## 4 Methods
### Lava Flow Mapping
Objects that are within a distance of \(\leq\)15 PlanetScope pixels (45 m) are assigned to the class \"potential lava flow area\" and form the object  
Figure 2: Workflow of OBIA change detection based on NHI pixels and the _dNDVI_ area. Input data: pre- and post-PlanetScope scene, temporally aggregated NHI pixels, _dNDVI_ layer, and the drainage system. Step 1: extraction of the drainage in the overprint area (NHI or _dNDVI_ area); step 2: classification of segments in the unvegetated areas using the combination of distance to drainage and changes in texture (GLCM) and brightness. Starting from the “lava flow area in vegetation or NHI area” objects, a pixel-based region growing into the “potential lava flow area with change” change areas is used to model the lava flow to its point of origin. level 2. In addition, all objects of the class \"non-vegetation area\" are intersected with the _dNDVI_ and NHI layers to identify objects with vegetation changes or thermal overprinting (class \"lava flow area in vegetation or NHI area\") (Figure 2). In the next step, texture and brightness changes in the objects of the potential lava area (class \"potential lava flow area\") are calculated. Since almost no spectral differentiation is possible between objects with lava deposits and the background [22; 24; 26], information about texture and brightness are included in the classification. Texture was calculated using a grey level co-occurrence matrix (GLCM) based on [PERSON] et al. [64] for all objects in the potential lava flow area class. In this analysis, the GLCM was calculated based on the individual objects using the red band for the pre- and post-PlanetScope scenes. Following the recommendation of [PERSON] et al. [64], the average of all four possible viewing diagonals (0\({}^{\circ}\), 45\({}^{\circ}\), 90\({}^{\circ}\), 135\({}^{\circ}\)) was calculated. The differences of the secondary statistics homogeneity, entropy and contrast were used. For this purpose, each feature was calculated in the pre- and post-scene and then subtracted from each other. In addition, two post-scene GLCM statistics, contrast and spatial standard deviation, were integrated into the classification. Another differentiator is the overall brightness of the objects. Here, a ratio of the overall brightness from the pre- and post-scene was formed to detect changes in the brightness of volcanic deposits. The mentioned texture and brightness parameters were used with the help of a respective threshold value for the classification of the objects of the class \"potential lava flow area\". The thresholds are strongly dependent on the local factors of the volcanic environment and were therefore defined manually for each individual volcano. The exact threshold values for the individual analyses are presented in Table 2. If an object exceeds or falls below one of the defined limits, it is assigned to the class \"potential lava flow area with changes\". These objects are located at a plausible distance from the drainage system and contain texture or brightness changes in the PlanetScope scenes. In the final process of the OBIA change detection, a pixel-based region-growing procedure is performed, which has as a starting point the objects of the class \"lava flow area in vegetation or NHI area\" (Figure 2). From these objects, which have a certain volcanic overprint due to vegetation changes or thermal activities, the algorithm grows pixel-based into all neighboring objects belonging to the class \"potential lava flow area with changes\". A pixel is included in the objects of the initial class if it fulfils one of the defined conditions of GLCM differences, GLCM post-scene, or overall brightness ratio (Table 2). This process is iterated until none of the adjacent pixels of the object class \"potential lava flow area with changes\" fulfil any of the defined threshold conditions. The resulting class \"lava flow area\" now contains all objects that represent the area of the lava flow. Finally, all objects of the class \"lava flow area\" were merged to one object.