Numerical Simulation of Historical Pyroclastic Flows of Merapi (1994, 2001, and 2006 Eruptions)
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Abstract:
Merapi has become one of the most enticing volcanoes due to its activity over the past century. Although we have to agree that the 2010 VEI = 4 (Volcanic Explosivity Index, [1]) eruption is the greatest in its recorded history, Merapi is more famous for its shorter cycle of smaller scale, making it one of the most active volcanoes on Earth. Many mechanisms are involved in an eruption, and pyroclastic flow is the most dangerous occurrence in terms of volcanic hazard. A pyroclastic flow is defined as a high-speed avalanche consisted of high temperature mixture of rock fragments and gas, resulted from lava dome collapse and/or gravitational column collapse. Researchers have studied Merapi’s history and behavior, and numerical simulations are an important tool for future hazard mitigation. By utilizing numerical simulation on basal part of pyroclastic flow, we investigated the applicability of the simulation on pyroclastic flows from historical eruptions of Merapi (1994, 2001, and 2006). Herein, we present a total of 32 simulations and discuss the areas affected by pyroclastic flows and the factors that affect the simulation results.Keywords:
Volcanic hazards
Pyroclastic fall
Lava dome
Peléan eruption
Each of the three phases of the 2006 eruption at Augustine Volcano had a distinctive eruptive style and flowage deposits. From January 11 to 28, the explosive phase comprised short vulcanian eruptions that punctuated dome growth and produced volcanowide pyroclastic flows and more energetic hot currents whose mobility was influenced by efficient mixing with and vaporization of snow. Initially, hot flows moved across winter snowpack, eroding it to generate snow, water, and pyroclastic slurries that formed mixed avalanches and lahars, first eastward, then northward, and finally southward, but subsequent flows produced no lahars or mixed avalanches. During a large explosive event on January 27, disruption of a lava dome terminated the explosive phase and emplaced the largest pyroclastic flow of the 2006 eruption northward toward Rocky Point. From January 28 to February 10, activity during the continuous phase comprised rapid dome growth and frequent dome-collapse pyroclastic flows and a lava flow restricted to the north sector of the volcano. Then, after three weeks of inactivity, during the effusive phase of March 3 to 16, the volcano continued to extrude the lava flow, whose steep sides collapsed infrequently to produce block-and-ash flows. The three eruptive phases were each unique not only in terms of eruptive style, but also in terms of the types and morphologies of deposits that were produced, and, in particular, of their lithologic components. Thus, during the explosive phase, low-silica andesite scoria predominated, and intermediate- and high-silica andesite were subordinate. During the continuous phase, the eruption shifted predominantly to high-silica andesite and, during the effusive phase, shifted again to dense low-silica andesite. Each rock type is present in the deposits of each eruptive phase and each flow type, and lithologic proportions are unique and consistent within the deposits that correspond to each eruptive phase. The chief factors that influenced pyroclastic currents and the characteristics of their deposits were genesis, grain size, and flow surface. Column collapse from short-lived vulcanian blasts, dome collapses, and collapses of viscous lavas on steep slopes caused the pyroclastic currents documented in this study. Column-collapse flows during the explosive phase spread widely and probably were affected by vaporization of ingested snow where they overran snowpack. Such pyroclastic currents can erode substrates formed of snow or ice through a combination of mechanical and thermal processes at the bed, thus enhancing the spread of these flows across snowpack and generating mixed avalanches and lahars. Grain-size characteristics of these initial pyroclastic currents and overburden pressures at their bases favored thermal scour of snow and coeval fluidization. These flows scoured substrate snow and generated secondary slurry flows, whereas subsequent flows did not. Some secondary flows were wetter and more laharic than others. Where secondary flows were quite watery, recognizable mixed-avalanche deposits were small or insignificant, and lahars were predominant. Where such flows contained substantial amounts of snow, mixed-avalanche deposits blanketed medial reaches of valleys and formed extensive marginal terraces and axial islands in distal reaches. Flows that contained significant amounts of snow formed cogenetic mixed avalanches that slid across surfaces protected by snowpack, whereas water-rich axial lahars scoured channels. Correlations of planimetric area (A) versus volume (V) for pyroclastic deposits with similar origins and characteristics exhibit linear trends, such that A=cV2/3, where c is a constant for similar groups of flows. This relationship was tested and calibrated for dome-collapse, column-collapse, and surgelike flows using area-volume data from this study and examples from Montserrat, Merapi, and Mount St. Helens. The ratio A/V2/3=c gives a dimensionless measure of mobility calibrated for each of these three types of flow. Surgelike flows are highly mobile, with c≈520; column-collapse flows have c≈150; and dome-collapse flows have c≈35, about that of simple rock avalanches. Such calibrated mobility factors have a potential use in volcano-hazard assessments.
Lava dome
Stratovolcano
Peléan eruption
Lahar
Effusive eruption
Pyroclastic fall
Phreatic eruption
Phreatomagmatic eruption
Scoria
Dome (geology)
Strombolian eruption
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Pyroclastic density currents (PDCs) are hot and fast ground-hugging mixtures of volcanic fragments and gases, which represent a major threat to people living near explosive volcanoes. Mechanisms causing the separation into the concentrated (the pyroclastic flow) and dilute (the pyroclastic surge) layers, as well as the mechanism causing their remarkably high mobility are still unclear. Here, we present a conceptual model based on field observations of lava dome collapses, laboratory experiments, and numerical modeling that unifies these mechanisms. Our model shows that they are caused by the fall of fine volcanic particles onto steep, irregular topography. The ambient air entrapped during the fall both creates the pyroclastic surge through elutriation and induces high fluidity in the pyroclastic flow by increasing its pore pressure. Our conclusion reveals the importance of topography in the destructive capacity of PDCs.
Pyroclastic fall
Peléan eruption
Lava dome
Fluidization
Elutriation
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On 13 to 14 February 2014 a ~4 h long, VEI 4 eruption occurred at Kelut volcano (Java, Indonesia). Pyroclastic density currents (PDCs) and extensive ash fall led to 7 fatalities and disruption to flights across the Asia-Pacific region. New sedimentological descriptions of the pyroclastic deposits from the 2014 eruption were compared with eyewitness and satellite reports to elucidate temporal variations in eruptive dynamics. The stratigraphy of the deposits is presented in 3 stages, associated with two eruptions that occurred approximately ~15–30 min apart. Stage 1 PDC deposits originate from the smaller onset eruption. The PDC deposits from Stage 2, and tephra fall deposits from Stage 3 originate from the second, plinian eruption. During the onset eruption (Stage 1), low energy PDCs were produced that ran out to <2.6 km. Basal layers show characteristics of deposits similar to ash-cloud surges that carried dominantly fine ash and crystal fragments. These are capped by deposits typical of high-particle concentrated pyroclastic flows. All Stage 1 deposits have high contents of dense lithic fragments (up to 44% by vol.), sourced from the 2007–2008 lava dome and conduit walls, indicating that the eruption onset was driven by an explosive release of gas-overpressure below the vent-capping dome. Increases in the magma flux and transition to a more constant eruption led to a growing eruption column during the ~2-hour long Stage 2 plinian eruption. Pumice rich (>70% by vol.) PDC deposits ran out to 4.7 km from the vent. The deposits reflect an increased output of fresh fragmented magma, and some conduit widening evidenced by dense lithic fragments. Vent instabilities and incorporation of dense material into basal margins of the plume led to the marginal collapse and formation of these PDCs. Stage 3 occurred in the final hour at the peak of the plinian eruption, around 01:00 to 02:00, and produced reversely graded lapilli fall deposits with ≤90 vol% pumice from a 26 km-high plume. This indicates that there was a sustained flux of juvenile magma to the now open vent system, and expansion and fragmentation of the gas-rich magma was at its most efficient. Our study of the eruptive sequence of Kelut provides some constraints on predicted patterns for future explosive activity, critical for further hazard assessment of the volcano. Since 1901 Kelut has erupted on intervals of 1 to 23 years, and the 2014 event characterises a typical “explosive” style of eruption that alternates regularly with effusive dome-formation and collapse events. This pattern depends on the dynamics of magma renewal to the system, and degassing conditions in the shallow magma reservoir and upper conduit. If this pattern holds, and the next eruption occurs within the next two decades, a return of prolonged dome growth could be anticipated.
Peléan eruption
Dense-rock equivalent
Pyroclastic fall
Lava dome
Phreatic eruption
Effusive eruption
Dome (geology)
Volcanic hazards
Phreatomagmatic eruption
Lateral eruption
Pumice
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Lava dome
Peléan eruption
Volcanic hazards
Dome (geology)
Dense-rock equivalent
Strombolian eruption
Effusive eruption
Phreatic eruption
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Pyroclastic fall
Lava dome
Peléan eruption
Effusive eruption
Strombolian eruption
Dense-rock equivalent
Silicic
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This article deals with the mechanism of eruption and transportation of the pyroclastic material and the nature of the resultant deposits from the geological standpoint.In Japan, the method of tephrochronology is best applied to pyroclastic deposits of the Quaternary central volcanoes and those related to the Krakatoan calderas. Most of the rocks are andesitic in composition with subordinate amount of basalt and dacite.Three modes of volcanic eruption may be distinguished: 1) projection of pyroclastic materials which form pyroclastic fall deposits, 2) eruption of pyroclastic flows, and 3) outflow of lava flows or extrusion of dome and spine. Table 1 shows characteristic features of the deposits formed by the three modes of volcanic eruption.Tephra, as originally defined by Thorarinsson, signifies only the air-fall pyroclastic materials and its relation to pyroclastic flow is not clear. In this article, all the pyroclastic materials directly connected with volcanic eruptions, irrespective of their origin (i. e. essential, accessory, or accidental) and of their mode of emplacement, are included in the term tephra. The chronology using the deposits of pyroclastic flows are included in the tephrochronology.The small-scale vesiculation occurring at or close to the top of the magma column results in the so-called Strombolian and Vulcanian eruptions. Larger scale vesiculation with longer time duration leads to the Plinian eruption. The greatest vesiculation takes place within the magma reservoir resulting in the formation of a depression caldera. The larger the size of eruption column, the more effective the sorting of the erupted pyroclastic fragments. The larger and denser particles fall first and closer to the vent while the smaller and more vesicular fragments fall farther away. Consequently the deposits of pyroclastic falls are well sorted and exhibit pronounced lateral regular grading in texture and composition. This is in strong contrast with the poorly sorted character of pyroclastic flow deposits, in which all particles travel en masse in a state of turbulent flow.Welding of the deposit is not uncommon in the pyroclastic flow deposits while it is rare in pyroclastic fall deposits except those deposited near the vents of basaltic eruptions.To reconstruct past eruptions from volcanic deposits, it may be necessary to establish definite correlation between stratigraphic units by which volcanic deposits are grouped and time duration by which specific eruptive activity is grouped. A single eruptive cycle, the deposits of which represent such a time unit, is defined as a series of eruptive events limited by fairly long intervals of quiescence. Historic examples indicate that the duration of a single eruptive cycle ranges from a day to several years in most cases. The intervening periods are generally far longer than the duration of single eruptive cycle.From many examples of single eruptive cycles, a rule has been established: the degree of vesiculation of magma gradually decreases toward the end of the cycle. This is expressed in successive eruption of pyroclastic fall, pyroclastic flow, and lava flow from the same vent in case of felsic magma, and of pyroclastic fall and lava flow in case of mafic magma, which fact may indicate that the original magma column responsible for the eruptive cycle was more enriched in volatiles in the upper part than the lower.The close correlation between the recorded sequence of single eruptive cycles and the reultant beds of volcanic materials is described for a few examples. The beds produced by a single cycle of witnessed eruption conformably superpose each other and do not include a layer representing weathering break. It is stressed that such a group of beds of volcanic ejecta, volcanic deposits of a single eruptive cycle, should be taken into account as a stratigraphic unit when precise tephrochronology is undertaken.
Peléan eruption
Pyroclastic fall
Strombolian eruption
Caldera
Lava dome
Dense-rock equivalent
Tephrochronology
Volcanic plateau
Phreatomagmatic eruption
Effusive eruption
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Volcano is located in the Narino Province, South of Colombia. It is an andesitic strato-volcano, which structure was formed by the interchange of lava flows and pyroclastic deposits of different sizes. In the last 4500 years, six major eruptions have been identified (4500, 4000, 2900, 2300, 1100 years before present and in the XIX century), with eruptive columns of small size and producing small pyroclastic flows. In the past 500 years, the eruptions have been characterized by gas and ash emissions, small lava flows and explosive eruptions which have also produced pyroclastic flows. Since INGEOMINAS started the monitoring in 1989, it has been recorded several manifestations of its activity, starting from its re-activation characterized by frequent phreatic eruptions (at the end of 1988 and beginning of 1989), the gradual arise of a viscous magma and its emplacement as a dome in the bottom of the main crater (second semester of 1991), and subsequent explosive eruptions related with the dome destruction and volcanic process development (eruptions on July 16,1992; January 14, March 23, April 4, April 13 and June 7, 1993)), as well as, the record of seismic sequences of Volcano-Tectonic events, related with fracturing process, located in the neighborhood of the volcanic edifice (April and November, 1993 and March, 1995). Since 1997, this volcano is the focus of the implementation and development of what here is called the Galeras Multiparameter Station, a project which consists in technological adequacy and research, and is carried out by the Institute for Research and Geoscientific, Mining - Enviromental and Nuclear Information (INGEOMINAS - Colombia) and the Federal Institute for Geosciences and Natural Resources (BGR - Germany). The INGEOMINAS - BGR Project is proposed in order to investigate the Volcanic activity through the combination of various geophysical and geochemical disciplines like broadband seismology, electro-magnetic methods, gas chemistry, thermography, gravimetry and geodesy in a continuos telemetric experiment for long time observations.
Lava dome
Peléan eruption
Phreatic eruption
Phreatic
Stratovolcano
Pyroclastic fall
Volcanic hazards
Dome (geology)
Effusive eruption
Phreatomagmatic eruption
Strombolian eruption
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During and after the 2006 eruption of Augustine Volcano, we compiled a geologic map and chronology of new lava and flowage deposits using observational flights, oblique and aerial photography, infrared imaging, satellite data, and field investigations. After approximately 6 months of precursory activity, the explosive phase of the eruption commenced with two explosions on January 11, 2006 (events 1 and 2) that produced snow-rich avalanches; little or no juvenile magma was erupted. Seismicity suggests that a small lava dome may have extruded on January 12, but, if so, it was subsequently destroyed. A series of six explosions on January 13–14 (events 3–8) produced widespread but thin (0–30 cm) pyroclastic-current deposits on the upper flanks above 300 m altitude and lobate, 0.5- to 2-m-thick pyroclastic flows that traveled down most flanks of the volcano. Between January 14 and 17, a smooth lava lobe formed in the east half of the roughly 400-m-wide summit crater and was only partially covered by later deposits. An explosion on January 17 (event 9) opened a crater in the new lava dome and produced a ballistic fall deposit and pyroclastic flow on the southwest flank. During the interval from January 17 to 27, a rubbly lava dome effused. On January 27, explosive event 10 generated a pyroclastic current that left a deposit, rich in dense clasts, on the north-northwest flank. Immediately following the pyroclastic current, a voluminous 4.7-km-long pyroclastic flow swept down the north flank. Three more explosive blasts on January 27 and 28 produced unknown but likely minor on-island deposits. The cumulative volume of erupted material from the explosive phase, including domes, flows, and fall deposits (Wallace and others, this volume), was 30×106 m3 dense-rock equivalent (DRE). The continuous phase of the eruption (January 28 through February 10) began with a 4-day period of nearly continuous block-and-ash flows, which deposited small individual flow lobes that cumulatively formed fans to the north and northeast of the summit. A single larger pyroclastic flow on January 30 formed a braided deposit on the northwest flank. Roughly 9×106 m3 (DRE) of magma erupted during this period. Around February 2, the magma flux rate waned and a northward lava flow effused and reached a length of approximately 900 m by February 10. Approximately 11×106 m3 (DRE) of magma erupted during the second half of the continuous phase. After a 23-day hiatus, lava effusion recommenced in early March (the effusive phase) and was accompanied by frequent (but volumetrically minor) block-and-ash flows. From March 7 to 14, extrusion increased markedly; two blocky lava-flow lobes, each tens of meters thick, moved down the north and northeast flank of the volcano; and a new summit lava dome grew to be ~70 m taller than the pre-2006 summit. This phase produced 26×106 m3 (DRE) of lava. Active effusion had ceased about March 16, but, in April and May, three gravitational collapses from the west margin of the north lava flow produced additional block-and-ash flows. The basic sequence of the 2006 eruption closely matches that of eruptions in 1976 and 1986.
Lava dome
Peléan eruption
Lateral eruption
Pyroclastic fall
Phreatic eruption
Dome (geology)
Dense-rock equivalent
Effusive eruption
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Lava dome forming volcanic eruptions are common throughout the world. They can be dangerous; nearly all dome-forming eruptions have been associated with explosive activity (Newhall and Melson, 1983). Most explosions are vulcanian with eruption plumes reaching less than 15km, and with a Volcanic Explosivity Index (VEI) <3 (for a definition of VEI see Newhall and Self 1982). Large Plinian explosions with a VEI ≥ 4 do sometimes occur in association with dome-forming eruptions. Many of the most significant volcanic events of recent history are in this category. The 1902-1905 eruption of Mt. Pelee, Martinique; the 1980-1986 eruption of Mount St. Helens, USA; and the 1991 eruption of Mt. Pinatubo, Philippines all demonstrate the destructive power of VEI ≥ 4 dome-forming eruptions. Hazards related to dome-forming eruptions are numerous and range from dome-collapse and column-collapse pyroclastic flows and surges to tephra fall to directed blasts, lahars, and landslides.
Global historical analysis is a powerful tool for decision-making as well as for scientific discovery. In the absence of monitoring data or a knowledge of a volcano’s eruptive history, global analysis can provide a method of understanding what might be expected based on similar eruptions. Important scientific information has been gleaned from disparate collections of dome-forming eruption hazard information, and modeling of volcanic phenomena often requires extensive data for development and calibration.
This study investigates the relationship between large explosive eruptions (VEI ≥ 4) and lava dome-growth from 1000 BCE to present and develops a world-wide database of all relevant information, including dome growth duration, pauses between episodes of dome growth, and extrusion rates. Data sources include the database of volcanic activity maintained by the Smithsonian Institute (Global Volcanism Program) and all relevant published review papers, research papers and reports. Hazards related to dome-forming eruptions, including pyroclastic falls, rockfalls, tephra fall, lahars, and debris avalanches have also been catalogued for Soufriere Hills Volcano, Montserrat. Analysis of the databases has provided useful information regarding the relationship between extrusion rates and large explosions, the identification of patterns in eruptive frequency between different volcanoes, and the timing of large explosions in relation to dome growth. Relational databases will be compiled to allow users to query the database, and additional dome-forming eruption hazard data is requested from any interested parties.
Volcanic hazards
Lava dome
Peléan eruption
Dome (geology)
Martinique
Dense-rock equivalent
Lahar
Effusive eruption
Volcanology
Phreatomagmatic eruption
Vulcanian eruption
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