Few cities around the world can claim a more beautiful setting than Managua (pop 2.223 million, 2012), Nicaragua, on the shores of tranquil Lago Xolotlán, Lake Managua. When the Conquistadores arrived, Masaya volcano 20 km from today’s Managua was in eruption and provided Europeans with their fist view of a lava lake. In a letter addressed to the Spanish Emperor Carlos V dated 10th April 1525, the Governor Pedrarias Davila of Castilla de Oro (Panamá) mentions the presence of Masaya and Momotombo volcanoes:
“In this province of Masaya there is a large mouth of fire which never ceases to burn and during the night it is so big as if it reaches the sky, and with a height of 15 leagues (75km) there is light as if it was day.”
Although an – ahem – slight exaggeration, it still gives us an idea how impressive the phenomenon must have been to the Conquistadores. Because of its resemblance to molten metal, it was speculated that it was in fact a pot of liquid gold or silver, and how to extract this vast reservoir of riches immediately occupied Spanish attentions when they were not concerned with theological attempts to classify the phenomenon. From the beginning of Nicaragua’s conquest, the Spaniards referred to the Masaya Volcano as “The Mouth of Hell” or simply “Masaya’s Hell” (“Infierno de Masaya”) with one brave soul; Mercedarian Fray Francisco de Bobadilla, climbing the volcano in 1529 to erect a cross with which to exorcise the “The Mouth of Hell”.
Masaya is classified as a complex volcano but is in reality a shield volcano caldera formed about 2.5 kA BP by a large, 8-km³ basaltic ignimbrite eruption that resulted in the formation of the 6 x 11 km caldera. The phreato-plinian Masaya Tuff has been identified as a 10-20 cm thick layer on the western side of Managua, opposite the Masaya caldera. It has been identified as the result of a wet pyroclastic surge that travelled 35 km from its source (Pérez and Freundt, 2006). After this eruption, a new basaltic complex has grown inside the caldera which includes Masaya and Nindiri cones with the latter the host of the Santiago, Nindiri, San Pedro and, confusingly, Masaya craters.
Across Lago Xolotlán and some 45-50 km NW of Managua lies the Momotombo volcano and Volcanic Field with Volcán Cerro Negro, Central America’s youngest (April 1850) and one of the most active volcanoes in Nicaragua almost immediately to its WNW. Momotombo volcano is one of Nicaragua’s most familiar landmarks. It is a somma volcano, meaning it has grown on the edge of the caldera of a mainly collapsed, previous edifice; Monte Galán. It began growing about 4.5 kA BP at the SE end of the Marrabios Range and the symmetrical cone has now attained a height a.s.l. of 1,297 m with a prominence in excess of 1,100 m. If we only take into account the portion above the 400-m isoline, the edifice has a volume on the order of 3.5 km3. In addition to this, there are the products of the geothermal volcanic field on the ESE flank as well as lava flows from Momotombo that have flowed down the NW flank into the 4-km-wide Monte Galán caldera to consider. Also, it has formed a 391-m-high island; Isla Momotombito, offshore in Lake Managua. In all, the volcanic products of Momotombo over the past 4½ millennia is in excess of five cubic km. Consequently, Momotombo has a long record of mainly strombolian eruptions punctuated by occasional larger explosive activity with at least fifteen eruptions since the arrival of the Conquistadores. The most recent in 1905 produced a lava flow that travelled from the summit to the lower NE base of the volcano.
There are two facts to keep in mind concerning Momotombo. First, volcanism seems to be migrating in the direction of Managua; from Monte Galán via Momotombo and into Lago Xolotlán, which is a cause for grave concern in the case of a large-ish, submarine eruption. Second, the copious amounts of juvenile magma fed into and mixing with the crust to form the andesitic lavas. At the very minimum, the rate is in excess of a cubic km per thousand years.
Looking at the map, there are further areas