Figure 8-21 Distribution of Lava Flow for the Model

Transcription

1 Figure 8-21 Distribution of Lava Flow for the Model 2) Pyroclastic Flow The energy cone model was used for the simulation. a. The angle of inclination of Energy Line, φ, from the summit was 5.3 degrees from the results of the field identification. Five degrees was adopted for the simulation. b. The eruption column altitude was set to be 10,000 meter or lower, as stromboian activities or subplinian activities are assumed as an eruption style. The eruption column is assumed the common item for the tephra fall and pyroclastic flow. c. An occurrence of pyroclastic flow is assumed to be at the central point of the summit where the degree of hazard is the highest from pyroclastic flow. d. Calibration is not necessary, since the area of influence is assumed from Energy Line based on the results from field identification. 3) Tephra fall (ash fall) The simulation is conducted based on the model of T. Suzuki (1983). a. The 1995 eruption of Cerro Negro is used as the model. Calibration is based on the distribution of tephra fall during the 1995 eruption of Cerro Negro. b. The total amount of erupted materials and distribution of particle sizes are incorporated based on the analysis of reference materials of the 1995 eruption of Cerro Negro. c. As for upper-layer metrological data, there was no data observed in Leon. The data in Managua provided form the counterpart is statistically processed and used. d. An eruption at the summit of the mountain which has the effects in large areas was assumed. e. The eruption column altitude is set to be 10,000 meter or lower, as stromboian activities or subplinian activities are assumed as an eruption style. 216

2 Table 8-6 Average Wind Velocity in the Altitude of 10000m or Less Altitude August October April Unit: m/s 4) Volcanic Bomb The simulation was conducted based on the model of Iguchi and Kamo (1984). a. An eruption possible areas were set as possible eruption that affects large areas. b. The dimension of the target volcanic bomb is 10cm or large that is not to be affected by the convection current in eruption column. c. In the ballistic calculation, the main axis is assumed to be inclined in advance for hazard map preparation at the time of a volcanic explosion (See Figure 8-22). That is, the main axis at the time of explosion is not set perpendicular, but it should have the gradient of 39 degrees from earth surface. When this is the case, the distance of ballistic travel distance becomes 1.69 times longer than that of the perpendicular case. For the preparation of hazard mapping, the main axis is assumed to be inclined to all the directions. d. Since there is no source material, calibration is not conducted. Vmax axis of explosion 39 degrees Figure 8-22 Diagram of Explosion Axis (Longest Distance Case) 5) Lahar The simulation is conducted in accordance with the hazard assessment by the USGS for the Volcán Telica (R.M. Iverson, et al., 1998). a. Generation of lahar is assumed to be in the following order: collapse of a volcanic edifice; debris mass movement; debris avalanche; erosion and mobilization of the mass accompanied with movement; and lahar. b. The area of influence is set according to a rule of thumb (R. M. Iverson, et al., 1998). 217

3 c. From the past data and geomorphologic conditions, we assumed that the starting point of lahar has, in general, a slope with 8 to 10 degrees at the ravine floor. d. The maximum scale of lahar is set at m from the experience of the lahar at Volcán Casita caused by Hurricane Mitch in In the simulation, along with the maximum scale, smaller scales of m, m 3, and m 3 are examined. e. Since there is no data or information, calibration is not conducted. (4) Development of Simulation Software The simulation software was developed based on the existing simulation software and the existing simulation program already available. Software was designed in a way to transfer the results of calculation to the GIS software. 1) Precondition Target volcanic phenomenon: lava flow, pyroclastic flow, tephra fall (volcanic ash), volcanic bomb, lahar Fundamental requirement: Since there are various cases: lava flow and tephra fall take time; volcanic bomb requires detailed topographic into consideration, the software needs to have independent calculation functions for each hazard type and to calculate individually instead of one integrated system. Geographical accuracy: Topographic-map accuracy of 1/50,000 2) Execution environment (a) Lava flow Geographical-feature model: 100 m mesh altitude Computation time: middle to long (30 minutes - about 6 hours) Program source: FORTRAN System creation: Visual FORTRAN Dispatching: Start an executable file from Windows. Output: ESRI grid ASC file (b) Pyroclastic flow Geographical-feature model: 100 m mesh altitude Computation time: Short to Medium (several minutes - about 30 minutes) Program source: FORTRAN System creation: Visual FORTRAN Dispatching: Start an executable file from Windows. Output: ESRI grid ASC file (c) Volcanic Bomb Topographic model: ESRI TIN or 10 m mesh altitude Computation time: Inside (about 30 minutes) Program source: Avenue or FORTRAN System creation: ArcView or Visual FORTRAN Dispatching: Perform a script from ArcView. Or an executable file is started from Windows. Output: shape file or ESRI grid ASC file (d) Tephra fall Geographical feature model: (nor required) 218

4 Computation time: It is greatly dependent on the number of particle diameter classification, and the number of altitude classification. Generally it is long (several hours to 10 hour). Program source: FORTRAN System creation: Visual FORTRAN Dispatching: Start an executable file from Windows. Output: ESRI grid ASC file (e) Lahar Geographical-feature model: 100 m mesh altitude Computation time: Medium (about 30 minutes) Program source: FORTRAN System creation: Visual FORTRAN Dispatching: Start an executable file from Windows. Output: ESRI grid ASC file (5) System Requirement The system requirement for the implementation of simulations is described as follows. In the system, Visual Fortran and Visual C ++.Net, one license each, are installed to a PC in the Department of Geography by the Study Team. 1) Visual FORTRAN Software vender: Intel Product Name: Windows Version Intel Corp. Visual Fortran Compiler 8.1 professional edition Web Site: 2) Visual C ++.Net Software vendor: MicroSoft Product Name: Visual C ++.Net 2002 Web Site: 3) Arc View Software vender: ESRI Product name: ArcView, 3D Analyst HP: (6) Default Values of the System The default values of the system were set. The values were the parameters recommended for hazard simulation in the Study area and recommended by theoretical papers, which were the bases of the system. As for actual operation, 2-2 Volcano in Manual 2, Hazard Mapping. shall be referred. The default values are set for the areas of the Telica-El Hoyo volcanic complex. For other volcano or other rock types, new parameters need to be set. Figure 8-23 is a sample of default values of the tephra fall case. 219

5 Figure 8-23 Sample of the Default Value of Tephra Fall Simulation (7) Implementation of Simulation Examples of simulation results are shown in figure from Figure 8-24 to Figure Figure 8-24 is the case of Volcán El Hoyo where a large scale lava flow took place. The direction of lava flow changes as landform changes near the volcano and other fine landforms that restrict flow directions and alter the courses of the flows. 220

6 Figure 8-24 Example of Simulation Result on Large Scale Lava Flow from Volcán El Hoyo The difference in color shows thickness of lava flows. Figure 8-25 Example of Simulation of Pyroclastic from the Summit of the Volcán El Hoyo and Energy Line Angle 221

7 Figure 8-26 Example of Simulation on Tephra fall from the Summit of the Volcán Telica (Top: The same condition as in Cerro Negro Middle: The eruption column is twice as high as in the case of the Cerro Negro 1995 eruption; other conditions are the same. Bottom: The amount of pyroclastic objects are twice as large as the case in the Cerro Negro 1995 eruption; other conditions are the same.) 222

8 Figure 8-27 Example of Lahar Calculation from Volcán Telica The difference in colors show the difference in the amount of flooded debris. The pink color shows the maximum amount of 3x10 6 m 3, and the blue color shows the minimum of 0.1x10 6 m 3. Figure 8-28 Example of Computation in an Case of Ejecta Discharge from the North of the Summit The difference in colors show the travel distances by diameters of ejecta. The red is the case of 30 cm; the yellow is 50 cm; and the light blue is 1 m with an initial velocity of 150 m/s. (8) Hazard Mapping 1) Existing Volcano Hazard Maps 223

9 In Nicaragua, the following hazard maps are already created in cooperation with the Mexico Local Autonomy College, etc. The maps have been distributed to municipalities and the Civil Defense and other related institutions. Volcán Concepción (Volcanic Bomb, Lava Flow) Volcán Concepción (Pyroclastic Flow, Tephra fall) Volcán Concepción (Lahar, Collapse of Volcani Edifice) Volcán Masaya (Volcanic Bomb) Volcán Masaya (Three types of ash fall by month) The Centeral - Northern Regional Volcanic Hazard Maps (Lava Flow, Lahar, Collapse of volcanic edifice, pyroclastic flow) Among the hazard maps listed the hazard maps for Volcán Concepción and Volcán Masaya are prepared in A0 size paper format. The contents seem to be targeted to academics; they are highly specialized for professionals. The existing hazard maps are too technical for the staffs in the municipal governments and the Civil Defense. 2) Map Users How hazard maps are to be prepared depends on the target users. For example, wording, technical terms, uses of illustrations, notations of hazards and other factors can be different. Also, how well the users can read maps is a factor, which affects how the hazard maps are to be prepared. Home use or targeted to persons in charge of disaster prevention is another factor to be considered. If the maps were to be used in the Civil Defense, a large format which could be put on a wall would be appropriate; for the general home uses, it would be appropriate to have a smaller format. The hazard maps prepared during the Study, after discussions with the counterpart, are targeted to the staffs in local governments and the Civil Defense; therefore, literacy has not been taken into consideration. Since the hazard maps, such as in the maps for Volcán Concepcion created by INETER are targeted for professional, the hazard maps for the Study are designed for general users. 3) Scale of Volcanic Activities and Return Period It is generally difficult to assume a scale of volcanic activities and return periods from statistical processing even when sufficient geological researches have been conducted. This is because almost all the stratums cannot be seen because of the structure in a case of the stratovolcano characterized in many parts of Nicaragua. For the reasons, when a hazard map is prepared, users' and decision makers' subjective purposes are taken into consideration. Alternatively, eruptions of similar volcano are studied and assumptions need to be set. Even using a historical record, one might not be able to assume the maximum scale to be a volcanic activity once in one thousand years. In general, following cases are considered to determine assumptions on a scale of volcanic activity. Which case to be employed needs to be determined by examining past records or social conditions one by one. (1) Gigantic or largest scale in historical records (2) Most frequent scale in historical records (3) Gigantic or largest scale in limited geological records (4) Most frequency scale in limited geological records (5) Scale of the specific event (6) Theoretically inferred scale (7) Designed Scale 224

10 When treating many volcanic phenomena in a volcanic hazard map, it is also unavoidable to have different assumption standards for each volcanic phenomenon; the data need to be available to determine the same standard level. For the Telica-El Hoyo volcanic Complex, existing reference materials, results from field identification and others were used to set assumptions on the scales of eruption. Lava flow: The maximum scale (apparent volume) among lava flows whose distribution can be identified on the surface at present. It was reported that the maximum lava flow of Volcán Telica had taken place in The eruption type like shield basalt or plateau basalt is not assumed. Tephra fall: The actual record of the scale (eruption column height, apparent descent alimentation) in the 1995 eruption of Cerro Negro was the basis of the assumption. A larger version was also considered. Pyroclastic flow: It is based on the field identification. Although the pyroclastic flow deposit is not confirmed by field identification in Volcán Telica, the same conditions (energy line angle) were considered as in Volcán El Hoyo. Volcanic bomb: The maximum initial velocity was set at a time of eruption from experiences. 4) Basic Structure Following subjects are the constitutions of planning the basic structure of the hazard maps: (1) The target area of the hazard map for the Telica-El Hoyo volcanic complex is about 1,300 km 2 ; (2) The hazard map includes five phenomena: lava flow, tephra fall, volcanic bomb; pyroclastic flow and lahar; (3) Among the five types, ash fall has larger impact areas; therefore, the scale of background map is different from other four types. (4) The target users are the staff in the Civil Defense or the staff with similar background. The smallest scale of the background topographic map is 1/100,000. With the scale, the target area can be shown with an A2 size paper. When explanation is included, an A1 size paper would enable to include all the information. However, in the case of ash fall in Volcán Telica and Volcán El Hoyo, the size becomes an A1 size. With other information included, an A0 size become the size of the hazard map. At most, six hazard maps, or when overlaid, about three hazard maps need to be prepared. When the condition (3) is considered, it would be better to use a large format for easier interpretation to be posted on the wall all the time. In the past, the size of hazard maps produced in INETER has been an A0 size. In Japan, the Mt. Fuji case used a multiple layer type of hazard maps that had multiple volcanic hazard phenomena in one sheet. The display of many lines was disrupting interpretation; therefore, in this Study, the intensive line expression was avoided. Considering the above situations, the Study Team concluded to prepared the hazard maps in one size for all the phenomena in the following structure. (1) Map 1: Only lava flow is included. Geology map is included to facilitate understandings on volcanic hazard (A0 size). (2) Map 2: Three types of phenomena were included: An overlay display of tephra fall and lahar and volcanic bomb (A0 size) (3) Map 2: Only ash fall is included (A0 size). 225

11 5) Information Included Examples of information to be included for the maps are listed in Table 8-7. Since the targeted users are municipal officials and the staffs in the Civil Defense, the pieces of information to be included are limited in the following items to have an intelligible structure. Title Explanation of volcanic phenomenon Description of hazard Photographs and illustration of volcanic phenomena for educational purpose Project name, year, contact Logo marks of INETER and JICA Location guide map for volcano Table 8-7 Basic knowledge on volcanic activities Information provider Characteristics of the volcano History of volcanic activities Disaster Prediction Disaster prevention base Evacuation information Emergency action agenda Transportation information Methods of communication, information collection and dissemination Surveillance establishment for volcanic activities Information Required for Hazard Mapping 6) The Draft Hazard Map The draft hazard map is shown in the following figure. Volcanic cycle Volcanic phenomena Volcanic disaster Responsible entity (Publisher Contact Date of publication Types of volcanic disasters within the scope Types of volcanic disasters out of the scope Disaster prediction results Location Name Contact Emergency contacts Emergency goods Knowledge in an emergency Major roads Emergency transport routes Transportation restriction Contacts and locations of related organizations Contacts for reporting abnormal phenomena Types Location 226

12 Figure 8-29 Geology (top) and Lava Flow (bottom) The photographs are Volcano Kilauea (Hawaii's) showing low viscosity basalt lava flows 227