This paper addresses the monitoring of volcanic eruption using a coherence change detection matrix constructed from a multitemporal InSAR image time series. The Piton de la Fournaise volcano (French island, La Reunion), one of the most active volcanoes worldwide, was selected as a case study. Changes on the ground related to eight volcanic eruptions were analyzed through a time series including 49 descending stripmap Sentinel-1 SAR images acquired from January 10, 2018 to August 21, 2019. The experimental results have shown the relevancy of the proposed framework.