Lahar has been applied as a general term for rapidly flowing, high-concentration, poorly sorted sediment-laden mixtures of rock debris and water (other than normal streamflow) from a volcano. Lahars are one of the most destructive phenomena associated with composite volcanoes, which are dominant in Java Island. Resulting deposits of lahar are poorly sorted, massive, made up of clasts (chiefly of volcanic composition), that generally include a mud-poor matrix. The aim of this research is threefold: to discuss the initiation of lahars occurrences, their dynamics, to assess the hazard and to analyse the deposition. Lahars are either a direct result of eruptive activity or not temporally related to eruptions. Syn-eruptive lahars may result from the transformation on pyroclastic flows or debris avalanches which transform to aqueous flows (e.g. at Papandayan in November 2002); They may be also generated through lake outburst or breaching (e.g. at Kelut in 1909 or 1966), and through removal of pyroclastic debris by subsequent heavy rainstorms. Post-eruptive lahar occurs during several years after an eruption. At Merapi, lahars are commonly rain-triggered by rainfalls having an average intensity of about 40 mm in 2 hours. Most occur during the rainy season from November to April. Non-eruptive lahars are flows generated without eruptive activity, particularly in the case of a debris avalanche or a lake outburst (e.g., Kelut). A lahar may include one or more discrete flow processes and encompass a variety of rheological flow types and flow transformations. As such, lahars encompass a continuum between debris flows and hyperconcentrated flows, as observed at Merapi, Kelut and Semeru volcanoes. Debris flows, with water contents ranging from 10 to no more than about 25% weight, are non-newtonian fluids that move as fairly coherent masses in what is thought to be predominantly laminar fashion. However, the relative importance of laminar versus turbulent regime is still debatable. Hyperconcentrated streamflows contain 25- to about 40%-weight-water; these flows possess some yield stress, but they are characteristically turbulent. Hazard-zone maps for lahar were produced for most of the the Javanese volcanoes, but these maps are on too small-scale to meet modern zoning requirements. More recently, a few large-scale maps (1/10,000 and 1/2,000-scale) and risk assessments have been completed for a few critical river systems at Merapi.
The 7.4 SR earthquake which occurred in The Donggala Regency, Central Sulawesi on September 28th 2018 was a shallow earthquake due to the Palukoro fault activity. The impact of the quake’s shaking created pressure on the rock and soil masses of 77 hilly locations in the Palu, Sigi, and Donggala, causing several landslides and the increasing the potential of more. One of the slopes of at risk of landslides which can trigger debris flow is found on the hills of Poi Village, Dolo Selatan District, Sigi Regency. The estimated volume of lose material which could fall in a landslide is 4.8 million m3. Rainfall in the area is predicted to trigger debris flow with the potential to bury settlements and block the flow of the Palu tributary located downstream. For this reason, it is necessary to conduct a study of the lose material deposits in the Poi River channel which can trigger debris flows during the rainy season. The problem-solving method in this study used is a rationalistic and descriptive qualitative approach. In predicting the distribution direction, propagation and hydrograph of the debris flow ths study applies the numerical modelling SIMLAR 2.1. This debris disaster risk management effort uses Sabo technology physically and non-physically. Keywords: earthquakes, landslides, debris flow, debris disaster management, Sabo technology physically and non-physically.
The lahar flow that occurred after the 2012 Gamalama Volcano eruption, leading to the eastern valley flowing downstream through the Togurara River to the center of Ternate City and Sultan Babullah Airport. To overcome the potential of lahar flow in the river since 2013 - 2016, several sabo dams and building facilities have been built. Based on the results of the calculation of deposits that potentially become lahar flows in 2016, the built-in capacity of the Sabodam has not been able to control the volume of sediment in the upstream of the river, then in the year 2017, 2018 constructed several additional Sabodam. In order to determine the effectiveness, feasibility and conditions of the completeness of Sabodam, is done field assessment on 25 ~ 27 September 2018, the method used was a mathematical approach based on sabo technology. The assessment was in the form of a field survey, simple measurements, interviews with the Sabodam management agency and local residents related to the lahar flow that had occurred. With the capacity of several additional Sabodams built in series, the average river bed slope was originally 9.09% to 6.83%. After the construction of Sabodam, the maximum lahar flow was once as high as 7 m, but now it decreases do 4.2 m. As the slope of the Togurara River slopes progressively, the lahar flow rate and its destructive power are reduced, so that Ternate City and Sultan Babullah Airport are spared from lahar disaster.Keywords: Lahar flow, sabodam, sabo technology, slope of riverbed, Togurara River.
The objective of the research was to analyse probability of lahar flows occurrence in Muntilan urban area, Central Java. By using integrated methods, which involve the numerical simulation program, Geographic Information System (GIS), Remote Sensing (RS) and field verification to produce lahar flows Hazard Map and Risk Map. Muntilan urban area located at western flank of Merapi volcano, and in down stream of Lamat river. The river is Lahar River that is endangering from Merapi volcano, which flowing down to cuts a cross of that area. Therefore, Muntilan urban area is vulnerable area from lahar flows disaster. Lahar flows, generally occur during intense rainfall on saturated volcanic deposit in upper stream of river or wall of volcano. Lahar flows are extremely dangerous especially to those living in valley areas near a volcano, which can undercut banks and cause houses destruction situated on the banks, and can bury and destroy resident, structures, infrastructure facilities including roads and bridges. Meanwhile, development of Muntilan urban area that caused many illegal settlements appears surrounding that area. Occasionally, un-benefit people constructing house in disaster prone area, such as down stream of river side that have lahar flows risk. The research was concluded that lahar flow occurrence in 100 years return period will be buried the Muntilan urban area. With the methods integrating of GIS, RS, field verification can be done analysing of lahar flows hazard map, and risks map to produce risk assessment in Muntilan urban area. Abstrak Tujuan dari penelitian ini adalah untuk menganalisis kemungkinan terjadinya aliran lahar di perkotaan Muntilan , Jawa Tengah. Metode penelitian ini merupakan metode terpadu dengan melibatkan program simulasi numerik, Sistem Informasi Geografis (SIG), Penginderaan Jauh (PJ) dan verifikasi lapangan untuk menghasilkan Peta Bahaya dan Peta Risiko aliran lahar. Daerah perkotaan Muntilan terletak di sisi barat Gunung
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