Extending the mid-18th century eruptive record of the Cordón Caulle Volcanic Complex (40,5° S) through the study of three lake sedimentary sequences

Abstract

The research focuses on the characterization of a tephra level extracted from sedimentary sequences obtained from three lacustrine environments from the northern Patagonia Andean range to define the volcano of origin. The dating of the tephra level corresponds to the mid-18th century but there is no scientific record nor geological evidence of this event. The sediment sequences were collected from lakes Nahuel Huapi, Moreno Oeste, and Tonček, in northern Patagonia, located downwind from the Cordón Caulle Volcanic Complex (CCVC), the potential source, at 45, 86, and 95 km respectively. These environments are frequently impacted by tephra falls from different sources in the Southern Volcanic Zone. Particle morphology, glass and mineral chemistry, together with textural analysis, provided a detailed characterization of the tephra layer recovered at each site. This characterization allowed the association of the tephra material with the CCVC predominantly, with minor Osorno volcano contributions. Historical records of both volcanic systems included eruptions in the mid-18th century (1759 CE and 1752–1796 CE, respectively). Hence, the characterization and the comparison with historical records of volcanic eruptions let us conclude that the tephra is composed of materials dispersed by CCVC in the nearby lakes, whereas contributions from Osorno volcano are observed in environments to the south of the study site, during the mid-18th century. The study demonstrates the potential of this type of detailed characterization in lake sequences to develop and support increasing research on historical volcanic records, helping to improve the knowledge of the volcanic hazard of a region.