Ice Stream C, Antarctica, sticky spots detected by microearthquake monitoring

Anandakrishnan, S.; Alley, Richard B.

doi:10.3189/172756494794587276

Cited by 57 publications

(45 citation statements)

References 17 publications

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“…Microseismicity observed with seismometers installed directly on ice streams has already been reported from Antarctica, in particular from the Whillans [ Anandakrishnan and Bentley , ], Kamb [ Anandakrishnan and Alley , ], and Rutford ice streams [ Smith , ; Smith et al , ]. Those events are very similar in their waveform pattern, range of magnitude (negative), and occurrence in clusters (swarms) to the stick‐slip icequakes observed on the GrIS.…”

Section: Discussionsupporting

confidence: 58%

“…P wave first‐motion polarity has been widely used to interpret source mechanisms of basal icequakes [e.g., Blankenship et al , ; Anandakrishnan and Bentley , ; Anandakrishnan and Alley , ; Zoet et al , ; Allstadt and Malone , ; J. I. Walter et al , ]. So‐called double‐couple source mechanisms exhibit radiation patterns divided into quadrants that depend on fault plane orientation.…”

Section: Deep Icequake Source Mechanismsmentioning

confidence: 99%

“…The majority of the 49 clusters located inside the network show mixed polarities corresponding to this low‐angle thrust fault along flow direction. This source mechanism is observed in Antarctica as stick‐slip motion of the glacial ice [e.g., Blankenship et al , ; Anandakrishnan and Alley , ; Zoet et al , ; Smith et al , ].…”

Section: Deep Icequake Source Mechanismsmentioning

confidence: 99%

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Meltwater influences on deep stick‐slip icequakes near the base of the Greenland Ice Sheet

et al. 2016

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We detected over 11,000 stick-slip icequakes near the base of the western margin of the Greenland Ice Sheet using a 17-seismometer array. These icequakes have negative (i.e., very small) moment magnitudes and, according to similarities in their waveforms, group into over 100 distinct clusters distributed beneath our 3 × 3 km study area. Some clusters were active for several weeks, while others have burst-like episodes lasting 1-6 days only. Some clusters correlate with subglacial water pressure measured within a nearby moulin. For these clusters, we observe high water pressure concurrent with many small yet numerous stick-slip icequakes and periods of lower water pressures with larger, less frequent icequakes. These patterns might change over time and are not common to all clusters. We explain these observations that the stick-slip icequakes are located at sticky spots at the interface of the ice sheet with the glacier bed that consists of basal till characterized by different connectivity to the subglacial drainage system. Because the till's frictional strength depends on its pore pressure, variations in subglacial water pressure can either weaken or strengthen the bed; this explains the variation in seismic moments and interevent times. Our results suggest that seismogenic stick-slip motion is an integral part of the flow mechanism in the ablation zone in western Greenland, which is highly sensitive to the configuration of the local subglacial drainage system. Stick-slip motion may therefore play a key role in the relationship between climate-induced changes of surface runoff and ice sheet dynamics.

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Section: Discussionsupporting

confidence: 58%

Section: Deep Icequake Source Mechanismsmentioning

confidence: 99%

Section: Deep Icequake Source Mechanismsmentioning

confidence: 99%

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Meltwater influences on deep stick‐slip icequakes near the base of the Greenland Ice Sheet

et al. 2016

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“…The acoustic impedance measurements here are consistent with this model being applicable to PIG, and as such indicate that basal conditions upstream will not inhibit further rapid retreat of PIG if the high‐friction region directly upstream of the grounding line, currently restraining flow, is breached. Furthermore, there is no evidence of “sticky spots” which increase basal drag, as observed, for example, beneath Rutford [ Smith et al ., ] or Kamb Ice Streams [ Anandakrishnan and Alley , ].…”

Section: Discussionmentioning

confidence: 99%

Bed conditions of Pine Island Glacier, West Antarctica

et al. 2017

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Although 90% of Antarctica's discharge occurs via its fast‐flowing ice streams, our ability to project future ice sheet response has been limited by poor observational constraints on the ice‐bed conditions used in numerical models to determine basal slip. We have helped address this observational deficit by acquiring and analyzing a series of seismic reflection profiles to determine basal conditions beneath the main trunk and tributaries of Pine Island Glacier (PIG), West Antarctica. Seismic profiles indicate large‐scale sedimentary deposits. Combined with seismic reflection images, measured acoustic impedance values indicate relatively uniform bed conditions directly beneath the main trunk and tributaries, comprising a widespread reworked sediment layer with a dilated sediment lid of minimum thickness 1.5 ± 0.4 m. Beneath a slow‐moving intertributary region, a discrete low‐porosity sediment layer of 7 ± 3 m thickness is imaged. Despite considerable basal topography, seismic observations indicate that a till layer at the ice base is ubiquitous beneath PIG, which requires a highly mobile sediment body to maintain an abundant supply. These results are compatible with existing ice sheet models used to invert for basal shear stress: existing basal conditions upstream will not inhibit further rapid retreat of PIG if the high‐friction region currently restraining flow, directly upstream of the grounding line, is breached. However, small changes in the pressure regime at the bed, as a result of stress reorganization following retreat, may result in a less‐readily deformable bed and conditions which are less likely to maintain high ice‐flow rates.

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“…Focusing on KIS here, hypotheses have generally involved loss of lubrication through some combination of drainage diversion, drainage concentration, or basal freeze‐on, leading to formation, expansion, or increased friction on “sticky spots” [ Alley , ; Anandakrishnan and Alley , ; Anandakrishnan and Bentley , ; Anandakrishnan and Alley , ; Anandakrishnan et al , ] while still leaving some basal water in places beneath the ice stream [ Atre and Bentley , ; Bentley et al , ; Catania et al , ; Engelhardt , ; Kamb , ]. Diversion of water from KIS to WIS (“water piracy”) was suggested as a mechanism to reduce the available water for KIS [ Alley et al , ; Anandakrishnan and Alley , ].…”

Section: Introductionmentioning

confidence: 99%

Characteristics of the sticky spot of Kamb Ice Stream, West Antarctica

et al. 2017

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Amplitude analysis of reflection seismic data reveals the presence of highly variable bed conditions under the main sticky spot and adjacent regions of the Kamb Ice Stream (formerly ice stream C). The sticky spot, which is a zone of bed that imparts high basal resistance to ice flow, is situated on a local topographic high composed of consolidated sediments or sedimentary rock. Any meltwater draining from upglacier along the base of the ice is routed around the sticky spot. The ice over the sticky spot includes, in at least some places, a seismically detectable basal layer containing a low concentration of debris, which locally thickens to 40 m over a topographic low in the bed. The ice‐contact basal material ranges from dilated and highly porous to more‐compacted and stiff, and perhaps locally frozen. The softer material is preferentially in topographic lows, but there is not a one‐to‐one correspondence between basal character and basal topography. We speculate that the 40 m thick frozen‐on debris layer formed by glaciohydraulic supercooling of lake‐drainage events along a basal channel during the former, active phase of the ice stream. We also speculate that loss of lubricating water, perhaps from piracy upstream, contributed to the slowdown of the ice stream, with drag from the sticky spot playing an important role, and with the basal heterogeneity greatly increasing after the slowdown of the ice stream.

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Ice Stream C, Antarctica, sticky spots detected by microearthquake monitoring

Cited by 57 publications

References 17 publications

Meltwater influences on deep stick‐slip icequakes near the base of the Greenland Ice Sheet

Meltwater influences on deep stick‐slip icequakes near the base of the Greenland Ice Sheet

Bed conditions of Pine Island Glacier, West Antarctica

Characteristics of the sticky spot of Kamb Ice Stream, West Antarctica

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