4.29), may be the major reason for the reduction of bulk density in the Bw horizon of
Andisols (Nanzyo et al. 2007).
4.4.6 Volcanic Ash Soils Under Various Drainage Conditions
The weathering of volcanic ash depends on moisture and drainage conditions in soil.
Under moist and well-drained conditions, active Al and Fe materials form as
summarized in Fig. 4.14. In contrast, halloysite formation prevails in volcanic ash
soils with restricted drainage or under semi-dry weather conditions. Figure 4.31
shows changes in the weathering of dacitic volcanic ash Numazawa-Numazawako
(Nm-NK) (4.6 ka, Ishizaki et al. 2009; Yamamoto 2003, 2007) with topography and
drainage conditions at Aizu basin, Japan. In this area, tephra from the Numazawa
caldera is distributed on the buried A horizon soil. At the well-drained hilly sites
(Jotohara and Urushihara in Fig. 4.31a, b), the color of Nm-NK tephra is brownish,
the range of Al o + Fe o /2 values is 12–19 g kg
À1 , and the clay fractions are mainly
composed of allophane and imogolite with small amounts of halloysite. On the other
hand, at the Yukawa and Amanuma sites (Fig. 4.31d, e) with restricted drainage, the
color of the Nm-NK is grayish, the range of Al o + Fe o /2 values is 1.2–5.3 g kg
À1 , and
the major clay mineral is halloysite. Although the Nm-NK tephra is thick at the
Yukawa site, the reason may be secondary deposition from sounding areas due to
transportation by water. At Sobanome (Figs. 3.6a, 4.31c), which is also inside the
Li Be
Ne
F
O
N
C
B
Na Mg
Al
Si
P
S
Cl
Ar
K
Ca Sc
Ti
V
Cr Mn Fe Co Ni Cu Zn Ga
Ge As
Se Br
Kr
Rb Sr
Y
Zr
Nb Mo
Tc Ru Rh Pd
Ag Cd
In
Sn Sb
Te
I
Xe
Cs Ba La Hf Ta
W
Re Os
Ir
Pt Au Hg
Tl Pb Bi
Po At
Rn
Ce Pr Nd
Pm
Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Fr
Ra Ac
Th
Pa
U
Lanthanides
Actinides
0
1
0
Wp/Ws -1
Ej,s
a
b
(a=b=Ej,p)
2
3Ej,p
Ej,s
Ej,p =
Wp/Ws -1 +1
Fig. 4.30 Changes in element concentration of andesitic tephra during Andisol formation. Red
lines show changes in concentration of elements with weight loss of soils if the elements are
immobile
4.4 Andisols: Soils Dominated by Non-crystalline Inorganic Constituents
91
Andisols (Nanzyo et al. 2007).
4.4.6 Volcanic Ash Soils Under Various Drainage Conditions
The weathering of volcanic ash depends on moisture and drainage conditions in soil.
Under moist and well-drained conditions, active Al and Fe materials form as
summarized in Fig. 4.14. In contrast, halloysite formation prevails in volcanic ash
soils with restricted drainage or under semi-dry weather conditions. Figure 4.31
shows changes in the weathering of dacitic volcanic ash Numazawa-Numazawako
(Nm-NK) (4.6 ka, Ishizaki et al. 2009; Yamamoto 2003, 2007) with topography and
drainage conditions at Aizu basin, Japan. In this area, tephra from the Numazawa
caldera is distributed on the buried A horizon soil. At the well-drained hilly sites
(Jotohara and Urushihara in Fig. 4.31a, b), the color of Nm-NK tephra is brownish,
the range of Al o + Fe o /2 values is 12–19 g kg
À1 , and the clay fractions are mainly
composed of allophane and imogolite with small amounts of halloysite. On the other
hand, at the Yukawa and Amanuma sites (Fig. 4.31d, e) with restricted drainage, the
color of the Nm-NK is grayish, the range of Al o + Fe o /2 values is 1.2–5.3 g kg
À1 , and
the major clay mineral is halloysite. Although the Nm-NK tephra is thick at the
Yukawa site, the reason may be secondary deposition from sounding areas due to
transportation by water. At Sobanome (Figs. 3.6a, 4.31c), which is also inside the
Li Be
Ne
F
O
N
C
B
Na Mg
Al
Si
P
S
Cl
Ar
K
Ca Sc
Ti
V
Cr Mn Fe Co Ni Cu Zn Ga
Ge As
Se Br
Kr
Rb Sr
Y
Zr
Nb Mo
Tc Ru Rh Pd
Ag Cd
In
Sn Sb
Te
I
Xe
Cs Ba La Hf Ta
W
Re Os
Ir
Pt Au Hg
Tl Pb Bi
Po At
Rn
Ce Pr Nd
Pm
Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Fr
Ra Ac
Th
Pa
U
Lanthanides
Actinides
0
1
0
Wp/Ws -1
Ej,s
a
b
(a=b=Ej,p)
2
3Ej,p
Ej,s
Ej,p =
Wp/Ws -1 +1
Fig. 4.30 Changes in element concentration of andesitic tephra during Andisol formation. Red
lines show changes in concentration of elements with weight loss of soils if the elements are
immobile
4.4 Andisols: Soils Dominated by Non-crystalline Inorganic Constituents
91