THE USE OF 'THERAN TEPHRA' IN AEGEAN TRADITIONAL BUILDING TECHNIQUES: A CASE-STUDY FROM THERASIA ISLAND, GREECE (Invited Presentation)

Diverse pyroclastic deposits produced during the cataclysmic Late Bronze Age Plinian eruption (around 1600 BCE) have been employed in the local architectural paradigm of cave dwellings on Therasia, part of the Santorini (Thera) archipelago in Greece. The most abundant and characteristic deposit used in these constructions is “Theran earth”, an aluminosilicate glassy tephra and natural pozzolan. “Theran earth” was a significant mineral resource in Greek industrial history. It was mined both in Thera and in Therasia from the 19^th century to the 1920s and is aligned with the first cement plant in Greece. It was employed in major hydraulic concrete construction projects in the Mediterranean region, including the Suez Canal.In the vernacular architecture, local craftsmen used the vitric-crystal-lithic tephra collected in situ from excavation debris during cave dwelling construction. After a standardized screening process they combined the tephra with lime putty and prepared diverse construction materials: binding mortars, plasters and concretes. Other pyroclastic products, mainly lavas and vesicular pumice bombs, were employed as coarse aggregate.

Petrographic examination, along with mineralogical analysis, sheds light on the morphology of the pumiceous tephra, as well as on variations of its vitric constituents, lithic fragments and crystals. Historic samples of the vernacular construction materials reveal a cementing matrix with abundant partially dissolved glass shards, zones of alteration on fine ash-sized pumice clasts indicative of pozzolanic reaction and poorly crystalline binding phases, in addition to calcite.

Our studies aim to enrich the knowledge on natural pozzolanic materials through the examination and documentation of traditional building techniques in the Aegean region and to trigger a dialogue over how the scientific research may enhance and update local traditions through the design of compatible and sustainable modern building materials.