Large Volume Volcanic Debris Avalanche in the East Carpathians, Romania

Debris avalanche deposits (DAD) have for the first time been identified in the Neogene to Quaternary volcanic arc of the Carpathians. Two large volume DADs are described from the Cãlimani-Gurghiu-Harghita volcanic chain (East Carpathians, Romania): (1) the Rusca-Tihu DAD in the Cãlimani and Northern Gurghiu Mts., and (2) the Vârghis DAD in the Harghita Mts. They represent an important component of the largely developed volcaniclastic aprons around the axial row of adjacent andesitic stratovolcanoes of the chain. The studied DADs display diagnostic features which closely resemble those described for DAD world-wide. Despite their old ages (ca. 8 Ma, and 5-6 Ma, respectively), the source volcanoes of the DAD in the East Carpathians can be identified, one of them (Vârghi) still displaying a recognisable debris-avalanche depression. Volume calculations resulted in ca. 26 km 3 (Rusca-Tihu DAD), one of the most voluminous reported in the literature world-wide, and ca. 13 km 3 (Vârghi-DAD), respectively. Runout distances are 55 km, and 40–50 km, respectively. The Rusca-Tihu DAD is spatially related to contemporaneous pyroclastic and effusive volcanics suggesting that the edifice failure occurred during an eruptive episode. The Vârghi-DAD was apparently unrelated to coeval eruptive activity, and it is associated, and grades to, debris flow deposits.