Sometimes they release gases, sometimes they blow out small ash clouds or emit lava flows. From time to time, the relatively gentle activity is interrupted by stronger, more destructive eruptions. The currently most active volcanoes in Central America include Santa María with its flank cone Santiaguito, Pacaya and Fuego in Guatemala, and Arenal in northwestern Costa Rica.
Altogether, far more than 200 magnitude VEI ≥ 2 eruptions have occurred in Central America during the past three centuries. Information on the frequency of past eruptions allows the probability of an impending eruption at the respective volcano to be calculated. In a study recently conducted at GEOMAR Helmholtz Centre for Ocean Research Kiel, such probabilities were calculated for seven Central American volcanoes. The greatest risk of an upcoming eruption is posed by Concepción and Cerro Negro Volcanoes in Nicaragua, which reach a 50 %-likelihood for a VEI ≥ 2 eruption within the next four to six years (seen from 2012). Further to the southeast, in Costa Rica, a new eruption from Poás and Irazú Volcanoes looms with a 50 %-probability within 5 to 9 years. Rincón de la Vieja in Costa Rica and the Salvadorian volcano San Miguel have a medium eruption probability. The very young Izalco Volcano in El Salvador, in contrast, will only reach the 50 % level in 30 years’ time. Its youthful magma reservoir is immature, characterised by incomplete interruptions of magma evolution and irregular quiescent degassing processes, impeding that a regular eruption cycle establishes.
In general, it can never be ruled out within an active volcanic chain that unexpected eruptions occur, even at volcanoes that have not shown activity for a seemingly long time. In Central America, a number of other volcanoes have erupted in the recent past. They were not taken into account in this study because their eruption time series were too short for the analysis.
The volcanoes of Central America are created by subduction of the Cocos Plate beneath the Caribbean Plate. The resulting volcanic arc follows the west coast of Central America, aligned at a distance of approximately 30–70 km inland from the coast. This is where the majority of the population lives, builds roads and pursues industrial and agricultural production activities. The large and densely populated capitals of Guatemala, El Salvador, Nicaragua and Costa Rica are all located in the immediate vicinity of large volcanoes. These regions offer attractive living conditions and good access to public transport systems, allow the use of thermal energy from the magma systems and attract tourists. At the same time, living in close proximity to active volcanoes intrinsically means to accept the dangers they pose. This delicate coexistence between man and volcano makes risk assessment and monitoring indipensable.