Franck Lavigne

Source of the great A.D. 1257 mystery eruption unveiled, Samalas volcano, Rinjani Volcanic Complex, Indonesia

Significance Based on ice core archives of sulfate and tephra deposition, one of the largest volcanic eruptions of the historic period and of the past 7,000 y occurred in A.D. 1257. However the source of this “mystery eruption” remained unknown. Drawing on a robust body of new evidence from radiocarbon dates, tephra geochemistry, stratigraphic data, a medieval chronicle, this study argues that the source of this eruption is Samalas volcano, part of the Mount Rinjani Volcanic Complex on Lombok Island, Indonesia. These results solve a conundrum that has puzzled glaciologists, volcanologists, and climatologists for more than three decades. In addition, the identification of this volcano gives rise to the existence of a forgotten Pompeii in the Far East. Polar ice core records attest to a colossal volcanic eruption that took place ca. A.D. 1257 or 1258, most probably in the tropics. Estimates based on sulfate deposition in these records suggest that it yielded the largest volcanic sulfur release to the stratosphere of the past 7,000 y. Tree rings, medieval chronicles, and computational models corroborate the expected worldwide atmospheric and climatic effects of this eruption. However, until now there has been no convincing candidate for the mid-13th century “mystery eruption.” Drawing upon compelling evidence from stratigraphic and geomorphic data, physical volcanology, radiocarbon dating, tephra geochemistry, and chronicles, we argue the source of this long-sought eruption is the Samalas volcano, adjacent to Mount Rinjani on Lombok Island, Indonesia. At least 40 km3 (dense-rock equivalent) of tephra were deposited and the eruption column reached an altitude of up to 43 km. Three principal pumice fallout deposits mantle the region and thick pyroclastic flow deposits are found at the coast, 25 km from source. With an estimated magnitude of 7, this event ranks among the largest Holocene explosive eruptions. Radiocarbon dates on charcoal are consistent with a mid-13th century eruption. In addition, glass geochemistry of the associated pumice deposits matches that of shards found in both Arctic and Antarctic ice cores, providing compelling evidence to link the prominent A.D. 1258/1259 ice core sulfate spike to Samalas. We further constrain the timing of the mystery eruption based on tephra dispersal and historical records, suggesting it occurred between May and October A.D. 1257.

Sediment transportation and deposition by rain-triggered lahars at Merapi Volcano, Central Java, Indonesia

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 Merapis 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.

The 1257 Samalas eruption (Lombok, Indonesia): the single greatest stratospheric gas release of the Common Era.

Large explosive eruptions inject volcanic gases and fine ash to stratospheric altitudes, contributing to global cooling at the Earth’s surface and occasionally to ozone depletion. The modelling of the climate response to these strong injections of volatiles commonly relies on ice-core records of volcanic sulphate aerosols. Here we use an independent geochemical approach which demonstrates that the great 1257 eruption of Samalas (Lombok, Indonesia) released enough sulphur and halogen gases into the stratosphere to produce the reported global cooling during the second half of the 13th century, as well as potential substantial ozone destruction. Major, trace and volatile element compositions of eruptive products recording the magmatic differentiation processes leading to the 1257 eruption indicate that Mt Samalas released 158 ± 12 Tg of sulphur dioxide, 227 ± 18 Tg of chlorine and a maximum of 1.3 ± 0.3 Tg of bromine. These emissions stand as the greatest volcanogenic gas injection of the Common Era. Our findings not only provide robust constraints for the modelling of the combined impact of sulphur and halogens on stratosphere chemistry of the largest eruption of the last millennium, but also develop a methodology to better quantify the degassing budgets of explosive eruptions of all magnitudes.

Tsunami‐resilient communities' development in Indonesia through educative actions

Purpose – Following the 26 December 2004 tsunami, Planet Risk NGO took part in the international research program TSUNARISK and ATIP‐CNRS Jeune Chercheur. The aim of this paper is to encourage the development of tsunami‐resilient communities essentially through educative actions.Design/methodology/approach – The tsunami risk in Indonesia was assessed by researchers. Planet Risk then used scientific findings and advice for building adapted prevention actions among Javanese populations.Findings – Many people could have survived if they had received a basic knowledge of tsunamis. The Indonesian public as well as local authorities must be educated to face tsunami risk. To be efficient, this education must be adapted to local cultural and geographical characteristics. Collaboration between researchers and practitioners is a good means of reaching such an objective.Originality/value – The paper is the result of a two‐year successful collaboration between interdisciplinary scientific teams and an NGO team. It de...

Coupling eruption and tsunami records: the Krakatau 1883 case study, Indonesia

The well-documented 1883 eruption of Krakatau volcano (Indonesia) offers an opportunity to couple the eruption’s history with the tsunami record. The aim of this paper is not to re-analyse the scenario for the 1883 eruption but to demonstrate that the study of tsunami deposits provides information for reconstructing past eruptions. Indeed, though the characteristics of volcanogenic tsunami deposits are similar to those of other tsunami deposits, they may include juvenile material (e.g. fresh pumice) or be interbedded with distal pyroclastic deposits (ash fall, surges), due to their simultaneity with the eruption. Five kinds of sedimentary and volcanic facies related to the 1883 events were identified along the coasts of Java and Sumatra: (1) bioclastic tsunami sands and (2) pumiceous tsunami sands, deposited respectively before and during the Plinian phase (26–27 August); (3) rounded pumice lapilli reworked by tsunami; (4) pumiceous ash fall deposits and (5) pyroclastic surge deposits (only in Sumatra). The stratigraphic record on the coasts of Java and Sumatra, which agrees particularly well with observations of the 1883 events, is tentatively linked to the proximal stratigraphy of the eruption.

Influence of the institutional and socio-economic context for responding to disasters: case study of the 1994 and 2006 eruptions of the Merapi Volcano, Indonesia

Abstract This article explores the institutional responses to the volcanic crises and related problems encountered during the 1994 and 2006 eruptions of the Merapi Volcano, Indonesia. It also illustrates traditional responses to the volcanic crisis led by the local community and provides recommendations to encourage a comprehensive institutional volcanic crisis management including community-based response. This study aims to understand and to explain the gap between institutional responses and the communitys perception during pre- to post-crisis situations. Interviews, questionnaires and focus group discussions revealed that top-down institutional responses to the volcanic crisis are not fully appropriate in regions with a high cultural perception. Working with the community is an ideal solution to minimize the gap between the government, scientists, non-governmental organizations and the community itself. A community-based methodology combined with natural hazard studies generates comprehensive risk and crisis management.

Application of a semiquantitative and GIS-based statistical model to landslide susceptibility zonation in Kayangan Catchment, Java, Indonesia

Kayangan Catchment, one of the extremely landslide susceptible areas in Indonesia, is situated on the eastern flank of Menoreh Mountain in Yogyakarta Province on the island of Java. Landslides cause land and infrastructure damages because of their frequency in human settlements. The objectives of this study are twofold: (1) to analyze the spatial distribution of landslides and its correlation using terrain parameters; and (2) to analyze landslide susceptibility using both semiquantitative and statistical methods, i.e., analytical hierarchy process (AHP) and information value (IV) methods. Nine parameter maps were introduced to assess landslide susceptibility. The parameter maps and landslide distribution map were spatially overlaid to calculate the contribution of each parameter to landslide susceptibility. The landslide susceptibility map encompassed four different categories: very high, high, medium, and low susceptibility. The map was validated through a success rate curve by determining the area under the curve using existing landslide events. The success rate curves indicated that the IV was more accurate than the AHP, although both of them had high correlations. Both methods show that the precondition factors represented approximately 80% of the influence on landslide occurrence, with the remaining 20% attributed to the triggering factors, primarily rainfall and seismic factors.

Contribution of anisotropy of magnetic susceptibility (AMS) to reconstruct flooding characteristics of a 4220 BP tsunami from a thick unconsolidated structureless deposit (Banda Aceh, Sumatra)

One of the main concerns of deciphering tsunami sedimentary records along seashore is to link the emplaced layers with marine high energy events. Based on a combination of morphologic features, sedimentary figures, grain size characteristics, fossils content, microfossils assemblages, geochemical elements, heavy minerals presence; it is, in principle, possible to relate the sedimentary record to a tsunami event. However, experience shows that sometimes, in reason of a lack of any visible sedimentary features, it is hard to decide between a storm and a tsunami origin. To solve this issue, the authors have used the Anisotropy of Magnetic Susceptibility (AMS) to evidence the sediment fabric. The validity of the method for reconstructing flow direction has been proved when applied on sediments in the aftermath of a tsunami event, for which the behaviour was well documented (2004 IOT). We present herein an application of this method for a 56 cm thick paleo-deposit dated 4220 BP laying under the soil covered by the 2004 IOT, SE of Banda Aceh, North Sumatra. We analysed this homogenous deposit, lacking of any visible structure, using methods of classic sedimentology to confirm the occurrence of a high energy event. We then applied AMS technique that allowed the reconstruction of flow characteristics during sediment emplacement. We show that all the sequence was emplaced by uprush phases and that the local topography played a role on the re-orientation of a part of the uprush flow, creating strong reverse current. This particular behaviour was reported by eyewitnesses during the 2004 IOT event.

Mass evacuation of the 2010 Merapi eruption

The last eruption of Merapi volcano occurred from October until December 2010. The existing contingency and evacuation plans were only able to handle the crisis from 26 October, 2010 until 3 November, 2010. By 3 November, 2010, the contingency and evacuation plans were no longer used. The authorities decided to move the refugee camps 15 km away from the summit instead of the initial 10 km. The largest and unexpected eruption occurred on 4 November, 2010 and the safety zone was raised to a radius of 20 km. This paper aims to analyse the difficulties during the evacuation and to examine the key issues that must be overcome in the evacuation and contingency plans in volcanic areas. The results show that contingency and evacuation plans should not be based on a single scenario. In the high volcanic risk areas such as Merapis region, a multiscale and multiscenario evacuation plan is crucial.

Modeling tsunami propagation and the emplacement of thumbprint terrain in an early Mars ocean

The identification of lobate debris deposits in Arabia Terra, along the proposed paleoshoreline of a former northern ocean, has renewed questions about the existence and stability of ocean-sized body of water in the early geologic history of Mars. The potential occurrence of impact-generated tsunamis in a northern ocean was investigated by comparing the geomorphologic characteristics of the Martian deposits with the predictions of well-validated terrestrial models (scaled to Mars) of tsunami wave height, propagation direction, runup elevation, and distance for three potential sea levels. Our modeling suggests several potential impact craters ~30–50 km in diameter as the source of the tsunami events. Within the complex topography of flat-floored valleys and plateaus along the dichotomy boundary, the interference of the multiple reflected and refracted waves that are observed in the simulation may explain the origin of the arcuate pattern that characterizes the thumbprint terrain.