Amatitlan, An actively resurging cauldron 10 km south of Guatemala City

Abstract

A 14×16 km diameter collapse caldera has been recognized 10 km south of Guatemala City, Guatemala. The caldera is north of the presently active volcano Pacaya and west of Agua, a large stratovolcano. The caldera was not previously recognized because its eastern and western margins coincide with faults that outline the Guatemala City graben and because the northern margin of the caldera is buried by pyroclastic rocks. The existence of the northern caldera margin is now established by gravity data and a variety of geological observations including circumferential faults, hot springs, well‐log data, and lithological changes in sedimentary rocks. A sequence of nine silicic pyroclastic deposits, totaling a volume of more than 70 km 3 dense rock were erupted from the caldera. The ages of these eruptions are mainly between about 300,000 years B.P. to less than 23,000 years B.P. The rocks erupted at the caldera and its associated vents consist of domes and nonwelded pyroclastic flow, surge, and fall deposits, mainly of rhyolitic to dacitic composition. Successive pyroclastic eruptions have generally become smaller in volume and more silicic with time. Major and minor element chemistry distinguish Amatitlan pyroclastics from those of other nearby calderas. The caldera lies at the intersection of an offset of the volcanic chain (the Palin Shear) and the faults along the volcanic front (Jalpatagua fault zone). The caldera has a heavily faulted resurgent dome crosscut by an impressive longitudinal graben. The graben's alignment with the Jalpatagua fault zone suggests a genetic relationship. The longitudinal graben and resurgent dome are morphologically youthful and are the sites of many young silicic vents. Available seismic data show a heavy concentration of epicenters over the northern part of the resurgent dome, near a young silicic intrusion. The caldera is active and will probably erupt again. Over 1 million people live within 20 km and would be threatened in the event of a moderate eruption. Suggestions for future research focus on hazard assessment and forecasting

Pacific offshore record of plinian arc volcanism in Central America: 2. Tephra volumes and erupted masses

“…[19] Amatitlán Caldera is the source of at least six tephras which are from bottom to top the L-flow and fall, Z-falls, T-flow and fall, C-fall, E-fall and J-falls [Koch and McLean, 1975;Wundermann, 1982;Wundermann and Rose, 1984]. L-tephra is found in our marine cores as correlated ash layer C23 and, using documented compositional data, also in DSDP Leg 67 as well as in cores of Bowles et al [1973].…”

“…Correlation of 119 ka old T-Fall Tephra to ash layers in DSDP core (Leg 66/493B-1-3) lead also to very rough estimates of $17 km 3 and corresponding magma mass of $3.7 Â 10 13 kg. [20] The E-tephra is a coarse grained reversely graded fall of white pumice clasts distributed across an area of $1300km 2 on land, corresponding to a tephra volume of >5 km 3 (2.5 km 3 DRE) [Wundermann, 1982;Wundermann and Rose, 1984]. Correlations based on published data of an ash layer at DSDP Leg 84 (570-2-3), the D3 ash layer of Bowles et al [1973] as well as the Y5 ash layer in the Gulf of Mexico documented by Rabek et al [1985], which all have the E-tephra glass composition [Kutterolf et al, 2008], yield a minimum distribution area (up to 1 cm isopach) of 6.3 Â 10 5 km 2 ( Figure S1), corresponding to a tephra volume of 45 km 3 (Figures 4 and S2 and Table 1; 6 Â 10 13 kg magma mass).…”

Pacific offshore record of plinian arc volcanism in Central America: 1. Along‐arc correlations

“…[8] The last three decades have seen a number of publications investigating predominantly the tephrostratigraphic successions of single volcanoes or eruptions and limited areas in Central America [Bice, 1985;Bonis et al, 1970;Borgia and van Wyk de Vries, 2003;Bosse et al, 1976;Commision Ejecutiva Hidroelectrica del Rio Lempa (CEL), 1992, 1995Chiesa, 1991;Chiesa et al, 1992;Drexler et al, 1980;Hahn et al, 1979;Hart, 1983;Hazlett, 1987;Kempter et al, 1996;Koch and McLean, 1975;McKnight and Williams, 1997;Newhall, 1987;Peterson and Rose, 1985;Pullinger, 1998;Reynolds, 1987;Rose, 1987a;Rose et al, 1982Rose et al, , 1987Rose et al, , 1999Scott et al, 2006;Self et al, 1989;Sussman, 1985;Vogel et al, 2004Vogel et al, , 2006Williams, 1983;Wundermann, 1982;Wundermann and Rose, 1984]. We have recently revised and extended some of that work in Nicaragua [Freundt et al, 2006a;Kutterolf et al, 2007a;Pérez and Freundt, 2006;Wehrmann et al, 2006], El Salvador and Guatemala.…”

Bromine and chlorine emissions from Plinian eruptions along the Central American Volcanic Arc: From source to atmosphere

“…Kutterolf et al, 2011;Newhall et al, 1987;Pérez et al, 2009;Peterson and Rose, 1985;Wundermann and Rose, 1984), geochemical along-arc variations with a special focus on the magma genesis (Carr et al, 1990;Hoernle et al, 2008;Patino et al, 2000) and crustal contamination (Vogel et al, 2006;Walker et al, 2007). Volatiles (H 2 O, CO 2 , Cl and S) in melt inclusions of mostly primitive magma compositions have been analyzed to reveal their influence on eruptive style (e.g., Roggensack et al, 1997) as well as the various contributions of their sources to magma genesis as subduction conditions change along the arc (Roggensack et al, 1997;Sadofsky et al, 2008).…”