Exceptional ablation arising from rainfall- induced slushflows: Brewster Glacier, New Zealand

Smart, C. C.; Owens, I. F.; Lawson, Wendy; Morris, Ashley

doi:10.1002/(sici)1099-1085(20000430)14:6<1045::aid-hyp995>3.0.co;2-9

Cited by 10 publications

(7 citation statements)

References 21 publications

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“…All of the floods are associated with precipitation events. Often warm rainfall is supplemented by sensible heat transfer (Marcus et al, 1985), and local firn runoff is supplemented by slush flows (Smart et al, 2000). Outburst events involving sediment seem to be associated with glacier advance, especially when the glacier overlies the sediment fill in the lower valley.…”

Section: Outburst Events and Associated Sediment Depositionmentioning

confidence: 88%

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Water and sediment outbursts from advanced Franz Josef Glacier, New Zealand

Davies

Smart

Turnbull³

2003

Earth Surf Processes Landf

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The Franz Josef Glacier, Westland, New Zealand, has a history of catastrophic sediment-laden outburst floods associated with extreme rainfall events when the glacier toe is advanced over its own sediments. Consideration of these events and inspection of recent sediment deposits suggest that there are three distinct modes of outburst. The first is associated with fans fed by overflow along the glacier margin. As the glacier has advanced across its own forefield gravels, it is inferred that the primary drainage conduit has developed a reach of negative slope. In high flows massive boulders can block the conduit, trapping lesser clasts. The resulting backup of water causes overflows through marginal moulins, producing the fan type of deposit.The second type of outburst deposits massive imbricated boulders at a greater or lesser distance from the glacier portal. In this case, pressure buildup drives the blockage out of the portal where the boulders deposit. Smaller materials are generally carried away.The third type consists of very shallow flows, and produces massive gravel deposits of uncertain provenance. In this condition, the excess pressure in the conduit results in slight uplift of the glacier and widespread discharge of water and sediment below the glacier snout; gravels and smaller sediments are laid down in a massive deposit across the forefield.The massive, boulder-veneered deposit from the December 1995 outburst is interpreted in the light of the above mechanisms as a hyperconcentrated flow deposit from hydraulic jacking, overlain by boulders emplaced by a subsequent conduit outburst. A possible association of outbursts with the present advanced position of the glacier is suggested.

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Section: Outburst Events and Associated Sediment Depositionmentioning

confidence: 88%

“…In some cases the water source may be inferred to lie beneath the glacier (e.g. Driedger and Fountain, 1989;Nye, 1976;Walder and Driedger, 1994;Haeberli, 1983) or there may be no obvious reservoir (Jackson et al, 1989;Smart et al, 2000). Ice-cavity outburst events reported in Europe occur Figure 1.…”

Section: Glacier Outburst Floods -Origins and Sedimentsmentioning

confidence: 99%

Water and sediment outbursts from advanced Franz Josef Glacier, New Zealand

Davies

Smart

Turnbull³

2003

Earth Surf Processes Landf

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“…Several studies of mass balance, ablation and climate sensitivity have been conducted on Brewster Glacier (Morris, 1997;Smart et al, 2000;George, 2005;Anderson et al, 2010). Brewster Glacier is also 1 of 50 index glaciers in the Southern Alps that has been surveyed using oblique aerial photography since 1977 to determine end of summer snowlines (Chinn et al, 2005a;Willsman et al, 2007), which have been used as a proxy for mass balance, suggesting that Brewster Glacier has experienced a positive mass balance in 16 of the 24 years it has been monitored (Chinn et al, 2006).…”

Section: Field Site and Data Collectionmentioning

confidence: 99%

Atmospheric controls on summer ablation over Brewster Glacier, New Zealand

Gillett

Cullen

2010

Intl Journal of Climatology

107

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Micrometeorological data collected from an automatic weather station over a total of 85 days during the summer of 2007/2008 in the ablation zone (1770 m a.s.l.) of the Brewster Glacier, New Zealand, were used to determine the main atmospheric processes controlling the magnitude and variability of daily ablation. During the field season, ablation was measured and modelled using an energy balance model (EBM) and a degree-day model (DDM). Calculation of the energy balance over the glacier using the EBM revealed that net radiation provided the largest source of energy for ablation (52%). The turbulent sensible heat flux was the next largest energy source (25%), followed by the turbulent latent heat flux (20%) and the rain heat flux (3%). While daily measured and modelled (EBM) ablation were both equal to approximately 40 mm w.e. d −1 , the EBM was used to demonstrate that rates were highly variable, ranging from less than 10 mm w.e. d accounted for almost 25% of total ablation, despite such events occurring on only 11 of the 85 days monitored. The contribution of the individual terms of the energy balance to observed air temperature is complex on Brewster Glacier, leading to a larger uncertainty in DDM ablation estimates (under prediction of total ablation by 11%). Advection of warm and moisture-laden air over Brewster Glacier, which is not uncommon given its close proximity to the ocean, is not well accounted for by the DDM. This is because the turbulent latent heat flux and the rain heat flux are poorly correlated to air temperature but are, nonetheless, important sources of energy during large ablation events.

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“…Thiel (1986) used a low frequency surface-impedance radar to measure a maximum ice depth of ¾100 m along one transverse of the glacier. Smart et al (2000) report on an exceptional ablation event across the glacier tongue due to snowpack saturation by rainfall followed by slushflows. The event occurred over 26 days during which ¾5 m of surface lowering released over 1Ð6 ð 10 6 m 3 of water.…”

Section: Field Sitementioning

confidence: 99%

Subglacial drainage system structure and morphology of Brewster Glacier, New Zealand

Willis

Lawson

Owens

et al. 2008

Hydrological Processes

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Abstract:A global positioning system and ground penetrating radar surveys is used to produce digital elevation models of the surface and bed of Brewster Glacier. These are used to derive maps of subglacial hydraulic potential and drainage system structure using three different assumptions about the subglacial water pressure (P w ): (i) P w D ice overburden; (ii) P w D half ice overburden; (iii) P w D atmospheric. Additionally, 16 dye-tracing experiments at 12 locations were performed through a summer melt season. Dye return curve shape, together with calculations of transit velocity, dispersivity and storage, are used to infer the likely morphology of the subglacial drainage system. Taken together, the data indicate that the glacier is underlain by a channelised but hydraulically inefficient drainage system in the early summer in which water pressures are close to ice overburden. By mid-summer, water pressures are closer to half-ice overburden and the channelised drainage system is more hydraulically efficient. Surface streams that enter the glacier close to the location of major subglacial drainage pathways are routed quickly to the channels and then to the glacier snout. Streams that enter the glacier further away from the drainage pathways are routed slowly to the channels and then to the snout because they first flow through a distributed drainage system.

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Exceptional ablation arising from rainfall- induced slushflows: Brewster Glacier, New Zealand

Cited by 10 publications

References 21 publications

Water and sediment outbursts from advanced Franz Josef Glacier, New Zealand

Water and sediment outbursts from advanced Franz Josef Glacier, New Zealand

Atmospheric controls on summer ablation over Brewster Glacier, New Zealand

Subglacial drainage system structure and morphology of Brewster Glacier, New Zealand

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