The enigmatic major eruption in the late 16th century, believed to have originated from Raung, the most active stratovolcano in the Ijen UNESCO Global Geopark in East Java, Indonesia, has ignited significant debate among researchers and historians due to its profound impact on the region. This research aims to substantiate Raung as the likely source of the major eruption by integrating geological, archaeological, and historical data. This study synthesizes current findings and explores ongoing debates surrounding historical volcanic activities. Eruption parameters suggest that the late 16th century eruption exhibited a Plinian type, characterized by an explosive eruption column reaching the stratosphere, widespread pumiceous tephra fallout, and pyroclastic density current (PDC). Stratigraphic succession reveals that the eruption occurred in five phases, with deposits from 10 eruptive units. These deposits are mainly concentrated on the northwestern flank of Raung. Archaeological findings, historical records, and local legends converge to pinpoint the occurrence of this catastrophic event in the late 16th century. These diverse sources estimate that the eruption resulted in approximately 10,000 casualties, marking it as one of the most significant volcanic disasters in the past 500 years. The implications of this eruption extend beyond historical documentation, providing a critical case study for advancing disaster mitigation strategies through geotourism in the geopark area. Moreover, the eruption record outcrops identified in this study can be proposed as potential new geosites within the Ijen UNESCO Global Geopark, enhancing its educational and touristic value. We propose the Jebung Kidul, Alas Sumur, and Batu Sappar sites as potential disaster-based geosites, considering that these sites record the eruption process and preserve archaeological structures. This addition would not only commemorate the historical event but also promote awareness and preparedness for future volcanic activities in the region.

Pandan volcano is a volcano formed on Tertiary sedimentary rocks from the Kendeng zone deposited in the basin of East Java. In addition to generating petroleum potentials, such as Cepu and Bojonegoro oil fields, this area also generates geothermal potential. As a source of heat from the geothermal system is igneous rock formed from the magmatism process. The type of rock formed by the process of magmatism in the Pandan geothermal system is basaltic-andesitic and hornblende andesite are medium-high K calk alkaline affinity located in the island arc. The interaction of hot rock from post magmatism process with hydrothermal fluid resulted in the manifestation of hot springs and calcite travertine in the study area. Prediction of the subsurface temperature of hot water from geothermometer silica analysis contained in Banyukuning and Jarikasinan show cristobalite Beta equilibrium (70oC) and quartz temperature (120oC). To study about magmatism and geothermal fluid using petrographic method and petrochemical analysis (X-ray fluorescence spectrometry method) to the sample of igneous rock. While to study the fluid type and geothermometer of geothermal fluid using data from previous researchers. This research study is expected to provide additional information on the field of geothermal and magmatism in this area.

Ungaran geothermal field is estimated to have a potential of 15 MWe. The volcano is located in the middle of Java Island which is a range of Quaternary volcanoes. As in other islands in Indonesia that indicate that this volcano has a potential energy of geothermal. This volcano is a strato volcano with andesitic composition. The Ungaran volcano geothermal system is located within a young cone depression, overgrown by Mount Gugon and Mount Megi that form the depressive ring. Geothermal manifestations contained in Gedongsongo include: fumarola, hot springs, travertine, steaming ground and alteration rocks. The temperature of the hot springs is about 50°C, the pH of hot water is acidic (ranging from pH 1.5 to 5.5), bubble gas and around fumarola are found sublimation of sulfur and pyrite.This research uses analytical methods of geochemistry (water and rock), petrography and petrophysics. Based on geothermometer analysis shows that the reservoir temperature is 300°C. The composition of fumaroles is strongly influenced by magmatic elements with temperatures greater than 300°C. While petrography analysis yields that the material of Ungaran volcano rock is andesite-basaltic. Knowing the geothermal potential of this area is expected to increase the Java-Bali power supply.

The Ijen volcano was a Pleistocene volcano and is one of the stratovolcanoes which was active in East Java Province. This volcano erupts by magmatic and phreatic eruptions. This volcano has the largest natural lake in the world, measuring around 960 x 600 m. Embankments limited the morphology of the crater with heights between 2.145-2386 m. The lowest height of the western embankment was upstream from Banyupait River. The water volume of the crater lake of Ijen volcano is quite large and very acidic. The acidic water from the crater lake flows from upstream Banyupait River to the north to the lower direction of the Asembagus Situbondo area. The purpose of this research was to study the pH distribution of the Banyupait river flow from upstream to the coast. It was because that Banyupait river acid water was used by residents for daily life and agriculture. The methodology used in this research was conducting field survey and measurements. Field survey was carried out along the flow Asembagus river in Banyupait, which started from the village of Bantal to the river mouth in the Java Sea. In conducting a field survey pH measurements were also carried out from the river water of the Kali Banyupait. The observations showed that the river water upstream of Banyupait River had a pH of around 2-3, while the more towards the downstream the pH of the river water changed to an increase of around 3- 4. The acidic water of this river experienced dilution from several rivers in its area. Whereas in river estuaries, the river water mixes with the sea, so water has a pH of 4.2. Because river water is acidic (low pH), no biota along the Banyupait river was found. Besides that, the other characteristics of river water are brown. Rocks exposed to the river flow will be reddis, experiencing iron oxide. It was due to the interaction process of acid river water with rocks. However, the river water was used by residents around the river for agriculture and daily necessities. Consequently, the health of the population around Bantal village was low.

The Ijen volcano has Pleistocene age (294.00 ± 0.03 Ma), and this stratovolcano was very acidic crater water with a pH of 0-1. The acidic crater water seeps into the Banyupait river flow. Asembagus is a research area located on the northern slope of the Ijen volcano, and the Banyupait River drains this. The acidic river water flows from the Ijen Crater Lake, so the pH of the water river was very acidic. This study used several different analytic methodologies with some previous researchers, namely using the method of geological mapping, pH measurement, spectrophotometry, IRMS (Isotope Ratio Mass Spectrometer), and the technique of Induced Coupled Mass Spectrometry (ICP-MS). Besides, the petrographic analysis is used to determine the composition of rock minerals due to rocks interacting with acidic water. Banyupait River water in the Asembagus area has a pH of river water around 3-7.3, SO4 (220-683 ppm), and the type of water is meteoric water. Also, concentrations of Ca, K, Mg in the west Banyupait river irrigation water flow showed higher levels when compared to the eastern Banyupait River water flow. Likewise, REE elements from the Asembagus region showed lower concentrations compared to Ijen Crater water. This change in the level of chemical elements is caused by the acidity of the Banyupait River being diluted or mixed with water from other water. However, the spring was not affected by acidic water. The process of acidic water interaction with rocks can also be observed from rocks traversed by the Banyupait River flow. Chalcedony and hematite replace the primary minerals of basaltic rocks. This research is expected to improve the quality of water needed by the Asembagus community so that people can live healthily.

The magma evolution of Ngebel Volcano, both temporally and spatially, is represented by the characteristics of its lava. Ngebel Volcano, located in East Java, is a Quaternary andesitic stratovolcano. This volcano is part of the Wilis Volcanic Complex. The volcanism stage of Ngebel Volcanic Complex can be divided into the Jeding with andesitic basalt (SiO2 49 - 59%), pyroxene andesite Kemlandingan (SiO2 49 - 59%), Manyutan with hornblende andesite (SiO2 49 - 59%), and Ngebel with dacite (SiO2: 49 - 59%). The variation of major elements combined with petrographic features such as plagioclase, pyroxene, hornblende, quartz, and opaque minerals from basaltic andesite to dacite is interesting. The minerals show that the magma differentiation process of Ngebel Volcanic Complex is the results of fractional crystallization of magma. The purpose of this study is to determine the evolution of magma from volcanic rocks of which stratigraphic positions have been determined. The analytical methodology used is petrographic and geochemical analysis. Detailed temporal evolution shows that magma from the Ngebel Volcanic Complex underwent a differentiation process that changed the magma composition from mafic to more felsic.