Size and shape measurements of ash particles from the May 18, 1980, eruption of Mount St. Helens
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Geology topics
Michael B. Sawyer
Publications and source records attributed to Michael B. Sawyer.
Image analysis as a method for determining grain-size distributions in sandstones
A Quantimet 720 image analyzing computer is useful for A Quantimet 720 image analyzing computer is useful for determination of grain-size distributions of sand-size material. Results including histograms and statistical measures of size can be produced in approximately 5 to 10 minutes per sample. Comparison with sieve results shows only small differences in the mean grain-sizes obtained. Research into operating methods for the image analyzing computer and into mathematical methods for combining data is continuing so that material coarser and finer than sand can be measured. The instrument, which is attached to a microscope via a black and white television scanner, uses the gray shades of features in the field of view as the means of detecting those features. The image analyzing computer can then measure the features including area, perimeter, and several types of diameters. These data are then analyzed by a computer and the results are plotted. Sample preparation for this technique is conventional. Samples can be run as loose disaggregated grains, grain mounts, or thin sections.
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Computer program for the calculation of grain size statistics by the method of moments
A computer program is presented for a Hewlett-Packard Model 9830A desk-top calculator (1) which calculates statistics using weight or point count data from a grain-size analysis. The program uses the method of moments in contrast to the more commonly used but less inclusive graphic method of Folk and Ward (1957). The merits of the program are: (1) it is rapid; (2) it can accept data in either grouped or ungrouped format; (3) it allows direct comparison with grain-size data in the literature that have been calculated by the method of moments; (4) it utilizes all of the original data rather than percentiles from the cumulative curve as in the approximation technique used by the graphic method; (5) it is written in the computer language BASIC, which is easily modified and adapted to a wide variety of computers; and (6) when used in the HP-9830A, it does not require punching of data cards. The method of moments should be used only if the entire sample has been measured and the worker defines the measured grain-size range. (1) Use of brand names in this paper does not imply endorsement of these products by the U.S. Geological Survey.
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