Tephra from large explosive eruptions can cause damage to buildings over wide geographical areas, creating a variety of issues for post-eruption recovery. This means that evaluating the extent and nature of likely building damage from future eruptions is an important aspect of volcanic risk assessment. However, our ability to make accurate assessments is currently limited by poor characterisation of how buildings perform under varying tephra loads. This study presents a method to remotely assess building damage to increase the quantity of data available for developing new tephra fall building vulnerability models. Given the large number of damaged buildings and the high potential for loss in future eruptions, we use the Kelud 2014 eruption as a case study. A total of 1154 buildings affected by falls 1–10 cm thick were assessed, with 790 showing signs that they sustained damage in the time between pre- and post-eruption satellite image acquisitions. Only 27 of the buildings surveyed appear to have experienced severe roof or building collapse. Damage was more commonly characterised by collapse of roof overhangs and verandas or damage that required roof cladding replacement. To estimate tephra loads received by each building we used Tephra2 inversion and interpolation of hand-contoured isopachs on the same set of deposit measurements. Combining tephra loads from both methods with our damage assessment, we develop the first sets of tephra fall fragility curves that consider damage severities lower than severe roof collapse. Weighted prediction accuracies are calculated for the curves using K-fold cross validation, with scores between 0.68 and 0.75 comparable to those for fragility curves developed for other natural hazards. Remote assessment of tephra fall building damage is highly complementary to traditional field-based surveying and both approaches should ideally be adopted to improve our understanding of tephra fall impacts following future damaging eruptions.
. The Cibaliung deposit is a low‐sulfidation type epithermal gold deposit situated about 70 km west of the Bayah dome complex. The gold‐bearing quartz veins are hosted by basaltic andesite of the Honje Formation, which is comparable to the host rock of gold deposits at the Bayah dome complex.
In order to clarify the timing of the mineralization and the volcanism at the Cibaliung area, two radiometric dating methods were applied. First, 40Ar/39Ar dating was conducted on six adularia samples to elucidate the age of mineralization. Second, K‐Ar method was applied to two samples of the host rock, andesite and the Cibaliung tuff, in order to reveal the timing of volcanism.
The 40Ar/39Ar dating determined mineralization ages in the range from 11.18 to 10.65 Ma while the K‐Ar dating indicated the age of the andesite and the Cibaliung tuff to be 11.4±0.8 Ma and 4.9±0.6 Ma, respectively. These results imply that the epithermal gold mineralization in the Cibaliung area is related to the volcanic activity that produced the Honje Formation, while the Cibaliung tuff played an important role in the preservation of the Cibaliung deposit. The Cibaliung deposit is the oldest epithermal gold deposit yet discovered in western Java.
Middle Ma) low sulfi dation-type epithermal gold mineralization occurred in the Cibaliung area, southwestern part of Java Island, Indonesia. It is hosted by andesitic to basaltic andesitic lavas of the Middle Miocene Honje Formation (11.4 Ma) and is covered by Pliocene Cibaliung tuff (4.9 Ma). The exploration estimates mineral resource of approximately 1.3 million tonnes at 10.42 g/t gold and 60.7 g/t silver at a 3 g/t Au cut-off. This equates to approximately 435,000 ounces of gold and 2.54 million ounces of silver. That resource resulted from two ore shoots: Cibitung and Cikoneng. Studies on ore mineralogy, hydrothermal alteration, geology, fl uid inclusion, stable isotopes and age dating were conducted in order to characterize the deposit and to understand a possible mechanism of preservation of the deposit. The ore mineral assemblage of the deposit consists of electrum, naumannite, Ag-Se-Te sulfi de minerals, chalcopyrite, pyrite, sphalerite and galena. Those ore minerals occur in quartz veins showing colloform -crustiform texture. They are enveloped by mixed layer clay illite/smectite zone, which grades into smectite zone outward. The temperature of mineralization revealed by fl uid inclusion study on quartz in the veins ranges from 170 and 220°C at shallow and deep level, respectively. The temperature range is in agreement with the temperature deduced from the hydrothermal alteration mineral assemblage including mixed layered illite/smectite and laumontite. The mineralizing fl uid is dilute, with a salinity <1 wt% NaCl equivalent and has stable isotopes of oxygen and hydrogen composition indicating a meteoric water origin. Although the deposit is old enough that it would have been eroded in a tropical island arc setting, the coverage by younger volcanic deposits such as the Citeluk tuff and the Cibaliung tuff most probably prevented this erosion.
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