Reply to comment by N. Kartal Toker, John T. Germaine, and Patricia J. Culligan on "Cavitation during desaturation of porous media under tension"

The simplistic and incomplete presentation of cavitation by Or and Tuller [2002] was justified by the need for a simple representation of potentially different mechanisms for liquid drainage in unsaturated porous media and their impact on common conceptual models and measurement methods [Chahal and Yong, 1965]. Toker et al. [2003] suggested a useful correction that we subsequently expanded to include the critical role of entrapped gas and to derive estimates for critical liquid pressure and critical bubble radius for cavitation. These derivations highlight the role of entrapped gas as cavitation nuclei whose formation and persistence are described by the "crevice model" of Atchley and Prosperetti [1989]. The model provides a more realistic framework for the interactions between pore space geometry (crevice), liquid and surface properties, gas dissolution, and formation of sustainable gas bubbles in porous media. A striking result is that gas bubbles entrapped at the bottom of a crevice can attain equilibrium with gas in the bulk liquid and can remain undissolved indefinitely to serve as potential nuclei for cavitation. Additionally, this relatively simple model yields a rich variety of behaviors that were not captured by standard spherical/cylindrical pore models [Or and Tuller, 2002]. The relationships between pore space geometry, roughness, and angularity [Tuller et al., 1999; Wapner and Hoffman, 2002] and wetting/drying dynamics and their potential contribution of cavitation processes to drainage from porous media will be explored in future studies.