Preliminary investigation on Cyclone Remal‑in‑ duced landslides in Aizawl, Mizoram, Northeast India, on the 28th of May 2024

Abstract

On the 28th of May 2024, Cyclone Remal brought intense rainfall, triggering catastrophic landslides in Aizawl, the state capital of Mizoram, northeast India. The region is prone to landslides due to its fragile geology and steep terrain, and it has experienced severe damage, including loss of life, destruction of property, and disruptions to essential services. It had a severe impact on society, resulting in 34 fatalities with 33 bodies recovered and affecting 72 families, leading to the evacuation of 54 houses within Aizawl. It also affected the cemeteries of four localities. Among the numerous landslides observed during the field survey, fourteen sites were selected for the study. This study aims to assess the social impacts of these landslides and analyze the failure mechanism involved to guide future disaster preparedness and mitigation strategies. In addition to the information gathered from the government and social media, a field-based method of investigation was used in this study. The methods involve site visits, interviews with local communities, and an analysis of geological, geotechnical, and rainfall data. Geotechnical investigations were conducted at nine sites of the studied areas, all involving rock slides. An investigation was done into the stability of the affected rock slopes, including kinematic analysis, uniaxial compressive strength test (UCS), rock mass rating (RMR), continuous slope mass rating (CoSMR), and slake durability test. The field survey and interviews determined that the landslides caused 25 fatalities, with ten houses and twenty-two vehicles damaged in the Melthum and Hlimen areas. The total property loss was estimated to be Rs.3.4 crores. Landslides displaced more than 300 graves. Most of the probable slope failure observed using kinematic analysis show planar and wedge types of sliding. The studied rock mass of the slope falls under the poor to fair class in RMR ratings and ranges from partially stable to completely unstable in the CoSMR assessment. The rock collected from nine locations of the study landslide area shows medium to high durability and a strength of 14.8 to 22.6 MPa using slake durability and uniaxial compressive strength test (UCS), respectively. The study concludes that while intense rainfall was the primary cause, contributing factors like lack of expert consultation on slope modifications, weak rock mass characteristics, steep slopes, inadequate infrastructure planning, and fragile geological conditions increased the likelihood of slope failure. It seriously impacts society, resulting in many lives and infrastructure loss, economic hardship, and psychological stress, especially among those living in landslide areas. The findings emphasize the necessity of comprehensive land-use planning, improved infrastructure resilience, and coordinated disaster preparedness efforts to mitigate the risk of future landslides.