal friction along unknown pinning points (e.g., Pirli and others, 2018) or near the grounding line due to the high ice flow speed (Aðalgeirsdóttir and others, 2008), and ii) surface cracking due to an enhanced longitudinal strain rate and tension due to vertical bending (Barruol and others, 2013; Podolskiy and others, 2016). Our GNSS measurements indicate that the vertical and along-flow ice flow speed and the longitudinal strain rate reach their maxima during the falling tide at Langhovde Glacier (Figs 2b and 8).…”

Section: Discussionmentioning

confidence: 99%

“…These studies hypothesized that the observed icequakes were generated by basal processes, such as the opening of basal crevasses due to ice-shelf bending. A seismic array was also deployed near the ice-front of Fimbul Ice Shelf, East Antarctica, where Pirli and others (2018) suggested that a stick–slip motion generated low-frequency seismicity (2–6 Hz) during rising tides at the ice/rock interface, where the ice shelf was locally grounded. These examples suggest that the physical mechanisms generating tide-modulated icequakes vary greatly (for more examples, see Podolskiy and others 2016).…”

Section: Introductionmentioning

confidence: 99%

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Tide-modulated ice motion and seismicity of a floating glacier tongue in East Antarctica

Minowa¹,

Podolskiy

Sugiyama

2019

Ann. Glaciol.

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We recorded the ice motion and icequakes on the floating part of Langhovde Glacier in East Antarctica to better understand the dynamic behavior of ice shelves and floating tongues. Diurnal and semi-diurnal variations in ice motion and seismicity were simultaneously observed at all four global navigation satellite system and three seismic stations over 2 weeks. The short-term along-flow ice motion is explained by the elastic response of the glacier to ocean tide-induced hydrostatic stress variations, which decayed at a rate of 0.8 km−1 toward the grounding line. We observed a large number of icequakes during mid-rising and high tides that covered a broad frequency range and formed two major groups of events centered at 10 and 120 Hz, respectively. The hourly occurrence rates were ~500 events h−1, with the observed seismicity consistent with fracture due to floating tongue bending. We also observed minor secondary peaks at high ice speeds, which could reflect surface cracking due to stretching or basal friction. Our observation demonstrates that tidal-modulation was the main factor to fracture the floating tongue of Langhovde Glacier.

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Section: Discussionmentioning

confidence: 97%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Tide-modulated ice motion and seismicity of a floating glacier tongue in East Antarctica

Minowa¹,

Podolskiy

Sugiyama

2019

Ann. Glaciol.

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“…One possible nonlinear mechanism is that vertical tidal motion causes the grounding line to migrate back and forth sufficiently far as to have an effect on ice flow. Evidence of tidal migration of grounding lines remains relatively sparse but measurements of this process have been inferred via remote sensing (Schmeltz et al, 2001;Brunt et al, 2011;Milillo et al, 25 2017) and cryoseismicity (Pirli et al, 2018). This could give rise to several nonlinearities: firstly this can result in the width of the ice shelf changing as the portion of floating ice changes over one tidal cycle (Minchew et al, 2016).…”

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confidence: 99%

Exploring mechanisms responsible for tidal modulation in flow of the Filchner-Ronne Ice Shelf

Rosier¹,

Gudmundsson²

2019

Preprint

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An extensive network of GPS sites on the Filchner-Ronne Ice Shelf and adjoining ice streams show strong tidal modulation of horizontal ice flow at a range of frequencies. A particularly strong (horizontal) response is found at the fortnightly (M sf ) frequency. Since this tidal constituent is absent in the (vertical) tidal forcing, this observation implies the action of some nonlinear mechanism. Another striking aspect is the strong amplitude of the flow perturbation, causing a periodic reversal in the direction of ice shelf flow in some areas, and a 10-20% change in speed at grounding lines. No model has yet been able 5 to reproduce the quantitative aspects of the observed tidal modulation on the Filchner-Ronne Ice Shelf. The cause of the tidal response has therefore remained an enigma, indicating a serious limitation in our current understanding of the mechanics of large-scale ice flow. A further limitation of previous studies is that they have all focused on isolated regions and interactions between different areas have, therefore, not been fully accounted for. Here, we conduct the first large-scale ice-flow modelling study to explore these processes using a viscoelastic rheology and realistic geometry of the entire Filchner-Ronne ice shelf, 10 where the best observations of tidal response are available. We evaluate all the relevant mechanisms that have hitherto been put forward to explain how tides might affect ice-shelf flow and compare our results with observational data. We conclude that, while some are able to generate the correct general qualitative aspects of the tidally-induced perturbations in ice flow, most of these mechanisms must be ruled out as being the primary cause of the large observed nonlinear response. We find that only tidally-induced lateral migration of grounding lines can generate a sufficiently strong long-periodic M sf response on the ice 15 shelf to match observations. Furthermore, we show that the observed short-periodic diurnal tidal motion, causing twice-daily flow reversals at the ice front, can be generated through a purely elastic response to basin-wide tidal perturbations in the ice shelf slope. This model also allows us to quantify the effect of tides on mean ice flow and we find that the Filchner-Ronne Ice Shelf flows on average ∼21% faster than it would in the absence of large ocean tides.

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“…Antarctic ice shelves have also been shown to respond mechanically to both ocean tides as well as tele-tsunamis and distantly generated ocean infragravity waves. Pirli et al (2018) showed that rates and magnitudes of cryogenic earthquakes at the Fimbul Ice Shelf (East Antarctica) fluctuate steadily with the cycles of the ocean tide, showing correlations with tide height and spring tides as well as migration of icequakes landwards during the rising tide. Adalgeirsdottir et al (2008) showed the basal seismicity and velocity of an Antarctic ice stream respond to tidal forcing as far as 40 km upstream.…”

Section: Discussionmentioning

confidence: 99%

Hydroacoustic, Meteorologic and Seismic Observations of the 2016 Nansen Ice Shelf Calving Event and Iceberg Formation

et al. 2019

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On April 7, 2016 the Nansen ice shelf (NIS) front calved into two icebergs, the first largescale calving event in >30 years. Three hydrophone moorings were deployed seaward of the NIS in December 2015 and over the following months recorded hundreds of short duration, broadband (10-400 Hz) cryogenic signals, likely caused by fracturing of the ice shelf. The majority of these icequakes occurred between January and early March 2016, several weeks prior to the calving observed by satellite on April 7. Barometric pressure and wind speed records show the day the icebergs drifted from the NIS coincided with the largest low-pressure storm system recorded in the previous 7 months. A nearby seismic station also shows an increase in low-frequency energy, harmonic tremor, and microseisms on April 7. Our interpretation is the northern segment of the NIS leading edge broke free during mid-January to February, producing high acoustic energy, but the icebergs remained stationary until a strong low-pressure system with high winds freed the icebergs. As the unpinning of Antarctic ice shelves is not a well-documented process, our observations show that storm systems may play an under-appreciated role in Antarctic ice shelf break-up.

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Localised thickening and grounding of an Antarctic ice shelf from tidal triggering and sizing of cryoseismicity

Cited by 8 publications

References 38 publications

Tide-modulated ice motion and seismicity of a floating glacier tongue in East Antarctica

Tide-modulated ice motion and seismicity of a floating glacier tongue in East Antarctica

Exploring mechanisms responsible for tidal modulation in flow of the Filchner-Ronne Ice Shelf

Hydroacoustic, Meteorologic and Seismic Observations of the 2016 Nansen Ice Shelf Calving Event and Iceberg Formation

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