**3. Materials and methods**

This chapter focuses on the volcanological and stratigraphic characterization and interpretation of the SLLFs of Monte Amiata volcano. The stratigraphic identification and cartography of the geological units studied are based on the stratigraphic criteria of the Unconformity Bounded Stratigraphic Units (UBSUs; [63]), following the

suggestions of the International Stratigraphic Guide (that can be accessed online http://www.stratigraphy.org). This type of stratigraphic unit is defined as a rocky body bounded to the top and bottom by specific, significant, and demonstrable surfaces of geologic discontinuity. The basic synthem unit can be divided into two or more subsynthems. Names of units adopted in this work have been introduced and described in previously published papers [45, 62].

The description of lava flows studied is based on the analysis of volcanic facies [64, 65]. For depositional facies, we mean the set of lithological characters of a rock, which allows its distinction according to some combination of physical features and composition, without nor genetic neither stratigraphic significance. Different facies record variations in conditions and processes of formation and deposition; consequently, they can lead to the interpretation of volcanological genetic processes and emplacement mechanisms. For each of the identified volcanic facies, we describe physical and morpho-structural features, internal and surface structures, and macroscopic and microscopic textures, and we propose their genetic interpretation. The internal arrangement of facies in terms of vertical and horizontal sequence and association contributes to recognize the architecture of the effusive volcano. We refer to a flow unit as the deposit of a discrete flow within an eruption event, whereas to an eruptive unit as all the products effused during a time- and space-distinct eruption event which can also be composed of several successive flow units. Individual eruptive unit outlines have been delineated and mapped from field evidence, and patterns and textural differences.

The petrographic observation of the Monte Amiata rock samples allowed to recognize several different exposed lithotypes [57] on the basis of different paragenesis, groundmass textures, and content in mafic magmatic enclaves and meta-sedimentary xenoliths. About 30 rock samples belonging to the SLLFs discussed in this work were analyzed under a polarizing microscope at Institute of Geosciences and Earth Resources (National Research Council of Italy), Pisa (Italy), in order to carry out a textural, petrographic, and mineralogical characterization. In addition, further textural investigations were performed at the National Institute of Geophysics and Volcanology (INGV), Pisa (Italy), using a Zeiss EVO MA 10 Scanning Electron Microscope (SEM), capturing selected back-scattered electron (BSE) images.

The morphometric parameters of Monte Amiata lava flows were determined in the field and with reference to the geologic map (**Figure 2**; see also [45]). The area, minimum length, and slope of each flow were calculated by means of the ruler tool of Google Earth on the basis of the performed geological mapping. The average thickness of each eruptive unit was estimated from outcrop relief scaled from the topographic base maps. Most calculated volumes are less than real volumes because a great part of the SLLFs are covered by the overlying volcanic units, and their extent to the source zone is actually unknown. Anyway, the calculated volume is essentially a dense-rock equivalent, since porosity in these lavas is generally very low to absent.
