Morphological Changes due to Anthropogenic Interferences in Gendol River Valley, Merapi Volcano

This research aims to identify the morphological changes in Gendol river, Merapi volcano. After the eruption 2010, Gendol river filled up by pyroclastic materials, then utilized as mining area. As the volcanic materials are abundance in Gendol river, sand mining activities are dominant, causing antrophogenic interferences that changes the morphology of Gendol valley. In this study, the morphological changes is measured by terrestrial survey, aerial mapping, and materials analysis through petrographic and granulometric analysis. Aerial mapping was conducted in February and August 2019 in order to identify the dynamic changes during 6 months observation. Vertical changes is found in the active mining zone, in western-side of research area, while horizontal changes was found in eastern-side. The comparison of widening and narrowing valley is 13:1 due to horizontal changes. Result of petrographic analysis showes that three different sampling locations originated from similar provenance, which is undissected arc provenance but may differ in period of sedimentation. Grain material found in research are categorized as suitable material for mining with the 0,733 mm grain size. However, the mining activities should be aware of material availability to minimize the riverbank failure

Impacts of volcanic eruptions on the landscape evolution of Lombok Island, Indonesia

En Indonésie, les études qui analysent de manière combinée les impacts physiques et sociétaux des éruptions passées sont encore limitées. Dans cette thèse, nous traitons de cette thématique, principalement pour évaluer les impacts de l'éruption de 1257 CE et ceux d'une avalanche de débris d’âge Holocène du volcan Samalas à Lombok. Le premier objectif était de reconstruire la morphométrie du dépôt d'avalanche de débris (DAD) Kalibabak et de dater cet événement. Nous concluons que ce DAD se classe parmi les trois premières avalanches de débris volcaniques les plus volumineuses d’Indonésie, et se classe au huitième rang des plus volumineux DAD dans le monde. Sur la base d'une série de 10 nouvelles datations de paléosols, nous suggérons que le DAD a été mis en place lors de l'éruption subplinienne qui a produit la « Propok pumice » entre 5000 et 2600 BCE. Le deuxième objectif était de reconstruire les impacts géomorphologiques de l'éruption du Samalas de 1257 CE dans la partie occidentale de Lombok. Les changements abrupts dans la partie amont de la zone d'étude ont été causés par des dépôts pyroclastiques (courants de densité pyroclastiques ou PDC) d’un volume total de 110+3 x 106 m3. En revanche, la zone en aval a connu des changements graduels dus aux lahars post-éruptifs et à la sédimentation fluviale (208+3 x 106 m3). Le dernier objectif de la thèse était d’analyser la réponse des habitants suite à l'éruption de Samalas en 1257 CE. Une exégèse de trois sources indigènes (babad) de Lombok a été réalisée. Le contexte géographique mentionné dans les babad est l'une des caractéristiques uniques des textes, qui ont permis de reconstituer la période de crise jusqu'à la période de relèvement.Volcanic eruptions in Indonesia and other parts of the world have had many impacts, both physical and social. However, only limited studies combine the investigation of physical and social impacts in a single eruption, especially for past events. The investigation of these issues is applied to Lombok Island, in this thesis, primarily assessing the impacts of the 1257 CE Samalas eruption and a Holocene debris avalanche. The first objective is to reconstruct the old sector collapse and the morphometry of the resulting debris avalanche deposit (Kalibabak DAD). The results show that Kalibabak DAD ranks among the top three DADs in Indonesia based on its volume (after Raung and Galunggung volcanoes), and ranks eighth among the largest DADs worldwide. This DAD was emplaced during the subplinian eruption that expelled the Propok pumice between 5,000 and 2,600 BCE. The second objective is to reconstruct the geomorphological impact of the 1257 CE Samalas eruption in western part of Lombok. The study area has undergone both abrupt and gradual changes. The abrupt changes in the upstream part were caused by the deposition of 110+3x106 m3 of pyroclastic density current (PDC) during the eruption. In contrast, the downstream area experienced gradual changes by post-eruptive lahars and fluvial sedimentation (208+3x106m3). The last objective is to analyze the inhabitant’s response following the eruption of Samalas in 1257 CE. Exegesis of three indigenous written sources (babad) form Lombok was conducted. The geographical context mentioned in the babad is one of the unique features of the texts from Lombok, which helps reconstruct the emergency-crisis up to the recovery period

Anthropogenic Signatures in the Context of Landscape Evolution: Evidence from Citanduy Watershed, Java, Indonesia

The impact of humans on landscapes may differ across regions because anthropogenic intervention on the respective landscapes occurs in different human-induced contexts. This study was designed to assess the human-induced landscape evolution of the Citanduy Watershed, Java, Indonesia, and determine its anthropogenic signatures. Several approaches were used, namely anthropogenic landscape identification, anthropogenic soil development, sediment analysis, and monitoring of changes to Segara Anakan lagoon at the mouth of the Citanduy Rier. Five types of anthropogenic landscapes were observed in the research area, from a slightly modified landscape to a fully anthropogenic landscape. The anthropogenic signature was also found in the sediment of the lagoon. Present and recent environmental evolution of the lagoon was reconstructed based on series changes in the lagoon area. This reconstruction was then linked to the governmental program and anthropogenic intervention to reveal the complexity of the human-induced landscape evolution. Anthropogenic phenomena were found to strongly influence the evolution of Segara Anakan lagoon, as recorded approximately through three phases of its evolution: 1) natural processes occurring continuously until 1960, 2) human-induced landscape evolution, the boundary of which occurred in 1960–1980, and 3) the recent anthropogenic evolution that has existed since 1980

Water quality and sustainability of Merdada Lake, Dieng, Indonesia

The volcanic lakes in Dieng Plateau offer some unique phenomena, which interest not only tourists but also scientists. However, as the land use changes, the lakes are now facing environmental degradation especially from agricultural practices. This research aims to study the impact of agricultural practices on the environmental degradation of the lakes especially the water quality and analyze the sustainability of the lakes to support water needs. Merdada Volcanic Lake, one of the lakes in Dieng Plateau was selected as the focus of this research. Method conducted on this research are fields survey to collect the physical parameters temperature and conductivity also chemical parameters like pH, Nitrate, BOD, phosphate, and coliform. A complementary data was acquired using interviews method for defining the sustainability of the lake. Based on observation, water level of the lake is gradually decreased, especially during the dry season. At the same time, the agricultural practices in the surrounding area led to soil erosion, which involved surface runoff that transporting sediments into the lake. This research found that the practices of potato cultivation pumped out the water from Merdada Volcanic Lake and distributed over the plantation area. This practice caused a dramatic decrease in the water surface. Besides that, the agricultural practices had several adverse effects on the volcanic lakes in Dieng Plateau especially eutrophication and decrease of water quality in Merdada Lake where nitrate is over from water quality standard class II. Coliform also has an over expected value, range from 3–11 MPN/100 ml

Water quality and sustainability of Merdada Lake, Dieng, Indonesia

The volcanic lakes in Dieng Plateau offer some unique phenomena, which interest not only tourists but also scientists. However, as the land use changes, the lakes are now facing environmental degradation especially from agricultural practices. This research aims to study the impact of agricultural practices on the environmental degradation of the lakes especially the water quality and analyze the sustainability of the lakes to support water needs. Merdada Volcanic Lake, one of the lakes in Dieng Plateau was selected as the focus of this research. Method conducted on this research are fields survey to collect the physical parameters temperature and conductivity also chemical parameters like pH, Nitrate, BOD, phosphate, and coliform. A complementary data was acquired using interviews method for defining the sustainability of the lake. Based on observation, water level of the lake is gradually decreased, especially during the dry season. At the same time, the agricultural practices in the surrounding area led to soil erosion, which involved surface runoff that transporting sediments into the lake. This research found that the practices of potato cultivation pumped out the water from Merdada Volcanic Lake and distributed over the plantation area. This practice caused a dramatic decrease in the water surface. Besides that, the agricultural practices had several adverse effects on the volcanic lakes in Dieng Plateau especially eutrophication and decrease of water quality in Merdada Lake where nitrate is over from water quality standard class II. Coliform also has an over expected value, range from 3–11 MPN/100 ml

Sand transport characterization on the foredune area of Parangtritis, Indonesia

The aim of the research are to determine the characteristics of sand deflation on Parangtritis foredune area. The development of tourism activity on surrounding area could be has a big impact to the sand transport process. Data required in this research are wind direction and its speed, the sand mass collected from sand sampler, sand grain size, roundness and sphericity, and interview from tourists. Sand that transported by wind collected by sand sampler with dimension of 0.76 cm height and 1 cm width. Sand transport rate or deflation calculated by Bagnold’s formula. The results showed that the deflation process is bigger at daytime observation that at night, it is average 2.42 g.m-1s-1during day and 0.03 g.m-1s-1during night. Each samples location have different deflation characteristics of material that transported. Grain diameters ranging from 0.318 mm to 0.395 mm with dominance texture is medium sand. Sphericity and roundness of sediment material was on a scale of 0.5 and 0.7. This natural process that occurred on the research area didn’t knowing well either by local communities or tourists. Therefore need some proper management for support the continuity of deflation process for supplying material to the main sand dune area of Parangtritis

L'éruption cataclysmique de 1257 CE du volcan Samalas (Indonésie) révélée par des sources écrites locales: royaumes oubliés, réponse aux situations d'urgence et relèvement de la société

International audienc

Avalanche de débris et événement éruptif associé au volcan Samalas, Lombok, Indonésie

International audienceWe propose a vast area in the middle of Lombok, Indonesia, dominated by hummock hills, is a debris avalanche deposit (DAD). We define this > 500 km2 area as Kalibabak DAD that may originate from Samalas volcano. No descriptions of the morphology, stratigraphy, mechanism, and age of this DAD have yet been reported; this contribution bridges this research gap. Here we present morphological and internal architecture analysis, radiocarbon dating, paleotopographic modeling, and numerical simulation of the DAD. We also present geospatial data e.g., topographical and geological maps, digital elevation models (DEMs), satellite imagery – in combination with stratigraphic data constructed from field surveys, archived data, and electrical resistivity data. Results show that the DAD was formed by a sector-collapse of Samalas volcano and covers an area of 535 km2, with a deposit width of 41 km and a runout distance up to 39 km from the source. The average deposit thickness is 28 m, reaching a measured local maximum of 58 m and a calculated volume of ~ 15 km3. Andesitic breccia boulders and a sandy matrix dominate the deposit. Using ShapeVolc, we reconstructed the pre-DAD paleotopography and then used the reconstructed DEM to model the debris avalanche using VolcFlow. The model provides an estimate of the flow characteristics, but the extent of the modelled deposit does not match the present-day deposit, for at least two reasons: (i) the lack of information on the previous edifice topography that collapsed, and (ii) limited understanding of how DADs translate across the landscape. Fourteen radiocarbon dating samples indicate that the DAD was emplaced between 7,000–2,600 BCE. The DAD's enormous volume, vast extent and poorly weathered facies strongly suggest that it was not triggered by a Bandai-type debris avalanche (solely phreatic eruption), but more likely by a Bezymianny-type (magmatic eruption). This event was potentially triggered by a sub-Plinian or Plinian eruption (high eruption column with umbrella-like cloud) dated ~ 3,500 BCE, which produced the Propok pumice fall deposits

Coastal sedimentation and topographic changes in the Mataram Plain, Lombok (Indonesia) following the 1257 CE eruption of Samalas volcano

International audienc