Basaltic Plinian and violent Surtseyan eruptions from the Masaya Caldera Complex, Nicaragua
The Masaya caldera complex in central-western Nicaragua consists of a 6x11 km, >150 m deep, oval caldera that hosts a cluster of intra-caldera cinder cones. Subsidence of the Masaya caldera was caused by highly explosive Plinian, Phreatoplinian and violent Surtseyan basaltic eruptions during the last 6,000 years. The first eruption at ~6 ka produced the 14 km3 San Antonio Tephra (SAT). The second eruption at 2.1 ka generated two deposit facies distinct in internal architecture and direction of distribution: La Concepción Tephra (LCT) and Masaya Triple Layer (MTL), with a combined tephra volume is 3.6 km3. The third eruption at ~1.8 ka formed the Masaya Tuff (MT) and the directly overlying Ticuantepe Lapilli (TIL), totalling 10 km3. Basaltic Plinian eruptions are generally considered as exotic events but are common at Masaya. Water contents of <3.4 wt% measured in melt inclusions are moderate and cannot explain this eruptive behavior which is rather discussed in terms degassing dynamics in the conduit, by access of external water. Central western Nicaragua is highly vulnerable for volcanic disasters, because it has the highest population density of the country, comprising the large cities of Managua, Granada and Masaya, and the principal lifelines. A risk analysis for the main population centers around the Masaya caldera shows that, in case of a similar eruption today, the most vulnerable communities would be Ticuantepe, Nindirí and Masaya. In addition, La Concepción southwest of the caldera, and the capital Managua, more than 15 km to the northwest, could be affected.