Magnetic fabrics in the basal ice of a surge-type glacier

Fleming, Edward J.; Lovell, Harold; Stevenson, Carl; Petronis, Michael; Benn, Douglas I.; Hambrey, Michael J.; Fairchild, Ian J.

doi:10.1002/jgrf.20144

Cited by 19 publications

(51 citation statements)

References 85 publications

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“…Tectonic deformation is evident within the thin debris laminae in the dispersed facies, which often display a strong linear component indicative of shear (Figure 3b). Such features within basal ice sequences have been termed stretching lineations [e.g., Fleming et al, 2013;Lovell et al, 2015] and are similar to stringers commonly described from glacitectonized sediments [e.g., Roberts and Hart, 2005].…”

Section: Dispersed Faciesmentioning

confidence: 91%

“…Distributions of ice facies and debris-rich structures exposed within terrestrially grounded ice cliffs at the NW and SE margins of Tunabreen were recorded as two-dimensional logs (Figure 2; see Fleming et al [2013] for section photographs). Ice facies classification was based on physical characteristics following Hubbard et al [2009], including overall facies thickness, structure, debris concentration, and bubble content (Table 1).…”

Section: Methodsmentioning

confidence: 99%

“…We build on work at this site by Fleming et al [2013], who used anisotropic magnetic susceptibility (AMS) to derive fabric data from the basal ice and linked this to surge ice flow dynamics.…”

Section: Research Aimsmentioning

confidence: 99%

“…The translucent nature of the clean ice layers within the banded facies is advantageous as it often allows folds to be observed in three dimensions, and various types are evident, ranging from steeply inclined to recumbent (Figure 3f), with tight to isoclinal interlimb angles and typically asymmetrical limbs. Boudinage is also common within the banded subfacies, forming augen-like rings of debris within the host englacial facies (e.g., Figure 10a in Fleming et al [2013]). The vergence direction of the folds is variable and in some cases appears to be in two opposite directions when viewed in the two-dimensional ice face, implying that the fold hinges are curvilinear (Figure 7g).…”

Section: 1002/2015jf003509mentioning

confidence: 99%

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Debris entrainment and landform genesis during tidewater glacier surges

et al. 2015

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The englacial entrainment of basal debris during surges presents an opportunity to investigate processes acting at the glacier bed. The subsequent melt-out of debris-rich englacial structures during the quiescent phase produces geometrical ridge networks on glacier forelands that are diagnostic of surge activity. We investigate the link between debris entrainment and proglacial geomorphology by analyzing basal ice, englacial structures, and ridge networks exposed at the margins of Tunabreen, a tidewater surge-type glacier in Svalbard. The basal ice facies display clear evidence for brittle and ductile tectonic deformation, resulting in overall thickening of the basal ice sequence. The formation of debris-poor dispersed facies ice is the result of strain-induced metamorphism of meteoric ice near the bed. Debris-rich englacial structures display a variety of characteristics and morphologies and are interpreted to represent the incorporation and elevation of subglacial till via the squeezing of till into basal crevasses and hydrofracture exploitation of thrust faults, reoriented crevasse squeezes, and preexisting fractures. These structures are observed to melt-out and form embryonic geometrical ridge networks at the base of a terrestrially grounded ice cliff. Ridge networks are also located at the terrestrial margins of Tunabreen, neighboring Von Postbreen, and in a submarine position within Tempelfjorden. Analysis of network characteristics allows these ridges to be linked to different formational mechanisms of their parent debris-rich englacial structures. This in turn provides an insight into variations in the dominant tectonic stress regimes acting across the glacier during surges.

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Section: Dispersed Faciesmentioning

confidence: 91%

Section: Methodsmentioning

confidence: 99%

Section: Research Aimsmentioning

confidence: 99%

Section: 1002/2015jf003509mentioning

confidence: 99%

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Debris entrainment and landform genesis during tidewater glacier surges

et al. 2015

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“…9d), or stretching lineation (Fleming and others, 2013), indicative of shear in the direction of ice flow (Table 2; Fig. 9i-k).…”

Section: Arcuate Shear Planes (S 2 )mentioning

confidence: 99%

Former dynamic behaviour of a cold-based valley glacier on Svalbard revealed by basal ice and structural glaciology investigations

et al. 2015

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ABSTRACT. Large numbers of small valley glaciers on Svalbard were thicker and more extensive during the Little Ice Age (LIA), demonstrated by prominent ice-cored moraines up to several kilometres beyond present-day margins. The majority of these glaciers have since experienced a long period of strongly negative mass balance during the 20th century and are now largely frozen to their beds, indicating they are likely to have undergone a thermal transition from a polythermal to a cold-based regime. We present evidence for such a switch by reconstructing the former flow dynamics and thermal regime of Tellbreen, a small cold-based valley glacier in central Spitsbergen, based on its basal sequence and glaciological structures. Within the basal sequence, the underlying matrix-supported diamict is interpreted as saturated subglacial traction till which has frozen at the bed, indicating that the thermal switch has resulted in a cessation of subglacial sediment deformation due to freezing of the former deforming layer. This is overlain by debris-poor dispersed facies ice, interpreted to have formed through strain-induced metamorphism of englacial ice. The sequential development of structures includes arcuate fracture traces, interpreted as shear planes formed in a compressive/transpressive stress regime; and fracture traces, interpreted as healed extensional crevasses. The formation of these sediment/ice facies and structures is indicative of dynamic, warm-based flow, most likely during the LIA when the glacier was significantly thicker.

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Thermal structure of Svalbard glaciers and implications for thermal switch models of glacier surging

et al. 2015

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Switches between cold‐ and warm‐based conditions have long been invoked to explain surges of High Arctic glaciers. Here we compile existing and new data on the thermal regime of six glaciers in Svalbard to test the applicability of thermal switch models. Two of the large glaciers of our sample are water terminating while one is land terminating. All three have a well‐known surge history. They have a thick basal layer of temperate ice, superimposed by cold ice. A cold terminus forms during quiescence but is mechanically removed by calving on tidewater glaciers. The other three glaciers are relatively small and are either entirely cold or have a diminishing warm core. All three bear evidence of former warm‐based thermal regimes and, in two cases, surge‐like behavior during the Little Ice Age. In Svalbard, therefore, three types of glaciers have switched from slow to fast flow: (1) small glaciers that underwent thermal cycles during and following the Little Ice Age (switches between cold‐ and warm‐based conditions), (2) large terrestrial glaciers which remain warm based throughout the entire surge cycle but develop cold termini during quiescence, and (3) large tidewater glaciers that remain warm based throughout the surge cycle. Our results demonstrate that thermal switching cannot explain the surges of large glaciers in Svalbard. We apply the concept of enthalpy cycling to the spectrum of surge and surge‐like behavior displayed by these glaciers and demonstrate that all Svalbard surge‐type glaciers can be understood within a single conceptual framework.

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Magnetic fabrics in the basal ice of a surge-type glacier

Cited by 19 publications

References 85 publications

Debris entrainment and landform genesis during tidewater glacier surges

Debris entrainment and landform genesis during tidewater glacier surges

Former dynamic behaviour of a cold-based valley glacier on Svalbard revealed by basal ice and structural glaciology investigations

Thermal structure of Svalbard glaciers and implications for thermal switch models of glacier surging

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