Fire-induced reddening of dune sands

Small campfire sites in the Erg of Azaouad, north-central Mali, reveal locally-reddened sands, as do campfire sites in many settings. The sand surface temperatures reached in such campfires are achieved in some cases of range fire or forest fire. To measure the extent to which such fires can affect dune sand color, sand samples were heated to temperatures commonly reached during brush and forest fires. Munsell colors and laboratory spectral reflectance measurements were used to quantify color changes. Reddening occurred in sands heated above 200°C. Munsell colors and reflectance values closely match the color of naturally-red dune sands. Characteristic hematite spectral features are absent. Sand from both active and stable dunes reddened substantially, and the red color is persistent through time.