Growth and erosion: The volcanic geology and morphological evolution of La Fossa (Island of Vulcano, Southern Italy) in the last 1000 years

Abstract

The Island of Vulcano (Aeolian Islands, Southern Italy) consists of several volcanic edifices whose formation overlapped in time and space beginning 120ka ago. The most recent volcano is the La Fossa cone, a 391m-high active composite cone that began to erupt 5.5ka ago. Eruptive activity at the La Fossa cone occurred in several cyclic phases separated by prolonged periods of erosion.The last 1000years of eruptive activity and morphological variations in the cone and its surrounding area were investigated through a stratigraphic reconstruction. This was based on 139 natural cuts, 26 machine-excavated and 5 hand-dug trenches in the volcaniclastic succession.The revised stratigraphy of the volcanic and volcaniclastic sequence was compared with geological maps based on the Unconformity-bounded Stratigraphic Units criteria compiled in 2006–2010. It was found that the last 1000-year period can be divided into (in hierarchical order) Eruptive Clusters and Units. Several unconformities of different hierarchical order were also identified (erosional surfaces and/or palaeosols). Stratigraphic relationships with the Vulcanello products and with rhyolitic tephras related to the eruptions of Mt. Pilato (the last-formed volcanic edifice of the Island of Lipari) were fundamental in assigning a calendar age to most of the tephra units in the studied sequence. The morphological evolution of the upper part of the cone was also reconstructed in order to assess the average cone growth rate. This work suggests a new stratigraphic and chronological interpretation of the evolution and “cyclic” activity of the La Fossa cone in the last 1000years. Several eruptions occurred in two main clusters. The stratigraphic record and morphological features reveal that the areas around the cone were affected by the deposition of reworked materials, with large amounts of tephra deposited on the steep slopes and within the major streams.