Alain Volentik, University of South Florida

Alain Volentik

PhD Candidate
Volcanology Group

USF Links

University of South Florida

Department of Geology at USF

USF Volcano Group

Lab Facilites

I am currently running the Grain Size Analysis Lab of the Volcanology Group here at the University of South Florida.

Facilites include basic sieves technics (both 1.0Φ and 0.5Φ increments) down to 4.0Φ together with the Malvern PharmaVision 820 optical device (PVS). The latter is a microscope (see the 2 pictures below), scanning the surface of a glass slide on which about 0.5gr aliquot of the sample has been homogeneously dispersed. The size range that is investigated is between 0.5 microns and 2.0 millimeters, but commonly, we analyze volcanic ash previously sieved down to 1.0 millimeter.

Figure 7 shows different morphological parameters measured by the PVS, such as: (i) the maximum distance within the particle, (ii) the length, (iii) the width, (iv) the mean diameter or (v) the projected area.

Figure 8 presents the variation in grain size distribution for some parameters (for sample PL19). Mean particle diameter is calculated from the measured radius value from the center of mass to each pixel on the circumference of the particle. The following results from PVS analysis are for mean particle diameter.

In order to validate the PVS method for grain size analysis, we compared the results acquired with the optical device with the results obtained by sieving. Figure 9 presents this comparison. The good agreement between the sieving and the PVS is encouraging and state that the PVS method for grain size distribution analysis is applicable.

The PVS optical device provides other important results, such as single image of each particle (Fig. 10-A and 10-B). These results will be used in the future to improve particle terminal velocity calculations for tephra fallout. Furthermore, parameters such as roundness, convexity and intensity (Fig. 10-A and 10-B, red rectangles) will be used as fingerprints of the sample material (pumice, crystal, lithics) and could be a powerful tool for componentry analysis of volcanic ash. This is work under progress right now.

Last Updated on June 2nd, 2006
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