Analysis of Sinkholes on the Najd Plateau Using InSAR

Sinkholes represent an escalating geohazard across the central Najd Plateau, a region in Saudi Arabia characterized by soluble sedimentary units and subject to both natural and anthropogenic influences. Subsidence often begins as a slight and barely visible settling of the surface, only later becoming apparent and damaging roads, services, and new developments. This is a concern because urban and infrastructural expansion is taking place across the Najd Plateau, where the sedimentary cover locally contains soluble carbonates and evaporites. When groundwater levels change or surface water is added, these units can dissolve, and the overlying ground loses support, leading to subsidence. In such geologically sensitive environments, this needs to be monitored and interpreted early.

This study presents a comprehensive, multi-temporal analysis of ground deformation from 2017 to 2024, utilizing interferometric synthetic aperture radar (InSAR) data acquired by European Space Agency (ESA) Sentinel-1 C-band SAR data. Interferograms were generated using the InSAR Scientific Computing Environment version 2 (ISCE2) processing framework, and timeseries analysis was performed to identify patterns of subsidence related to sinkhole activity.

Four sites located near the city of Riyadh on the Najd Plateau were studied for sinkhole-related subsidence. These sites are in sinkhole-prone areas, and each site represents distinct geological and hydrological contexts. Some of the sites have developed sinkholes, while others have shown indications of potential sinkholes.

Primary time series analysis of Sentinel-1 InSAR data reveals correlations between the InSAR analysis and optical satellite images at certain sites. In some locations, the data indicate that the ground subsided even before collapse events and continues to do so afterwards, which aligns with a scenario where a roof gradually gives way over a dissolution cavity. This matches the field mapping, which showed that the collapse features enlarged in subsequent years.

Subsidence in this region is primarily attributed to soluble sedimentary units that are affected by local changes in groundwater or surface water. The 2017–2024 InSAR time series indicates that this deformation occurs well before any collapse is visible at the surface. This information can now be used to flag locations that require follow-up in the field and to refine the sinkhole-susceptibility maps for the broader Najd Plateau region.