You don't form in the wet sand
by Nicasio T. Jiménez-Morilo, IRNAS-CSIC / MED_Soil , Seville, Spain
Water repellency is a property of some soils that delays water infiltration during variable periods of time, due to the presence of hydrophobic organic molecules (lipids, waxes and other compounds) in the soil matrix or coating the external surface of soil mineral particles and aggregates. The photograph shows a drop resting on the surface of a water-repellent soil sample. The soil sample was collected under the canopy of cork oak (Quercus suber) in a sandy area of the Doñana National Park, in SW Spain. In order to take the picture under laboratory conditions, the soil material was air-dried and dry-sieved (<2 mm) to remove coarse elements. Cool light (LED) was used as light source and a water-saturated atmosphere was prepared to prevent evaporation. The photograph was taken using a macro lens and a focal length of 100 mm, with an exposure time of 1/30 s.
Red Hot Chili Peppers were right: "you don't form in the wet sand".
Nicasio T. Jiménez-Morilo (distributed via imaggeo.egu.eu)