Passage IV

Wind spread ash from a volcanic eruption eastward over a large area. An ash sample was collected at each of 5 different distances east of the volcano. The diameters of the particles in each sample were determined and con­verted to phi (see Table 1). Figure 1 shows the weight percent of each sample's ash particles belonging in each of 10 different ranges of phi (see Figure 1).

†Weight percent is the percent of a sample's weight from particles having diameters in a given range as defined in Table 1.

Figure 1

Figure 2 shows the weight percents of the 4 types of ash particles—rock fragments, glass shards , feldspar crys­tals, and mafic crystals (various iron magnesium silicate compounds)—in 13 ash samples, each collected at a differ­ent distance east of the volcano.

†Weight percent is the percent of a sample's weight from particles of a specific type.

Figure 2

Figures 2 adapted from Steven Carey and Haraldur Sigurdsson, "Influence of Particle Aggregation on Deposition of Distal Tephra from the May 18, 1980, Eruption of Mount St. Helens Volcano." ©1982 by the American Geophysical Union.