The Vaporous Breath of Sand Dunes
By way of a recent major technical breakthrough, research scientists have discovered that sand dunes inhale and exhale water vapor — a revelation that may hold broad implications for better understanding the earth’s hydrosphere, climate change, and possibly far beyond.
By Eric Herman
Most people do not associate desert sand dunes with water and rightfully so. In fact, arid dunes are seemingly some of the driest and most lifeless places on our planet. That assumption is dramatically challenged in a recent study published in the Journal of Geophysical Research: Earth Surface where a group of Cornell researchers report that the barren appearance of the world’s many vast expanses of arid sand dunes is deceiving.
For decades, geologist and others who study and inhabit deserts with sand dunes have recognized the complexity of their “behavior” as they rise, reform, shift and some would say even interact with each other. Now, there is conclusive evidence that sand dunes breathe; inhaling and exhaling water vapor, even in some of the driest climates.
Researchers were aided by a highly accurate probe, decades in development. The system is able to detect minor changes in microscopic water films that form on grains of sand. The research behind the recent report was conducted in Qatar by a team lead by mechanical engineer Michel Louge from Cornell University’s Sibley School of Mechanical and Aerospace Engineering in Ithaca, NY.
Using the new scanning technology, the team was able to track changes in temperature and moisture in as little 20 second intervals. In their report, the readings were evidence of an “evanescent wave of humidity.”
Louge developed the new form of instrumentation called “capacitance probes,” which deploy an array of sensors to record everything from solid concentration to velocity to water content, all with at fine resolutions never before achieved.
What did they find?
“Deserts inhale and exhale water vapor through their surface,” the researchers write in the report’s plain-language abstract. “Although this process affects the water balance over vast sand seas, it was poorly understood for want of sensitive instruments. We discover how it operates using a new probe that detects tiny amounts of moisture on sand grains. Our analysis reveals that vapor infiltration is considerably slower in dry sand, and that wind flowing over a dune creates weak internal air currents contributing to the transport of moisture.”
In a recent article published on sciencealert.com, science writer, Carly Cassel explains, “In combination with data on wind speed and direction as well as ambient temperature and humidity, the authors have revealed an extremely subtle behavior of sand in the desert. Unlike heat, which is conducted through individual sand grains, water vapor seems to percolate between grains. The pores of a sand dune, therefore, carry moisture from the surface downward, and these pathways are made and remade as the wind blows.”
The findings open up a set of interesting possibilities and further avenues of investigation, such as whether or not this exchange of moisture between the dunes and atmosphere enable microbes to thrive in sand dunes, with delicate ecosystems developing where there is no apparent source of moisture.
The team predicts the technology will could lead to a variety of applications and further avenues of study including climate change, pollution from pharmaceutical waste, to how soils absorb and release water in agriculture, and even someday measuring extraterrestrial dunes that possibly contain water — all possible by understanding the breath of sand dunes.
Image by Dmitry Rukhlenko | Shutterstock