The flank collapse of Anak Krakatau on 22 December 2018 caused massive topography losses that generated a devastating tsunami in Sunda Strait, which then followed by eruptions that progressively changed the topography and structure of Anak Krakatau. Here, we investigated topography and structural changes due to the December 2018 flank collapse and the following eruptions by using high resolution Digital Elevation Model (DEM) before and after the events and sentinel 1A satellite image post-flank collapsed. Results show that the volumetric losses due to the 22 December 2018 flank collapsed is ~127 x 106 m3, while the following eruptions caused ~0,8 x 106 m3 losses. Structural investigation suggests two structures that may act as failure planes. The first structure is located at the western part of volcanic edifice that associated with hydrothermal alteration and the second failure is an old crater rim which delineated an actively deform volcanic cone.

Limboto Lake—Pentadio area is located in the province of Gorontalo on the northern arm of Sulawesi Island, Indonesia, which experienced a tectonic process from the Sula Platform collision in the mid-Miocene. This tectonic process led to the westward subduction of the early Miocene and post-collision rifting and uplifting of the arc and subduction along the North Sulawesi Trench during the Late Miocene to the Quaternary periods. The rifting process of the North Sulawesi arc resulted in the formation of the Gorontalo graben zone in the W–E direction. There are geothermal surface manifestations near Limboto Lake, such as hot spring complexes, with temperatures ranging from 74.8 °C to 78.5 °C. To understand the geological structure and prospective geothermal characteristics beneath the investigated area, we performed integrated magnetotelluric and gravity surveys. The preferred 3D resistivity model confirmed the presence of a fault system and a graben system that was filled with conductive bodies (~1–15 Ωm) corresponding to alluvium deposits. This result was in accordance with the 2D density model inferred from the gravity data, where a low-density value indicates the presence of a graben zone. The conceptual model of Limboto Lake—Pentadio was constructed using the information from the MT and gravity results, and from the geological study. The conceptual model illustrates the geothermal system in Limboto Lake—Pentadio, which is controlled by the fault system and the Gorontalo graben system.

Le volcan indonésien Papandayan est entré en éruption en novembre 2002, éjectant plus d'un million de mètres cubes de cendres volcaniques. Malgré la faible magnitude de l'éruption, les pertes directes ont été considérables (1,5 M US$) et l'ensemble du bassin versant a été bouleversé par plusieurs processus morphodynamiques qui se sont succédés dans le temps et dans l'espace.

AbstrakSejak awal Maret 2014 status aktifitas Gunungapi Slamet di Jawa Tengah dinaikan dari Normal menjadi Waspada seiring dengan peningkatan jumlah gempa vulkanik. Seismisitas Gunungapi Slamet memperlihatkan gempa letusan 1106 kejadian dan gempa hembusan 6857 per hari.  Sementara itu,  gempa vulkanik dalam hanya terekam 2 kali selama periode Maret – Agustus 2014. Sumber gempa berada pada kedalaman antara 1 - 2 km di bawah kawah Gunungapi Slamet sebagai indikasi gempa permukaan. Peningkatan aktifitas vulkanik Slamet menghasilkan pelepasan gas CO2 yang berpengaruh terhadap fluida panas bumi yang ditunjukan dengan terjadinya perubahan keasaman air dari normal menjadi alkalin, pembentukan bualan gas CO2 pada air panas Pancuran 3 di Baturraden, dan peningkatan saturasi kalsit.  Bualan gas CO2 menjadi indikasi terjadinya proses pendidihan pada temperatur 273 C pada kedalaman 454 m di bawah permukaan laut. Kondisi ini menjadikan temperatur reservoir lebih tinggi sebagai indikasi sistem panas bumi Gunungapi Slamet merupakan sistem panas bumi aktif bertemperatur tinggi. Kata kunci : gempa permukaan, fluida panas bumi, bualan gas, saturasi kalsitAbstractSince the beginning of March 2014 the status of activities Slamet volcano in Central Java has been declared from Normal becomes Alert due to significant increase in the number of volcanic earthquakes. Slamet volcano seismicity shows eruption earthquakes as many as 1106, and gas emission earthquakes as many as 6857 events per day. Meanwhile, the deep volcanic earthquake recorded only 2 times during the period March to August 2014. The hypocentre of these earthquake was at a depth of 1-2 km below Slamet volcano crater as an indication of the surface earthquakes.Increased magmatic activity resulted in the release of CO2 gas effect on the geothermal fluid which is indicated by changes in water acidity from normal to alkaline, formation of CO2 bubble gas on Pancuran 3 hot spring at Baturraden area, and calcite saturation enhancement. The presence of CO2 bubble gas is indication of boiling at temperatures 273 C at a depth of 454 m below sea level. This condition makes the reservoir temperature becomes higher as indication that the geothermal system of Slamet volcano is active geothermal systems with high temperature (high enthalpy).Keywords: surface earthquake, geothermal fluid, bubble gas.