6 research outputs found
Stratigraphy, volcano tectonics and evolution of the Colli Albani volcanic field
The Colli Albani volcano has been active since c. 600 ka and is presently quiescent.
Rock stratigraphy indicates that the activity of the volcano has undergone major changes in
terms of eruption style, average eruption rate and location of active vents. The chemistry of the
Colli Albani products is remarkably mafic, K-rich and silica undersaturated. Nevertheless, the
volcano has experienced all types of eruption styles, from plinian explosive paroxysms, to
milder strombolian and hawaiian eruptions, to effusive, including large- and small-scale
phreatomagmatism.
The first period of activity of the volcano is termed the ‘Vulcano Laziale’ period, and lasted from
c. 600 ka to c. 355 ka. During this period, the volcanism was predominantly explosive, with an
average eruption rate of 1 km3 ka21. At least seven intermediate- to large-volume ignimbrites
(VEI 5–7) were erupted and emplaced over an area larger than 1600 km2, forming an extensive
ignimbrite shield around the central, continuously forming c. 8 8 km2 caldera. The caldera
complex and the ignimbrite shield are named the ‘Vulcano Laziale edifice’. The Vulcano
Laziale edifice can in turn be subdivided into a lower ‘Pisolitic Tuffs succession’ (c. 600–
500 ka), in which ignimbrites are dominated by large-scale phreatomagmatism associated with
the likely presence of an early caldera lake, and an overlying ‘Pozzolane Tuffs succession’, in
which ignimbrites show a dominantly magmatic fragmentation style, probably in response to progressive
exhaustion of the caldera lake. The typical succession of these mafic ignimbrites is composed
of a sub-plinain to plinian basal scoria fall deposit covered by the main dark scoria and ash
tabular ignimbrite sheet found as far as.30 km from the caldera rim and across ridges several hundreds
metres in elevation, and is characterized by co-ignimbrite breccias at proximal locations.
Major ignimbrites erupted with an average interval of c. 40 ka. After each paroxysmal ignimbrite
eruption, volcanic activity was predominantly effusive to mild explosive, and was concentrated
along peri-caldera fissure systems, forming continuous scoria cone and lava ridges, together
with more explosive eruptions from intracaldera vents. The last major caldera-forming eruption
of the Vulcano Laziale period occurred at c. 355 ka, emplacing the ignimbrites of the Villa
Senni formation. Following this eruption, the complex Tuscolano-Artemisio peri- and extracaldera
fissure system, predominantly composed of scoria cones and lavas, formed in response to the deflation
of the caldera and peri-caldera area, together with formation of the intracaldera Faete stratovolcano.
These edifices were emplaced between c. 355 and c. 180 ka, an interval termed the
‘Tuscolano–Artemisio–Faete period’. Although similar peri-caldera and intracaldera activity
occurred earlier, that is, after each major caldera-forming eruption during the Vulcano Laziale
period, the Tuscolano–Artemisio–Faete period was subject to a significant reduction in average
eruption rate, by one order of magnitude, of 0.1 km3 ka21, which can be related to a consistent
reduction in the deep recharging of the plumbing system, and suggesting why no further ignimbrite
eruptions occurred after 355 ka.
Peri-caldera activity began along the northern and eastern peri-caldera ring fractures (Tuscolano
and Artemisio sections, respectively) and after c. 300 ka progressively migrated outwards to extracaldera
positions (Pantano Borghese section) and to the western peri-caldera fractures (S. Maria
delle Mole section). The activity of these latter fracture systems ended almost simultaneosly,
together with that of the Faete intracaldera stratovolcano, between c. 280 and c. 250 ka. After
250 ka, activity migrated to the south (Monte Due Torri section). The most recent activity along this latter peri-caldera area interfingers (between c. 200 ka and c. 180 ka) with phreatomagmatic
products, which instead became dominant in the most recent activity of the Colli Albani
volcano. Beginning from c. 200 ka (Via dei Laghi period), the western section of the pericaldera
area has been the site of repeated very small- to small-volume, maar-forming phreatomagmatic
eruptions, which formed both monogenetic and polygenetic maars, collectively named the
Via dei Laghi maar field. The most recent of these maars is the polygenetic Albano maar, which
was formed after c. 70 ka by at least seven eruptions migrating along a NW–SE-trending,
3.5-km-long fracture. The last eruption of the maar occurred at ,23 ka. Subsequent phreatic
activity occurred throughout the Holocene, with lahars originating from dramatic withdrawals of
the deep maar lake, at least up to the Eneolithic time (6000–5000 years ago) and probably up to
Roman times (fourth century BCE), when the Romans dug a tunnel drain to keep the lake at a constant
low level. The Albano area is currently the site of volcanic gas emissions, ground uplift and
periodic seismic swarms, which may indicate persistent activity of a magmatic body at depth