The Anak Krakatau Island and volcano caldera are located at the Sunda Strait between the Java and Sumatra Islands of Indonesia. The volcano started erupting on 22^nd December 2018 and collapse of the volcano resulted in Tsunami, the large tidal waves caused mass destruction and life loss in the Java and Sumatra islands. The objective of this work is the interferometric SAR coherence and backscatter images based analysis of the Anak Krakatau Island using Sentinel-1 SAR data. 7 datasets of ESA’s Sentinel-1 C-band satellite acquired from 25^th November 2018 to 24^th January 2019 were used in this study. The InSAR RGB composite images were generated by stacking together the Interferometric coherence magnitude images and the sigma nought backscatter images. The Sentinel-2 True Colour Composite (TCC) images before and after volcanic eruption were used to verify the results obtained through InSAR coherence analysis. The sigma nought backscatter image of the 22^nd December 2018 clearly indicates the volcano eruption centre and the ocean waves moving away from the Anak Krakatau due to the seismic shock waves caused due to the volcano eruption. The combined interpretation of the results revealed that the severe volcanic eruption on 22^nd December 2018 caused a large portion of the volcano to collapse and all the rock debris which submerged to the ocean displaced the ocean water and resulted in the Tsunami in the Indonesian islands.