Experimental frost weathering of sandstone by various combinations of salts

Weathering experiments are reported combining frost and a range of salts that occur naturally on rock faces in western and central Europe. Potassium and ammonium alums enhanced frost weathering quite considerably, both singly and in combination, though they were less potent than halite, the destructiveness of which, at sub‐zero temperatures, was again confirmed. By contrast, alunogen and gypsum had little or no effect on rates of frost weathering either singly or in combination. Combining halite and gypsum produced breakdown that was intermediate between that of the two salts individually, as did the combination of gypsum and potassium alum. Breakdown in solutions of ammonium alum and gypsum, and in a combination of potassium and ammonium alum with gypsum, caused greater breakdown over 25 cycles of freeze–thaw than was recorded with the salts singly. The results extend the range of salts known to enhance frost weathering, and show that it is difficult to predict the aggressiveness of combinations of salts by experimenting with each salt separately. Copyright © 2001 John Wiley & Sons, Ltd.