## 6 Discussion  
The supervised classification neural network analysis was used to view and calculate the area of pyroclastic flow deposits. From the Landsat imagery data, differences in appearance can be seen between pyroclastic flow deposits, forests, lakes and plantations. Landsat image data were used as an object for supervised neural network classification analysis. The supervised neural network classification divides the area based on the pixels that have been selected according to the class. The results of the supervised neural network analysis show that there are differences in the distribution of pyroclastic flow deposits between Mount Merapi and Mount Sinabung. The apparent differences in the Landsat imagery data that have been found by classification by the supervised neural network are the direction of flow, the area of deposit and the distribution of pyroclastic flow deposits. The differences in the distribution of pyroclastic flow deposits between Mount Sinabung and Mount Merapi were caused by several influential factors, such as the formation of volcanoes, regional geological conditions, volcano magmatic properties, volcanic type, lava domes and the Volcanic Explosivity Index. The geological conditions of Sumatra affect the formation of Mt. Sinabung. The outline of Sumatra Island consists of three tectonic systems, namely the Sumatra Subduction System, the Mentawai Fault \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Mount Merapi. No**} & \multirow{2}{*}{**Year**} & \multicolumn{2}{c}{**Pyroclastic Deposit Area**} \\ \cline{3-4}  & & **Pixel** & **km\({}^{2}\)** \\ \hline
1 & 2007 & 18,270 & 16.443 \\
2 & 2011 & 42,504 & 38.2536 \\
3 & 2014 & 34,708 & 31.2372 \\
4 & 2017 & 28,543 & 25.6887 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Time series of pyroclastic flow deposit. Figure 8: Time series of pyroclastic flow deposit for Mount Merapi. system and the Sumatra Fault System. Based on the geological reconstruction by [PERSON] (2000) [35], the initial formation of the Sumatra region began \(\sim\)50 million years ago (early Eocene). There are at least 19 C-section segments, each with lengths of \(\pm\)60-200 km, in the Sumatra Fault System, which has a total length of \(\pm\)1900 km. Lake Toba on the island of Sumatra is evidence of a supervolcano and is the remains of the largest eruptions of Caldera Crescent (scale: 8 VEI). The eruptions of Mount Sinabung eject many volcanic materials, one of which is pyroclastic flow. The pyroclastic flow deposits of Mount Sinabung spread to the southeast, tend to widen and are not transported far from the crater of Mount Sinabung. These characteristics result from the acid-intermediate (andesitic-rhyolitic) [17] magma of Mount Sinabung, which tends to be thick and prevents the pyroclastic flow deposit from being transported far. The other factor is due to the shape of the slopes of Mt. Sinabung, where the pyroclastic flows and the direction of the river in Sinabung valley are almost perpendicular. Mount Sinabung is a Type B mountain, which means there was no track record of eruption before it erupted in 2010 [14]. The eruption of 2010 was a phreatic-type eruption, as defined by the presence of volcanic dust. A phreatic eruption is the process of magma escaping to the surface because of the influence of steam caused by the direct or indirect interaction between water and magma [36]. The second eruption of Mount Sinabung was larger than that in 2010, which could have been caused by the formation of an old dome on Mount Sinabung after the first eruption. The material ejected in the next eruption mixed with the material on the surface or around the crater, destroying the already formed lava dome and forming a new lava dome. The eruptions of Mount Sinabung are generally rated as VEI 2, which means the eruption is relatively small [37]. However, the eruptions are continuous and interfere with the activity of the residents.