Smithsonian Institution Global Volcanism Network Bulletin v. 20, no. 10, October 1995 Rincon de la Vieja (Costa Rica) New eruption; lahars damage a bridge and lead to evacuations Rincon de la Vieja Costa Rica 10.83 N, 85.33 W; summit elev. 1,916 m All times are local (= GMT - 6 hours) A new phreatomagmatic eruption followed three months of declining seismicity. During 1995 the number of local earthquakes peaked in July and then progressively decreased (figure 1). Prior to the eruption, during October, OVSCICORI-UNA reported that park rangers who ascended to the main summit saw increased degassing and noted the appearance of fumaroles along cracks at the E and NE crater margins. Rangers described the crater lake~s color as green and the smell as strong and sulfurous. ICE described the eruption as phreatomagmatic, beginning at 1504 on 6 November, and climaxing on 8 November with 25 explosions. They noted the ash-bearing and steam-rich columns rose to 1 and 4 km, respectively, above the crater. Ash blew WSW; medium- to fine-grained ash reached up to 30 km from the volcano (Santa Rosa National Park). According to ICE, on 9 November the eruption entered a steam-rich phase. Columns typically rose 200 m, but sometimes as much as 1.5 km after some steam explosions. During the course of the eruption, ballistic ejecta were thrown over a zone extending to ~1 km N. Ejecta formed lahars that followed two key rivers (Penjamo and Azul rivers) and their tributaries. Heavy rains beginning on 10 and continuing on 11 November triggered secondary lahars and associated floods; a bridge 7 km N of the crater (Penjamo bridge) was damaged but not destroyed, interrupting traffic flow. During this episode, lahars along a tributary of the Penjamo river produced a gully 8-m deep and 25-m wide, isolating some inhabitants. Initial inspections of ash and the lahar matrix indicated that they mainly consisted of hydrothermally altered fragments, lake-sediment mud, and vesiculated glassy andesite fragments. Some residents living near the volcano were evacuated to a safe village 9 km NW of the crater. News reports on 8 November by both Associated Press and Deutsche Presse- Agentur stated that about 100 families were evacuated. Two days later Enrique Coen reported relocation of 300 families. The volcano sits near Costa Rica~s N border, 85 km SE of Concepcion, the volcano forming a prominent island in the W part of Lake Nicaragua. Rincon de la Vieja is a compound volcano that has erupted at least twelve times since 1860. Information Contacts: E. Fernandez, E. Duarte, and V. Barboza, Observatorio Vulcanologico y Sismologico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica; G.J. Soto, Oficina de Sismologia y Vulcanologia del Arenal y Miravalles: OSIVAM, Instituto Costarricense de Electricidad (ICE), Apartado 10032-1000, San Jose, Costa Rica; Enrique Coen, Departamento de Fisica, University Nacional, Heredia; Costa Rica; P.O. Box 86, Heredia 3000; Associated Press; Deutsche Presse-Agentur.