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Franck Lavigne - One of the best experts on this subject based on the ideXlab platform.
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Post-eruptive Lahars at Kali Putih following the 2010 eruption of Merapi volcano, Indonesia: occurrences and impacts
Natural Hazards, 2018Co-Authors: Danang Sri Hadmoko, Edouard De Belizal, Franck Lavigne, Muh Aris Marfai, Bachtiar W. Mutaqin, Gilang Arya Dipayana, Junun Sartohadi, Suratman Worosuprojo, Colette C.a. Starheim, Christopher GomezAbstract:Following the 2010 VEI 4 eruption of Merapi volcano, more than 250 Lahars were triggered during two rainy seasons from October 2010 to March 2012. This high number of post-eruption Lahars mainly occurred in the Kali (valley) Putih watershed and was mostly associated with high-magnitude rainstorms. A Lahar occurring on January 8, 2011, caused significant damage to homes in several communities, bridges, sabo dams, and agricultural crops. The aims of this contribution are to document the impacts of Lahars on the Kali Putih watershed and specifically (1) to analyze the Lahar frequency during the period of 1969–2012 on an inter-annual and intra-annual basis and to determine the link between the volume of tephra and the frequency of Lahars; (2) to detail the Lahar trajectory and channel evolution following the January 8th Lahar; (3) to map the spatial distribution of the thickness and geomorphic effects of the Lahar deposit; and (4) to determine the impacts of the Lahar on the infrastructure (sabo dams and roads) and settlements in the distal area of the volcano. The Kali Putih watershed has experienced 62 Lahars, which represent 22% of all Lahars triggered on 17 rivers at Merapi between 2010 and 2012. The main geomorphic impacts are: (1) excessive sedimentation in valleys, settlements and agricultural areas; (2) undercutting of the river banks by as much as 50 m, accompanied by channel widening; and (3) abrupt changes in the river channel direction in the distal area (15–20 km downstream of the volcano). About 19 sabo dams were damaged, and 3 were totally destroyed. Over 307 houses were damaged, and the National Road Yogyakarta–Semarang was regularly cut (18 times during approximately 25 days). Although the sabo dams on Kali Putih were originally constructed to protect distal areas from Lahar damage, they had little effect on the 2010–2012 rain-triggered Lahars. The underlying design of those dams along this river is one of the main reasons for the major destruction in this sector of the volcano’s lower slope. The catch basin capacity of the sabo dam was only 1.75 × 106 m3, whereas the total volume of the 2010–2011 Lahars exceeded 5 × 106 m3. In order to prepare for future Lahars, the government has invested in significant mitigation measures, ranging from structural approaches (e.g., building new sabo dams and developing an early warning system) to non-structural approaches (e.g., contingency and preparedness planning and hazard education).
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Lahars in Java: Initiations, Dynamics, Hazard Assessment And Deposition Processes
Forum Geografi, 2016Co-Authors: Franck Lavigne, Jean-claude Thouret, Danang Sri Hadmoko, Bambang SukatjaAbstract: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.
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rain triggered Lahars following the 2010 eruption of merapi volcano indonesia a major risk
Journal of Volcanology and Geothermal Research, 2013Co-Authors: Edouard De Belizal, Franck Lavigne, Danang Sri Hadmoko, Jeanphilippe Degeai, Gilang Aria Dipayana, Bachtiar Wahyu Mutaqin, Muh Aris Marfai, Marie Coquet, Baptiste Le Mauff, Annekyria RobinAbstract:Abstract The 2010 VEI 4 eruption of Merapi volcano deposited roughly ten times the volume of pyroclastic materials of the 1994 and 2006 eruptions, and is recognized as one of the most intense eruption since 1872. However, as the eruptive phase is now over, another threat endangers local communities: rain-triggered Lahars. Previous papers on Lahars at Merapi presented Lahar-related risk following small-scale dome-collapse PDCs. Thus the aim of this study is to provide new insights on Lahar-related risk following a large scale VEI 4 eruption. The paper highlights the high number of events (240) during the 2010–2011 rainy season (October 2010–May 2011). The frequency of the 2010–2011 Lahars is also the most important ever recorded at Merapi. Lahars occurred in almost all drainages located under the active cone, with runout distances exceeding 15 km. The geomorphic impacts of Lahars on the distal slope of the volcano are then explained as they directly threaten houses and infrastructures: creation of large corridors, avulsions, riverbank erosion and riverbed downcutting are detailed through local scale examples. Related damage is also studied: 860 houses damaged, 14 sabo-dams and 21 bridges destroyed. Sedimentological characteristics of volcaniclastic sediments in Lahar corridors are presented, with emphasis on the resource in building material that they represent for local communities. Risk studies should not forget that thousands of people are exposing themselves to Lahar hazard when they quarry volcaniclastic sediment on Lahar corridors. Finally, the efficient community-based crisis management is explained, and shows how local people organize themselves to manage the risk: 3 fatalities were reported, although Lahars reached densely populated areas. To summarize, this study provides an update of Lahar risk issues at Merapi, with emphasis on the distal slope of the volcano where Lahars had not occurred for 40 years, and where Lahar corridors were rapidly formed.
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in flow evolution of Lahar deposits from video imagery with implications for post event deposit interpretation mount semeru indonesia
Journal of Volcanology and Geothermal Research, 2013Co-Authors: Colette C.a. Starheim, Franck Lavigne, Christopher Gomez, Tim Davies, Patrick WassmerAbstract:Abstract The hazardous and unpredictable nature of Lahars makes them challenging to study, yet the in-flow processes characterizing these events are important to understand. As a result, much of the previous research on Lahar sedimentation and flow processes has been derived from experimental flows or stratigraphic surveys of post-event deposits. By comparison, little is known on the time-dependent sediment and flow dynamics of Lahars in natural environments. Using video-footage of seven Lahars on the flanks of Semeru Volcano (East Java, Indonesia), the present study offers new insights on the in-flow evolution of sediment in natural Lahars. Video analysis revealed several distinctive patterns of sediment entrainment and deposition that varied with time-related fluctuations in flow. These patterns were used to generate a conceptual framework describing possible processes of formation for subsurface architectural features identified in an earlier lateral survey of Lahar deposits on Semeru Volcano (Gomez and Lavigne, 2010a). The formation of lateral discontinuities was related to the partial erosion of transitional bank deposits followed by fresh deposition along the erosional contact. This pattern was observed over the course of several Lahar events and within individual flows. Observations similarly offer potential explanations for the formation of lenticular features. Depending on flow characteristics, these features appeared to form by preferential erosion or deposition around large stationary blocks, and by deposition along channel banks during episodes of channel migration or channel constriction. Finally, conditions conducive to the deposition of fine laminated beds were observed during periods of attenuating and surging flow. These results emphasize the difficulties associated with identifying process–structure relationships solely from post-event deposit interpretation and illustrate that an improved understanding of the time-dependent sediment dynamics in Lahars may be advantageous when interpreting post-event structural features.
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Sediment transportation and deposition by rain-triggered Lahars at Merapi Volcano, Central Java, Indonesia
Geomorphology, 2002Co-Authors: Franck Lavigne, Jean-claude ThouretAbstract:Abstract A Lahar is a general term for a rapidly flowing mixture of rock debris and water (other than normal streamflow) from a volcano and refers to the moving flow. Located in the populated area of Central Java, the stratovolcano Merapi (2965 m) is prone to Lahar generation, due to three main factors: (1) millions of cubic meters of pyroclastic deposits are the product of frequent pyroclastic flows, which have occurred on 2- to 4-year intervals; (2) rainfall intensity is high (often 40 mm in 2 h on average) during the rainy season from November to April; and (3) drainage pattern is very dense. Following the 22 November 1994 eruption of Merapi, 31 rain-triggered Lahar events were recorded in the Boyong River between December 1994 and May 1996. On Merapi's slopes, instantaneous sediment concentration at any given time of the Lahars varies widely over time and space. Lahars are transient sediment-water flows whose properties are unsteady, so that the sediment load fluctuates during the flow. The boundary between the flow types (debris flow, with sediment concentration >60% volume, or hyperconcentrated flow, with sediment concentration ranges from 20% to 60% volume) may fluctuate within the flow itself. Grain-size distribution, physical composition of sediments, shear stress, yield stress, and water temperature play each a role on this boundary. Natural self-damming and rapid breakout are partly responsible for the sediment variations of the flows. Debris-flow phases at Merapi typically last a few minutes to 10 min, and are often restricted to the Lahar front. Debris-flow surges are sometimes preceded and always followed by longer hyperconcentrated flow phases. As a result, mean sediment concentration of the Lahars is low, commonly from 20% to 50% volume. Besides, transient normal streamflow phases (sediment concentration Low sediment load and frequent transient flows in the Merapi channels may result from at least three factors: (1) several breaks-in-slope along the channel increase the deposition rate of sediment, and hinder the bulking capacity of the Lahars; (2) source material is mainly coarse debris of “Merapi-type” block-and-ash flows. Consequently, the remobilization of coarse debris is more difficult and the clast deposition is accelerated; (3) variations of rainfall intensity over time and space, common in tropical monsoon rainfall, also influence the sediment load variations of the Lahars. Sedimentologic analyses of the Lahar deposits in the Boyong River at Merapi encompass clast-supported and matrix-supported debris-flow deposits, hyperconcentrated flow deposits, and streamflow deposits. The stratigraphic succession of massive and stratified beds observed immediately after any given Lahar event in the Boyong River indicates that the sediment concentration varies widely over time and space during a single Lahar event. Sedimentation rate varies from 3 to 4.5 cm/min during relatively long-lived surges to as much as 20 cm/min during short-lived surges. These results indicate that the sediment load fluctuates during Lahar flow, further demonstrating that Lahars are transient sediment-water flows with unsteady flow properties.
Shane J. Cronin - One of the best experts on this subject based on the ideXlab platform.
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Lahar hazard assessment using titan2d for an alluvial fan with rapidly changing geomorphology whangaehu river mt ruapehu
Geomorphology, 2010Co-Authors: Jonathan Procter, Shane J. Cronin, Vincent E. Neall, Michael F Sheridan, Ian C Fuller, Harry KeysAbstract:Abstract Rapid changes in small areas at the apex of alluvial fans may have devastating consequences by directing downstream flood or Lahar impacts into catchments of widely varying population or infrastructure vulnerability. During a series of Lahars in 1995 at Mt. Ruapehu, New Zealand, aggradation of the Whangaehu fan apex (draining the eastern edifice) caused the onset of avulsion of flows northward into the highly vulnerable Tongariro catchment. An earth training dike (or bund) was constructed to protect this catchment by retaining flows on the southern side and the normal Lahar outlet path to the south. Surveys in 2001, late 2005, and following a major Lahar in March 2007 now show net degradation of a channel in the Whangaehu fan apex, bordered by the bund. This indicates a net increase in the channel capacity at this site and shows that the bund remains at its effective design capacity. Past hydrological modelling used for the bund design provided a large range of discharge estimates but lacked precise constraints on the size and nature of Lahars from eruption and lake-breakout events. New modelling has been carried out using Titan2D to examine the impacts of a 6 × 106 m3 volume granular flow down this catchment. This simulates either an eruption or a lake breakout-induced Lahar with a historically typical volumetric bulking factor of 4. These simulations predict minimum discharges between 1800 and 2100 m3/s at the bund site. By comparison, the largest 1995 flow at this site was estimated at around 1200 m3/s. Further, any single modelled flow from the normal outlet channel of Crater Lake could not be induced to overtop the bund because discharge appears to be limited by the narrow upper reaches of the Whangaehu Gorge. Theoretical discharge levels required to overtop the bund are estimated to be > 6800 m3/s, assuming no aggradation of the channel by the decelerating flow. Maximum potential discharge at the bund site is additionally modified by potential bifurcation of Lahars above a certain size threshold at a point 2.5 km upstream of the bund. A major side channel (“the chute”) effectively diverts part of the flows away to the southern side of the Whangaehu fan. This potential for splitting of the flow appears to have increased since 1995, from aggradation of Lahar deposits and reworked sediment in the area immediately upstream of the divide. Despite remaining at design capacity for Lahar events in the Whangaehu, erosion of new channels following the 2007 Lahar renders the bund vulnerable to undercutting.
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A fluid dynamics approach to modelling the 18th March 2007 Lahar at Mt. Ruapehu, New Zealand
Bulletin of Volcanology, 2009Co-Authors: Jonathan L. Carrivick, Vern Manville, Shane J. CroninAbstract:Lahars are water-sediment mass flows from a volcanic source. They can be triggered by a variety of mechanisms and span a continuum of flow rheology and hydraulic properties, even within the same event. Lahars are extremely powerful landscaping agents and represent a considerable hazard potential. However, this highly dynamic character and a lack of direct measurements has made modelling Lahars difficult. This study therefore applies a fluid dynamics model; Delft3D, to analyse the 18th March 2007 dam break Lahar at Mount Ruapehu, New Zealand. The modelled Lahar routed through the Whangaehu gorge in ~30 min, crossed the Whangaehu fan in ~60 min, and then over a further 3 h travelled an additional ~22 km distance along the Whangaehu River to the Tangiwai bridge. The modelled mean frontal velocity was 6.5 m s^−1 along the gorge although peak velocity reached up to 19.6 m s^−1. The modelled Lahar flow front progressively slowed across the fan but along the River it accelerated from 2.1–3.3 m s^−1. Calculated peak velocity along the River was
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a fluid dynamics approach to modelling the 18th march 2007 Lahar at mt ruapehu new zealand
Bulletin of Volcanology, 2009Co-Authors: Jonathan L. Carrivick, V Manville, Shane J. CroninAbstract:Lahars are water-sediment mass flows from a volcanic source. They can be triggered by a variety of mechanisms and span a continuum of flow rheology and hydraulic properties, even within the same event. Lahars are extremely powerful landscaping agents and represent a considerable hazard potential. However, this highly dynamic character and a lack of direct measurements has made modelling Lahars difficult. This study therefore applies a fluid dynamics model; Delft3D, to analyse the 18th March 2007 dam break Lahar at Mount Ruapehu, New Zealand. The modelled Lahar routed through the Whangaehu gorge in ~30 min, crossed the Whangaehu fan in ~60 min, and then over a further 3 h travelled an additional ~22 km distance along the Whangaehu River to the Tangiwai bridge. The modelled mean frontal velocity was 6.5 m s−1 along the gorge although peak velocity reached up to 19.6 m s−1. The modelled Lahar flow front progressively slowed across the fan but along the River it accelerated from 2.1–3.3 m s−1. Calculated peak velocity along the River was <4.5 m s−1. These results generally compare well with gauged records, with historical records, and with other modelling approaches. However, discrepancies in frontal velocity and time to peak stage arise due to (1) specifying roughness, which arises from slope variations between adjacent computational nodes, and which is stage-dependant, and (2) due to rapid topographic changes that produce frequent hydraulic jumps, which are inadequately accommodated in the numerical scheme. The overall pattern of discharge attenuation, and of relationships between topographic and hydraulic variables, is similar to that calculated for Lahars on other volcanoes. This modelling method could be applied at other similar sites where a likely source hydrograph and high-resolution topographic data are available. These results have important implications for hazard management at Ruapehu and for examining geomorphic and sedimentary impacts of this Lahar.
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Dynamic interactions between Lahars and stream flow: A case study from Ruapehu volcano, New Zealand
Geological Society of America Bulletin, 1999Co-Authors: Shane J. Cronin, Vincent E. Neall, Jérôme A. Lecointre, Alan PalmerAbstract:Three Lahars were sampled in the Whan-gaehu River on the eastern flank of Ruapehu volcano, New Zealand, at 23.5 and 42 km from the source as they were flowing on September 27 and 29 and October 6, 1995. The Lahars were generated by water explosively ejected from the highly mineralized Crater Lake. We used the chemical contrast between the Lahars and resident stream water in their paths to describe a four-phase model of a noncohesive Lahar wave in a river channel: (1) ambient stream water pushed ahead of the Lahar in a process of miscible displacement due to hydrodynamic dispersion; (2) a zone of mixing between the stream water and the Lahar that increases in length with distance from source; (3) a remnant of the original Lahar, least diluted by stream water, that decreases in length and dilutes downstream; (4) the tail of the Lahar surge. Peak discharge occurs at the end of phase 1 as water is pushed ahead of the Lahar. Peak sediment concentration occurs at the end of phase 2, where debris entrainment by the flow is at its greatest (i.e., in front of the Lahar proper). Deposits record only phases 2 and 3 of the Lahar wave, phase 1 flow left only a tide line of organic debris, and phase 4 deposits were rapidly eroded by later streamflow. Downstream dilution by stream water eventually caused transformation of phases 2 and 3 of the Lahars from debris flow to hyperconcentrated streamflow and then to normal streamflow as the flows became progressively finer grained and more turbulent.
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Lahar history and hazard of the Tongariro River, northeastern Tongariro Volcanic Centre, New Zealand
New Zealand Journal of Geology and Geophysics, 1997Co-Authors: Shane J. Cronin, Vincent E. Neall, Alan PalmerAbstract:Abstract Lahar deposits beside the Tongariro River have been mapped and dated using andesitic and rhyolitic marker tephras. Coupling the stratigraphic record obtained with that of the Tongariro and Ruapehu ring plains has enabled reconstruction of the history of Lahars along the Tongariro River. This forms the basis of a Lahar hazard map for the entire catchment. Six Lahar hazard zones, with assigned recurrence intervals ranging from 1 in 35 yr to 1 in >15 000 yr, have been mapped. Lahar deposits between the ages of 14.7 and 9.8 ka cover the greatest areas, while younger Lahar deposits are confined to lower surfaces closer to the present river channel. Holocene Lahar deposits along the Tongariro River are not as well preserved as older units, probably because the Holocene Lahars were confined to a more deeply incised channel and were more readily eroded following emplacement. All recorded post‐11.85 ka Lahars in the Tongariro catchment were derived from Ruapehu volcano. The Mangatoetoenui Stream has been ...
David Palacios - One of the best experts on this subject based on the ideXlab platform.
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smoothed particle hydrodynamic modeling of volcanic debris flows application to huiloac gorge Lahars popocatepetl volcano mexico
Journal of Volcanology and Geothermal Research, 2016Co-Authors: B. Haddad, David Palacios, M Pastor, Jose Juan ZamoranoAbstract:Abstract Lahars are among the most catastrophic volcanic processes, and the ability to model them is central to mitigating their effects. Several Lahars recently generated by the Popocatepetl volcano (Mexico) moved downstream through the Huiloac Gorge towards the village of Santiago Xalitzintla. The most dangerous was the 2001 Lahar, in which the destructive power of the debris flow was maintained throughout the extent of the flow. Identifying the zone of hazard can be based either on numerical or empirical models, but a calibration and validation process is required to ensure hazard map quality. The Geoflow-SPH depth integrated numerical model used in this study to reproduce the 2001 Lahar was derived from the velocity–pressure version of the Biot–Zienkiewicz model, and was discretized using the smoothed particle hydrodynamics (SPH) method. The results of the calibrated SPH model were validated by comparing the simulated deposit depth with the field depth measured at 16 cross sections distributed strategically along the gorge channel. Moreover, the dependency of the results on topographic mesh resolution, initial Lahar mass shape and dimensions is also investigated. The results indicate that to accurately reproduce the 2001 Lahar flow dynamics the channel topography needed to be discretized using a mesh having a minimum 5 m resolution, and an initial Lahar mass shape that adopted the source area morphology. Field validation of the calibrated model showed that there was a satisfactory relationship between the simulated and field depths, the error being less than 20% for 11 of the 16 cross sections. This study demonstrates that the Geoflow-SPH model was able to accurately reproduce the Lahar path and the extent of the flow, but also reproduced other parameters including flow velocity and deposit depth.
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geomorphological evolution of a fluvial channel after primary Lahar deposition huiloac gorge popocatepetl volcano mexico
Geomorphology, 2010Co-Authors: Luis M Tanarro, David Palacios, J. J. Zamorano, Nuria Andres, Chris S RenschlerAbstract:Abstract Popocatepetl volcano (19°02′ N, 98°62′ W, 5424 m) began its most recent period of volcanic activity in December 1994. The interaction of volcanic and glacier activity triggered the formation of Lahars through the Huiloac Gorge, located on the northern flank of the volcano, causing significant morphological changes in the channel. The most powerful Lahars occurred in April 1995, July 1997 and January 2001, and were followed by secondary Lahars that formed during the post-eruptive period. This study interprets the geomorphological evolution of the Huiloac Gorge after the January 2001 Lahar. Variations in channel morphology at a 520 m-long research site located mid-way down the gorge were recorded over a 4 year period from February 2002 to March 2005, and depicted in five geomorphological maps (scale 1:200) for 14 February and 15 October 2002, 27 September 2003, 9 February 2004, and 16 March 2006. A GIS was used to calculate the surface area for the landforms identified for each map and detected changes and erosion–deposition processes of the landforms using the overlay function for different dates. Findings reveal that secondary Lahars and others types of flows, like sediment-laden or muddy streamflows caused by precipitation, rapidly modified the gorge channel following the January 2001 non-eruptive Lahar, a period associated with volcanic inactivity and the disappearance of the glacier once located at the headwall of the gorge. Field observations also confirmed that secondary flows altered the dynamics and geomorphological development of the channel. These flows incised and destroyed the formations generated by the primary Lahars (1997 and 2001), causing a widening of the channel that continues today. After February 2004, a rain-triggered Lahar and other flows infilled the channel with materials transported by these flows. The deposits on the lateral edges of the channel form terraces. A recent lull in Lahar activity contrasts with the increasing instability of the edges of the channel and the continuous edification and destruction of recent Lahar terraces.
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on the geochronological method versus flow simulation software application for Lahar risk mapping a case study of popocatepetl volcano mexico
Geografiska Annaler Series A-physical Geography, 2010Co-Authors: Esperanza Munozsalinas, Vlad Constantin Manea, Marina Manea, Miguel Castillorodriguez, David PalaciosAbstract:Lahars are hazardous events that can cause serious damage to people who live close to volcanic areas; several were registered at different times in the last century, such as at Mt St Helens (USA) in 1980, Nevado del Ruiz (Colombia) in 1985 and Mt Pinatubo (Philippines) in 1990. Risk maps are currently used by decision-makers to help them plan to mitigate the hazard-risk of Lahars. Risk maps are acquired based on a series of tenets that take into account the distribution and chronology of past Lahar deposits, and basically two approaches have been used: (1) The use of Flow Simulation Software (FSS), which simulates flows along channels in a Digital Elevation Model and (2) The Geochronological Method (GM), in which the mapping is based on the evaluation of Lahar magnitude and frequency. This study addresses the production of a Lahar risk map using the two approaches (FSS and GM) for a study area located at Popocatepetl volcano – Central Mexico. Santiago Xalitzintla, a town located on the northern flank of Popocatepetl volcano, where volcanic activity in recent centuries has triggered numerous Lahars that have endangered local inhabitants, has been used for the case study. Results from FSS did not provide satisfactory findings because they were not consistent with Lahar sediment observations made during fieldwork. By contrast, the GM produced results consistent with these observations, and therefore we use them to assess the hazard and produce the risk map for the study area.
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A SPH depth integrated model for Popocatépetl 2001 Lahar (Mexico): Sensitivity analysis and runout simulation
Engineering Geology, 2010Co-Authors: B. Haddad, David Palacios, Manuel Pastor, Esperanza Muñoz-salinasAbstract:Abstract Lahars are debris flows of volcanic origin, which can endanger or even destroy communities located near the flanks of volcanoes. Lahars are not always triggered by eruptions; they can form during heavy rainfall or after hydrothermal alteration and volcanic edifice collapse. Decision makers need Lahar hazard maps to devise hazard prevention measures that will prevent casualties, so Lahar modelling is an important tool for assessing flow behavior and determining inundation areas. The depth integrated numerical model used in this study is derived from the velocity–pressure of the Biot–Zienkiewicz model and was discretized using the smoothed particle hydrodynamics (SPH) method to simulate a Lahar that occurred at Popocatepetl volcano in 2001. In order to investigate the convergence of the model, we used a range of different SPH mesh resolutions. Once the optimum mesh resolution was bounded, we analyzed the model's sensitivity to the initial Lahar volume, the density of the geomaterial, and the rheological parameter of the Bingham fluid. The results show that the SPH depth integrated model produced a highly accurate simulation of the distribution and velocity of the 2001 Lahar. The study also shows the effects of SPH mesh resolution and the relevant influence of rheological parameters.
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Tree-ring reconstruction of past Lahar activity at Popocatépetl volcano, Mexico
The Holocene, 2009Co-Authors: Michelle Bollschweiler, Lorenzo Vázquez-selem, Markus Stoffel, David PalaciosAbstract:Lahars represent a major threat on the slopes of volcanoes all over the world. In order to realistically assess hazards, knowledge on the occurrence and timing of past Lahar activity is of crucial importance. However, archival data on past events is usually scarce or completely missing. Tree-ring records have repeatedly proved to be a reliable data source for the reconstruction of past geomorphic events. However, tree rings have seldom been applied for the identification of past Lahars. Therefore, it was the aim of this study: (i) to identify and describe disturbances in tree growth induced by well-documented Lahar events and on this basis; and (ii) to recognise older, unknown Lahar events with tree-ring analyses. Based on these goals, we collected 140 tree-ring series from 62 trees (Abies religiosa, Pinus hartwegii and Pinus ayacahuite) standing inside or adjacent to the Lahar channel in the Huiloac gorge at Popocatepetl volcano, central Mexico. Most commonly, the known Lahar events of 1997 and 2001 resulted in abrupt changes in tree-ring width as well as injuries. The same growth disturbances could be identified in the tree-ring series, indicating that five previously unknown Lahar events would have occurred during the 20th century. Popocatepetl is one of the best surveyed volcanoes in the world and past eruptions are precisely noted in archives. As most of these unknown events occurred during periods with no volcanic activity, we believe that they were rainfall-induced rather than related to volcanic activity. In order to assess rainfall intensity threshold values for the triggering of events, the analyses of meteorological data needs to be integrated. In general, the investigated tree species proved to be highly suitable for the reconstruction of mass-movement processes. Therefore, the applied methods can be transferred to other locations where data on past events are missing.
Jean-claude Thouret - One of the best experts on this subject based on the ideXlab platform.
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Examining the impact of Lahars on buildings using numerical modelling
Natural Hazards and Earth System Sciences, 2017Co-Authors: Stuart Mead, Christina Magill, Vincent Lemiale, Jean-claude Thouret, Mahesh PrakashAbstract:Lahars are volcanic flows containing a mixture of fluid and sediment which have the potential to cause significant damage to buildings, critical infrastructure and human life. The extent of this damage is controlled by properties of the Lahar, location of elements at risk and susceptibility of these elements to the Lahar. Here we focus on understanding Lahar-induced building damage. Quantification of building damage can be difficult due to the 15 complexity of Lahar behaviour (hazard), varying number and type of buildings exposed to the Lahar (exposure) and the uncertain susceptibility of buildings to Lahar impacts (vulnerability). In this paper, we quantify and examine the importance of Lahar hazard, exposure and vulnerability in determining building damage with reference to a case study in the city of Arequipa, Peru. Numerical modelling is used to investigate Lahar properties that are important in determining the inundation area and forces applied to buildings. Building vulnerability is 20 quantified through the development of critical depth-pressure curves based on the ultimate bending moment of masonry structures. In the case study area, results suggest that building strength plays a minor role in determining overall building losses in comparison to the effects of building exposure and hydraulic characteristics of the Lahar.
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quantifying Lahar damage using numerical modelling
Natural Hazards and Earth System Sciences, 2016Co-Authors: Stuart Mead, Christina Magill, Vincent Lemiale, Jean-claude Thouret, Mahesh PrakashAbstract:Lahars are volcanic flows containing a mixture of fluid and sediment that have caused significant damage to buildings, critical infrastructure and human life. The extent of this damage is controlled by properties 10 of the Lahar, location of elements at risk and susceptibility of these elements to the Lahar. Here we focus on understanding Lahar-induced building damage. Quantification of building damage can be difficult due to the complexity of Lahar behaviour (hazard), uncertainty in number and type of buildings exposed to the Lahar (exposure) and the uncertain susceptibility of buildings to Lahar induced damage (vulnerability). In this paper, we quantify and examine the relative importance of Lahar hazard, exposure and vulnerability in determining building 15 damage with reference to a case study in the city of Arequipa, Peru. Numerical modelling is used to investigate Lahar properties important in determining the inundation area and forces applied to buildings. Building vulnerability is quantified through the development of critical depth-pressure curves based on the ultimate bending moment of masonry structures. In the case study area, results suggest that building strength plays a minor role in determining overall building losses in comparison to the effects of building exposure and Lahar hazard 20 properties such as hydraulic characteristics of the flow.
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Lahars in Java: Initiations, Dynamics, Hazard Assessment And Deposition Processes
Forum Geografi, 2016Co-Authors: Franck Lavigne, Jean-claude Thouret, Danang Sri Hadmoko, Bambang SukatjaAbstract: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.
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Geological and geotechnical characteristics of recent Lahar deposits from El Misti volcano in the city area of Arequipa, South Peru
Geotechnical and Geological Engineering, 2015Co-Authors: Carlos Pallares, Jean-claude Thouret, Denis Fabre, Claude Bacconnet, Juan Antonio Charca-chura, Kim Martelli, Aurélie Talon, Calixtro Yanqui-murilloAbstract:This study provides geotechnical characteristics of recent Lahar deposits on which the city of Arequipa (South Peru) is built. Geological and sedimentological observations point out the existence of three types of Lahar deposits in the Arequipa region: fine hyperconcentrated-flow deposits, coarse hyperconcentrated-flow deposits, and debris-flow deposits. The mineral components identified in the three types of Lahars show that they are linked to the outcropping volcanic rocks around Arequipa city. Physical measurements (dry density, grain-size distribution, specific surface of the grains based on methylene blue tests) and mechanical tests (in situ dynamic cone penetration soundings, oedometric and Casagrande shear-box tests) were performed on the three main categories of soils. Our results highlight that hyperconcentrated-flow deposits are fine sand- and silt-rich deposits that lack clay particles. Their dry density is low (ρd = 1.25 g/cm3) and their friction angle is high (ϕ = 38°) which contribute to the peculiar dynamics of Lahar flows and to their high erosive power. The low apparent density provides a better capacity for the debulking process, whereas the high friction angle takes part in the erosion process. Finally, the geotechnical properties observed here suggest that the high contents in silica pyroclastic particles and the lack of clay or fine particles control the rheological behavior of Lahar deposits. We can also consider that the rheological behavior of Lahars through time is complex and that existing older Lahars can be remobilized by heavy rain or future stream flows and Lahars.
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Sediment transportation and deposition by rain-triggered Lahars at Merapi Volcano, Central Java, Indonesia
Geomorphology, 2002Co-Authors: Franck Lavigne, Jean-claude ThouretAbstract:Abstract A Lahar is a general term for a rapidly flowing mixture of rock debris and water (other than normal streamflow) from a volcano and refers to the moving flow. Located in the populated area of Central Java, the stratovolcano Merapi (2965 m) is prone to Lahar generation, due to three main factors: (1) millions of cubic meters of pyroclastic deposits are the product of frequent pyroclastic flows, which have occurred on 2- to 4-year intervals; (2) rainfall intensity is high (often 40 mm in 2 h on average) during the rainy season from November to April; and (3) drainage pattern is very dense. Following the 22 November 1994 eruption of Merapi, 31 rain-triggered Lahar events were recorded in the Boyong River between December 1994 and May 1996. On Merapi's slopes, instantaneous sediment concentration at any given time of the Lahars varies widely over time and space. Lahars are transient sediment-water flows whose properties are unsteady, so that the sediment load fluctuates during the flow. The boundary between the flow types (debris flow, with sediment concentration >60% volume, or hyperconcentrated flow, with sediment concentration ranges from 20% to 60% volume) may fluctuate within the flow itself. Grain-size distribution, physical composition of sediments, shear stress, yield stress, and water temperature play each a role on this boundary. Natural self-damming and rapid breakout are partly responsible for the sediment variations of the flows. Debris-flow phases at Merapi typically last a few minutes to 10 min, and are often restricted to the Lahar front. Debris-flow surges are sometimes preceded and always followed by longer hyperconcentrated flow phases. As a result, mean sediment concentration of the Lahars is low, commonly from 20% to 50% volume. Besides, transient normal streamflow phases (sediment concentration Low sediment load and frequent transient flows in the Merapi channels may result from at least three factors: (1) several breaks-in-slope along the channel increase the deposition rate of sediment, and hinder the bulking capacity of the Lahars; (2) source material is mainly coarse debris of “Merapi-type” block-and-ash flows. Consequently, the remobilization of coarse debris is more difficult and the clast deposition is accelerated; (3) variations of rainfall intensity over time and space, common in tropical monsoon rainfall, also influence the sediment load variations of the Lahars. Sedimentologic analyses of the Lahar deposits in the Boyong River at Merapi encompass clast-supported and matrix-supported debris-flow deposits, hyperconcentrated flow deposits, and streamflow deposits. The stratigraphic succession of massive and stratified beds observed immediately after any given Lahar event in the Boyong River indicates that the sediment concentration varies widely over time and space during a single Lahar event. Sedimentation rate varies from 3 to 4.5 cm/min during relatively long-lived surges to as much as 20 cm/min during short-lived surges. These results indicate that the sediment load fluctuates during Lahar flow, further demonstrating that Lahars are transient sediment-water flows with unsteady flow properties.
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Instrumental Lahar monitoring at Merapi Volcano, Central Java, Indonesia
Journal of Volcanology and Geothermal Research, 2000Co-Authors: Franck Lavigne, Jean-claude Thouret, Barry Voight, Kirby D. Young, R. Lahusen, J. Marso, Hiroshi Suwa, A Sumaryono, Dewi Sri Sayudi, M. DejeanAbstract:Abstract More than 50 volcanic debris flows or Lahars were generated around Mt Merapi during the first rainy season following the nuees ardentes of 22 November 1994. The rainfalls that triggered the Lahars were analyzed, using such instruments as weather radar and telemetered rain gauges. Lahar dynamics were also monitored, using new non-contact detection instrumentation installed on the slopes of the volcano. These devices include real-time seismic amplitude measurement (RSAM), seismic spectral amplitude measurement (SSAM) and acoustic flow monitoring (AFM) systems. Calibration of the various systems was accomplished by field measurements of flow velocities and discharge, contemporaneously with instrumental monitoring. The 1994–1995 Lahars were relatively short events, their duration in the Boyong river commonly ranging between 30 min and 1 h 30 min. The great majority (90%) of the Lahars was recognized at Kaliurang village between 13:00 and 17:30 h, due to the predominance of afternoon rainfalls. The observed mean velocity of Lahar fronts ranged between 1.1 and 3.4 m/s, whereas the peak velocity of the flows varied from 11 to 15 m/s, under the Gardu Pandang viewpoint location at Kaliurang, to 8–10 m/s at a section 500 m downstream from this site. River slopes vary from 28 to 22 m/km at the two sites. Peak discharges recorded in various events ranged from 33 to 360 m3/s, with the maximum value of peak discharge 360 m3/s, on 20 May 1995. To improve the Lahar warning system along Boyong river, some instrumental thresholds were proposed: large and potentially hazardous Lahars may be detected by RSAM units exceeding 400, SSAM units exceeding 80 on the highest frequency band, or AFM values greater than 1500 mV on the low-gain, broad-band setting.
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Lahars at Merapi volcano, Central Java: an overview
Journal of Volcanology and Geothermal Research, 2000Co-Authors: Franck Lavigne, Jean-claude Thouret, Barry Voight, H Suwa, A SumaryonoAbstract:Abstract Merapi volcano, in Central Java, is one of the most active volcanoes in the world. At least 23 of the 61 reported eruptions since the mid-1500s have produced source deposits for Lahars. The combined Lahar deposits cover about 286 km 2 on the flanks and the surrounding piedmonts of the volcano. At Merapi, Lahars are commonly rain-triggered by rainfalls having an average intensity of about 40 mm in 2 h. Most occur during the rainy season from November to April, and have average velocities of 5–7 m/s at 1000 m in elevation. A wide range of facies may be generated from a single flow, which may transform downvalley from debris flow to hyperconcentrated streamflow. Because of the high frequency and magnitude of the Lahar events, Lahar-related hazards are high below about 450–600 m elevation in each of the 13 rivers which drain the volcano. Hazard-zone maps for Lahar were produced by Pardyanto et al. (Volcanic hazard map, Merapi volcano, Central Java (1/100,000). Geol. Surv. of Indonesia, Bandung, II, 4, 1978) and the Japanese–Indonesian Cooperation Agency (Master plan for land conservation and volcanic debris control in the area of Mt Merapi, Jakarta, 1980), but these maps are of a very small scale to meet modern zoning requirements. More recently, a few large-scale maps (1/10,000- and 1/2000-scale) and risk assessments have been completed for a few critical river systems.
