Seasonal Variation in Ablation and Surface Velocity on a Temperate Maritime Glacier: Fox Glacier, New Zealand

Abstract

Seasonal variations in ablation and surface velocity were investigated on the lower part of Fox Glacier, South Westland, New Zealand. A large variation between summer and winter ablation was recorded, with daily averages of 129 mm d 21 and 22 mm d 21 , respectively. Variations in measured climatic variables were found to account for ,90% of variation in ablation during both summer and winter seasons, with significant increases in ablation occurring in conjunction with heavy rainfall events. Surface velocity also showed seasonality, averaging 0.87 m d 21 during summer and 0.64 m d 21 in winter, a reduction of ,26%. It is thought that the general reduction in velocity during winter can be attributed to a decrease in the supply of surface meltwater to the subglacial zone. Short-term velocity peaks appeared to coincide with heavy rainfall events, with surface velocity responses typically occurring within 24 hours of each rainfall event. During winter, moderate rainfall events (#100 mm over 24 hours) created a surface velocity response up to 44% greater than the prevailing velocity. Though difficult to deconvolve, magnitudes of surface velocity response to rainfall inputs appear linked to time lags between rainfall events and subglacial drainage efficiency and water storage. The longer-term dynamics of Fox Glacier appear linked to fluctuations in the Southern Oscillation Index (SOI), with positive mass balances of Southern Alps' glaciers appearing to mirror negative SOI (El Niñ o) conditions. Given the calculated response time of ,9.1 years for Fox Glacier, the current terminus advance may be linked to mass gains reported in the mid-1990s, with current mass balance gains perhaps leading to terminus advances ,9 years hence.

Structural glaciology of a temperate maritime glacier: lower fox glacier, new zealand

“…Transverse crevasses are visible at the top of the lower icefall, due to longitudinal extension as flow accelerates down the icefall. As ice descends the lower icefall, rapid surface melt (c. 13 cm d -1 ; Purdie et al 2008a) means that crevasse morphology becomes obscured due to sérac development on the intervening ablating ice units. Longitudinal crevasses form in the Victoria Flat basin, due to lateral extension in this wider valley segment (Fig.…”

Subglacial till behaviour derived from in situ wireless multi-sensor subglacial probes: Rheology, hydro-mechanical interactions and till formation

“…The largest case stress maxima relate (within a 2 day lag period) to variations in external weather conditions. We suggest that, during the winter, surface water, generated from rainfall or surface melt, takes a long time to pass through the glacier since the majority of englacial pathways have closed and the glacier is snow covered (Roberts et al, 2006;Purdie et al, 2008). The water that does reach the subglacial environment may cause an increase in glacier velocity (Iken et al, 1983;Mair et al, 2001;Bartholomaus et al, 2008;Walter et al, 2008).…”

Modeling Glacier Elevation Change from DEM Time Series

“…Franz Josef and Fox Glaciers are very maritime with assumed precipitation rates of up to 12 m· w.e.a −1 [19][20][21][22]. Ablation at the tongues is substantial at all seasons with a mean summer ablation of ~130 mm· d −1 and a mean winter ablation of ~20 mm· d −1 , i.e., several tens of meters as annual sum [23]. The two glaciers are believed to react especially sensitive to temperature variations, with reaction and response times of only around 3-4 and 10-20 years, respectively [22][23][24].…”

“…Ablation at the tongues is substantial at all seasons with a mean summer ablation of ~130 mm· d −1 and a mean winter ablation of ~20 mm· d −1 , i.e., several tens of meters as annual sum [23]. The two glaciers are believed to react especially sensitive to temperature variations, with reaction and response times of only around 3-4 and 10-20 years, respectively [22][23][24]. Glacier elevation close to the tongues is able to change by many tens of meters within just a few years, and lateral terminus position by several hundred meters [15,25].…”