Field-based measurements of volcanic ash resuspension by wind

The resuspension of volcanic ash by wind is a significant source of hazard during and after volcanic eruptions. Parameterizing and modeling ash resuspension requires direct measurement of the minimum wind shear stress required to move particles, usually expressed as the threshold friction velocity U⁎th, a parameter that, for volcanic ash, has been measured only scarcely and always in the laboratory. Here, we report the first field measurements of U⁎th for volcanic ash, with a portable wind tunnel specifically developed, calibrated, and tested. Field measurements, performed on natural reworked ash deposits from Sakurajima (Japan) and Cordón Caulle (Chile) volcanoes, agree well with our laboratory determinations on ash from the same deposits, with values of U⁎th ranging from 0.13 to 0.38 m/s. Our results show that the median grain size of the deposit and particle shape have a stronger control on U⁎th than the local substratum nature and deposit texture. •We measured wind erosion threshold friction velocity of volcanic ash in the field.•Field measurements are efficient, cheap, fast, and congruent with laboratory ones.•Shape and median grain size of particles exert first order control on resuspension.•Ash resuspension is controlled secondarily by local substratum and deposit textures.