New insights into the Belbaşhanı Pumice Plinian eruption: tephrostratigraphy, eruptive history and implications for volcanic hazards posed by Hasandağ (Central Anatolia)

Hasandağ has been one of the most active volcanoes in the Central Anatolian Volcanic Province (CAVP) during the late Pleistocene and Holocene. The past volcanic activity of Hasandağ is characterised by the eruption of multiple lavas, domes, block-and-ash flows (e.g., Aydar and Gourgaud, 1998; Kuzucuoğlu et al., 2020; Friedrichs et al., 2020). Additionally, this volcano has also experienced significant Plinian eruptions such as the Belbaşhanı Pumice, which is the focus of this work. Here, we present a complete volcanological investigation to better characterise this pumice fallout deposit and reconstruct the large explosive eruption that formed the Belbaşhanı Pumice approximately 400 ka ago.

By combining different methodological approaches (i.e., tephrostratigraphy, geological mapping, granulometric distribution, glass chemistry, geochronology, and shard morphology), we have derived isopach and isopleth maps, volume estimation, column height, and location of the eruption vent. The Belbaşhanı Pumice was formed by a Plinian column of about 23 km in height, which erupted ~2 km³ of bulk pyroclastic material. This column was erupted from a Hasandağ vent located at the intersection of the Tuz Gölü fault and a circular shape depression resembling a volcanic caldera. Major and trace element abundances show that the rhyolitic Belbaşhanı Pumice follows a compositional trend similar to those of documented for other Hasandağ pyroclastic deposits. The dispersal axis of the Belbaşhanı Pumice plume extended towards the NNE, leading to the accumulation of a pumice layer of at least 17-m-thick in proximal deposits and up to 2-m-thick in medial-distal areas (20 km from the vent). The highly vesiculated nature of the pumices and glass morphology indicate that Belbaşhanı Pumice was purely a magmatic eruption without any wet phases. Based on the abovementioned observations, we infer that the eruptive history of Hasandağ was related to VEI > 5 Plinian eruptions.

This contribution is relevant for a better understanding of hazard assessment within the CAVP, especially considering the current increase in fumarolic vents around the summit area, and in the seismic events  below and near the Hasandağ. In addition, the geochemical and geochronological data set is an important step to 1) foster future tephrochronological correlations, 2) constrain the distribution of the Belbaşhanı Pumices distal ashes and its eruptive magnitude, and 3) synchronize paleoenvironmental, paleoclimatic and archaeological records.

This research is part of Rengin Özsoy's Ph.D. thesis, funded through a PhD scholarship from La Sapienza – University of Rome and by the PÜSKÜRÜM project, a Marie Curie Action (Grant No. 101024337) funded by the European Union’s Horizon 2020.

 

References:

• Aydar, E. and Gourgaud, A. (1998). The geology of Mount Hasan stratovolcano, central Anatolia, Turkey. J Volcanol Geotherm Res 85:129–152. https://doi.org/10.1016/S0377-0273(98)00053-5
• Friedrichs, B., et al. (2020). Late Pleistocene eruptive recurrence in the post-collisional Mt. Hasan stratovolcanic complex (Central Anatolia) revealed by zircon double-dating. J Volcanol Geotherm Res 404:107007. https://doi.org/10.1016/j.jvolgeores.2020.107007
• Kuzucuoğlu, C., et al. (2020). Geomorphology and tephrochronology review of the Hasandağ volcano (southern Cappadocia, Turkey). Mediterranean Geosciences Reviews, https://doi.org/10.1007/s42990-019-00017-1