Abstract
Sediment cores from lakes and bogs in the Río Cisnes valley contain tephra from explosive eruptions of volcanoes in the southern part of the Andean Southern Volcanic Zone (SSVZ). These tephra, which thicken and coarsen to the west, are attributed to eruptions from Melimoyu, Mentolat, Hudson, and potentially either Macá, Cay or one of the many minor eruptive centers (MEC) located both along the Liquiñe-Ofqui Fault Zone (LOFZ) and surrounding the major volcanoes. Correlation of the tephra between two new cores in the lower Río Cisnes valley, and amongst other cores previously described from the region, and source volcano identification for the tephra, has been done using lithostratigraphic data (tephra layer thickness and grain size), petrography (tephra glass color, vesicle morphology, and type and abundance of phenocryst phases), and by comparison of bulk tephra trace-element characteristics with previously published whole-rock and bulk tephra chemical analysis. Four tephras in these cores are attributed to eruptions of Mentolat, four to eruptions from Melimoyu, one possibly to Hudson, and six cannot be assigned to a specific source volcano. Some of these tephra correspond to pyroclastic tephra fall deposits previously observed in outcrop, including the MEL2 eruption of Melimoyu and the MEN1 eruption of Mentolat. However, others have not been previously observed and represent the products of newly identified small to medium sized eruptions from volcanoes of the SSVZ. These results provide new information concerning the frequency and magnitude of explosive eruption of SSVZ volcanoes and contribute to the evaluation of volcanic hazards in the region.
Highlights
Tephra produced by explosive eruptions can disperse over large distances in a very short period of time
Others have not been previously observed and represent the products of newly identified small to medium sized eruptions from volcanoes of the SSVZ. These results provide new information concerning the frequency and magnitude of explosive eruption of SSVZ volcanoes and contribute to the evaluation of volcanic hazards in the region
Some of the tephras were not sampled, such as tephra A and B from Laguna Las Mellizas (LLM) because of their small size (
Summary
Tephra produced by explosive eruptions can disperse over large distances in a very short period of time. Tephras deposited in lakes and bogs preserve exceptional records of volcanic activity (Weller et al, 2015), which provide insight into the frequency and magnitude of explosive eruptions, because of the relatively continuous record of sedimentation in these depositional environments. We use the bulk trace-element chemistry, lithostratigraphic data (tephra thickness and grain size), and petrographic features to characterize each tephra, to identify potential source volcanoes, and correlate these deposits with other tephra previously identified in both outcrops and in other lake cores from the region (Naranjo and Stern, 2004; Stern et al, 2015, 2016; Weller et al, 2014, 2015)
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