Geomorphological Evolution of Phlegrean Volcanic Islands Near Naples, Southern Italy1
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Berlin .Stuttgart Geomorphological evolution of Phlegrean volcanic islands near Naples, southern Italy1 by G.AIELLO, D.BARRA, T.DE PIPPO, C.DONADIO, and C.PETROSINO with 9 figures and 5 tables Summary. Using volcanological, morphological, palaeoecological and geoarchaeological data we reconstructed the complex evolution of the island volcanic system of Procida-Vivara, situated west of Naples betweenthe lsland of lschia and the PhlegreanFields, far the last 75 ky. Late Pleistocenemorphological evolution was chiefly controlled by a seriesof pyroclas tic eruptions that resulted in at least eight volcanic edifices, mainly under water. Probably the eruptive centresshifted progressively clockwise until about 18 ky BP when volcanic develop ment on the islands ceased. The presenceof stretches of marine terraces and traces of wave cut notches, both be low and abovè'current sea levels, the finding of exposed infralittoral rnicrofossils, and the identification of three palaeo-surfacesburied by palaeosoilsindicates at least three differen tial uplift phases.These phases interacted with postglacial eustaticfIuctuations, and were sep arated by at least two periods of generai stability in vertical movements. A final phase of ground stability, characterisedby the deposition of Phlegrean and lschia pyroclastics, start ed in the middle Holocene. Finally, fIattened surfacesand a sandy tombolo developedup to the present-day. Recent archaeological surveys and soil-borings at Procida confirm the presence of a lagoon followed by marshland at the back of a sandy tombolo that were formed after the last uplift between the Graeco-Roman periodandthe15di_16dicentury. These areaswere gradu ally filled with marine and continental sedimentsup to the 20di century. ' Finally, our investigation showed that the volcanic sector of Procida-Vivara in the late Pleistocene-Holocenewas affected by vertical displacementswhich were independent of and less marked than the concurrent movement in the adjacent sectors of lschia and of the Phle grean Fields. The displacementswere probably controlled by volcano-tectonic phenomena rather than bradyseism (slow pseudo-elasticdeformation of soil due to underground magma intrusion and/or gasand steampressure). Zusammenfassung. Die geomorpholog'ischeEntwicklung derphlegreischenVulkaninseln bei Neapel. - Mit vulkanologischen, morphologischen, palaokologischen und geoarchaologischen Daten wurde die Entwicklung der vulkanischen lnseln Procida-Vivara fur die letzten 75.000 Jahre rekonstruiert. 1 This work is the result of a research carried out by ali the authors. Particularly, T. De Pippo, C. Dona dio and C. Petrosino carried out the geological and geomorphological description of the island volcanic system of Procida- Vivara; G. Aiello and D. Barra took care of palaeoecological analysis; finally, geomor phological interpretation and reconstruction of complex evolution of the island volcanic system as well as conclusions afe the result of ali authors collaboration. DOI: 10.1127/0372-8854/2007/0051-0165 0372-8854/07/0165$ 6.50 @2007GebriiderBorntraeger.0-14129Berlin.0-70176Stuttgart 166 G.AIELLO et al. Die spatpleistozaneEntwicklung wurde durch mindestensacht submarinepyroclastische Ausbriiche gesteuert,deren Zentren sich dextral verschobenund 18.000BP endeten.Marine Terrassen,Wellenkerben, infralittorale Mikrofossilien sowie drei Palaooberflachenmit Boden dokumentieren drei Hebungsphasen.Diese iiberlappen mit den holozanen Meeresspiegel schwankungenund bewirken zwei Periodenan Hohenkonstanz.Eine letzte Phase,belegt durch Ablagerungen von pyroclastischenSedimenten aus Ischia und den PhlegreischenFeldern, be ginnt im mittleren Holozan und es entwickelte sich ein flachesRelief und ein Tombolo. Archaologische Studien und Bohrungen belegen eine Lagune und Marschland hinter einem sandigen Tombolo. Diese bildeten sich nach einer Hebungsphasezwischen der grie chisch-romischenPeriode und dem 15-16. Jahrhundert und wurden bis ins 20.Jahrhundert mit marinen und kontinentalen Sedimentenaufgefiillt. Letztlich zeigen die Untersuchungen, dass Procida-Vivara im Untersuchungszeitraum durch vertikale vulkanotektonische Bewegungenbeeinflusst wurde, die unabhangig von den angrenzendenSektoren von Ischia und den PhlegreischenFeldern abliefen. Résumé. En employant les donnéesvolcanologiques, morphologiques, palaeoecologiqueset geoarcheologiquesnous avons reconstruit l'évolution complexe, dans les derniers 75 ky, du systèmevolcanique de l'ile de Procida-Vivara, situé à l'ouest de Naples entre l'ile d'Ischia et des Champs Flégréens. L'évolution morphologique du PléistocèneterminaI a été principalement commandéeFar une série d'éruptions pyroclastiques qui ont originè au moins huit édifices volcaniques,prin cipalement sousmarines.Probablement les centreséruptifs ont décaléprogressivement dans le sensdes aiguille~d'une montre jusqu'à environ 18 ky BP, quand le développementvolcanique sur les iles a cessé: La présencedes bords des terrasseset des traces marines des sillions de battant emergè et submergè,la découvertedes microfossils infralittoral exposéset de trois palaeo-surfacesévi dentesenterrées Far despalaeosoils a accordél'identification d'au moins trois phasesdifféren tielles de soulèvement. Ces phasesont agi l'un sur l'autre avec des fluctuations eustatiques postglacialeset ont été séparéesFar au moins deux périodes de stabilité généraledans les mou vementsverticaux; une phasefinale de stabilité, commençantdans l'Holocène moyen et carac térisée Far le dép6t des pyroclastites des Champs Flégréenset d'Ischia, le développementdes surfacesaplaties et un tombolo arénacé,continue à l'actuel. Les aperçusarchéologiques récents et les investigations geognosticchez Procida confir ment la présenced'une lagunesuivie du maraisau fond d'un tombolo arénacé,formée aprèsque la dernière phasede soulèvementdu sol, entre les périodes Graeco-Romaines'etles 15ème-16ème siècles,et graduellementcomblée de sédimentsmarins et continentaux jusqu'au 20èmesiècle. En conclusion, notre recherche a prouvé que le secteur volcanique de Procida-Vivara pendent le Pléistocèneterminal-Holocène a été affectéFar le mouvement vertical du sol ce qui était indépendant et moins marqué que le mouvement concourant dans les secteurscontigus d'Ischia et des Champs Flégréens,très probablement commandéFar des phénomènesvolcan otectoniques plut6t que le bradyseism. 1 lntroduction The islandsi-gf Procida and Vivara (fig. 1), situated in the northwestern part of the Bay of Naples, are located at the edge of the large multi-crater volcanic area known as the Phlegrean Fields (ROSI & SBRANA1987). The geological history, physiography and active volcanism of this area bave led to research towards the volcanological elements, especially in sight of the bradyseismic crises in the 1970s and 1980s. Our studies, however, aim to enhance the understanding of the evolutionary dynamics of regional morphology, highlighting the mutuaI, complex interaction between eruptive mor Geomorphological evolution 167 Cl.'" "'-=~ I ;,.~ I I > ~... ~ o = u... = o~ o.. = 8 8 :.= ~ o 2 o o .. .. '" .. ..c'" - u ~ ... u o o~ "~°..E~ ~~~~Cl.g u ~ o o~ , o A .~ Cl., '"t ~;!.. o~ > , c'-= , C';3 N 0bS) "'=t'"\.~~..cC"' "'.~ :§" - = ,,".~ " ~ , - O,US ~-, '~o E O..e~U Q; = 8 ~0~.~., U " ~, 8 '-="..o~- ~ ~.. ... Cl. U - '--' ..U , ... o """"' ... ... '",~ O", o o ~ ", Ir\'-"'-'d";3" ~'",... 8 > ... ~ ~ o~ ~ ..c'" ~ .. ;3 800 , =u o -~~..~v > o'" ~ " ... ~ C> .. .. r~ ~ I.::'..E ;3 8.~ °C o ~ bS)> v ~~~- -.~ ~. o~'" ~,I ,-", '" ... .. ~ ,00 - o~, .. ... = - o..~N-t"".-= o~ .~... ...~~ U ..c0-0:'= Cl... ... 0:0'" g ~ S Cl.--a1:3 2 'iE 8 8 ~ ~ """""'8 I "'~'-"'...:'=oo~o ~ o ~ '--"--' o '" '" '" U ... U Cl. U E C> z-.c:: g . ~ l,,") """,.Y L...(~" ,~ C> ~"" " " ' , z " ' z Y' C " g , % " f ' e " u,.. , £~ , 'o 1. \: -' w z z C % U J~~~'+I(:'~~mrn~ ~ - I . i /.. '" ~~.. 1 % .,,~N"'~ Il) CC...~o)O~N ~ ~ ~ ..~ -.t... ~ - b 168 G.AIELLOet al. phologies, volcano-tectonic phenomena and eustatic oscillations in the late Pleis tocene-Holocene. These afe documented by severalforms above and below current sealevel, palaeo-environmental analysisand geoarchaeologicaldata. 2 Volcanologicaland structural context The PhlegreanFields lie within the CampanianPlain, which is a Pliocene-Quaternary broad structural depressionin the southern sector of the Tyrrhenian basin, delimited by NW-SE faults (Apenninic trend) along the northeastern border and E-W faults (anti-Apenninic trend) along the northern and southern edges(BRANCACCIO et al. 1991).The current conformation of Procida and Vivara is the result of complex geo logical events:uplift dynamics of the southern Apennine Chain, late Quaternary sea level fluctuations, the Phlegrean Pleistocene-Holocene volcanic eruptions (SCAN DONEet al. 1991),and changeswrought by human impact aver the last 25 centuries. The PhlegreanFields - together with the islands of Ischia, Procida and Vivara - afe a complex volcanic area (DI GIROLAMOet al. 1984, ROSI & SBRANA1987, VEZZOLI 1988, FEDELEet al. 2006), formed by many monogenic pyroclastic edifices. They include active though quiescentstructures (Solfatara)characterized both by explosive events (pyroclastic products) and, to a lesser extent, effusive products (lavas, lava domes). Volcanic activity started in the upper Pleistoceneand continued up to 1538 AD. One or more pyroclastic eruptions gaverise to the formation of CampanianIgn imbrite (Campanian Grey Tuf/), frequently found in outcrops and in the subsoil of the region (ORTOLANI& APRILE 1985).