4.4.4 B Horizon Soil with Andic Soil Properties
The 2Bw1 horizon consists of weathered Nt-S tephra. Figure 4.24a shows part of a
polished section prepared from a clod consisting of weathered pumice. Although the
color is yellowish brown, the inside of the pumice retains its highly vesicular
structure. The outside of pumice is browner than the inside. The Al element map
(Fig. 4.24d) shows that the Al concentration is high along the rim of weathered
pumice. The EDX spectrum (Fig. 4.24e) suggests that the dashed square e in the
Fig. 4.24d is an allophanic material. Regarding the inside of the weathered pumice,
the Al concentration also appears to be increasing. Al and Si element maps were also
examined for the dashed square (c) in Fig. 4.24a.
Figure 4.25 shows a magnified SEM image of the dashed square Fig. 4.24c.
Weathered phenocrysts and many small bubbles, probably owing to inadequate
penetration of resin to the small vesicular pores, are observed. Nevertheless, comparing the color intensity of the Al and Si element maps, Fig. 4.25b, c, respectively,
the concentration of Al appears to be higher in the vesicular or sponge-like part than
that of Si. To further examine the distribution of Al and Si, the dashed squares
(d) and (e) in Fig. 4.25a were magnified and are shown in Figs. 4.26 and 4.27,
respectively.
Fig. 4.21 SEM-EDX analyses of a reticulated pattern found in the polished section (Fig. 4.20f). (a)
SEM image of Fig. 4.20f, (b and c) EDX spectra of the selected areas (b) and (c) in (a), respectively.
(d and e) Al and Si element maps of (a), respectively
4.4 Andisols: Soils Dominated by Non-crystalline Inorganic Constituents
83
The 2Bw1 horizon consists of weathered Nt-S tephra. Figure 4.24a shows part of a
polished section prepared from a clod consisting of weathered pumice. Although the
color is yellowish brown, the inside of the pumice retains its highly vesicular
structure. The outside of pumice is browner than the inside. The Al element map
(Fig. 4.24d) shows that the Al concentration is high along the rim of weathered
pumice. The EDX spectrum (Fig. 4.24e) suggests that the dashed square e in the
Fig. 4.24d is an allophanic material. Regarding the inside of the weathered pumice,
the Al concentration also appears to be increasing. Al and Si element maps were also
examined for the dashed square (c) in Fig. 4.24a.
Figure 4.25 shows a magnified SEM image of the dashed square Fig. 4.24c.
Weathered phenocrysts and many small bubbles, probably owing to inadequate
penetration of resin to the small vesicular pores, are observed. Nevertheless, comparing the color intensity of the Al and Si element maps, Fig. 4.25b, c, respectively,
the concentration of Al appears to be higher in the vesicular or sponge-like part than
that of Si. To further examine the distribution of Al and Si, the dashed squares
(d) and (e) in Fig. 4.25a were magnified and are shown in Figs. 4.26 and 4.27,
respectively.
Fig. 4.21 SEM-EDX analyses of a reticulated pattern found in the polished section (Fig. 4.20f). (a)
SEM image of Fig. 4.20f, (b and c) EDX spectra of the selected areas (b) and (c) in (a), respectively.
(d and e) Al and Si element maps of (a), respectively
4.4 Andisols: Soils Dominated by Non-crystalline Inorganic Constituents
83