The physical parameters controlling pyroclastic density currents (PDC) are very difficult to measure in the field. Inferences for velocity, bulk density and temperature are often based on the analysis of PDC deposits. PDC temperature for example can be inferred from burnt trees, because it needs a minimum temperature to ignite wood. What often remains unknown is the temperature of the volcanic particles during deposition.
Here we present measurements of a thermometer, which was buried below two successive sequences of PDCs traveling down the south flank of Volcán de Colima on 10 and 11 July 2015. The thermometer was part of a larger monitoring installation that was partly destroyed during the 10 July sequence of PDCs that lasted almost 50 minutes. The data logger, including the thermometer survived and recorded also the second sequence of PDCs one day later on 11 July 2015 that took almost 2 hours.
We make use of simple 1D and 2D finite element models for thermal evolution in heterogeneous media with complex geometries coupled to non-linear inversion algorithms to invert the temperature history recorded by the thermometer for the history of successive deposition events during the sequences of PDCs, their layer thicknesses, and deposition temperatures.