inian and deposited the up to two metres thick Mateare B layer. Then as the source of dacitic magma was exhausted the eruption changed and more andesitic magma was erupted to produce the 20 cm thick Mateare C pumice and Mateare D ash and lapilli layers. (Freundt et al 2005)
With the Nejapa-Miraflores fault which marks the eastern boundary of the Managua Graben running all the way to the twin craters Apoyeque and Xiloá, there is a case to be made for the latter marking the Northern end of the Nejapa Volcanic Field. If we accept this, the NVF is shown to be capable of highly explosive dacitic to rhyodacitic eruptions ranging from VEI 4 and up to VEI 6 with less than a thousand years between over the past 6-7 thousand years. If compared with the preceding period up to about 17 kA BP, it would seem that the interval between larger eruptions has decreased significantly with the most powerful eruption <2.1 kA BP.
In most of these eruptions, including the final one at Masaya 2.1 kA BP, water plays a major part which results not only in pyroclastic base surges but also a very great risk of devastating tsunamis. Should a repeat of the Mateare eruption occur on the Eastern side of the Chiltepe Peninsula today, the danger of a major tsunami striking Managua City and its 2.223 million inhabitants within minutes of the first, great explosions is overwhelming. Even a repeat of the Nejapa eruption could be catastrophic on a scale never seen before. The greatest danger of course comes from the pyroclastic base surges travelling through densely populated areas to the city centre a scant 5 km away. However, many of the (residential) buildings in Managua are of such a standard that even 2 cm of ash poses a serious risk of roof collapse. The Nejapa eruption deposited such a blanket up to at least five km from the vent.
In addition to the dangers posed by the Apoyeque-Xiloá complex and Nejapa Volcanic Field, the Momotombo volcano must be considered too. Highly active over the past 5,000 years and with a magma supply of >1 km3 per millennium, the trend shown by recent earthquakes; that volcanic activity may be migrating into Lago Xolotlán where there already has been a major eruption that formed Isla Momotombito, must be considered and closely monitored. And if this isn’t enough, Masaya is another potential MDE volcanic system and there are indications that the magma system of the older Apoyo Caldera is still more or less intact even if it at present is dormant.
Finally, I would like to give my thanks to Dr Hans-Ulrich Schmincke for making his and his fellow researchers’ work available online. It is as exemplary as laudable.
Armin Freundt, Steffen Kutterolf, Heidi Wehrmann, Hans-Ulrich Schmincke, Wilfried Strauch ”Eruption of the dacite to andesite zoned Mateare Tephra, and associated tsunamis in Lake Managua, Nicaragua”, 2005
Kutterolf, Freundt, Pérez, Wehrmann, Schmincke, “Late Pleistocene to Holocene temporal succession and magnitudes of highly-explosive volcanic eruptions in west-central Nicaragua” 2007. http://www.researchgate.net/profile/H_Schmincke/publication/228488958_Late_Pleistocene_to_Holocene_temporal_succession_and_magnitudes_of_highly-explosive_volcanic_eruptions_in_west-central_Nicaragua/links/0deec5164442f44371000000.pdf
Pardo N, Avellan D R, Macias J L, Scolamacchia T, Rodriguez D, 2008. The ~1245 yr BP Asososca maar: new advances on recent volcanic stratigraphy of Managua (Nicaragua) and hazard implications. J Volc Geotherm Res, 176: 493-512
Rauch, Schmincke, “Nejapa Tephra: The youngest (c. 1 ka BP) highly explosive hydroclastic eruption in western Managua (Nicaragua)” J Volc Geotherm Res, 2010