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.

22. A student claimed that if the ash particles in the sample collected closest to the volcano are compared with those in the sample collected farthest from the volcano, the weight percent of larger particles will be higher in the sample collected closest to the volcano. Is this claim supported by Table 1 and Figure 1 ?

Answer and Explanation

Your Answer is

Correct Answer is H

Explanation

Look at figure 1 first. The distance=27 km in the first picture is the closest to the volcano. At this time, the phi corresponding to the particles with relatively high weight percent is about -1 to 2;

Look at the figure again In the fourth picture of 1, distance=405km is the furthest away from the volcano, and phi is concentrated in the range of 3-9 at this time.

Corresponding to table 1, it is known that the larger the phi, the smaller the diameter, so it can be seen that the closer to the volcano, the larger the particles, the student's statement is correct, choose yes