From the caldera rim to cathedral stones - A self‑guided geoheritage walk through Bolzano/Bozen (South Tyrol, Italy) across the Athesian Volcanic Group

DOI: https://doi.org/10.3301/GFT.2026.11 - Pages: 1-31

¹Museum of Nature South Tyrol, Bindergasse/Via Bottai 1, 39100 Bozen/Bolzano, Italy.

²Department of Natural History, Tiroler Landesmuseen, Krajnc-Straße 1, 6060 Hall in Tirol, Austria.

³Office for Geology and Building Materials Testing, Provincia Autonoma di Bolzano, Via Val d'Ega, 48, 39053 Cardano, Italy.

⁴South Tyrol Museum of Mining, Provincia Autonoma di Bolzano-Alto Adige, Stadelgasse 8b, 39042 Brixen/Bressanone, Italy.

Corresponding author e-mail: e.kustatscher@tiroler-landesmuseen.at

The city of Bolzano/Bozen (South Tyrol, northern Italy) offers an exceptional opportunity to link field volcanology at an early Permian caldera margin with urban geology and building stones in a single half‑day walk through the city and its surroundings. The walk starts with the Passeggiata di Sant'Osvaldo/Oswaldpromenade, where a steep transect exposes welded ignimbrites, epiclastic volcaniclastic deposits and rhyolitic lavas of the Athesian Volcanic Group. This uphill walk culminates near exposures of the Ora/Auer Formation, close to the caldera margin, where welding fabrics, alteration patterns and brittle structures can be discussed in the context of collapse tectonics and post‑eruptive deformation. Walking back to the city, the path continues through the historical centre of Bolzano/Bozen, where the same and also additional lithologies can be observed as cobbles, blocks and dimension stones in churches, cloisters, castles, fountains and pavements, illustrating how erosion, fluvial transport and quarrying history shaped the stone palette of the city.

Athesian Volcanic Group, Ora/Auer Formation, caldera margin, volcaniclastic deposits, building stones, urban geology, geoheritage.