Glacier Movement

Quantification of glacier movement can supplement measurements of surface elevation change to allow an integrated assessment of glacier mass balance. Glacier velocity is also closely linked to the surface morphology of both clean-ice and debris-covered glaciers. Here, a distinction exists between active and inactive ice, where the latter can often represent a boundary condition for glacial lake development and subsequent accelerated ablation. Surface displacements can be surveyed manually in the field using trigonometric principles and a total station or theodolite for example, or dGPS measurements, which allow horizontal and vertical movement to be quantified for accessible areas. Semi-automated remote sensing techniques such as feature tracking (optical or radar imagery) and synthetic aperture Radar (SAR) interferometry (radar imagery), can provide spatially distributed and multi-temporal velocity fields of horizontal glacier surface displacement. Remote-sensing techniques are more practical and can provide a greater distribution of measurements over larger spatial scales. Time-lapse imagery can also be exploited to track surface displacements, providing high temporal resolution and centimetre horizontal resolution depending on the range between camera and glacier surface. This chapter outlines the costs, benefits, and methodological considerations when using field-based and remote sensing techniques for deriving glacier velocity, and example workflows are presented.