Figure 3
Temporal changes at Merapi summit dome. (a) Drone data was processed to generate high resolution orthomosaic representing the Merapi dome in map view (upper row) for 2015 (left) and for 2017 (right). The principle component analysis for PC2 is suggesting an increasing area of hydrothermal alteration. Shadowed regions are not further considered. White box indicates the area of the zoom-in. (b) Zoom-in of the orthomosaic and PCA maps, highlighting for the observed 2-year period, that the degree of steaming and alteration notably increases along the eastern segment of the horseshoe-shaped fracture, as well as at the southern flank of the lava dome. Note that this area has collapsed and is the site of frequent mass wasting events and the origin of pyroclastic density currents during the recent (post 2019) crisis of Merapi volcano. Orthomaps and PCA analysis were created using ArcMap (v10.5) (https://desktop.arcgis.com/de/arcmap/).
