## 2 Study Area  
Karangetang (2.781\({}^{\circ}\)N; 125.407\({}^{\circ}\)E) (Figure 1) is an active stratovolcano located on Siau Island on the Sangihe Island Arc in NE Indonesia [29]. The volcanic cone (1797 m a. s. l.) is characterized by andesitic to basaltic-andesitic rocks and is one of the most active volcanoes in Indonesia, with more than 40 eruptions since 1675. For the most part, the explosive eruptive behavior of Karangetang results in pyroclastic flows, lahars, as well as lava flows, and thus poses an immediate risk to the population [12; 30]. In this work, lava flow deposits were mapped during two different eruptive phases at Karangetang (Table 1). The first eruptive phase (Karangetang I) began in November 2018 and continued until March 2019. During this period, large lava effusions developed at the N crater, resulting in a lava flow towards NNW. A second lava flow also flowed NNW from the N crater in late November 2018 [31]. Effusive activity continued throughout December 2018 into January 2019 and was repeatedly accompanied by avalanches and pyroclastic flows. On 2 March 2019, the lava flow on the NNW flank crossed a road near the coast. Two days later, the lava flow reached the coastline in the NNW of the island and ended in the ocean. During the activity in February 2019, 190 people had to be evacuated. From 12 February 2019 onwards activity decreased and the eruption phase ended in March 2019 [31]. The second eruptive phase at Karangetang (Karangetang II) occurred between July 2019 and January 2020 (Table 1) and was characterized by a variety of incandescent block debris avalanches, lava flows, frequent gas and steam emissions, and ash clouds [32,33]. In addition to block debris avalanches with incandescent material, a WNW lava flow developed from the main crater in late July 2019. Lava effusion increased in the following weeks and continued to develop downslope in August and September 2019. Lava effusion was also observed at the N crater during this period. Following a large Strombolian eruption in late November 2019, steady lava effusion intensified, creating a large-scale lava field on the W flank of Karangetang [32]. During December 2019, lava effusion gradually increased the height of the N crater, and the height of the N crater. The N crater was also observed at the N crater during this period. decreased and incandescent block debris avalanches became dominant on the W flank. This activity continued until mid-January 2020. Thereafter, volcanic activity abruptly stopped, and only isolated hotspots were sighted in both craters [33]. Mount Agung (8.343\({}^{\circ}\)S; 115.508\({}^{\circ}\)E) (Figure 1) is an active stratovolcano (2997 m a. s. l.) located in the east of the island of Bali on the Sunda Island Arc [34]. The volcano is composed mainly of basaltic-andesitic rocks and has a partly explosive Plinian or Sub-Plinian eruptive form. This often results in pyroclastic flows and lahars [34]. Due to the high population density of the island of Bali, Agung is a particularly dangerous volcano [35]. In mid-August 2017, a new eruptive phase began (Agung I) after a prolonged period of inactivity [34; 36]. This intensified in November 2017 (Table 1), with massive ash eruptions occurring on 21 November 2017 and the subsequent days. In the process, ash columns rose to heights ranging from 4.8 to 9.3 km a. s. l. between 25 and 26 November 2017 [37]. During this period, the ash cloud drifted mainly W and SW [36; 37]. The eruptions resulted in the closure of the international airport in Bali (60 km SW of Agung) for several days between 26 and 29 November 2017. In addition, approximately 25,000 people were evacuated in the immediate vicinity of Agung. The largest eruptions continued until 30 November 2017. After that, only smaller ash and gas eruptions were observed [36]. Krakatau (6.102\({}^{\circ}\)S; 105.423\({}^{\circ}\)E) (Figure 1) is a volcanic complex in the Sunda Strait that consists of a caldera with a stratovolcano inside.