Land subsidence occurs in Ha Long and Cam Pha cities due to human activities in which the underground coal mining exploitation plays a crucial responsibility. For mapping the spatial distribution of this phenomenon and monitoring its evolution over the time, the Persistent Scatterer Interferometric Synthetic Aperture Radar (PSInSAR) approach was applied to 56 Sentinel-1A images, captured from June 2015 to June 2019. This approach allows monitoring ground displacement by continuously measuring the position of objects that persistently scatter radar beams. This interferometric synthetic aperture radar (InSAR) technique extracts deformation signals and it can be applied to areas where the discontinuous land subsidence is occurring. The mean land subsidence velocity map shows that two principal areas in Ha Long city including Ha Lam, Ha Trung, Ha Khanh, and Ha Tu wards, and Cam Pha city, specifically Mong Duong ward have been subsided in recent years with the maximum velocity of 14.5 mm year⁻¹ and a cumulative displacement ranging from 30 to 50 mm in the Line Of Sight (LOS) direction over 4 years. Field investigation recognized the direct impact of this phenomenon on houses, infrastructures, and natural features located above the underground coal mining utilities. This hazard has a close relationship with the exploiting process of coal seams, which alternately lay inside the sedimentary layers of the Hon Gai formation.

Socio-economic development has promoted the modification of land cover patterns in the coastal area of Ha Long, Cam Pha cities since the 1990s. The urban growth, together with intensive coal mining activities, has improved the life quality of residents. However, it has also caused many environmental problems in this region. Change detection techniques based on post-classification comparison were applied for monitoring the spatial and temporal evolution of land covers. The confusion matrix for 2001 and 2019 showed high overall accuracy (97.99%, 94.95%) and Kappa coefficient (0.97, 0.92), respectively. Statistics from classified images have revealed that man-made features increased by about 15.32%, while natural features, mangrove jungles, and water bodies decreased 10.64%, 1.96%, 2.72%, respectively, and urban evolution presents various dynamics, soft in the first period (1991–2001), but stronger in the second period (2001–2019) with different characteristics. The study also expresses the constraint of topographic and geologic resources, which have prevented the urban development in this coastal area. Such obtained results are very important for understanding interactions and relations between natural and human phenomena and they may help authorities by providing indicators and maps able to highlight necessary actions for sustainable development.