Estimation of emplacement temperatures of pyroclastic flows using H/C ratios of carbonized wood

Laboratory experiments aimed at allowing estimation of emplacement temperatures of pyroclastic deposits flows using H/C ratios of entrained carbonized wood were carried by simulating the thermal conditions in pyroclastic flows. Live wood cuttings of four tree genera (Cryptomeria, Pinus, Quercus and Gonystylus) were implanted in volcanic ash heated in an electric furnace. In one group of experiments, wood samples were inserted into the ash in separate runs at temperatures ranging from 238 to 714°C, and then slowly cooled. In a second group, samples were held at temperatures between 241 and 743°C for one, three or five days. H/C ratios of the carbonized woods produced were then determined by combustion analysis. tematic differences in H/C ratios were observed between genera at given temperatures. H/C ratios from the first group of experiments show a strong correlation with temperature, yielding the equation log T(°C)=2.50−0.530 log (H/C) where H/C ratios are <1.0 and T is >300°C. Similar relations are also shown by the second group, although the equations produced differ with time of maximum heating. The relations between H/C ratios and temperature from the experiments were tested by analysis of natural carbonized wood fragments from Holocene pyroclastic flow deposits, coupled with independent emplacement temperature estimation from paleomagnetic blocking temperatures of clasts within the flows. The two methods produced comparable results, suggesting that the H/C thermometer is a simple and reliable method for estimating maximum emplacement temperatures of pyroclastic flows. Cooling rates can also be approximated when combined with paleomagnetic studies.