A major dome collapse of the Soufrière Hills volcano, Montserrat, on 26 December 1997 generated a devastating pyroclastic density current that destroyed vegetation and left a distinctive tar-like deposit on the surface. The deposit included a range of charred, mainly herbaceous angiosperm, axes and roots. Studies of reflectance of these charcoalified plants indicated mean reflectances of 0.72–1.16 for the three samples with a maximum reflectance of 1.77 recorded for all readings. These data provide minimum temperatures of the flow of 300–425 °C, consistent with organic geochemical data obtained by 13C solid-state nuclear magnetic resonance and gas chromatography–mass spectrometry. These temperatures have been used to calculate characteristics of the pyroclastic density current. We estimate flow front current densities near the ground of 1.8–3 kg/m3, using constraints from a mean flow speed of 90 m/s estimated from seismic data. The mean temperature of the ash component is estimated as 400–610 °C.