Preliminary results on the numerical modeling of eruptive scenarios of Volcán Tacaná, México Rosario Vázquez Instituto de Geofísica, Unidad Michoacán - Universidad Nacional Autónoma de México Contact:
[email protected]
BACKGROUND
PRELIMINAR RESULTS
Volcán Tacaná located in the south border between México and Guatemala, in the state of Chiapas and San Marcos Department respectively, is the westernmost active volcano in the Central American Volcanic Arc (CAVA, Fig. 1a), and is part of the Tacaná Volcanic Complex (TVC), which consist of 4 volcanic structures aligned NE, from oldest to youngest: Chicuj caldera, Tacaná volcano, Plan de las Ardillas dome and San Antonio volcano (Macías et al., 2000). Since the fumarolic activity presented by Tacaná in 1950 and 1986, geologic mapping of the stratigraphy around the volcano, along with geochemistry studies and hydrothermal monitoring, has been done (Mülleried, 1951; Martíni et al., 1987; De Cserna et al., 1988; De la Cruz-Reyna et al., 1989; Macías et al., 2000; Rouwet et al., 2004, 2009; García-Palomo et al., 2006). From these studies, a Plinian eruption (Arce et al., 2012), several flankcollapses and Pelèan-style eruptions (Macías et al., 2000) have been indentify in the main deposits of the TVC, along with the widespread laharic and flood deposits on the southern flanks of the volcano (Murcia & Macías, 2014) as could be observed in Fig. 1b.
In the figures below, ash-fall distribution maps are shown, the first two (Figs. 4a and b) were modified from the inferred isopachs proposed by Mercado & Rose (1992) and Arce et al. (2012) for the massive member of the Sibinal Pumice (~23.5 ky BP Plinian eruption of Volcán Tacaná); meanwhile the figures below (Figs. 4c and d) are isomass maps obtained from simulations with Tephra2, according to the input parameters of Table I.
a
b
c
d
b
a
TVC
Fig.1. a) Regional location of the TVC. b) Distribution of the volcaniclastic deposits related to the historic activity of the TVC (Modified from Arce et al. 2012 and Macías et al. 2000).
However, besides the preliminar hazard maps proposed by Mercado & Rose (1992), and Macías et al. (2000) from the deposits, and a photointerpreted map proposed by Albarrán-Guerrero (2013), no further work has been made, which couples the observed deposits in the field, with results obtained from numerical modeling of future eruption scenarios.
Fig.4. Comparative maps of the ash-fall distribution due to the last Plinian eruption of the TVC. a) Isopach map modified from Mercado & Rose, 1992; b) Isopachs of the massive member of the Sibinal Pumice (modified from Arce et al., 2012); c) Isomass map obtained from a simulation using Tephra2 with a west-wind profile; d) Isomass map obtained with Tephra2 using a wind profile from April 2015 (input parameters of Table I).
MOTIVATION AND OBJECTIVE
CONCLUSIONS
Nowadays, more than 300,000 people lives in the surroundings of Volcán Tacaná (Fig. 2), and due to their eruptive history, it should be considered as one of the most hazardous volcanoes for both countries (Mexico and Guatemala), not just for the menace that poses for the population, but for the potential hazard for the agricultural activities that maintains this region. At present time, only exist hazard maps based on the ancient deposits of the volcano or in photointerpretation. The main goal of the project is to obtain accurate values of maximum runouts from numerical modeling of: pyroclastic density currents, debris avalanches and lahars, as well as ash-fall dispersion forecasts of Volcán Fig.2. Panoramic view of Volcán Tacaná under specific eruptive scenarios, in order to Tacaná and the populated Tapachula city in its skirts. integrate a new comprehensive volcanic hazard map.
FUTURE WORK
EMERGING METHODOLOGY
For the preliminar modeling, the Tephra2 (Connor & Connor, 2006) numerical code under the VHub online platform (https://vhub.org/resources/tephra2) was used in order to simulate the tephra dispersion of the ~23.5 ky BP plinian eruption of Volcán Tacaná, known as the Sibinal Pumice (Arce et al., 2012). From this, two members have been described: the massive and the stratified member, from which for technical reasons only the massive member was simulated. INPUT PARAMETERS
a
December ----- April
Calm:
The comparison between the maps of Fig. 4 show that the ash-fall distributions do not match, not even the isopachs proposed by Mercado & Rose (1992), and Arce et al. (2012) from the ancient deposits. This could be due to the lack of the information by the time the first isopach map was suggested. .The main reason of the variation in the distribution of the isomass maps (Fig. 4c and d) is the wind profiles used during the simulation, however, the map of Fig. 4d is very similar to the distribution of the isopachs of Arce et al. (2012) in Fig. 4b. The difference between the isopach and isomass maps is determinant, especially for the estimation of the total mass dicharged and the volume of the eruption. In this case, the bias in the ash-fall distribution is evident due to this issue. A detailed study of the ash-fall deposits to the W-SW of the volcanic edifice should be done in order to better constrain the features of the eruptive scenarios (especially the wind profile) to be modelled. A greater number of simulations should be done to constrain the input parameters.
b
June ----- October
Parameter
Tephra2
Duration (hrs)
16.5
Mass discharge rate (kg/s)
8.1x10 7
Column height (km)
21
Wind velocity (m/s)
5.5
Eruption Mass (kg)
4.9x10 12
Vol (km3)
4.6
Diffusion coefficient (m2/s)
6330
Max. and Min. Grainsize (phi)
-5, 2
Lithic and pumice densities (kg/m 3)
2500, 700
Falltime threshold (s)
59400
Time steps
100
Calm:
Fig.3a. Composite stratigraphy column of the TVC (modified from Arce et al., 2012), marking the layer of the Sibinal Pumice. Fig.3b. Dominant wind direction up to 10,000-50,000 ft height over Guatemala city (modified from Mercado & Rose,
Plume ratio
0.1
Eddy constant
0.04
Table I. Summary of the input parameters used in Tephra2 from the massive member of Sibinal Pumice (Arce et al., 2012).
Design a field campaign to explore the southern side of the volcano and taking granulometric samples of the ash-fall deposits. To estimate adequately the diffusion coefficient for this region, along with other input parameters required for the numerical modeling of the other volcanic hazards. Test other numerical models related to tephra dispersal and other volcanic hazards. Select the best method to obtain the wind profiles. Verification and validation of the models*. Investigate about other plinian eruptions on the CAVA volcanoes, in order to compare their magnitudes and reaches with that of the TVC. REFERENCES Albarrán-Guerrero, F.M. (2013). Restitución fotogramétrica del Volcán Tacaná para desarrollar un mapa de riesgos. Thesis, UNAM, 64 pp. Arce, J.L., Macías, J.L., Gardner, J.E., Rangel, E. (2012). Reconstruction of the Sibinal Pumice, an andesitic Plinian eruption at Tacaná Volcanic Complex, Mexico-Guatemala. J. Volcanol. Geotherm. Res. 217-218, 39-55. Connor, L.J. and Connor, C.B. ( 2006). Inversion is the key to dispersion: understanding eruption dynamics by inverting tephra fallout. In: Mader,H.M., Connor, C.B., Coles S.G., and Connor L.J. (eds.) Statistics in volcanology, Special publications of IAVCEI, Geological Society, London, 231–242. De Cserna, Z., Aranda-Gómez, J.J., Mitre-Salazar, L.M. (1988). Mapa fotogeológico preliminar y secciones estructurales del volcán Tacaná. UNAM, Instituto de Geología, Cartas Geológicas y Mineras 7, scale 1:50,000, 1 sheet. De la Cruz-Reyna, S., Armienta, M.A., Zamora, V., Juárez, F. (1989). Chemical changes in spring waters at Tacaná Volcano, Chiapas, México. J. Volcanol. Geotherm. Res. 38, 345-353. García-Palomo, A., Macías, J.L., Arce, J.L., Mora, J.C., Hughes, S., Saucedo, R., Espíndola, J.M., Escobar, R., Layer, P. (2006). Geological evolution of the Tacaná Volcanic complex, México-Guatemala. In Rose, W.I., Bluth, G.J.S., Carr, M.J., Ewert, J.W., Patino, L.C., Vallance, J.W. (Eds.), Volcanic hazards in Central America: Geological Society of America Special Paper 412, 39–57. Macías, J.L., Espíndola, J.M., García-Palomo, A., Scott, K.M., Hughes, S., Mora, J.C. (2000). Late Holocene Peléan-style eruption at Tacaná volcano, Mexico and Guatemala: Past, present and future hazards. GSA Bull., 112(8), 1234-1249. Martíni, M., Capaccioni, B., Giannini, L. (1987). Ripresa dell'attivita sísmica e fumarolica al Vulcano di Tacaná (Chiapas, Messico) dopo un quarantennio di quiescenza. Estrato da Bollettino del Grupo Nazionale per la Vulcanología, 467-470. Mercado, R. and Rose, W.I. (1992). Reconocimiento geológico y evaluación preliminar de peligrosidad del Volcán Tacaná, Guatemala/México. Geofis. Int. 31, 205-237. Mülleried, F.K.G. (1951). La reciente actividad del Volcán Tacaná, Estado de Chiapas, a fines de 1949 y principios de 1950. Informe del Instituto de Geología UNAM, 28 pp. Murcia, H. and Macías, J.L. (2014). Volcaniclastic sequences at the foot of Tacaná Volcano, México: implications for Hazard assessment. Bull. Volcanol. 76, 27 pp. Rouwet, D., Taran, Y., Inguaggiato, S., Varley, N. (2004). Hydrothermal activity at Tacaná volcano, Mexico-Guatemala. In: Wanty, R. and Seal, R. (Eds.) WRI-11. Taylor and Francis Group, London, 173-176. Rouwet, D., Inguaggiato, S., Taran, Y., Varley, N., Santiago, J.A. (2009). Chemical and isotopic compositions of thermal springs, fumaroles and bubbling gases at Tacaná Volcano (Mexico-Guatemala): implications for volcanic surveillance. Bull. Volcanol. 71, 319-335.
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