Abstract
Abstract. Glacier Lake Outburst Floods (GLOFs) depict an environmental risk with an increasing damage potential in many regions of the world. GLOFs are often caused by glacier margin lakes, which suddenly find a drainage path underneath the bottom of a glacier, which is destabilized and retreating as a consequence of local or global climate changes. In a typical GLOF event, a glacier margin lake may drain completely in 24 hours, causing a large flood wave in the area downstream the glacier. The paper documents some recent GLOF events in the Northern Patagonian Icefield (Chile) and presents a terrestrial photogrammetric glacier margin lake monitoring system. The system is based on a camera taking images at regular time intervals. In these images, variations of the water level can be detected by tracking the water-land interface at pre-defined image spots. Due to the drainage mechanism, which is characterized by progressive erosion and melting at the bottom of the glacier, GLOFs are indicated by a progressive water level drop in the lake. Water level changes may be detected with subpixel accuracy by image sequence processing methods. If a 3D model of the lake bottom topography (or at least one height profile through the lake) exists, water level changes in monoscopic image sequences may be transformed into volume loss. The basic idea herein is the intersection of a terrain profile with a water level detected in the image and projected into object space. The camera orientation is determined through a GPS-supported photogrammetric network. Camera orientation changes, which may for instance be induced by wind, can be compensated by tracking some fiducial marks in the image. The system has been used in a pilot study at two glacier margin lakes in the Northern Patagonian Icefield. These lakes have a depth of about 80 - 100 meters. The larger one has a length of 5 km and a maximum volume of about 200,000,000 cubic meters. During the pilot study, several GLOF events could be recorded and processed. Water level changes can be determined at decimeter level precision. The results prove the feasibility of the concept, which has to be completed by a data telemetry and alarm system.
Highlights
Glacier Lake Outburst Floods (GLOFs) occur in many regions of the world and are caused by various mechanisms
Regions with a high GLOF potential are for instance the Himalayas, Alaska, Iceland, the Andes and Patagonia
GLOFs often occur by the sudden drainage of lakes, which are dammed by glacier tongues or moraines
Summary
GLOFs occur in many regions of the world and are caused by various mechanisms. Regions with a high (or increasing) GLOF potential are for instance the Himalayas, Alaska, Iceland, the Andes and Patagonia. With glaciers retreating in most regions of the world, the risk of GLOFs is increasing (Rosenzweig et al, 2007) This is partly caused by the increasing amount of melt water accumulating in glacier margin lakes. A major reason is in the fact that a retreating and thinning glacier tongue will give less detention to the hydrostatic pressure of the dammed lake water This process is known as ‘Glen mechanism’ (Glen, 1954; Higgins, 1970): The increasing hydrostatic pressure of a glacier margin lake together with the decreasing detention from a thinning glacier enforces the development of a tunnel at the glacier bottom, through which the lake drains. The goal of the work presented here was to perform a pilot study on the use of photogrammetric techniques for glacier margin lake water level change monitoring.
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