Abstract
In recent years, many glaciers all over the world have been distinctly retreating and thinning. One of the consequences of this is the increase of so called glacier lake outburst flood events (GLOFs). The mechanisms ruling such GLOF events are still not yet fully understood by glaciologists. Thus, there is a demand for data and measurements that can help to understand and model the phenomena. Thereby, a main issue is to obtain information about the location and formation of subglacial channels through which some lakes, dammed by a glacier, start to drain. The paper will show how photogrammetric image sequence analysis can be used to collect such data. <br><br> For the purpose of detecting a subglacial tunnel, a camera has been installed in a pilot study to observe the area of the Colonia Glacier (Northern Patagonian Ice Field) where it dams the Lake Cachet II. To verify the hypothesis, that the course of the subglacial tunnel is indicated by irregular surface motion patterns during its collapse, the camera acquired image sequences of the glacier surface during several GLOF events. Applying tracking techniques to these image sequences, surface feature motion trajectories could be obtained for a dense raster of glacier points. Since only a single camera has been used for image sequence acquisition, depth information is required to scale the trajectories. Thus, for scaling and georeferencing of the measurements a GPS-supported photogrammetric network has been measured. <br><br> The obtained motion fields of the Colonia Glacier deliver information about the glacier’s behaviour before during and after a GLOF event. If the daily vertical glacier motion of the glacier is integrated over a period of several days and projected into a satellite image, the location and shape of the drainage channel underneath the glacier becomes visible. The high temporal resolution of the motion fields may also allows for an analysis of the tunnels dynamic in comparison to the changing water level of the lake.
Highlights
Glacier lake outburst flood events (GLOFs) occur when lakes that have been dammed by a glacier spontaneously start to drain through a subglacial channel underneath the glacier due to their outweighing hydrostatic pressure
The formation of the subglacial drainage system can be documented during the whole glacier lake outburst flood events (GLOFs) cycle with high temporal resolution
Special thanks go to the Institute of Planetary Geodesy (IPG) of TU Dresden for providing equipment and positioning data. In this pilot study we present the successful localisation and change detection of subglacial channels during GLOF events via a terrestrial monoscopic image sequence analysis approach
Summary
Glacier lake outburst flood events (GLOFs) occur when lakes that have been dammed by a glacier spontaneously start to drain through a subglacial channel underneath the glacier due to their outweighing hydrostatic pressure. In a short period of time, the lake water drains under the glacier and causes floods in downstream valleys. In many cases the latter become hazardous for people and their property. Further information about outburst events of ice-dammed lakes is given in Blachut & Ballantyne (1976) and Tweed & Russell (1999). Due to global warming the frequency of glacier lake outburst flood events (GLOFs) increased during the past years and the scientific interest in these phenomena intensified (Dussaillant et al, 2010). While one issue of research in the field is the early warning and prediction of GLOF events to prevent settlement zones from hazards (e.g. (Huggel et al, 2004), (Mulsow et al, 2015)), another issue is the general understanding of the mechanisms ruling a GLOF event (e.g. (Clague & Evans, 1994))
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