THE ROLE OF ATMOSPHERIC HUMIDITY IN DRIVING SALT WEATHERING OF ROCKS IN NATURAL HYPERARID ENVIRONMENTS

Rock weathering is ubiquitously observed at or near Earth’s surface as a fundamental rate-limiting component for many subsequent landscape evolution processes. In arid landscapes, where limited moisture availability restricts the effectiveness of chemical and biological weathering – salt shattering (regarded herein as the physical disintegration of rocks in the presence of salts) is commonly acknowledged as an especially effective rock-weathering mechanism. While volumetric salt expansion and contraction in response to changes in ambient moisture conditions are broadly recognized as primary drivers of salt shattering, our understanding of the environmental conditions that facilitate such moisture dynamics in extremely dry settings remains less developed.

Here, we present preliminary results from uniquely quantitative field-based measurements documenting the environmental conditions under which salt-shattering occurs in some of Earth’s driest landscapes: Timelapse photography in the hyperarid and frigid Antarctic Dry Valles revealed that atmospheric relative humidity (RH) variations can drive repeated cycles of salt deliquescence/efflorescence within boulder cracks during otherwise completely dry conditions. Temperature (T) and RH measurements in a salt cave in the hyperarid Dead Sea basin demonstrated that salt deliquescence/efflorescence dynamics driven by RH fluctuations can fracture carbonate rocks experiencing negligible T gradients below 0.2°C/day. Field-based acoustic emission (AE) measurements (~100 days) from boulders with salt-laden cracks perched on abandoned shorelines of the hypersaline Dead Sea revealed daily fracturing activity that occurred mainly in the early predawn and afternoon hours when T changes were minimal and RH fluctuations reached maximum or minimum values, respectively. Continuous T, moisture and RH measurements in late Pleistocene reg soils in the hyperarid Negev desert demonstrated that salt-driven fracturing of rocks was limited to the upper ~60 cm of the soils, where subsurface microclimatic dynamics allow for repeated cycles of salt deliquescence/efflorescence. Altogether our results suggest that atmospheric RH is a key driver of salt weathering processes in extremely dry environments with otherwise limited sources of moisture.