Glacial lake outburst floods (GLOFs) are outbursts caused by the failure of glacial lake moraine dams. Longer ongoing processes, such as moraine dam degradation, or instantaneous events, such as landslides, can trigger dam failure. GLOFs have a catastrophic downstream impact leading to significant economic damages and more than 12000 casualties worldwide until 2015, with Bhutan and Nepal being impacted the most. Climate change causes increasing temperature and precipitation, leading to the expansion of glacial lakes and the destabilisation of glaciers, slopes and moraine dams. Consequently, GLOFs are likely to become more frequent, and glacial lakes require continuous monitoring and analysis to understand and predict GLOF-related hazards.

Since glacial lakes often lie in inaccessible mountainous regions, on-site monitoring is challenging and remote sensing proposes a safe and cost-effective solution. Satellite radar is unaffected by nighttime and clouds, enabling continuous displacement measurements. Interferometric synthetic aperture radar (InSAR) using Sentinel-1 data from 2014 to 2021 was applied at six Himalayan glacial lake areas (Imja, Lunana, Barun, Rolpa, Thulagi and Lumding) to identify potential GLOF hazards and to investigate InSAR's capability as a monitoring tool. Optical, meteorological and topographical data were used to aid in interpreting the InSAR observations; linking displacements to potential hazards and evaluating the limitations of an InSAR-based analysis.

Significant deformation was detected at the terminal moraines of Imja, Thulagi, Rolpa, Lunana and Barun Lakes; on lateral moraines at Rolpa and Lunana Lakes; and on rock glaciers at Imja, Rolpa, Barun and Lunana Lakes. In addition, significant seasonal variation could be distinguished, showing the impact of temperature and precipitation on geomorphological processes and potential hazard developments at glacial lakes. InSAR-related limitations arose in regions with significant topographic variations, extant snow or vegetation covers, and rapid displacements.

This study demonstrates the capability of satellite InSAR as a glacial lake monitoring tool. An InSAR-based analysis is instrumental in highlighting areas from where GLOFs could originate, requiring mitigation measures or further investigation to map the impact of failure. By extending the research frame over multiple years, continuous and long-term monitoring could demonstrate the climatic influence on displacements and GLOF trigger developments.

The fluid flow in a reservoir largely depends on faults, as faults can act like conduits or barriers. The influence of three fault parameters (permeability, thickness and angle) on the temperature and pressure behaviour of a geothermal reservoir, has been investigated by modelling a faulted reservoir in 2D in MATLAB, based on the Finite Element Method. The reservoir is assumed to be sandstone with a permeability of 40*10-14 m2. The fault has been modelled with a permeability ranging from 10-11 m2 to 10-17 m2, a thickness ranging from 10 cm to 150 m and an angle ranging from 0 to 90 degrees. While varying one parameter, the other two stayed fixed. The base values for the fault permeability, thickness and angle were 10-14 m2, 20 m and 0 degrees respectively. Both a finite and infinite fault have been modelled in the reservoir. Decreasing the permeability led to a higher production temperature, especially at a finite fault, where the fluid is able to bypass the fault and thus sweep the warmth of a larger part of the reservoir. At a fault permeability of 10-14 m2 the fluid has seemed to have extracted the maximum amount of heat in the reservoir, further decrease in permeability did not lead to a higher production temperature. At an infinite fault there is only a small increase in temperature at a fault permeability of 10-16 m2. The impedance at a finite fault is not much affected, as the fluid is able to flow around the fault. The impedance at an infinite fault, however, rapidly builds up with decreasing permeability. A thickness of 20 m, at the base permeability value of 10-14 m2, results in the highest production temperature. Larger thicknesses cause larger amounts of unrecoverable area and consequently less heat can be extracted. At a finite fault the impedance climbs only to a value of 4 MPa at a thickness of 150 m, but at an infinite fault the impedance already reaches 10 MPa at a thickness of 80 m. The fault has its largest influence at a perpendicular position to the flow. At a parallel position, the results are the same as a reservoir without fault, as the fluid will not have to dodge a lot to reach the production well. All three fault parameters have a significant influence on the temperature and pressure behaviour of the geothermal reservoir. They are all able to enlarge and eliminate the influence of the fault. A finite fault can cause a favourable higher production temperature without a large impedance, as the fluid is able to bypass the fault. An infinite fault has less effect on the temperature and causes the impedance to build up rapidly, which requires an unrealistic high pumping power and consequently an unprofitable geothermal system.