Temperatures of the AD 79 pyroclastic density current deposits (Vesuvius, Italy)

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 180–380C, although most of the samples show temperatures (T) in the range 240–340C. 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.