1995 eruptions of Cerro Negro volcano, Nicaragua, and risk assessment for future eruptions

Cerro Negro volcano, Nicaragua, continued a 147-yr-long duration of cinder-cone activity with a major eruption in 1995. Small, phreatically driven eruptions began in May 1995 and continued for 79 days. Following 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 in the city of Leon. Although the damage from the 1995 eruptions was fortunately 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 cone, Cerro Negro has mass-flow rates typical of arc-related basaltic cinder cone volcanoes. Volcanic hazards beyond 3 km from Cerro Negro consist of tephra falls. Few models are available to calculate tephra-fall risks from basaltic volcanoes such as Cerro Negro, and none have been applied to dispersive cinder cone eruptions. A convective-dispersive model of Suzuki is modified and evaluated using detailed data from the 1995 Cerro Negro eruption and is found to reasonably calculate tephra-fall thickness between 8 and 30 km from the vent. This model is used with detailed data from previous Cerro Negro eruptions in a tephra-fall hazard assessment. Cerro Negro also appears to have had a steady-state eruption rate since about A.D. 1900, which is used to estimate the timing of the next eruption as before A.D. 2006. The potential tephra fall from Cerro Negro in Leon, Nicaragua, is calculated as 2.2 mm/yr until 2006, with 95% confidence that deposits will be <11 cm thick.