C. Colombo, M.V. Sellitto, G. Palumbo, F. Terribile and G. Stoops. Introduction. South Central Italy ...... tom part of EUR03. Table 5. Chemical extractions of the ...
Characteristics and genesis of volcanic soils from South Central Italy: Mt. Gauro (Phlegraean Fields, Campania) and Vico lake (Latium) C. Colombo, M.V. Sellitto, G. Palumbo, F. Terribile and G. Stoops
Introduction South Central Italy (Latium and Campania regions) is an interesting geographic area to study soil development in volcanic materials because of: (a) the presence of volcanoes active during late Pleistocene and Holocene; (b) the occurrence of several pyroclastic deposits of known ages, and c) the Mediterranean climate (mesic and ustic/xeric pedoclimate). This district, often called “Campano-Laziale”, is geographically divided into the Roman and Campanian petrographic provinces (Figure 1), and is characterized by extensive volcanic deposits with a wide variety in composition of lava and volcanic tephra ranging from alkali-trachytic to latitic (Scandone et al. 1991, Di Vito et al. 1999, De Vivo et al. 2001). Many of the volcanoes in Central Italy are stratovolcanoes formed by alkali-potassic magmatic lava, characteristic of the Campano-Roman petrographic Province. The activity dates back 1300 ka (Sollevanti 1983, Bidini et al. 1984, Barbieri et al. 1988). Two areas have been investigated: an old volcano, the Vico Caldera in the Latium district and a young volcano in the Phlegraean Fields, Campania. Eruptions have been characterized by a variety of explosive event sequences and magnitudes in the past 1500–2000 ka. The Vico volcano consists of lavas of various composition, including leucitites, leucite– tephrites or leucite–phonolites in the first cycle and trachy-andesitic or latitic products in the second cycle (Lulli and Bidini 1978, Lulli et al. 1988, Scandone et al. 1991). The actual body of the Vico volcano is a lake of 7–8 km in diameter that occupies an area of 150 km2 but the surroundings covered by Vico’s pyroclastics are much larger. The Monte Gauro volcano is formed during the last period of activity (10 ka) of the Phlegraean Fields and is therefore considered as very young. The purpose of this study is to investigate the genesis and the properties of four pedons, formed in different tephra-derived materials inside the main caldera of Gauro and Vico volcanoes, to investigate the influence of the parent material and time on pedogenic processes under a Mediterranean climate.
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Latera V.
Gauro V. Vico V.
Volsino V.
Roman Province
0
10 km
Vico V. Sabbatini V.
Colli Albani V.
Campanian Province
Central Italy Gauro V. Roma Naples
Phlegraean Fields N
N 0
50
150 km
0
50
100 km
Figure 1. Location of the study area in Central Italy with Roman (Vico volcano) and Campanian (the Phlegraean Fields, Gauro volcano) petrographic districts.
Description of the study area Profiles EUR01-02 (Gauro volcano)
The Monte Gauro volcano lies in the Phlegraean Fields district in the centre of Campania (north of Naples), between latitude: 40°51'36'' N and longitude: 14°06'26.40'' E (EUR01) and latitude: 40°52'4'' N longitude: 14°06'38,40'' E (EUR02). The Phlegraean Fields were formed by about 30 different volcanic events, beginning approximately 30 ka ago (Rosi and Sbrana, 1987; Scandone et al, 1991). The Phlegraean Fields caldera has a very complex volcanic and deformational evolution and consists of heterogeneous pyroclastic rocks. It is formed by two major collapses related to the Campanian Ignimbrite (Di Vito et al. 1999, De Vivo et al. 2001). The intense urbanization and the potential volcanic activity mark this environment as a high volcanic risk area. Monte Gauro is a well-preserved volcano with elliptical structure having axes of about 2 by 1 km (Figure 1). The volcano has a maximum elevation of 253 m a.s.l and was formed by a
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series of rapidly succeeding eruptions during the last period of activity (10 ka). The eruptions were mostly phreatomagmatic, with subordinate magmatic explosions, and produced large amounts of pyroclastic falls and surges. The surge beds are generally confined to depressions. Lava domes were emplaced during single effusive eruptions and during the final phases of explosive eruptions. The texture of the pyroclastic deposits varies according to the distance from the vent. The unconsolidated upper part, called “pozzolana” consists of glass shards with an alkali-trachytic composition with a slightly trachytic to latitic trend towards the top. The zeolitisation of this glass by fluids linked to the eruptive mechanism gave rise to a large deposit of yellow tuff with phillipsite, subordinate chabazite and, in some cases, analcime minerals (de Gennaro et al. 2000). At present, Monte Gauro volcano is a green area used for recreation with a park and chestnut forest (private owner). The dominant natural vegetation in the study area is chestnut (Castanea sativa, P. Mill.) forest, but in the past the flat and gently sloping areas inside the caldera were used for agriculture. Pedon EUR01, is located on a flat terrace cultivated as apple and peach orchard on the slope of Mt Gauro; Pedon EUR02 is located in a chestnut copse, cut 10 years ago and exhibiting some relict signs of soil erosion in the surface horizon, induced by the drag of wood. Overall these sites are strongly affected by human disturbance.
Profile EUR03-04 (Vico volcano)
The Vico volcano lies in Northern Latium (northwest of Rome), between latitude 42°10’ and 42°31’N and longitude 11°55’ and 12°28’E (Figure 1). The Vico volcano stands out from a large ignimbrite plateau formed about 1300 ka ago, typical of the Quaternary south central Italian volcanism (Bidini et al. 1984, Quantin and Lorenzoni 1992, Lorenzoni et al. 1995). The Vico volcano is a stratified volcano with a terminal caldera, now filled by a lake, which received flows of pyroclastic magma, ignimbrite and tuff. Its activity started 419 ka ago and ended 95 ka ago with three intense volcanic phases. The first period of activity began with several Plinian-type eruptions, with different eruptive styles, which discharged tephra and minor pyroclastic flows. Around 400 ka, Plinian eruptions persisted but were accompanied by lava flows. These pyroclastic and effusive products are spread out in the northeastern sector and to a lesser extent in the western area. During the second period, several eruptions occurred from the main crater, which built up and subsequently destroyed the edifice. Post-caldera effusive and explosive activity during the third period came from different
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intra- and peri-caldera vents as well as from caldera fractures. The rocks of this volcanic area are composed of lavas of various compositions including phonolitic tephrites, tephritic phonolites and slightly undersaturated trachytes. Phreatomagmatic activity after collapse of the caldera led to the accumulation of pyroclastic deposits and potassium-rich lava with leucitebearing rocks. During the last two periods, the eruptions were fed mainly by evolved, mildly to strongly silica undersaturated potassium-rich magmas of the Roman Magmatic Province (Bidini et al. 1984, Barbieri et al. 1988, Barbieri et al. 1994). The permanent vegetation changes toward higher altitudes from oak forest (Quercus pubescens), to chestnut forest (Castanea sativa) and to beech forest (Fagus sylvatica) following the change from a xeric to an udic pedoclimate. Soil temperature regimes change accordingly from thermic to mesic. Pedons EUR03 and EUR04 are located respectively in Monte Venere and Caldera di S. Matteo on tephritic-phonolitic leucite-bearing lava, to represent soil development on lava with a large variety of tephrites, tephritic phonolites and slightly undersaturated trachytes (Lulli and Bidini 1978, Bidini et al. 1984, Quantin et al. 1988, Quantin and Lorenzoni 1992). These sites, and especially the EUR03 soil, are very little disturbed by human activity.
Laboratory methods The studied profiles were sampled by Working Group 5 of the COST-622 action and profile descriptions are given in the attachments to this book. All samples were treated with H2O2 to remove organic matter. Afterwards, the sand fraction (0.25–1 mm) was separated from the H2O2 treated
