Nejapa Tephra: The youngest (c. 1kaBP) highly explosive hydroclastic eruption in western Managua (Nicaragua)

Rausch, Juanita and Schmincke, Hans-Ulrich (2010) Nejapa Tephra: The youngest (c. 1kaBP) highly explosive hydroclastic eruption in western Managua (Nicaragua) Journal of Volcanology and Geothermal Research, 192 (3-4). pp. 159-177. DOI 10.1016/j.jvolgeores.2010.02.010.

[img] Text
Rausch.pdf - Published Version
Restricted to Registered users only

Download (2926Kb) | Contact

Supplementary data:

Abstract

Nejapa Maar (2.5 × 1.4 km, c. 120 m deep), the largest maar along the 15-km-long Holocene Nejapa–Miraflores Lineament (NML), is the source vent of the youngest relatively widespread basaltic tholeiitic tephra blanket (Nejapa Tephra: NT) in western central Nicaragua, as shown by isopachs and isopleths (Rausch and Schmincke, 2008). The NT covers an area of > 10 km2 in W/NW Managua. The minimum total magma volume erupted is estimated as 0.09 km3. Juvenile, dominantly slightly vesicular (20–40 vol.%) basically tachylitic cauliflower-shaped lapilli with an average density of 2.1 g/cm3, make up > 90 vol.% of the deposit, while lithoclasts comprise < 10 vol.% except proximally. This, the paucity of fine-grained tuffs and the dominant plane-parallel bedding all suggest fragmentation by shallow interaction of a rising magma starting to vesiculate and fragment pyroclastically with external water. The complex particles so generated erupted in moderately high eruption columns (at least 7–10 km) and were dominantly deposited as dry to damp, warm to cool fallout. Minor surge transport is inferred from fine-grained, locally cross-bedded tephra beds chiefly north of Nejapa and just west of Asososca Maars. Synvolcanic faulting along the NML is inferred. Faults in the study area indicate that activation of the N–S-trending Nejapa–Miraflores Fault (NMF), representing the western flank of Managua Graben, preceded deposition of NT and underlying Masaya Tuff (c.1.8 ka BP), Chiltepe Pumice (c. 1.9 ka BP) and Masaya Triple Layer (2.1 ka BP). The NT deposit is underlain regionally by a paleosol and topped by a soil. The basal paleosol contains pottery sherds made by the Usulután negative technique during the Late Formative period (700 BCE–300 CE) (2.7–1.7 ka BP). The soil overlying NT contains pottery related to the Ometepe technique dated as between 1350 and 1550 CE (650–450 a BP). These, and the radiocarbon dates of the pottery-bearing paleosols (1245 ± 125 and 535 ± 110 a BP) obtained by Pardo et al. (2008) indicate that Nejapa Maar erupted between c. 1.2 and 0.6 ka BP.

Future eruptions in this area of similar magnitude, eruptive and transport mechanisms would represent a major hazard and risk to the densely populated western suburbs of Managua, a city expanding rapidly westward. Assuming a similar eruption scenario, poor-quality roofs, common in Nicaragua, would be prone to collapse up to 12 km peripheral to Nejapa Maar or another close-by eruptive site, and buildings at a distance of up to 500 m are likely to be severely affected. In view of the past frequency of eruptions along the NML, further eruptions are likely to occur in the near future.

Document Type: Article
Keywords: Volcanology; Nejapa–Miraflores Lineament (NML); hydroclastic eruption; Nejapa Maar; Managua (Nicaragua)
Research affiliation: OceanRep > SFB 574
OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-MUHS Magmatic and Hydrothermal Systems
Refereed: Yes
DOI etc.: 10.1016/j.jvolgeores.2010.02.010
ISSN: 0377-0273
Projects: SFB574
Contribution Number:
ProjectNumber
SFB 574180
Date Deposited: 13 Jul 2010 10:26
Last Modified: 09 Aug 2017 12:21
URI: http://eprints.uni-kiel.de/id/eprint/8615

Actions (login required)

View Item View Item

Document Downloads

More statistics for this item...