Grain-Size Data
In this exercise I would like you to work with the program SFT to analyze grain-size data. This program allows you to plot and interpret size distributions of tephra. The samples taken from outcrops in the field were dried and then passed through a series of screens with progressively smaller openings. The mass of the particles resting on the screens was recorded next to the size opening of the screen. The sizes are based on the f scale was used where f = -log2 (diam. in mm). Hence 4 mm = -2f; 0.5 mm = 2 f, etc
You can run the SFT executable code by clicking on the box, or you can download a ZIP version of the code to run on your own PC (sorry, no MACS allowed). The data can be found in the size data file.
In this exercise you have data from analyses of several types of pyroclastic materials of 4 volcanic eruptions. These eruptions are: Bishop fall, Bishop Flow, Mount St. Helens stair-step deposits, and Sugarloaf tuff ring.
I want you to use the SFT
program to make a histogram of the data and to determine the best fit of
one or more populations to the total size spectrum. You should use
the sequential transport mode for the analysis. The main properties
of the total distribution that you should report include: number of modes,
median size of each mode, and g (shape
factor) for each mode. I would like you to make some interpretation
about the eruption from the data that you analyze. Please analyze
at least two data sets from each eruption.