Smithsonian Institution Global Volcanism Network Bulletin v. 20, no. 4, April 1995 Rincon de la Vieja (Costa Rica) Description of the crater lake and fumaroles Rincon de la Vieja Costa Rica 10.83N, 85.33W; summit elev. 1,916 m The remote Rincon de la Vieja volcanic complex continues to display unsettled seismic and fumarolic activity. OVSICORI-UNA reported that during April fumarolic venting continued from the W wall, creating noise audible from the crater's rim. Escaping gases stung the skin. Radial fractures encircled the crater on its NE, N, and NW sides. G. Soto (ICE), Jean-Philippe Ran on, and Gorges Boudon climbed the volcano on 1 May and reported that the lake contained a scum of floating sulfur and was pale turquoise in color. No lake temperature measurements were made but the entire surface steamed slightly. In contrast to a previous visit in March 1994, the lake level seemed significantly higher, although the amount has yet to be quantified from photographic records; zones of bubbling (previously several meters across) were absent. Fumaroles on the crater's inner SE wall were quite active and fumed noiselessly. Gas plumes, clearly visible from the volcano's N flank, rose up to 100 m above the crater before being blown by the wind. Small, steam-rich fumaroles adjacent to concentric fractures surrounded the crater, typically near the 1,640 m contour. These fumaroles were also active last year. At least two other noteworthy fumaroles, expelling steam and sulfurous gases, sit on the N flank (along the valley called Quebrada Azufrada at around 1,200- and 1,300-m elevation). In clear weather, these fumaroles are visible from local villages and residents stated that they had been active for the past several years. Information Contacts: Erick Fernandez, Vilma Barboza, and Jorge Barquero, Observatorio Vulcanologico y Sismologico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica; Gerardo J. Soto, Oficina de Sismologia y Vulcanologia del Arenal y Miravalles: OSIVAM; Instituto Costarricense de Electricidad (ICE), Apartado 10032-1000, San Jose, Costa Rica; Jean-Philippe Ran on, BRGM, Orleans, France (presently at USGS Cascades Volcano Observatory, 5400 MacArthur Blvd., Vancouver, WA 98661-7095 USA); Gorges Boudon, Observatoires Volcanologiques, Institut de Physique du Globe de Paris, 4 Place Jussieu, 75252 Paris 05, France.