Citation:
Perez.E, B. Shibazaki, Y. Fujii and H. Yanagisawa (2019), Numerical simulation for tsunami
caused by debris avalanche in Lake Nicaragua, Synopsis of IISEE-individual study report.

NUMERICAL SIMULATION FOR TSUNAMI CAUSEDBY DEBRIS AVALANCHE IN LAKE NICARAGUA
Elliet PEREZ1

Supervisor:

Bunichiro SHIBAZAKI 2
Yushiro FUJII 2

ABSTRACTThis study performs the numerical simulation for the tsunami caused by the debris avalanche in Lake
Nicaragua based on past events that occurred in the surroundings of Mombacho Volcano and theanalysis of future scenarios of the debris avalanche in Conception Volcano. We used the Yanagisawa
code for tsunami simulations and obtained arrival time and tsunami height. The model considered thevolume, speed, distance, and width of the debris avalanche. We used the bathymetry and topography
from the Nicaraguan Institute of Territorial Studies (INETER) for the simulation. A total of fivesimulations were modeled considering one simulation for Past Event and four simulations for Scenario
Event. For these simulations, two directions of the debris avalanche in Conception Volcano, northeastand southwest, and two volumes such as maximum and minimum were considered. The worst impact
was found in Rivas city when modeling the debris avalanche in the southwest direction with the
maximum case in Conception Volcano. The arrival time of the tsunami was 10 minutes to the city, andthe amplitude of the wave was from 4 m to 5.5 m. This case can be taken as an example to work on atsunami disaster mitigation and evacuation plans.
Keywords: Tsunami in the lake, debris avalanche, Lake Nicaragua, volume, speed.
1. INTRODUCTION
A volcanic tsunami is rarely observed but is commonly known to be violent and destructive(Nishimura and Satake, 1993). The volcanic process could generate debris avalanche. A Debris
avalanche occurs when part of the flank of volcanoes collapse in volcanic islands at underwater or on
land. As Nicaragua has very large lakes existed, a historical record of tsunamis occurred in the twolakes. In historical documents, we can find the evidence of the volcanic activity in Nicaragua near the
shore of both Lake Managua and Lake Nicaragua, which were likely to have caused a tsunami in thelakes. In Nicaragua, there is also the evidence of volcanos collapse; for instance, in Mombacho
Volcano, two huge debris avalanches were generated, both with an extension of 10 km deposit. An ofthe debris avalanche of this volcano entered into the water of the Lake Nicaragua and formed a small
islet “Las Isletas of Granada” this event provoked a tsunami, but there is no a record of this event. In
Conception volcano, an event could occur with the same magnitude or higher magnitude at any time.
The objective of this study is to assess the tsunami hazard in the lakes of Nicaragua based on past
events occurred in the surroundings of Mombacho Volcano and the analysis of future scenarios ofdebris avalanche in Conception Volcano.
1

Institute of Geology of and Geophysics of the National Autonomous University of Nicaragua(IGG-CIGEO/UNAN-MANAGUA).
2
International Institute of Earthquake Engineering (IISEE), Building Research Institute (BRI) Tsukuba, Japan.

12. DATA

Figure 1. Bathymetry grid
data used for tsunami
simulations. Red triangles
show output points forcalculated
tsunamiwaveforms.

The bathymetry was used in this work we obtained from INETER.
The bathymetry of Lake Nicaragua was prepared by Swain (1976)
and INETER (1992). Both data were combined to obtain a goodbathymetry resolution. Then, the topography of Mombacho Volcano
was obtained from Shuttle Radar Topography Mission (SRTM)(NASA, 2019). Data of 1 arc-second (30-m resolution) was used inthe 3D model with a 1:200 000 scales. Other calculation was madewith Google Earth.
The displacement of debris avalanche speed wasapproached, using two historical events Mount St Helens volcanic
eruption occurred in May 1980 in Washington, USA(Voight,1981)
and Oshima-Oshima volcanic eruption occurred in August 1741 in
Hokkaido, Japan (Satake and Kato, 2001).

3. THEORY AND METHODOLOGY

3.1. Order of analysis
To assess the tsunami hazard in Lake Nicaragua based on past events occurred in the surroundings ofMombacho Volcano and the analysis of future scenarios of the debris avalanche in Conception
Volcano, we will conduct the following studies: 1. Characterize the debris avalanche of Mombacho
Volcano “Past Event” and calculate the total volume of the debris avalanche and the volume thatgendered the Granada islets deposit. 2. Determine the direction of possible debris avalanche inConception Volcano “Scenario Events.” 3. Create two cases of the tsunami by debris avalanche basedon the volume calculated in Past Event. 4. Perform a tsunami simulation in Past Event and four
tsunami simulations in Scenario Events.
3.2. Simulation of tsunami
Tsunami simulation is based on or supported by the non-linear long wave theory. This study deals
with the Yanagisawa code, which was modified and integrated equations for the simulation oftsunamis generated by debris avalanche of the subaerial type.
3.2.1. Equations for tsunami modeling
The code developed by Yanagisawa (2019), which includes the source of a tsunami caused by alandslide or debris avalanche also governing equations are based on the non-linear long wave theory.
Nonlinear long-wave equations with Manning bottom friction term with the spherical coordinate
system are Eqs. (1) -(3) as follows:
1  M ++( N cos  ) = 0t R cos    


(1)

M
gD 
1
 M2 1
 
MN  gn2
2
2

 +
+
+
cos


+ 7 3 M M + N = 0
t R cos  R cos   D  R cos  
D  D

(2)
(3)

2

where  and  are latitude and longitude respectively,  is water level, M and N are thedischarge fluxes in the  and  directions, R is the radius of the earth, t is time, g is
gravitational acceleration, and h is water depth. D is the total depth = (h +  ) ,  is Manning’s
coefficient, M and N are the discharge fluxes in the directions x and y.
3.2.2. Equations in case of input by line flow in a semi-elliptical shape modified by Yanagisawa
The important parameter is the assumption of the geometric form of the avalanche. In this study, we
assumed a semi-elliptical geometric shape of debris avalanche (Figure 2). Input boundary is the line
where the material of the debris avalanche starts entering into and displacing water. V is the volume ofthe semi-elliptical shape in cubic meters of landmass thatenters into water, which is calculated by Eq. (4).

V=
LDW (m3 )2(4)

where L is the longitude of displacement of the debris
avalanche, W is the width of the debris avalanche. The
velocity U of the total event is calculated by Eq. (5):U=

Figure 2. The draw of line flow in a semielliptical shape modified by Yanagisawa.

L(m s )
T(5)

3.3.Source scenarios for tsunami
In order to obtain the variables, a workflow of five stages was proposed. In the first stage, the volume
of Past Event was estimated. This information lets stage (2) provide inputs for the building of Scenario
Event based on Past Event. Then, this information was validated in stage (3). The informationacquired in the previous stages was useful for the tsunami simulation scenarios for Scenario Events instage (4). Finally, the information obtained by the simulation of both events created the synthetic
tsunami waveform.
Scenario Events was defined as two likely areas where the debris avalanche may occur inshore of Conception Volcano. The first Tsunami simulation of Scenario Event (northeast direction) the
second Tsunami simulation of Scenario Event (southwest direction). In order to simulate two scenarios,
two cases for Scenario Events were considered: (1) a debris avalanche in the flank of Conception
Volcano (Medium case) and (2) a debris avalanche that enters into the Lake Nicaragua (MaximumCase).
4. RESULTS
We calculated the tsunami generation in Lake Nicaragua for the debris avalanche caused by the Past
Event in Mombacho Volcano and Scenario Events in Conception Volcano.
4.1. Past Event
4.1.1. Reconstruction of bathymetry and topography before the Past Even
Currently, the bathymetry of Lake Nicaragua shows the area of deposit in the lake that originated Las
Isletas. The area of this zone was removed in order to create a new bathymetry and topography so as toreconstruct the wave generated in the Past Event3

Table 1. Debris avalanche parameters used fortwo-case tsunami simulations.

Figure 3. (Left) Present bathymetry andtopography grid data around Granada.
(Right)Reconstructed
grid
data
assuming the lakefront and water depth
before the Past Event. Gray grid points
show the land area.
4.1.2.

Table 1 shows the parameters obtained in the calculation
for the geometric form of the debris avalanche. We
used a total time of 5 hours in the tsunami modeling forboth events.

Tsunami simulation of Past Event

The bathymetry and topography created for this specific event were explained before and used for thistsunami modeling combined with the data of Table 1.
The results of numerical simulation showed that the area of the largest impact was
Granada city (Table 2). The arrival time of the tsunami was 3 minutes to the city, and the amplitude of
the tsunami was 0.98 m and 1.45 m in the Medium case and Maximum case, respectively. Then, thesecond impact was in Puerto Diaz, which is located at 34 kilometers away from the source, after 67
minutes from the occurrence of the event with a maximum amplitude of 1 m in the Medium case andafter 65 minutes of the event with a maximum amplitude of 1.17 m in the Maximum case (Figure 4).
Table 2. Tsunami arrival time and maximum amplitude from thecalculated waveforms for the Past Events in Mombacho Volcano.

Figure 4 Blue lines and redlines indicate the calculated
waveforms for the Medium
case and Maximum case,respectively.
Amplitude (m)Amplitude (m)Amplitude (m)Figure 5. Snapshots of tsunami propagation from the debris avalanche model (Maximum case) for the
Past Event in Mombacho Volcano.

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4.2.

Scenario Events

We used the bathymetry and topography given by
INETER to create the tsunami modeling in both
directions of northeast and southwest, combined withthe data of Table 1. In Figure 6 we can see the input
volume vectors of the width (W) of the debris
avalanche for the Maximum case for, Scenario Event(Northeast direction) and Scenario Event (Southwest
direction).
Figure 6. Input volume vectors of the right:
northeast-direction and left:
4.2.1.
Scenario Event (Northeast direction).
southwest-direction for Maximum case for
The results of numerical simulation showed the area
the Scenario Events in Conception Volcano.
of the largest impact, which could be Puerto Diaz inthis case (Table 3). The arrival time of the tsunami was 57 minutes and 56 minutes to the port, and theamplitude of the tsunami was 1.20 m and 1.40 m for the Medium case and Maximum case,respectively. Then, the second largest impact could be in Granada, which is located at 52 kilometers
away from the source after 81 minutes from the occurrence of the event with a maximum amplitude of
0.48 m in the Medium case, and after 80 minutes of the event and a maximum amplitude of 1.40 m in
the Maximum case (Figure 7).
Table 3. Tsunami arrival time and maximum amplitude from thecalculated waveforms for the Scenario Event (northeast direction)

Figure 7 Blue lines and red
Scenario Event (Southwest direction).
lines indicate the calculated
waveforms for the Medium
The result of numerical simulation showed that the most affectedcase and Maximum case,area would be Rivas city, which is located11 kilometers from therespectively.
source (Table 4). The arrival time of the tsunami was 10 minutes
to the city, and the amplitude of the tsunami was 4.09 m and 5.61
m for the Medium case and Maximum case, respectively. Then, thesecond largest impact could be in Sapoa, which is located at 27
kilometers away from the source after 38 minutes from theoccurrence of the event with a maximum amplitude of 0.54 m in theMedium case, and then 37 minutes after the event with a maximum
amplitude of 0.72 m in the Maximum case(Figure 8).

4.2.2.

Table 4. Tsunami arrival time and amplitude from the calculated
waveforms for the scenario events (southwest direction)
Figure 8 Blue lines and redlines indicate the calculated
waveforms for the Medium
case and Maximum case,respectively.

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Figure 9. Snapshots of tsunami propagation from the southwest-direction debris avalanche model(Maximum case) for the Scenario Event.
Amplitude (m)Amplitude (m)5.

Amplitude (m)CONCLUSIONS

Past Event. The results of numerical simulation show the area of the larges impact was in Granada city.
The arrival time of the tsunami was 3 minutes to the city, and the amplitude of the tsunami was 0.98 m
and 1.45 m for Medium case and Maximum case, respectively. Then, the second impact was in PuertoDiaz. These areas were the most vulnerable and were possibly affected by this event in the past.
Scenario Event (Northeast direction). The result of numerical simulation shows that thearea most be affected will be Puerto Diaz. The arrival time of the tsunami could be 57 minutes and 56
minutes to the Port and the amplitude of the tsunami will 1.20 m and 1.40 m for Medium case andMaximum case, respectively.
Scenario Event (Southwest direction). The result of numerical simulation shows that thearea most be affected will be Rivas city. The arrival time of the tsunami could be 10 minutes to thecity and the amplitude of the tsunami will 4.09 m and 5.61 m for Medium case and Maximum case,respectively.

ACKNOWLEDGEMENTS
This research was conducted during the individual study period of the training course “Seismology,
Earthquake Engineering and Tsunami Disaster Mitigation” by the Building Research Institute, JICA,
and GRIPS.I would like to express my gratitude to my supervisor, Dr. B. Shibazaki, who shared his
wide experience and gave me his continuous support in this study. In the same way, I want to thank Dr.
Y. Fujii, who helped me with the use of the model and the simulations. Also, I want to thank Prof. H.
Yanagisawa for letting me use his code for simulation and helping me with Prof. Miyagi generate themethodology for the model of debris avalanche

REFERENCES
NASA, 2019,Shuttler Radar Topography Mission (SRTM):https://www2.jpl.nasa.gov/srtm/index.html.
Nishimura, Y., and Satake, K., 1990, IUGG/IOC International Tsunami Symposium, 573-583.
Satake, K., and Kato, Y., 2001, Geophys.Res.Lett., 28, 427-430.
Swain, F., 1976, Sedimentary Petrology, Vol.36, 522-540.
Voight, B., 1981, USGS Professional paper, 1250, 69-86.
Yanagisawa, H., 2018-2019, IISEE,BRI Lecture Note.

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