Geotechnical Problems on Madeira Island: Slope Protection in Central Funchal—A Case Study

Volcanic islands are highly exposed to interacting geotechnical and hydrogeomorphological hazards, particularly where steep relief, intense rainfall, fractured volcanic rocks, and urban development coincide. This study analyzes the slope located along Avenida Sá Carneiro in central Funchal, Madeira Island, as an example of an urban coastal volcanic slope functioning under multi-hazard conditions. The study is based on literature analysis, field observations, and a sequential photographic inventory of existing protection measures. The results show that the analyzed slope should not be interpreted as a single retaining structure, but as a complex geological–hydrological–engineering–urban system. Its stability depends on the combined action of historical stone retaining walls, reinforced concrete elements, tunnel portals, drainage components, passive rockfall protection systems, terraced structures, vegetation, and local architectural solutions. The effectiveness of this system results from the spatial cooperation of many locally adapted measures rather than from one dominant stabilization method. The study also highlights the dual role of vegetation, which may support erosion control and near-surface stabilization, but may also obscure damage, seepage zones, and discontinuities. The findings emphasize that integrated slope management in densely urbanized volcanic island environments requires simultaneous consideration of water control, structural protection, maintenance, and landscape integration.: