Numerical modelling of tsunamis generated by mass flows at Stromboli Volcano

2021 ◽  
Author(s):  
Irene Manzella ◽  
Symeon Makris ◽  
Federico Di Traglia ◽  
Karim Kelfoun ◽  
Paul Cole ◽  
...  
Keyword(s):  
Tsunami Wave ◽  
Back Analysis ◽  
Monitoring Network ◽  
Early Warning Systems ◽  
Pyroclastic Density Currents ◽  
Density Currents ◽  
Tsunami Waves ◽  
Two Fluids ◽  
Mass Flows ◽  
Sciara Del Fuoco

<p>As demonstrated by the Anak Krakatau eruption-induced flank collapse in 2018 in Indonesia, tsunamis generated by large mass flows like landslides and pyroclastic density currents can have devastating effects in volcanic areas. However, these phenomena are still poorly understood as they are unusual and complex events, largely unpredictable and often poorly constrained. </p><p>Stromboli is one of the most active volcanoes in the world, extensively monitored and studied in the last few decades. Many tsunamigenic landslides (sub-aerial and/or submarine) have taken place; at least seven have occurred in the last 150 years and a devastating one is believed to have reached the coast of Naples, at more than 200 km distance, during the Middle Ages. Because the level of activity of the volcano has remained similar ever since and the likelihood of such disastrous events is not negligible, the hazard related to tsunamigenic mass flows in this area needs to be carefully assessed.</p><p>Associated with the 3<sup>rd</sup> of July 2019 eruption, at least three mass flows were triggered along the Sciara del Fuoco slope; two subaerial Pyroclastic density currents (PDCs) and a submarine landslide. Simultaneously, three buoys registered the height of the resulting tsunami wave ranging from 0.2 m in front of the Ginostra village to 1.5 m in front of the Sciara del Fuoco. Thanks to the dense monitoring network and the accurate bathymetry survey carried out by the IGAG-CNR, these events have been well constrained. </p><p>The tsunami waves studied here are smaller than those that could constitute a threat for the population living in this area, nevertheless they can be used to characterize the behaviour of the tsunamigenic mass flows. Back analysis of these events were undertaken with the two-fluids version of VolcFlow; this is a continuum mechanics model based on the depth-average approximation that has been developed for the simulation of volcanic flows. VolcFlow can take into account several different rheologies for each of the two fluids. In the present case, one fluid was used for the water body and one for simulating the mass flow. For the latter one, a constant retaining stress type of rheology was used (Dade and Huppert, 1998). Backanalysis suggested that it was the PDC which generated the tsunami wave during the events of July 2019 and best fitting simulations identified a constant retaining stress of 7kPa. With these input parameters it has been possible to run a large number of numerical simulations of possible scenarios. This has allowed to assess threshold values of volume and discharge of mass flows which could generate significant and potentially destructive tsunami waves. This constitutes an important input to improve early warning systems and to reduce the risk related to these unpredictable but extremely dangerous phenomena.</p>

scholarly journals Overflows and Pyroclastic Density Currents in March-April 2020 at Stromboli Volcano Detected by Remote Sensing and Seismic Monitoring Data

2020 ◽  
Vol 12 (18) ◽  
pp. 3010 ◽  
Author(s):  
Sonia Calvari ◽  
Federico Di Traglia ◽  
Gaetana Ganci ◽  
Flora Giudicepietro ◽  
Giovanni Macedonio ◽  
...  
Keyword(s):  
Monitoring Network ◽  
Weather Conditions ◽  
Satellite Monitoring ◽  
Pyroclastic Density Currents ◽  
Density Currents ◽  
Stromboli Volcano ◽  
Volcanic Event ◽  
Lava Flow Field ◽  
Flow Features ◽  
The Impact

Between 28 March and 1 April 2020, Stromboli volcano erupted, with overflows from the NE crater rim spreading along the barren Sciara del Fuoco slope and reaching the sea along the NW coast of the island. Poor weather conditions did not allow a detailed observation of the crater zone through the cameras monitoring network, but a clear view of the lower slope and the flows expanding in the area allowed us to characterize the flow features. This evidence was integrated with satellite, GBInSAR, and seismic data, thus enabling a reconstruction of the whole volcanic event, which involved several small collapses of the summit cone and the generation of pyroclastic density currents (PDCs) spreading along the slope and on the sea surface. Satellite monitoring allowed for the mapping of the lava flow field and the quantification of the erupted volume, and GBInSAR continuous measurements detected the crater widening and the deflation of the summit cone caused by the last overflow. The characterization of the seismicity made it possible to identify the signals that are associated with the propagation of PDCs along the volcano flank and, for the first time, to recognize the signal that is produced by the impact of the PDCs on the coast.

Experimental constraints on volcanic ash generation and clast morphometrics in pyroclastic density currents and granular flows

2021 ◽  
Author(s):  
Adrian Hornby ◽  
Ulrich Kueppers ◽  
Benedikt Maurer ◽  
Carina Poetsch ◽  
Donald Dingwell
Keyword(s):  
Experimental Approach ◽  
Direct Evidence ◽  
General Description ◽  
Pyroclastic Density Currents ◽  
Density Currents ◽  
Shape Factors ◽  
Material Density ◽  
Bed Height ◽  
Rotary Drum ◽  
Basal Flow

<p>Pyroclastic density currents (PDCs) present perhaps the greatest proximal primary hazard of volcanic activity and produce abundant fine ash that can present a range of health, environment and infrastructure hazards. However, direct, fully quantitative observation of ash production in PDCs is lacking, and little direct evidence exists to constrain the parameters controlling ash generation in PDCs. Here, we use an experimental approach to investigate the effects of starting mass, material density and ash removal on the efficiency of ash generation and concurrent clast rounding in the dense basal flow of PDCs. We employ a rotary drum to tumble pumice and scoria lapilli clasts over multiple transport “distance” steps (from 0.2 to 6 km). We observe increased ash generation rates with the periodic removal of ash during the experiments and with increasing starting mass. By scaling to the bed height and clast diameter we obtain a general description for ash production in all experiments as a function of flow distance, bed height and average clast diameter. We confirm that changes in lapilli shape factors correlate with the ash fraction generated and that the grain size of ash produced decreases with distance. Finally, we estimate shear rate in our experiments and calculate the inertial number, which describes the ratio between clast-scale and flow-scale rearrangement during flow. We show that, under certain conditions, fractional ash production can be calculated accurately for any starting mass solely as a function of the inertial number and the flow distance. This work sheds light on some of the first systematic and generalizable experimental parameterizations of ash production and associated clast evolution in PDCs and should advance our ability to understand flow mobility and associated hazards.</p>

The numerical reconstruction of three past eruptions at Gede volcano (Indonesia)

2021 ◽  
Author(s):  
Eleanor Tennant ◽  
Susanna Jenkins ◽  
Annie Winson ◽  
Christina Widiwijayanti ◽  
Hendra Gunawan ◽  
...  
Keyword(s):  
Epistemic Uncertainty ◽  
Source Parameters ◽  
Frictional Resistance ◽  
Collapse Mechanism ◽  
Eruption Dynamics ◽  
Pyroclastic Density Currents ◽  
Density Currents ◽  
Basal Friction ◽  
Column Collapse ◽  
Hazard And Risk

<p>Understanding past eruption dynamics at a volcano is crucial for forecasting the range of possible future eruptions and their associated hazards and risk. In this work we reconstructed pyroclastic density currents and tephra fall from three eruptions at Gede volcano, Indonesia with the aim of gaining further insight into past eruptions and identifying suitable eruption source parameters for future hazard and risk assessment. Gede has the largest number of people living within 100 km of any volcano worldwide, and has exhibited recent unrest activity, yet little is known about its eruption history. For pyroclastic density currents, we used Titan2D to reconstruct geological deposits dated at 1200 and c. 1000 years BP. An objective and quantitative multi-criteria method was developed to evaluate the fit of over 300 pyroclastic density current (PDC) model simulations to field observations. We found that the 1200 years BP geological deposits could be reproduced with either a dome collapse or column collapse as the generation mechanism although a relatively low basal friction of 6 degrees would suggest that the PDCs were markedly mobile. Lower basal frictions may reflect the occurrence of previous PDCs that smoothed the path, reducing frictional resistance and enabling greater runout for the reconstructed unit. For the 1,000 years BP PDC, a column collapse mechanism and higher basal friction was required to fit the geological deposits. In agreement with previous studies, we found that Titan2D simulations were most sensitive to the basal friction; however, we also found that the internal friction – often fixed and considered of low influence on outputs - can have a moderate effect on the simulated average deposit thickness. We used Tephra2 to reconstruct historic observations of tephra dispersed to Jakarta and other towns during the last known magmatic eruption of Gede in 1948. In the absence of observable field deposits, or detailed information from the published literature, we stochastically sampled eruption source parameters from wide ranges informed by analogous volcanic systems. Our modelling suggests that the deposition of tephra in Jakarta during the November 1948 eruption was a very low probability event, with approximately a 0.03 % chance of occurrence. Through this work, we exemplify the reconstruction of past eruptions when faced with epistemic uncertainty, and improve our understanding of past eruption dynamics at Gede volcano, providing a crucial step towards the reduction of risk to nearby populations through volcanic hazard assessment.</p>

scholarly journals Tsunami wave propagation by voronoi diagram

2018 ◽  
Vol 7 (3) ◽  
pp. 1233
Author(s):  
V Yuvaraj ◽  
S Rajasekaran ◽  
D Nagarajan
Keyword(s):  
Wave Propagation ◽  
Voronoi Diagram ◽  
Tsunami Wave ◽  
Fast Marching Method ◽  
Coastal Regions ◽  
Fast Marching ◽  
Tsunami Waves ◽  
The Finite Difference Method ◽  
Run Up ◽  
Marching Method

Cellular automata is the model applied in very complicated situations and complex problems. It involves the Introduction of voronoi diagram in tsunami wave propagation with the help of a fast-marching method to find the spread of the tsunami waves in the coastal regions. In this study we have modelled and predicted the tsunami wave propagation using the finite difference method. This analytical method gives the horizontal and vertical layers of the wave run up and enables the calculation of reaching time.  

scholarly journals The hazards of unconfined pyroclastic density currents: a new synthesis and classification according to their deposits, dynamics, and thermal and impact characteristics

2021 ◽  
Author(s):  
Geoffrey Lerner ◽  
Susanna Jenkins ◽  
Sylvain Charbonnier ◽  
Jean-Christophe Komorowski ◽  
Peter Baxter
Keyword(s):  
Volcanic Hazards ◽  
High Energy ◽  
Significant Loss ◽  
Lessons Learned ◽  
Pyroclastic Density Currents ◽  
Density Currents ◽  
Loss Of Life ◽  
New Synthesis ◽  
End Members ◽  
Impact Characteristics

Pyroclastic density currents (PDCs) that escape their confining channels are among the most dangerous of volcanic hazards. These unconfined PDCs are capable of inundating inhabited areas that may be unprepared for these hazards, resulting in significant loss of life and damage to infrastructure. Despite their ability to cause serious impacts, unconfined PDCs have previously only been described for a limited number of specific case studies. Here, we carry out a broader comparative study that reviews the different types of unconfined PDCs, their deposits, dynamics and impacts, as well as the relationships between each element. Unconfined PDCs exist within a range of concentration, velocity and temperature: characteristics that are important in determining their impact. We define four end-member unconfined PDCs: 1. fast overspill flows, 2. slow overspill flows, 3. high-energy surges, and 4. low-energy detached surges (LEDS), and review characteristics and incidents of each from historical eruptions. These four end-members were all observed within the 2010 eruptive sequence of Merapi, Indonesia. We use this well-studied eruption as a case study, in particular the villages of Bakalan, 13 km south, and Bronggang 14 km south of the volcano, which were impacted by slow overspill flows and LEDS, respectively. These two unconfined PDC types are the least described from previous eruptions, but during the Merapi eruption the overspill flow resulted in building destruction and the LEDS in significant loss of life. We discuss the dynamics and deposits of these unconfined PDCs, and the resultant impacts. We then use the lessons learned from the 2010 Merapi eruption to assess some of the impacts associated with the deadly 2018 Fuego, Guatemala eruption. Satellite imagery and media images supplementing fieldwork were used to determine the presence of both overspill flows and LEDS, which resulted in the loss of hundreds of lives and the destruction of hundreds of buildings in inundated areas within 9 km of the summit. By cataloguing unconfined PDC characteristics, dynamics and impacts, we aim to highlight the importance and value of accounting for such phenomena in emergency management and planning at active volcanoes.

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