A high-resolution tephra record from Castiglione maar reveals the timing and unveils cryptic eruptions over the most recent volcanic activity at Colli Albani, central Italy

Abstract

Integrating proximal and medial-distal tephra records from continuous sedimentary archives has recently proven to be crucial for obtaining more complete and highly resolved stratigraphic and chronological histories of explosive activity, allowing a detailed and accurate assessment of volcanic hazards. The sedimentary succession from the Castiglione maar, about 20 km east of Rome, hosts a long and continuous lacustrine record extending back to ca. 365 ka, including a number of tephra layers derived from the explosive activity of peri-Tyrrhenian volcanic centres. An integrated tephrochronological investigation, which combines stratigraphic, textural, mineralogical, geochemical and ⁴⁰Ar/³⁹Ar geochronological analyses, was conducted on six tephra layers occurred between 11 and 15 m-depth of the Castiglione composite section. This section records the history of the most recent explosive activity of the Colli Albani volcano and relates to the Albano maar. Results reveal that the Albano maar volcanic history actually comprises six explosive events that are younger than previously thought and occurred in a narrower time interval. Specifically, ⁴⁰Ar/³⁹Ar ages determined on four of the six tephra, along with the modelled ages for the remaining two, indicate that the eruptive activity of the last sub-cycle of the Albano maar lasted 3.4 +0.4/-0.6 ka, and occurred between 37.71 ± 0.34 ka (⁴⁰Ar/³⁹Ar age of the first eruption) and 34.34 +0.25/-0.45 ka (modelled age of the last eruption). Results refine the history of the most recent explosive activity at Colli Albani volcano and underscore the importance of studying tephra preserved in medial-distal continuous sedimentary archives for a comprehensive reconstruction of the eruptive history. Based on the data collected, the previously unrecognised explosive eruptions were likely of medium magnitude but sufficiently large to produce highly fragmented and widely dispersed ash. We argue that these new findings should be considered for an updated long-term hazard assessment of the Colli Albani volcanic area. Results, and especially the new high-precision ages, also allow to improve the tephrochronological framework in the dispersal area of the Albano tephra, including the iconic paleoclimatic archives of Monticchio and Fucino.