Raphaël Paris

Numerical assessment of boulder transport by the 2004 Indian ocean tsunami in Lhok Nga, West Banda Aceh (Sumatra, Indonesia)

Abstract Few studies have been conducted on modeling boulder transport by tsunamis despite considerable research on the analysis of boulder deposits. A detailed description of the derivation of governing equations for boulder transport in submerged, partially submerged, and subaerial (not in contact with fluid) is presented, and then a numerical model is proposed to solve the governing equations in one dimension. Subsequently, the model is used to analyze the transport of calcareous boulders detached from a seawall in Lhok Nga (northwestern Sumatra, Indonesia) by the 2004 Indian Ocean tsunami. A few simulated transport distances match field observations, but the others are higher than the field measurements. Clast-to-clast interactions at the inception of transport would have a major impact on changes in transport distance, dissipating the energy in impulses as destruction of the seawall releases different sizes of boulders with different velocities. Moreover, surface microtopographical effects could completely stop the transport prematurely. The difference between the simulated results and the field observations is partly attributed to limitations of the numerical model. No landward fining was observed in the field measurements, but numerically predicted results showed a reasonable trend of landward fining.

Volcanic tsunami: a review of source mechanisms, past events and hazards in Southeast Asia (Indonesia, Philippines, Papua New Guinea)

AbstractSoutheast Asia has had both volcanic tsunamis and possesses some of the most densely populated, economically important and rapidly developing coastlines in the world. This contribution provides a review of volcanic tsunami hazard in Southeast Asia. Source mechanisms of tsunami related to eruptive and gravitational processes are presented, together with a history of past events in the region. A review of available data shows that many volcanoes are potentially tsunamigenic and present often neglected hazard to the rapidly developing coasts of the region. We highlight crucial volcanic provinces in Indonesia, the Philippines and Papua New Guinea and propose strategies for facing future events.

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.

Simulating the thermorheological evolution of channel-contained lava: FLOWGO and its implementation in EXCEL

Abstract FLOWGO is a one-dimensional model that tracks the thermorheological evolution of lava flowing down a channel. The model does not spread the lava but, instead, follows a control volume as it descends a line of steepest descent centred on the channel axis. The model basis is the Jeffreys equation for Newtonian flow, modified for a Bingham fluid, and a series of heat loss equations. Adjustable relationships are used to calculate cooling, crystallization and down-channel increases in viscosity and yield strength, as well as the resultant decrease in velocity. Here we provide a guide that allows FLOWGO to be set up in Excel. In doing so, we show how the model can be executed using a slope profile derived from Google™ Earth. Model simplicity and ease of source-term input from Google™ Earth means that this exercise allows (i) easy access to the model, (ii) quick, global application and (iii) use in a teaching role. Output is tested using measurements made for the 2010 eruption of Piton de la Fournaise (La Réunion Island). The model is also set up for rapid syneruptive hazard assessment at Piton de la Fournaise, as we show using the example of the response to the June 2014 eruption.

Onshore tsunami sediment transport mechanisms inferred from heavy mineral assemblages

The aim of this study is to discuss and to extend the characterization of (palaeo)tsunami deposits, and their source materials, based upon the detailed study of their heavy mineral assemblages. Results obtained from three distinct locations (Portugal, Scotland and Indonesia), different coastal contexts and chronologies (the tsunami events studied took place at 1500 cal. yr BP, AD 1755 and 2004) are summarized and discussed in order to contribute to the sedimentological study of onshore (palaeo)tsunami deposits. Results indicate that heavy mineral assemblages primarily reflect local specific conditions. For example, in the Portuguese sites, ca. 90% of the heavy mineral population consists of tourmaline+andalusite+staurolite, whereas in the Scottish samples garnet+amphiboles can be dominant in 90% of the assemblage, where at the Indonesian study site amphiboles+andalusite were the most frequent minerals. The application of Principal Component Analysis for each site reveals that the first two components explain at least 55% of the total variance. In the three studied areas, hydraulic sorting by density was observed and a higher presence of the denser heavy minerals of the assemblages was detected. However, it is important to stress that the sediment source plays a key role in the establishment of the heavy mineral assemblages of the (palaeo)tsunami deposits. In this study, relationships between the likely source sediments and the (palaeo)tsunami deposits were described and whenever possible sediment sources were clearly identified. Furthermore, it was also possible to detect the backwash signal using the analysis of the heavy minerals (e.g. higher frequency of denser minerals or variation in the presence of rounded or euhedral zircon). The work presented here, in contributing to the enhancement of sedimentological criteria presently available to recognize and differentiate extreme marine inundation deposits, also highlights new areas for future research.

Source mechanisms of volcanic tsunamis.

Volcanic tsunamis are generated by a variety of mechanisms, including volcano-tectonic earthquakes, slope instabilities, pyroclastic flows, underwater explosions, shock waves and caldera collapse. In this review, we focus on the lessons that can be learnt from past events and address the influence of parameters such as volume flux of mass flows, explosion energy or duration of caldera collapse on tsunami generation. The diversity of waves in terms of amplitude, period, form, dispersion, etc. poses difficulties for integration and harmonization of sources to be used for numerical models and probabilistic tsunami hazard maps. In many cases, monitoring and warning of volcanic tsunamis remain challenging (further technical and scientific developments being necessary) and must be coupled with policies of population preparedness.

Recent unrest at Canary Islands' Teide Volcano?

When a volcano that has been dormant for many centuries begins to show possible signs of reawakening, scientists and civil authorities rightly should be concerned about the possibility that the volcanic unrest might culminate in renewed eruptive activity. Such was the situation for Teide volcano, located on Tenerife in the Canary Islands, when a mild seismic swarm during April–July 2004 garnered much attention and caused public concern. However, that attention completely ignored the fact that the seismic recordings of the swarm were due to a much improved monitoring system rather than due to an actual event of alarming magnitude or extent. It is important in any effective program of volcano-risk mitigation that the response to an apparent change in the status of a volcano should include the immediate implementation or augmentation of monitoring studies to better anticipate possible outcomes of the volcanic unrest. Equally important, emergency-management officials, using available scientific information and judgment, must take appropriate precautionary measures—including information of the populations at potential risk—while not creating unjust anxiety or alarm.

Tsunami hazard related to a flank collapse of Anak Krakatau Volcano, Sunda Strait, Indonesia

Abstract Numerical modelling of a rapid, partial destabilization of Anak Krakatau Volcano (Indonesia) was performed in order to investigate the tsunami triggered by this event. Anak Krakatau, which is largely built on the steep NE wall of the 1883 Krakatau eruption caldera, is active on its SW side (towards the 1883 caldera), which makes the edifice quite unstable. A hypothetical 0.280 km3 flank collapse directed southwestwards would trigger an initial wave 43 m in height that would reach the islands of Sertung, Panjang and Rakata in less than 1 min, with amplitudes from 15 to 30 m. These waves would be potentially dangerous for the many small tourist boats circulating in, and around, the Krakatau Archipelago. The waves would then propagate in a radial manner from the impact region and across the Sunda Strait, at an average speed of 80–110 km h−1. The tsunami would reach the cities located on the western coast of Java (e.g. Merak, Anyer and Carita.) 35–45 min after the onset of collapse, with a maximum amplitude from 1.5 (Merak and Panimbang) to 3.4 m (Labuhan). As many industrial and tourist infrastructures are located close to the sea and at altitudes of less than 10 m, these waves present a non-negligible risk. Owing to numerous reflections inside the Krakatau Archipelago, the waves would even affect Bandar Lampung (Sumatra, c. 900 000 inhabitants) after more than 1 h, with a maximum amplitude of 0.3 m. The waves produced would be far smaller than those occurring during the 1883 Krakatau eruption (c. 15 m) and a rapid detection of the collapse by the volcano observatory, together with an efficient alert system on the coast, would possibly prevent this hypothetical event from being deadly.

Explosive eruption, flank collapse and megatsunami at Tenerife ca. 170 ka

Giant mass failures of oceanic shield volcanoes that generate tsunamis potentially represent a high-magnitude but low-frequency hazard, and it is actually difficult to infer the mechanisms and dynamics controlling them. Here we document tsunami deposits at high elevation (up to 132 m) on the north-western slopes of Tenerife, Canary Islands, as a new evidence of megatsunami generated by volcano flank failure. Analyses of the tsunami deposits demonstrate that two main tsunamis impacted the coasts of Tenerife 170 kyr ago. The first tsunami was generated during the submarine stage of a retrogressive failure of the northern flank of the island, whereas the second one followed the debris avalanche of the subaerial edifice and incorporated pumices from an on-going ignimbrite-forming eruption. Coupling between a massive retrogressive flank failure and a large explosive eruption represents a new type of volcano-tectonic event on oceanic shield volcanoes and a new hazard scenario.