Turrialba Volcano's Threat to the Cities of the Central Valley of Costa Rica

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Turrialba volcano's threat to the cities of the Central Valley of Costa Rica Gerardo J.SOTO(1, 2, 3) , Raúl MORA (3, 4) , Mauricio MORA (2, 3) , Rafael BARQUERO (1, 3) , Waldo TAYLOR (1, 3) , Alberto VARGAS(1, 3) , Guillermo E. ALVARADO (1, 2, 3) , Carlos RAMÍREZ (3, 4) , Gino GONZÁLEZ (3, 4) , Rolando MORA(2, 4) , Claudio PANIAGUA (1) , José F. FERNÁNDEZ (1)

(1) Instituto Costarricense de Electricidad, (2) Escuela Centroamericana de Geología, Universidad de Costa Rica, (3) Red Sismológica Nacional, (4) Centro de Investigaciones en Ciencias Geológicas, Universidad de Costa Rica, San José, Costa Rica

Turrialba volcano lies on the easternmost edge of the Central Barva V. Nicaragua Turrialba has had summit Caribbean Volcanic Range of Costa Rica, Sea <30 km away from the western fumaroles at least since Central Valley (~2.1 million 1723 and a strombolian- Turrialba V. vulcanian eruption inhabitants in 2010). Since the Turrialba winds mainly blow from the occurred in 1864-66, N volcano Western A Caribbean into mainland (E-W), Irazú V. severely affecting a radius P Central R C and Central Valley is downwind Valley of 3 km around the volcano, J T from Turrialba, this poses a and blowing ashes over the potential major threat to cities in capital San José, and down A: Present Airport there. Six powerful eruptions have Eastern to the Pacific coast, C:C artago taken place from Turrialba during Central ~130 km away. Since then, N: Nicoya Valley P: Puntarenas Pacific Ocean the last 3400 years, and isopachs fumarolic activity (T~90ºC) J: San José has been present. R: San Ramón show that ashfall mainly affected 010km T: Turrialba the western Central Valley (where Panama the present cities of San José, Distribution of ashes between September 1864 and February 1866, Heredia and Alajuela lie) and Turialba volcano and the CentralV alley of Costa Rica.The ellipsoidal contour drawn according to the accounts lesser, the eastern Central Valley is the 10-cm isopach of the plinian-subplinian eruption that occurred aprox. in Above: Intense fumarolic activity, drawn by Thomas Francis Meagher contained in González (1910). (where Cartago is). 40 A.D (Reagan et al., 2006). The other two contours mark the possible limits in 1858 (Harper´s New Monthly Magazine, 1860). Below: drawing of tephra fall during the last 3400 years. Prevailing winds blow to the W-SW. by geologist Karl von Seebach in 1865, during eruption. Higher winds blow to the NE.

Location of main faults around 556 560 564 Tectonic swarms with epicenters the summit of Turrialba volcano 224 5km (in red, from Soto, 1988; and N along the main tectonic feature Linkimer, 2003), and areas of (a SW-trending zone with craters, seismicity since April 2007.

faults, pyroclastic cones and Epicenters June 2007-late 2009 fumaroles) have been recorded at

least since 1982. Epicenters Mayl 2007 220

Epicenters mid-late April 2007

Epicenters early-mid April 2007

New fracture with steaming in 2007 216 Areas affected by acid rain Aerial photograph and location of main seismicity 0 2km in the surroundings of Turrialba volcano since 1982. May 17, 2009. Southwestern crater Photo by A. Sanabria from Area with frequent acid rain (pH<5.6) 20 SW of the volcano Area with occasional acid rain (pH<5.6) km

A restless stage initiated in 1995 and particularly since 2007, when wider fumarolic areas (similar to those observed in the 1850s-60s, see above), Seismicity 1992-1996 escalating temperatures (T=200-300ºC) in them, EQ swarm Sept. 1982 and seismicity around the southwestern crater Aerial view, Dec. 26, 2009 EQs 1991 have appeared. Resulting acid rain (pH<5) has remarkably affected ~50 km2 on the western flank.

On January 5-6, 2010, lithic ash was erupted due to strong fumarolic-phreatic activity from a small newly-opened fumarolic Distribution of ashes, January 5-6, 2010 vent (T>500ºC). The very fine ashes distributed in well accordance N to previous expectations, to southwest and west, reaching the capital, San José (35 km away).

Microphotography TURRIALBA VOLCANO of the lithic ashes erupted on 01/05/2010 (Courtesy of Research Center in Microscopic CORONADO Structures). SANTA CRUZ MORAVIA

Turrialba Volcano emits a translucent plume ALAJUELITA of volcanic gases in this natural-color satellite image from January 21, 2010. NASA Earth ASERRI Observatory image by Robert Simmon, using EO-1 ALI data provided by the NASA EO-1 team. Caption by Robert Simmon. Available at http://earthobservatory.nasa.gov/images/ imagerecords/42000/42425/turrialba_ali_ 2010021_lrg.jpg. 5km New vent opened during the eruption Oblique aerial view of the craters of in early January 2010. Turrialba, with fumaroles from the SW crater and the new vent.

Eruption

Future eruptions (months to decades on), phreatic or magmatic, pose a major threat for farms and

housing 5 km around the Counts RSAM volcano and significant threats to agriculture,

Time (days) pastures and telecommu- nications on the western side of the volcano. The Different views of the exhalative (intense most likely “biggest- fumarolic) activity of the volcano. scenario eruption” would • From the northeast (far left). • From the southwest (upper center) affect up to 1.5 million • From the west (30 km away, lower) people (see above on showing Irazú volcano with clouds in the prehistorical distribution foreground and Turrialba in the background. Upper right is the RSAM from the CIMA of ashes) and aerial trans- seismic station on the summit, from portation, because the November 2009 to February 2010. There is main Costa Rican a sharp change previous to the phreatic- fumarolic eruption in early January. First, international airport lies a decrease and then an increase during on the ash dispersion the event. It is interpreted as a trend (see figure above pressurization of the system due to fracture closure previous to the eruption. on 1864 ash dispersal).

GONZALEZ VIQUEZ, C., 1910: Temblores, terremotos, inundaciones y erupciones volcánicas en Costa Rica 1608-1910. - Tipografía de Avelino Alsina, 239 pp. LINKIMER, L., 2003: Geotectónica del extremo oriental del Cinturón Deformado del Centro de Costa Rica. - 103 pp. Universidad de Costa Rica [Tesis Licenciatura]. References REAGAN, M., DUARTE, E., SOTO, G.J. & FERNANDEZ, E., 2006: The eruptive history of Turrialba volcano, Costa Rica, and potential hazards from future eruptions. - 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: 235-257, doi: 10.1130/2006.2412(13). SOTO, G.J., 1988: Estructuras volcano-tectónicas del Volcán Turrialba, Costa Rica, América Central. - Actas V Congreso Geológico Chileno, Santiago, 8-12 de agosto de 1988, Tomo III: I 163-I 175.