1995 ERUPTIONS OF CERRO-NEGRO VOLCANO, NICARAGUA, AND RISK ASSESSMENTFOR FUTURE ERUPTIONS

Cerro Negro volcano, Nicaragua, continued a 147-yr-long duration of ci nder-cone activity with a major eruption in 1995. Small, phreatically driven eruptions began in May 1995 and continued for 79 days. Followin g a 95 day repose, the main eruption produced 8 x 10(6) m(3) of basalt from Cerro Negro over 13 days of activity and deposited 5 mm of ash i n the city of Leon. Although the damage from the 1995 eruptions was fo rtunately minor, previous tephra falls from Cerro Negro have produced significant crop damage and multiple deaths through building collapse. In spite of its apparent longevity for a historically active cinder c one, Cerro Negro has mass-flow rates typical of are-related basaltic c inder cone volcanoes. Volcanic hazards beyond 3 km from Cerro Negro co nsist of tephra falls. Few models are available to calculate tephra-fa ll risks from basaltic volcanoes such as Cerro Negro, and none have be en applied to dispersive cinder cone eruptions. A convective-dispersiv e model of Suzuki is modified and evaluated using detailed data from t he 1995 Cerro Negro eruption and is found to reasonably calculate teph ra-fall thickness between 8 and 30 km from the vent. This model is use d with detailed data from previous Cerro Negro eruptions in a tephra-f all hazard assessment. Cerro Negro also appears to have had a steady-s tate erup tion rate since about A.D. 1900, which is used to estimate t he timing of the next eruption as before A.D. 2006. The potential teph ra fall from Cerro Negro in Leon, Nicaragua, is calculated as 2.2 mm/y r until 2006, with 95% confidence that deposits will be <11 cm thick.