Monitoring forest degradation at fine scale over large area is critical from an environmental point of view since it provides crucial information for many ecological applications. We introduce an automatic method based on optical Landsat time series (2000–2017) to detect and quantify forest disturbances and to identify the causes of forest degradation. The method is based on i) an automatic spectral unmixing to detect forest's disturbances and on ii) landscape metrics and temporal indicators to detect the causes of forest degradation. We applied the approach in the Brazilian Amazon municipality of Paragominas to map forested areas affected by reduced impact logging, conventional logging or illegal logging and fires.