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Modelling volcanic tsunamis
No full textTsunamis generated by volcanic eruptions have caused about 25% of all deaths associated with volcano activity. The 1883 Krakatau eruption is one example of a fairly recent eruption that produced large tsunamis (-35 m) which caused a high death toll. Concern has also been raised by the potential tsunami generation of the Auckland Volcanic Field, and the impact of such events on the Auckland Region.
Although the generation of tsunamis by volcanic eruptions is a major hazard, the processes of tsunami generation are poorly understood. A review of volcanic tsunamis identified 10 main mechanisms. Four of these - caldera collapse, debris avalanches, submarine explosions, and pyroclastic flows - have been suggested as the mechanisms producing the largest tsunamis. All four mechanisms have also been suggested as being responsible for the tsunamis produced by the Krakatau eruption.
A combination of physical and numerical modelling was used to develop predictive tools to be applied to volcanoes in Indonesia and New Zealand. The physical modelling involved two main investigations:
• A 3 dimensional scale model of the Straits of Sunda and Krakatau. This examined the nature of tsunamis produced by caldera collapse, submarine explosions, and water displacement by debris avalanches and pyroclastic flows.
• A series of 2 dimensional simulations of the entrance of pyroclastic flows into the sea. A finite element numerical model was applied to the simulation of pyroclastic flow, maar formation and submarine explosion generation of tsunamis within the Auckland Volcanic Field.
The physical and numerical model results indicate that large scale pyroclastic flows are probably the cause of the main 1883 Krakatau tsunamis. A tsunami wave can easily be generated by gravity flows entering the water, regardless of the slope. The wave properties depend on the relative densities of the flow and the receiving body, and the velocity of the flow. The angle of entry of the flow into the water determines the deposition pattern of sediment. The formation of the Calmeyers and Steers shallow area on Krakatau event 1883 was reproduced by the pyroclastic experiments using coarse sand and mud with steep entry angle ~ 60°). The more dilute upper component of the pyroclastic flow that traveled along the sea surface for up to 45 km and killed more than 1000 people at Katimbang, Sumatera Island can also be explained. The experiments showed that less dense material from the pyroclastic flow propagates near the water surface. This is even more likely if the material is hot and gas-rich.
Physical and numerical model results showed that a single explosion cannot produce a high wave. If a super violent explosion did occur during the Krakatau event, then the water waves (tsunamis) that caused the devastating effect on the surrounding island coastal land were not caused by the direct transfer of explosive forces. Instead a sequence of one or more pyroclastic flows, or collapsing column in and around the Krakatau complex are the most likely mechanism causing the largest tsunami.
Numerical modelling of the Auckland Volcanic Field examined 4 scenarios:
• A series of submarine explosion;
• Pyroclastic flows from Rangitoto Island;
• Pyroclastic flows from Browns (Motukorea) Island;
• Submarine explosion within the Tamaki Estuary.
The first 3 scenarios produced regional effects, while the last was purely local event.
It was also found that the efficiency of the submarine explosion mechanism was increased by using a sequence of smaller explosions, instead of one large explosion. However the timing between explosions was found to be critical; if the explosions are too close together or too far apart, the efficiency decreases. It is considered that the optimal timing will vary with water depth and explosive yield.
The numerical modelling showed that volcanic tsunamis are not a major threat to Auckland. However under suitable conditions a volcanic eruption could produce moderately large tsunamis that generate strong currents
Catastrophic Tsunamis In the Indonesian Archipelago
Full text linkTsunamis are not rare events for the Indonesian Archipelago as a consequence of four major plate boundaries that meet and collide, and producing highly active seismic zone that is mostly located under the sea. The ‘tsunami season’ within this region started in 1992 at Hading Bay, Flores Island, with casualties of more than 2000 people, followed almost every two years with the 1994 East Java Tsunami, 1996 Tonggolobibi Sulawesi Tsunami, 1996 Biak Tsunamis, 1998 Papua New Guinea Tsunami, and the Banggai Tsunami in 2000. These represent the tsunami season for the eastern part of the Archipelago, since the western part of Archipelago was mostly quiet until the 26 December 2004 Great Sumatra Earthquake and Tsunami, which occurred at a place that never been thought before on the western-most part of the Archipelago. This earthquake and accompanying tsunamis not only a starting point of tsunami season for the western part of the Indonesian Archipelago, but also as a defining moment for the people who lived in the region in looking at the constellation of the archipelago, that changed the development paradigm into natural hazards based development program. The 26 December 2004 event (Mw > 9.0) is a turning point for the tsunamigenic earthquake studies along the subduction zone. Intensive research of this event provides a new insight into tsunami dynamics and characteristics as reflected by the erosional and deposition patterns of the coastal areas, wave run-up height, flow depth and inundation, wave front and bore formation, wave-structure interactions, coastal protection and management of the low-lying areas, and the importance of consistent education and local knowledge about natural hazards (earthquake and tsunamis). The following event on 28 March 2005 (Mw = 8.5), occurred only 250 km distant from the 26 December 2004 event, and continued further south to Java Island on 17 July 2006 (Mw = 7.6) and 12 September 2007 (Mw = 8.4) on southwest Sumatra Island (Bengkulu) along the Java Trench. Field surveys results, and analysis of the source mechanism and distribution of the resulting tsunami waves along the coast, shows that each near-field tsunami generated within the subduction zone is unique and complex. Scientists have urged the public and policy makers to consider all subduction-type tectonic boundaries to be “locked, loaded and dangerous” zones that possess potential tsunami threats. Reliable and comprehensive databases for past and recent events and subsequent scientific analysis are needed in mitigating the tsunami hazards. Fourteen (14) segments of potential catastrophic tsunamigenic earthquake and 21 volcanogenic tsunami sources were identified based on seismotectonic assessment, historical record, paleotsunami deposits and micro-atoll studies, as well as volcanic type and activities. Most of the volcanogenic tsunamis sources are located in the eastern archipelago around the Banda Arc and the Molluca Sea. Tsunamis from volcanic sources had different characteristic to tsunamis generated by an earthquake mechanism, both in the near field and also far field as revealed by numerical modelling assessment. A numerical modeling of tsunami based on scenarios developed, shows the region is very susceptible to tsunamis with elevation at the shoreline greater than 8 m. With this elevation, there is no structural mitigation that is economically feasible to protect long a coastline based on the assessment of the 26 December 2004 event. The nonstructural mitigation measures such as mangroves and coastal forest or in combination with other soft options such as sand dunes, provides protection to some extent. However, further research needs to be carried out in defining appropriate mitigation measures. These high hazard zones require ‘sacrifice zone’ of at least 1 km from the shoreline, and vertical evacuation is needed to save lives. iii Detailed assessment of tsunami inundation based on the 26 December 2004 event revealed that the distributions of the flow depths are not always inline with distribution of the flow speed. The areas that experienced the deepest flooding does not necessarily experience the fastest flows, while the damage within urban and rural areas mostly coincided with the flow speed distribution rather than runup and inundation depth distribution. Consequently, in assessing the tsunami hazards, especially when making inundation maps, the overland flow speed should be taken into account or incorporated into the inundation map. However, the problem is that not all coastal areas have nearshore bathymetry and topography data at a resolution needed to represent the nearshore and overland flow dynamics. Results from assessment of the tsunami field survey and damage data from recent events provide the necessity information to derive the hazards level that correlate the tsunami elevation at a shoreline with destruction scale inland. This provides enough information to permit the construction of hazard maps for the region where detailed nearshore bathymetry and topography data are not available. The tsunami elevation at the shoreline can be derived from numerical models. As demonstrated during the 26 December 2004 event, the impacts of tsunamis on the coastal areas include not only the destruction of the infrastructure, buildings, housing, coastal landforms as well as a massive casualties, but also the resulting waste and debris that mixes with other flotsam during wave runup and backwash. This may create another huge problem that leads to serious long term adverse environmental consequences. Debris dispersal modelling is applied to the Banda Aceh region based on that event, and shows that understanding the pathway and distribution of the suspended materials and flotsam caused by tsunamis is important for proper hazard mitigation planning and waste management action. In assessing the potential future events, there is uncertainty and some disagreement from results of the tsunamigenic earthquake recurrence interval based on the empirical formula used. These need to be refined with more data such as from continuous Global Position System measurements. Likewise for volcanogenic tsunamis sources, which are better defined by their location but difficult to determine which processes are dominant to generate catastrophic tsunamis for the next events. The rule of thumb of the sea receding as a sign for impending tsunamis from the subduction zone earthquake source is not applicable for most of the volcanogenic tsunamis. For a tsunami generated by volcanic eruption, the warning is the eruption itself, which could be several days before a tsunami event. More research is required to better understand the characteristic of volcanogenic tsunamis. In general, the arrival time of tsunamis along the subduction zone within the Indonesian Archipelago is within 10 – 30 minutes. The best lesson learned is from the people in Simeulue, who recognized a simple messaged, if a significant ground shaking was felt, and the sea recedes; then evacuate to higher ground. This type of community warning and self-evacuation are a challenge for modern life style in the city. Integration of life-long efforts to educate the population about the hazards and preparedness for an extreme event is needed. The most favorable way is to include earthquake and tsunami hazards, and preparedness as part of educational curricula taught at schools
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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