FIRE-ACCELERATED BOULDER WEATHERING IN THE PILBARA, WESTERN-AUSTRALIA

Fracturing and spalling of granophyre boulders has resulted from spini fex fires. Boulders with a history of firing show up to three generati ons of fire spalling, differences in depth and colour of weathering cr usts, and both angular and rounded edges on the same stone. Sharp-edge d small stones (fire spalls) are most numerous in lower slope position s where spinifex cover is greatest. Fire-accelerated rock breakdown is significant in arid to semiarid environments like the Pilbara where c hemical alteration and most physical weathering processes operate rela tively slowly. Fire effects are most pronounced at the junction betwee n spinifex vegetation and rock (boulder) slopes, and where boulders an d stones lie on or adjacent to sediment-mantled, spinifex-covered slop es or pockets.