Volcanic eruptions induce often widely dispersed, multimodal flows such as volcanic ash, pyroclastics, layers, and lava. Lahars triggered by heavy rain may extend far beyond ash deposits. Indonesia, which has 127 volcanoes along its archipelago, is at high risk for such disasters. The 2010 Merapi volcano eruption, for example, generated pyroclastic flows up to 17 km from the summit along the Gendol River, killing over 300 residents. The February 13, 2014, eruption of the Kelud volcano produced a gigantic ash plume over 17 km high, dispersing tehpra widely over Java Island. Ash falls and dispersion closed 7 airports and caused many flights to be cancelled.
Volcanoes in Japan have recently become active, with the 2014 phreatic eruption at the Ontake volcano leaving 63 hikers dead or missing. The eruption of the Kuchinoerabujima volcano on May 29, 2015, forced all island residents to be evacuated.
All of these events undeerscore how underedeveloped Japan’s early warning alert levels remain. The Sakurajima volcano, currently Japan’s most active, maintained high activity in the first half of 2015. Ash from Janaury 2015, for example, was moved down the volcano’s slopes by extremely heavy rain in June and July, accumulating as thick sediment near villages.
Regarding such situations of volcano countries, we will develop an integrated system to mitigate many kinds of disasters which are generated by volcanic eruptions and extended by rain fall and wind, based on scientific knowledge. We are developing an integrated warning system to be used by local and national governments to mitigate volcanic and sediment disasters. We are also creating measure against volcanic ash for airlines.
This special issue summarizes basic scientific knowledge and technology on the present warning system to be used in the integrated system for decision-making.
A method for evaluating the volcanic ash discharge rate by using seismic and ground deformation signals is proposed to obtain this rate in real time for southern Kyushu’s Sakurajima volcano. This volcano repeats vulcanian eruptions accompanying significant ground deformation showing deflation and nonvulcanian type eruptions that emit the minor emissions of volcanic ash associated with volcanic tremors but without significant ground deformation. We examined ground deformation and seismic amplitude as they relate to monthly sums of volcanic ash weight ejected from craters. We found that in monthly sums, both deflation ground deformation and the amplitude of volcanic tremors correlate positively with the weight of ejected volcanic ash. A linear combination of terms for ground deformation, seismic amplitude and a correction factor correlates better than single parameter of deflation or seismic amplitude with volcanic ash weight. The linear combination provides the volcanic ash discharge rate in quasi-real time and the total amount of volcanic ash distributed over a wide area immediately after a volcanic eruption ends.
Preliminary results of quantitative analysis of volcanic ash clouds observed over the Sakurajima volcano in Kagoshima, Japan, were obtained by using weather radar and surface instruments. The Ka-band Doppler radar observations showed the inner structure of a volcanic ash column every two minutes after an eruption. Operational X-band polarimetric radar provides information on three-dimensional ash fall amount distribution. The terminal fall velocity of ash particles was studied by using optical disdrometers, together with the main specifications of observation instruments.
In order to evaluate airborne ash densities, a real-time volcanic ash dispersion model, PUFF, is applied to the February 13, 2014 eruption of Kelud volcano in Indonesia. The emission rate of the ash mass from the vent is estimated based on the empirical formulae tested at Sakurajima volcano using ground deformation and seismic monitoring data.
According to the result of the PUFF model simulation, the circular shape of the anvil ash cloud 17 km in height extends during the first two hours over a radius of 200 km from the volcano. The core region within 50 km of the volcano shows an airborne ash density of 1000 mg/m3. Three hours after the initial eruption, the area with 100 mg/m3 extends 300 km to the west, covering Yogyakarta Airport. Due to low-level winds, Surabaya Airport to the northeast also becomes part of the area with 100 mg/m3. The result of the ash plume dispersal 7 hours into the eruption indicates that the entire island of Java is in the danger zone for commercial airliners, as ash exceeds 10 mg/m3. Although satellite images show that the ash plume is located only in the southern half of western Java, the simulation results quantitatively indicate much wider extents of the aircraft danger zone.
The present study shows the possibility of using X-band multi-parameter radar to detect volcanic tephra for estimating the amount of volcanic tephra in the air even when the amount of volcanic tephra is very low. The model proposed in this study can detect tephra with diameters of 0.5 mm to 3 mm. Through the observation experiment and the model proposal, the present study shows successful detection of volcanic tephra in the air by using X-band multi-parameter radar.
Ash thicknesses reported by the media and witnessed by local residents may be exaggerated. A good example of such exaggeration is ash thicknesses reported following the Plinian eruption on February 13, 2014 at Kelud volcano, East Java, Indonesia. Volcanic ash thicknesses reported by the media and local residents were generally by 2–7 times larger than the actual values measured by volcanologists. Sensational news reports and strong fresh impressions may cause such exaggeration, or these exaggerated values may simply represent abnormal concentrations of volcanic ash. It is important to pay careful attention to the parameters that are being documented by the media and by people who do not have scientific backgrounds when utilizing such reports in scientific analyses.
Indonesia’s Mount Merapi is one of the world’s most active, dangerous volcanoes. Its 2010 eruption – the largest following the 20th century – and succeeding 2011 lahar events killed 389 persons and injured and displaced many more. One way to mitigate a disaster’s impact is the provision of reliable information to the public through a well-established early warning system (EWS). A well-managed information flow network is the key to delivering early warning information, however, there is a lack of understanding on the information transfer down to the citizens. In addition, implementing the 2007 disaster management law may have affected Merapi’s EWS. This study reinvestigates Merapi’s EWS information flow through the construction of an information flow network. A single information flow network was difficult to construct due to the inconsistency of structures per district. Different networks had to be constructed for volcanic eruptions and lahars in each district. Inconsistencies were also found in the roles of the agencies that determine when evacuation orders would be issued. The system also had data transfer gaps and vulnerabilities such as redundancies, mistransfers and bottlenecks. Its use of forecasting information as a basis for decision-making must be reviewed for lahar information flow networks. Improving Merapi’s EWS must involve handling these issues.
The science of measuring airborne volcanic ash concentrations supports research in such fields as atmospheric environmental science and the modeling of atmospheric pollution from volcanoes, and is thus very valuable to the aviation industry. These measurements show large scatter directly traceable to turbulent fluctuations responsible for diffusing volcanic dust. Before semistationary components in observations can be compared to each other or to simulation results, they must be separated from fluctuations. In the design of the separation process, however, neither seasonal or diurnal periodicity nor random disturbance with known properties exists to serve as a guideline. It has been suggested that fluctuations could be eliminated through repeated convolutions of a simple 3-point filter enough times. The number of convolutions is chosen from the change in the rate of increase of a special variability parameter. When semistationary concentrations are separated from fluctuations, their statistics are compared to turbulence parameters and the autocorrelation of the series. The method is demonstrated using three measurement series from Sakurajima, Japan measured in 2013. It is concluded that this new method is simple and trustworthy where knowledge and experience of the environmental parameters can be utilized to support the results. They indicate a variability of 40% in the relative fluctuations of the PM10 and around 20% of the PM2.5. The relative fluctuations may be considered completely random, but normally distributed rather than a white noise with an evenly distributed variance spectrum.
Volcanic eruptions have caused very costly disturbances of international air traffic. This problem has been dealt with by simulating the formation and migration of dangerous ash plumes. However, the results of the simulations have sometimes been too safe, producing ash clouds that are too large. This was especially the case for the North Atlantic in 2010 (Eyjafjallajökull) and 2011 (Grímsvötn). Since 2012, an international cooperation team led by the Disaster Prevention Research Institute (DPRI) of Kyoto University has conducted airborne measurements of volcanic ash concentrations in the plume from Mount Sakurajima in Kagoshima Prefecture, Japan. This volcano was chosen because of its frequent but limited eruptions, which allow close observation. These measurement campaigns have provided data showing gravitational flattening of the plume, a new and previously unknown dispersion process of volcanic plumes. A new and previously unknown fallout process, called streak fallout, also has been measured. Results concerning plume flux, concentration distributions, aerosol (PM10) content of the plume, and content of very fine particles (PM2.5 and PM1) are presented, and the ways by which the observational methods can be used to produce reliable initial data and boundary values for simulations of plume dispersion are discussed.
Shaking table test of a quarter-scale 20-story reinforced concrete building model was carried out. Employed input waves were kinds of long period and long duration ground motion. Test results showed that structural slabs were fully effective for building strength, which could be expressed in detailed analysis using nonlinear FEM. However, the observed hysteretic damping after yielding was fairly smaller than the expected by the current design custom, which caused smaller and unsafe estimated response than that observed in the test.
Recent vibration resistant designs for buildings in Japan often adopt a vibration control structure with dampers arranged in the framework. Generally, the dampers are arranged in the building’s core in a geometry that works most effectively to protect against story shearing deformation. It is already known, however, that the above-mentioned arrangement of dampers does not provide good damping effects for the upper stories of high-rise buildings with large aspect ratios, because the protection mechanism is designed to decrease the shearing deformation components of the building’s horizontal deformation caused by its horizontal loads.
A new type of dampers, called force-restricted tuned viscous mass dampers (FRTVMD), has been recently developed for such circumstances, amplifying the deformation of viscous dampers with their tuned mass effects. This paper, therefore, first presents a tuned mass damper (TMD) system, effective for high-rise buildings with large aspect ratios against great earthquakes, and then proposes a new vibration control structural system capable of generating better damping effects with FRTVMD. In addition, we review its characteristics and effects by analyzing its vibration response, as well as verify that a combined use of such vibration control structural systems will generate far greater damping effects than an individual system.
This study reviews and discusses several recent design approaches for passively controlled structures. First, an optimized arrangement method for the energy dissipation members (EDMs) of various infrastructures is introduced. Next, seismic isolation and passive control techniques for freeform space structures are discussed. Finally, research on various spine-frame concepts with EDMs is reviewed. All these approaches are being introduced to actual structural design, and recent examples are reported here.
Shear panel dampers consisting of stiffeners and panels surrounded by four flanges are used as aseismic hysteretic dampers for buildings in Japan. Cracks can form easily in a shear panel damper when shear buckling occurs during the cyclic loading caused by a severe earthquake.
For a relatively thin panel with a large width-to-thickness ratio, the damper’s plastic deformation capacity and the presence of shear buckling can be evaluated from the maximum deformation angle. However, when it is relatively small, very-low-cycle fatigue life for a relatively thick panel must be known to predict the usage limit of the damper, because the failure pattern changes when cracks form in the weld between the panels and flanges. Fatigue life relations for a thick shear panel damper with parameters of normalized width-to-thickness ratio and deformation angle are presented. A method for predicting the fatigue life under severe earthquake conditions is also presented. To validate the prediction expression, cyclic loading tests were performed on a shear panel damper and reviewed. The applicability of the method for predicting the fatigue life was confirmed through non-stationary cyclic loading tests. These results showed the validity and effectiveness of the expressions and the method.
Studies on evacuation behavior are often based on regular favorable scenarios, but more urban areas are adversely affected by natural disasters, many of them under extreme geographic conditions, and very little is known on how these conditions affect evacuation processes, especially in communities with neither experience nor disaster education.
We collected empirical data during announced evacuation practices in a landslide-prone urban area from La Paz, Bolivia. Based on this experiment, we measured time, velocity and participants’ behavior, then process results and input them as parameters to a 3-dimensional (3D) agent-based evacuation simulation model of the evacuation practice location to simulate real scenario evacuations focused on community residents walking on stairs and steep streets.
Our objective is to explain procedures for simulating two evacuation cases with different premises and to compare results from the two.
Results show that one case is more effective simply by following a simple rule of evacuation path selection. Our ultimate purpose is to create a compelling graphic tool for teaching persons about early short-term evacuation, including the importance of early planned evacuation. It also provides persons with opportunities participate in virtual drills.