Temperatures of the A.D. 79 pyroclastic density current deposits (Vesuvius, Italy)

Abstract

[1] The temperature of the deposits left by different types of pyroclastic density currents (PDCs) of the A.D. 79 ''Pompei'' eruption of Vesuvius was estimated by measuring the thermal remanent magnetization (TRM) of lithic clasts carried by the currents. More than 200 lava clasts and roof tile fragments were collected at different sites and distances from the vent. The estimated temperatures fall in the range 180-380°C, although most of the samples show temperatures (T) in the range 240-340°C. This interval occurs for both the deposits of the same eruptive unit sampled at different sites and those derived from PDCs with similar physical characteristics. The sedimentological features coupled with the TRM data allow us to highlight the main processes controlling the T variability of the deposits and of their emplacing currents. The results reveal that air ingestion, involvement of external water, as well as transport and emplacement processes of the PDC are the most important factors in decreasing the emplacement T. The amount of lithic clasts carried by the currents does not play an important role in changing the final temperature because of the grain size and initial high T of these fragments.

The historic magmatic-hydrothermal eruption of the Breccia di Commenda, Vulcano, Italy

“…80%) in the BC belong to Type C of Cioni et al (2004): their NRM consists of two components, the blocking temperature (T b ) spectrum of which is well defined (Figs. 10a and 10c) and the reheating temperature is well constrained within an interval of 40 °C.…”

“…The temperature of the deposit (T dep, Cioni et al 2004) was estimated according to the procedure of Cioni et al (2004) and Zanella et al (2007Zanella et al ( , 2008. Measurements were carried out at the University of Torino's Alpine Laboratory of Paleomagnetism (Peveragno-Italy) using a JR-6 spinner magnetometer and Schonstedt furnace.…”

“…Zijderveld (1967) diagrams and Principal Component Analysis (PCA) (Kirschvink 1980) were used to isolate the low-and high-temperature remanence components of single clasts, and compute their directions in cases where they had been oriented. T dep at each site was then obtained from the overlapping reheating ranges for all lithic clasts collected at that site (Cioni et al 2004). …”

Late bronze age pottery as indicator of the deposition temperatures of the Minoan pyroclastic products, Santorini, Greece.

“…Several relevant studies have been also conducted in Italy, Mexico and Argentina (e.g. Cioni et al, 2004;Zanella et al, 2007;Sulpizio et al, 2008;Porreca et al, 2008;Di Vito et al, 2009;Lesti et al, 2011) and recently this technique was improved and extended involving also the study of human artefacts such as tiles and pottery.…”

“…Due to the small size of the collected ceramics the preparation of standard cylindrical specimens (diameter 25.4 mm; height 22.5 mm) was not possible. To measure such small pieces, plastic boxes and white plasticine were used, following the procedures described by Cioni et al (2004). In the case of samples larger than 2 cm, two specimens were prepared from individual fragments in order to improve the accuracy in the estimation of the deposition temperature interval .…”