habitat rupestre.pdf - Società Friulana di Archeologia

S. Del Prete, M. PariseMorphological factorsThe erosion and degradation processes that model the landscapehave a primary role in the definition of rupestrian structuresand subterranean works and in their preservation intime. Earth pyramids, butte, mesa, plateau are morphologiesproduced by the action of weathering (physical disintegrationand chemical alteration), of gravity (landslides) and of watererosion; for this same reason, they are destined to decay.The same process that generated particularly suitable morphologies(Succhiarelli, 2002) can ruin the rupestrian settlements,and sometimes very quickly, as in the case of landslides(Fig. 10); they also can generate accumulations that are moresuitable than the original morphology to the development ofrupestrian architecture.A tuff cliff can collapse, and this can bring undergroundrooms to open air (Fig. 11), but a further evolution of the processcan bring to a total loss of the hypogeal heritage.Some collapses due to landslides produce big tuff blocks(thousands of cubic metres) that can bring to the realization ofanother particular rupestrian settlement (Fig. 12). Green tuffblocks in the island of Ischia island detached from the tuffridge of Mount Epomeo: they were excavated to realize differentrupestrian structures, including multilevel habitations(D’Arbitrio & Ziviello, 1991; Cappa & Cappa, 1991; Mele &Del Prete, 1998). The stone blocks were used in their originalmorphology without plaster, leaving the rude tuff surfacecovered with lichens and altered by the erosion of rain andwind (Del Prete & Mele, 2005); this helped the adaptation ofthe structures to the environmental setting of the territory insearch of a defensive mimesis.Some areas are characterized by frequent thermal variationsof freeze/thaw cycles: in these areas there is frequent physicaldisintegration due to constant heating and freezing, whose effectsare gradually evident in time. The level of porosity andthe kind of fissuring characterize the attitude of rocks to sufferthese processes, leading to the crumbling of the rock insmall blocks or flakes (exfoliation). The effect of exfoliation inthe Valley of Meskendir (Cappadocia) on the walls of drainingtunnels (Fig. 9) contributed to the remodelling of the originalsections during thousands years (Bertucci et al., 1995; Castellani,2002).Fig. 11 The tuff cliff has collapesed, and the subterranean rooms have beenrevealed (Tatlarin, Cappadocia – Central Turkey) (photo: G. Bologna –Centro Studi Sotterranei).Fig. 12 Rupestrian tomb in a collapsed rock (Soganli, Cappadocia - CentralTurkey) (photo: R. Bixio – Centro Studi Sotterranei)Endogenous factorsVolcano eruptions deposit tuff pyroclastic material: this is oneof the main influences of endogenous strengths, as it is thegenerating event of one of the most suitable rock layer of hypogealworks.Another interesting and risky endogenous aspect, which is associatedto mines and especially to carbon mines, is the presenceof gas (also known as grisou), which is difficult to localizeand has caused so many deaths in different times.Similar problems can rise during the excavation of tunnels inclay formations, if they are rich of organic substances; sometimeshypogea in volcanic areas can intercept the uprising ofendogenous gas: a very famous example is the Grotto of theDog in Agnano (Baldi, 2001; Varriale, 2005; Fig. 13).Another interesting aspect of endogenous factors is the influenceof fossil fumaroles (degassing pipes) on the lithotechniquecharacteristics of tuff formations, since degassing canoccur when the pyroclastic falls cool down. This may bring to23volumeRicerca_OK_2012-11-15.indd 23 16/11/2012 15:00:47