Abstract
Abstract. Although animated images are very popular on the internet, they have so far found only limited use for glaciological applications. With long time series of satellite images becoming increasingly available and glaciers being well recognized for their rapid changes and variable flow dynamics, animated sequences of multiple satellite images reveal glacier dynamics in a time-lapse mode, making the otherwise slow changes of glacier movement visible and understandable to the wider public. For this study, animated image sequences were created for four regions in the central Karakoram mountain range over a 25-year time period (1990–2015) from freely available image quick-looks of orthorectified Landsat scenes. The animations play automatically in a web browser and reveal highly complex patterns of glacier flow and surge dynamics that are difficult to obtain by other methods. In contrast to other regions, surging glaciers in the Karakoram are often small (10 km2 or less), steep, debris-free, and advance for several years to decades at relatively low annual rates (about 100 m a−1). These characteristics overlap with those of non-surge-type glaciers, making a clear identification difficult. However, as in other regions, the surging glaciers in the central Karakoram also show sudden increases of flow velocity and mass waves travelling down glacier. The surges of individual glaciers are generally out of phase, indicating a limited climatic control on their dynamics. On the other hand, nearly all other glaciers in the region are either stable or slightly advancing, indicating balanced or even positive mass budgets over the past few decades.
Highlights
1.1 Visualizing glacier dynamicsAnalysis of sequential satellite images has become a common tool for deriving glacier changes through time in all parts of the world
The high repetition rate of 1/10 s per frame gives the impression of continuous glacier flow and reveals changes in morphology and dynamics with a clarity that cannot be achieved with side by side comparison of static images or colour-coded glacier outlines from different points in time
Though changes are not determined in a quantitative way, the time-lapse mode of the animations provides insights that are difficult to obtain otherwise
Summary
Analysis of sequential satellite images has become a common tool for deriving glacier changes through time in all parts of the world. Wulder et al, 2012), it is possible to combine sequential satellite images into longer sequences (> 20 years) and demonstrate landscape changes in a time-lapse mode (e.g. world.time.com/timelapse2) including glacier flow and dynamic changes over large regions This provides new insights and a more intuitive access to phenomena such as the mutual interaction of different glaciers, fast and slow flow of different glacier segments, advance and retreat patterns, downwasting (i.e. surface lowering without retreat), and the dynamics of supraglacial and proglacial lakes and river streams. In this study animated sequences of orthorectified satellite images covering a 25-year time period (1990–2015) are used to demonstrate glacier dynamics and other landscape changes in four regions of the central Karakoram Though this might be seen as a less quantitative approach than that of studies determining the exact rates of glacier change, the information obtained by looking at high-speed animations of the individual images provides insight into dynamic glacier behaviour on a different level. The format has recently become increasingly popular on the internet (e.g. giphy.com) and in mobile communication (Isaac, 2015) for short repetitive animations due to its easy use (no special software required) and relatively small file size
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