Sediment transport drives tidewater glacier periodicity

Brinkerhoff, Douglas; Truffer, Martin; Aschwanden, Andy

doi:10.1038/s41467-017-00095-5

Cited by 64 publications

(111 citation statements)

References 46 publications

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“…The classical view of the tidewater glacier cycle holds that climate plays a weak role in tidewater glacier advance and retreat (Meier & Post, ; Post, ) and that, especially during retreat, glacier behavior is independent of the climatic mass balance (Pfeffer, ). However, if the advance and retreat phases of the tidewater glacier cycle are truly independent of climate, then the vast majority of tidewater glaciers should be advancing at any given time (Brinkerhoff et al, ; IPCC, ; Post et al, ). This expectation is inconsistent with observations of widespread tidewater glacier retreat throughout the Arctic (Carr et al, ), even in Greenland (Howat & Eddy, ), where the vast interior ice sheet reservoir enables quick recovery of glaciers from retreat (Howat et al, ; Joughin et al, ).…”

Section: Introductionmentioning

confidence: 99%

Evolving Environmental and Geometric Controls on Columbia Glacier's Continued Retreat

et al. 2018

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Geometry strongly controls the dynamic behavior of marine‐terminating (tidewater) glaciers, significantly influencing advance and retreat cycles independent of climate. Yet the recent, nearly ubiquitous retreat of tidewater glaciers suggests that changes in atmospheric and oceanic forcing may also drive dynamic change. To isolate the influence of geometry on tidewater glacier dynamics, we analyzed detailed observational time series from 2012 to 2016 for two tidewater glaciers with shared dynamic histories and environmental forcing: Columbia Glacier and its former tributary (Post Glacier) in southcentral Alaska. We find that although terminus retreat has driven decadal‐scale changes in dynamics of the Columbia‐Post system, environmental factors contribute to short‐term (i.e., seasonal) dynamic variability. In particular, analysis of force balance time series indicates that observed variations in speed result from seasonal changes to the subglacial hydrologic system and associated changes in basal drag. Variations in terminus position only drive noticeable speed change when the terminus retreats from regions of relatively high basal drag. In agreement with long‐term analyses of Columbia Glacier, we find that terminus geometry can perturb the timing of seasonal ice flow patterns. Specifically, our data support the idea that retreat of a glacier terminus into deeper water is accompanied by a shift in the primary control on frontal ablation. Although our analysis focuses on two Alaskan glaciers, our data suggest that changes in the relative importance of surface meltwater and buoyancy effects on submarine melting and/or calving may manifest as a shift in terminus change seasonality and offer a mechanism to identify frontal ablation controls.

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Section: Introductionmentioning

confidence: 99%

Evolving Environmental and Geometric Controls on Columbia Glacier's Continued Retreat

et al. 2018

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“…Tidewater glaciers are unstable if the toe of the glacier approaches flotation (e.g., Post et al, ). Thus, addition of sediment in front of the toe of this tidewater glacier allows for it to advance (Brinkerhoff et al, ). A comparison of landslide and shoreline positions from 25 October 2015 to 29 May 2016 shows how the glacier advanced by up to 300 m (Figures and ).…”

Section: Resultsmentioning

confidence: 99%

Submarine Deposition of a Subaerial Landslide in Taan Fiord, Alaska

et al. 2018

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A large subaerial landslide entered Taan Fiord, Alaska, on 17 October 2015 producing a tsunami with runup to 193 m. We use LiDAR data to show the slide volume to be 76 + 3/−4 million cubic meters and that 51,000,000 m3 entered Taan Fiord. In 2016, we mapped the fjord with multibeam bathymetry and high‐resolution seismic data. Landslide and postlandslide deposits extend 6 km downfjord, are up to 70 ± 11 m thick, and have a total volume of ~147,000,000 m3. Seismic data image a blocky landslide unit and two units deposited immediately after the landslide. The blocky landslide unit is ~65,000,000 m3. We infer it consists dominantly of subaerially derived material and secondarily of fjord floor sediment. The overlying units are likely megaturbidites presumably deposited within minutes to days after the landslide. We infer that these deposits dominantly consist of fjord floor material mobilized and suspended as the slide entered and traveled downfjord. The lower postlandslide unit is up to 35 ± 6 m thick, and the upper unit is up to 12 ± 3 m thick. These deposits are distinctive and will leave a lasting record of the event. This subaerial‐to‐submarine landslide deposit is distinct from other submarine landslide deposits studied in Alaskan fjords because it has a much greater thickness, larger and more angular blocks, distinctive postlandslide megaturbidites, and a higher‐amplitude acoustic signature of the blocky deposit. The tight constraints on the landslide source and deposit volumes, topography, bathymetry, and tsunami runup heights and flow directions should make this a benchmark site for landslide‐tsunami models.

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“…This glacial advance may either have been climate‐triggered (cooling) or, alternatively, originated from a reduction of the water depth. Such a shallowing could have either been due to a RSL fall forced by a GIA consecutive to the ice‐margin retreat and/or to the accumulation of sediments in front of the grounding zone and possibly underneath the floating ice shelf that would have permitted the anchoring of the ice and then its advance (Alley et al , ; Anandakrishnan et al , ; Brinkerhoff et al , ; Batchelor et al , ). It is here thought that positive feedback existed between pre‐glacial topography, ice‐margin stabilization and deposition of sediments: ice anchorage and position of the grounding zone immediately after the initial ice‐margin retreat were at least partly controlled by bedrock pinning points, which in turn also controlled the position of the GZWs themselves, acting to further stabilize the ice margin and even permitting its autogenic re‐advance.…”

Section: Discussionmentioning

confidence: 99%

Ice‐margin fluctuation sequences and grounding zone wedges: The record of the Late Palaeozoic Ice Age in the eastern Karoo Basin (Dwyka Group, South Africa)

Dietrich

Hofmann

2019

The Depositional Record

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In the eastern part of the Karoo Basin of South Africa, the sedimentary record of the Late Palaeozoic Ice Age, the Dwyka Group, consists of an up to 200 m thick accumulation of massive to crudely stratified diamictite occasionally interstratified with siltstone, sandstone and conglomerate horizons. Three distinct sedimentary units, separated by intervening glacial erosion surfaces, are viewed as ice‐margin fluctuation sequences. The lowermost one, resting on highly uneven, glacially abraded Archaean basement, has been interpreted as a grounding zone wedge deposited after the retreat and stabilization of the ice margin after the inundation of the Karoo Basin. The grounding zone wedge interpretation is based on its thickness (up to 100 m), the dominance of diamictite, and its facies assemblage and inferred depositional processes (rain‐out of debris, dropstone dumping, mass and debris flow, till). Overlying the grounding zone wedge, deposits are sedimentary units interpreted as glaciofluvial or ice‐contact delta and grounding zone wedges, respectively. By analogy with Quaternary sedimentary sequences, deposition of the Dwyka Group in the study area might have been very rapid (tens to hundreds of thousand years) and may hence correlate with the ultimate deglacial sequence of the Western Karoo Basin, as both successions are covered by the postglacial Ecca Group. Although commonly observed and imaged on modern, high‐latitude continental shelves, grounding zone wedges have never been interpreted in the ancient geological record. This paper therefore outlines a model defining criteria necessary for their identification.

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Sediment transport drives tidewater glacier periodicity

Cited by 64 publications

References 46 publications

Evolving Environmental and Geometric Controls on Columbia Glacier's Continued Retreat

Evolving Environmental and Geometric Controls on Columbia Glacier's Continued Retreat

Submarine Deposition of a Subaerial Landslide in Taan Fiord, Alaska

Ice‐margin fluctuation sequences and grounding zone wedges: The record of the Late Palaeozoic Ice Age in the eastern Karoo Basin (Dwyka Group, South Africa)

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