The equilibrium flow and mass balance of the Taku Glacier, Alaska 1950–2006

Abstract

Abstract. The Taku Glacier, Alaska has advanced 7.5 km since the late nineteenth century, while all other primary outlet glaciers of the Juneau Icefield are in retreat. The Juneau Icefield Research Program has completed field work on the Taku Glacier annually since 1946. The collected observations of surface mass balance, glacier velocity and glacier thickness at Profile IV 29 km above the terminus and 4 km above the equilibrium line provide a means to assess the equilibrium nature of the Taku Glacier. Velocity measured over a twelve month span and annual summer velocity measurements completed at a Profile IV from 1950–2006 indicate insignificant variations in velocity seasonally or from year to year. The consistency of velocity over the 56-year period indicates that in the vicinity of the equilibrium line, the flow of the Taku Glacier has been in an equilibrium state. Surface mass balance was positive from 1946–1988 averaging +0.42 m a−1. This led to glacier thickening. From 1988–2006 an important change has occurred and annual balance has been −0.14 m a−1, and the glacier thickness has ceased increasing along Profile IV. Field measurements of ice depth and surface velocity allow calculation of the volume flux at Profile IV. Volume flux is then compared with the surface balance flux from the region of the glacier above Profile IV, determined annually in the field. Above Profile IV the observed mean surface flux is 5.50×108 m3/a (±5%), while the calculated volume flux range flowing through profile IV is 5.00–5.47×108 m3/a. The mean surface flux has been greater than the volume flux, which has led to slow thickening of the Taku Glacier up to 1988. The thickening has not led to a change in the flow of Taku Glacier at Profile IV.

Seismic Tremor Reveals Spatial Organization and Temporal Changes of Subglacial Water System

“…We also assume that ice melt is the only melt that contributes to water input and that ice melt is not stored englacially before entering the subglacial water system. Although snowmelt just above the snow line likely contributes to the subglacial water system, we expect that most meltwater from snow either refreezes as it percolates through the snowpack or is otherwise stored in a densifying snowpack in the majority of the glacier's accumulation area (Pelto et al, ). Due to our inability to specify the elevation at which snowmelt storage in the snowpack stops, we omit it all together.…”

“…Glacier‐deployed sensors outside their tilt tolerances, instrumentation failures, power failures, and wildlife damage limited the number of usable stations to seven, each of which suffered from data gaps. All seven of the working seismic stations (Figure ) were deployed below the glacier's equilibrium line altitude (found near 925 m; Pelto et al, ), with the highest elevation station, TWLV (named for the nearby approximately 1,200‐m ice thickness, Nolan et al, ), at approximately 600‐m elevation. Each station consisted of Nanometric Meridian Compact Posthole sensors, with 120‐s low‐frequency corners and sampled at 200 Hz.…”

Satellite-derived volume loss rates and glacier speeds for the Juneau Icefield, Alaska

“…It continues to advance due to the long history of positive mass balance (e.g. Pelto and Miller, 1990; Post and Motyka, 1995; Pelto and others, 2008, 2013), and ASTER imagery shows the front advancing from 2002 to 2009 to 2010, with roughly 100–200 m of total advance from 2002 to 2010.…”

Rising ELA and expanding proglacial lakes indicate impending rapid retreat of Brady Glacier, Alaska

“…Brady Glacier and Taku and Baird glaciers are the only land terminating glaciers in southeast Alaska that did not significantly retreat between 1950 and 2000 (Molnia, ). Taku Glacier has maintained a generally positive mass balance (Pelto et al ., ), while Baird Glacier is thinning and appears poised to begin a retreat (Molnia, ). Brady Glacier is unique among these glaciers because it presently dams at least ten proglacial lakes, each greater than ≥1 km 2 , seven of which are examined here.…”