ALBERT

Description: Modelling landscape evolution requires quantitative estimates of erosional processes. Dating erosional landscape features such as escarpments is usually difficult because of the lack of datable deposits. Some escarpments and valley margins are associated with the formation of mass-movement caves, sometimes known as ‘gull’ or ‘crevice’ caves, which are typically restricted to within 0.5 km of the valley margin or scarp edge. As in other caves, these mass-movement cavities may host speleothems. As gull-caves develop only after valley incision, uranium-series dating of speleothems within them can provide a minimum age for the timing of valley excavation and scarp formation. Here we present data from several gull-caves in the Cotswold Hills, which form the eastern flank of the Severn valley in southern England. U-series ages from these gull-caves yield estimates for both the minimum age of the Cotswold escarpment and the maximum scarp retreat rate. This is combined with data from geological modelling to propose a model for the evolution of the Severn valley and the Cotswold Hills. The data suggest that the location of the escarpment and regional topography is determined not by valley widening and scarp retreat, but by the in situ generation of relief by differential erosion.

Description: Traditional methods for evaluating groundwater resources rely on in-situ observations, which are often limited due to sparsely distributed monitoring wells and temporal inconsistencies in measurements. However, InSAR techniques have the potential to measure groundwater storage change indirectly through measuring ground deformation. The ground deformation associated with groundwater withdrawal is mainly recoverable or as a result of elastic compression. However, when effective stress exceeds the maximum past stress on the aquifer, inelastic subsidence occurs, which can permanently lower the storage capacity of the aquifer. Thus, in addition to monitoring changes in the volume of groundwater storage, analysing elasticity properties is necessary to fully understand the influence of overextraction on long-term aquifer sustainability. This research aims to investigate the capability of InSAR to contribute to a detailed understanding of groundwater storage change and the sustainability of groundwater use across Delhi, India. Specifically, we apply the ISBAS-InSAR technique to Sentinel-1 SAR data to produce a time-series of deformation across the region and investigate the relationship between in-situ groundwater storage change and ground deformation. Finally, the spatio-temporal variability and trends of elasticity in the underlying aquifer system, quantified using the elastic skeletal storage coefficient, will be analysed by examining the ratio of seasonal deformation signal provided by InSAR and groundwater level change from well measurements across the time-series of observations. These results shall inform both groundwater management in the Delhi region and provide insights into the applicability of InSAR for inferring large-scale aquifer dynamics.