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A geophysical and geological study of Laguna de Ayarza, a Guatemalan caldera lake

Journal of Volcanology and Geothermal Research
By: , and 

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Abstract

Geologic and geophysical data from Laguna de Ayarza, a figure-8-shaped doublecaldera lake in the Guatemalan highlands, show no evidence of postcaldera eruptive tectonic activity. The bathymetry of the lake has evolved as a result of sedimentary infilling. The western caldera is steep-sided and contains a large flat-floored central basin 240 m deep. The smaller, older, eastern caldera is mostly filled by coalescing delta fans and is connected with the larger caldera by means of a deep channel. Seismicreflection data indicate that at least 170 m of flat-lying unfaulted sediments partly fill the central basin and that the strata of the pre-eruption edifice have collapsed partly along inward-dipping ring faults and partly by more chaotic collapses. These sediments have accumulated in the last 23,000 years at a minimum average sedimentation rate of 7 m/103 yr. The upper 9 m of these sediments is composed of > 50% turbidites, interbedded with laminated clayey silts containing separate diatom and ash layers. The bottom sediments have >1% organic material, an average of 4% pyrite, and abundant biogenic gas, all of which demonstrate that the bottom sediments are anoxic. Although thin (<0.5 cm) ash horizons are common, only one thick (7-16 cm) primary ash horizon could be identified in piston cores. Alterations in the mineralogy and variations in the diatom assemblage suggest magnesium-rich hydrothermal activity. ?? 1985.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title A geophysical and geological study of Laguna de Ayarza, a Guatemalan caldera lake
Series title Journal of Volcanology and Geothermal Research
Volume 25
Issue 1-2
Year Published 1985
Language English
Larger Work Type Article
Larger Work Subtype Journal Article
Larger Work Title Journal of Volcanology and Geothermal Research
First page 125
Last page 144
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