Preliminary conceptual model of the Arjuno Welirang hydrogeological system, and comparison with the Bromo Tengger: An illustration of the hydrogeological systems diversity in volcanic areas

While basaltic volcanic aquifers are well described in the literature, andesitic groundwater systems are less studied. Nevertheless, these aquifers supply a large population in all the subduction areas, where this volcanism mainly occurs. In Indonesia, the growing needs of the population induce an increase of the pressure on such aquifers. We present in this paper the case study of the Arjuno-Welirang, and compare it with a well-known hydrogeological system, the Bromo-Tengger. Based on geological, geomorphological, and water chemistry data, this study highlights the diversity of andesitic history inherent to this kind of volcanism, and its strong implications on the groundwater availability downstream. The aim of this paper is also to show that simple investigations can help building a preliminary conceptual model (PCM) of complex volcanic settings. Such PCM is needed to define further detailed hydrogeological investigations required to set-up aquifer exploitation, management and preservation rules.