Heinz Blatter

Glacier mass-balance determination by remote sensing and high-resolution modelling

An indirect methodology for determining the distribution of mass balance at high spatial resolution using remote sensing and ice-flow modelling is presented. The method, based on the mass-continuity equation, requires two datasets collected over the desired monitoring interval: (i) the spatial pattern of glacier surface-elevation change, and (ii) the mass-flux divergence field. At Haut Glacier d’Arolla, Valais, Switzerland, the mass-balance distribution between September 1992 and September 1993 is calculated at 20 m resolution from the difference between the pattern of surface-elevation change derived from analytical photogrammetry and the mass-flux divergence field determined from three-dimensional, numerical flow modelling constrained by surface-velocity measurements. The resultant pattern of mass balance is almost totally negative, showing a strong dependence on elevation, but with large localized departures. The computed distribution of mass balance compares well ( R 2 = 0.91) with mass-balance measurements made at stakes installed along the glacier centre line over the same period. Despite the highly optimized nature of the flow-modelling effort employed in this study, the good agreement indicates the potential this method has as a strategy for deriving high spatial and temporal-resolution estimates of mass balance.

Stress and velocity fields in glaciers : Part II. Sliding and basal stress distribution

Numerical methods are used to examine the interaction between the spatial distribution of the basal shear traction and the corresponding basal velocity for an inclined slab geometry. In our improved treatment, we reject the common assumption that basal velocity is a simple function of local variables in favour of a non-local treatment that includes normal deviatoric stress and takes basal velocity to be an integrated response to spatially varying influences. Computationally, one must either iterate the basal velocity with a friction parameterization that relates basal shear traction to basal velocity or, alternatively, prescribe the basal shear traction that results from bed decoupling and substrate deformation. The average of basal shear traction over the entire bed of the ice mass is invariant under changes in sliding distribution and thus constitutes a useful reference; any local relative reduction of traction leads to basal movement, either sliding over the bed or moving with a deforming subglacial layer. The local stress reduction is accompanied by a concentration of traction up- and down-glacier of the moving base. Growth, decay and possible migration ofbasal stress concentrations may be closely related to short-lived sliding events and to surges.

Spatial pattern and stability of the cold surface layer of Storglaciären, Sweden

The mechanisms controlling the spatial distribution and temporal fluctuations of the thermal structure in polythermal glaciers have, to date, been poorly investigated and are not fully understood. ...

How does the Greenland ice sheet geometry remember the ice age

Abstract The response of the Greenland ice sheet geometry to glacial/interglacial climatic transition is studied by using a numerical ice sheet dynamical model. The possible contribution due to the increase in melting, snow accumulation, ice temperature and accumulation of harder ice during the Holocene is examined. The results imply that: (1) within 1000 years after the termination of the Ice Age, the present ice sheet became thicker than that during the Ice Age, mainly due to the increase in snow accumulation, (2) at present, about 10,000 years after the transition, the ice sheet is still reacting to the change in ice temperature and the advection of harder Holocene ice, effects which are partly compensating each other, (3) the central part of the ice sheet may be slightly by about 4 mm per year because of the somewhat quicker response of the ice sheet to temperature change than to advection of the harder Holocene ice, (4) the influence due to the repetition of the ice age cycles is negligible. Since the rate of change at present is below the detection thresholf, observation of the elevation change must be explained by the short-term climatic change.