Introduction and Aims

Alpine glaciers act as natural reservoirs, storing water during winter & releasing it during summer. As glaciers shrink in response to climate change, a valuable resource is lost. To predict the details of how specific glaciers will shrink in the future, numerical models linking glacier climate, mass balance and dynamics are required. Such models need to be calibrated against past measurements.

 This study aims to: 

•Apply a  high resolution ice flow/mass balance model to Haut Glacier d'Arolla in Switzerland (Fig 1)

•Reconstruct historical changes in glacier extent, area, frontal position and volume from LIA onwards

•Evaluate the ability of the model to replicate past and present ice extents and volumes using digitised historical records

•Use the results gained from the model to visualise the movements of the glacier in three dimensions.

•Allow us to predict the future response of the Haut Glacier d'Arolla to best and worse case IPCC global climate change scenarios, and to determine whether this could be used as a wider range indicator of the effects on similar glaciers around the world.

HGA is a temperate valley glacier which throughout the 1990s and continues to be the focus for intensive research into glacier energy balance, melt, hydrology, dynamics and geochemistry. In 2000 it covered ~6.3 km2, was ~ 4.0km long, and had an altitude range of ~1650m - 2350m a.s.l.

Data Sets

1880, 1890, 1911, 1934, 1946 & 1968 Historical ‘Siegfried’ 1:50k Maps 531 “Matterhorn” Contour interval = 30m.

1946, 1955, 1968, 1983 National 1:25k Maps 1347 “Matterhorn” Contour Interval = 10m.

1992, 1993, 1994, 2000 & 2003 Vertical stereo air photographs.

DEM creation from maps: contours were digitised, TINs created from digitised points, GRIDs created from TINs.

DEM creation from air photos: GRIDS created directly using analytical photogrammetry and ground control points on and off the glacier. Undertaken by HEP Co., Grande Dixence SA (1992-1994) & by ETH, Zurich (2000 & 2003).

Consecutive DEMs subtracted to derive maps of elevation change. Converted to units of water equivalent per year by multiplying by ice density (0.91 g cm-3 ) and dividing by number of years between surveys.

Glacier volumes and volume changes calculated using a bed DEM derived using radio echo sounding in 1989/90 (Sharp et al, 1993).

Volume Change Results

From 1880 and 2003 glacier area shrank from 10.2 to 4.5 km2 and volume declined from 1.15 to 0.21  km3 (a reduction of 82%) with the greatest rates of decline taking place most recently.

Between 1890 & 1934, the tributary glaciers beneath Dents de Bouquetins detach from the main glacier tongue on the east.

Between 1934 & 1946, Haut Glacier d’Arolla separated from Bas Glacier d’Arolla to form 2 separate glaciers.

Between 1968 & 1983, the tributary glacier beneath Mitre de L’Evêque detaches from the western glacier tongue.

Patterns of surface elevation change generally show that the greatest deflation is consistently across the lower tongue as it retreats up-valley with net mass loss up to -10 ma-1.  Across the upper tributaries, patterns are more heterogeneous with inter-annual variability in snowfall and net accumulation playing a factor.  Generally though, there is much less net surface mass loss but also periods and zones of net mass gain.

Errors in the calculations are largely due to errors in original map contours, difficulties geo-referencing the maps, and DEM production from digitised contours and direct from air photos over textureless snow surfaces.

 

 

Animation showing the retreat of Haut Glacier d'Arolla from the Litle ice age  through to 2100 with warming rate of 0.02° yr after 2005

3D Time-Depedent Flow Modelling

A higher-order, isothermal flow Model (Blatter, 1995; Hubbard et al., 1999) is applied to the 100 m basal topography.

Coupled to a simple mass-balance paraterisation based on the Sion (1860AD onwards) temperature and precipitation time-series scaled to the local Bricola record (1970s onwards).

Calibrated against mass balance measurements made at HGA 1989-1995 and velocity data 1990-1999.

Dynamic senstivity & parameter optimisation from against the mean sum residual of the modelled v’s surface DEMs.

Forced from Little Ice Age maximum extent c. 1800AD when HGA extended >10 km down valley to near the village of Arolla through to present day.

Future scenarios of ‘no change’, 0.02 & 0.04ºCa-1 warming with 0, 10 & 20% precipitation increase modelled until 2100AD

Results confirm that the future is bleak for HGA even under the ‘no change’ scenario (based on 1989–95 mass-balance) which yields complete wastage to 3200 m a.s.l. by 2075AD.

 

Thanks to my supervisors  Alun Hubbard and Pete Nienow