## 1 Introduction  
Hazards triggered by volcanic activity have massive environmental, economic, and humanitarian impacts [1, 2]. Lava flows can destroy entire settlements and infrastructure [3]. Ash and tephra deposits cause damage to critical infrastructure, buildings, and agricultural land [4] and pose a threat to human health [5]. Furthermore, pyroclastic flows [6, 7] and lahars [8] are responsible for a large number of the fatalities due to volcanic hazards [1]. Secondary volcanic hazards, particularly volcano-induced tsunamis, also possess large destructive forces [9, 10]. Due to the catastrophic impacts of volcanic hazards, monitoring these processes is an essential component for risk assessment and planning in disaster management [11, 12, 13]. For that, satellite-based data are increasingly being integrated into the monitoring process of volcanoes, as they allow large-scale views of areas that are difficult to reach and hazardous to active eruptions. In addition to the frequently used infrared (IR) (e.g., [14, 15, 16]) and synthetic aperture radar (SAR) (e.g., [10, 17]) data, optical satellite data are also useful for the monitoring of active volcanoes. Very high-resolution (VHR) optical systems have been used to map ash and tephra deposits [18], lava flows [19], pyroclastic flows, and lahars [20, 21] at volcanoes. Lower-resolution optical imagery (e.g., Sentinel-2, Landsat-7/-8) (10-30 m) have also been successfully used to detect volcanic hazards (e.g., [22, 23, 24]). A commonly used method for mapping and quantifying volcanic hazard deposits using optical satellite data is the differencing of the Normalized Difference Vegetation Index (NDVI) [18, 23]. The results of this methodology can provide information about secondary volcanic hazards (e.g., precipitation-induced lahars) [25]. However, NDVI differentiation (dNDVI) is limited exclusively to the vegetation area of a volcano, leaving land surface changes in the crater area or sparsely vegetated flank areas undetected [18]. Especially in these areas, the differentiation between volcanic deposits (esp. lava flows) and the sparsely vegetated or completely unvegetated background is particularly difficult due to the similar spectral signatures [22; 26]. In addition, clear sky conditions are required when using optical systems. Due to the highly dynamic nature of volcanic hazards and the resulting small-scale morphological changes, as well as the frequent cloud cover in volcanic environments, the temporal and geometric resolution of optical systems is critical for a successful classification of volcanic hazards [18; 26]. The daily temporal and 3 m spatial resolution of PlanetScope represent significant advantages over previously used remote sensing data, making it a potentially suitable data source for monitoring volcanic hazards. Despite all this, so far only few studies have used PlanetScope to monitor and investigate active volcanoes. [PERSON] et al. [18] successfully used PlanetScope data to determine the spatial extent of ash and tephra deposits following an eruption of Fuego, Guatem. Other studies used PlanetScope data exclusively for visual analysis of geomorphological changes at Krakatau, Indonesia, [19] or to generate multi-temporal digital elevation models (DEMs) from which lava flow deposits at Nabro, Eritrea, could be derived [14]. This work therefore aims to investigate the potential of PlanetScope for detecting land surface changes due to volcanic hazards. The focus is on the development of new change detection methods for lava flow classification that take advantage of PlanetScope data. For this purpose, existing change analysis methods for identifying vegetation changes due to volcanic deposition were further developed and combined with hydrological runoff modelling from digital elevation models. Multi-sensor analysis can compensate for limitations of individual data sources and thus exploit the full potential of satellite data for monitoring active volcanoes (e.g., [13; 14; 16; 17; 27; 28]).