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Surface Erosion Associated with Tephra Deposition on Mt. Usu and Other Volcanoes
Chinen, Tamio
Environmental science, Hokkaido : journal of the Graduate School of Environmental Science, Hokkaido
University, Sapporo, 9(1): 137-149
1986-08-20
http://hdl.handle.net/2115/37189
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9(1)_137-149.pdf
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Hokkaido University Collection of Scholarly and Academic Papers : HUSCAP
137
Environ. Sci. Hokkaido
9 (1)
137N149
June 1986
Surface Erosion Associated with Tephra Deposition
on Mt. Usu and Other Volcanoes
Tamio Chinen
Laboratory of Fundamental Research, Division of Environmental
Structure, Graduate School of Environmental Science,
Hokkaido University, Sapporo, e60, Japan
Abstract
The 1977-1978 eruptions of Mt. Usu, Hokl<aiclo, altered erosion regime of its summit atrio
through destruction of pre-existing vegetation, new tephra deposition and crustal cleformation,
resulting in heavy rilling and gullying. Slope erosion rate in the atrio culminated on slopes of
150-30e owing to severe gullying. The 4th Crater catchment, located on sumrnit atrio, represented
an extraordlnarily high erosion rate at 13.6cmlyr when averaged ever the 4 post-eruption years.
However, the erosion rate was deceleratecl within 3 years after the latest tephra deposition and
before revegetation and erosion control worl<s were done. The pattem, initial rapid erosion
￡ollowed by an exponential decline, was observed for several other volcanoes, indicating rapid
adjustment of a slope to the new erosion-sedimentation regime.
Key Words: Volcanic eruption, Tephra cleposltion, Surface erosion rate, Temporal variation.
1. Introduction
Volcanic eruptions often destroy vegetal cover and also produce huge quantities
of tephra. The present study aims to discuss responses of slope erosion processes
to a new tephra deposition with reference to the 1977-1978 eruptions of Mt. Usu,
Japan and several other volcanic eruptions. Focuses are on time series of surface
erosion rate after new tephra accumulation.
"Surface eyosioR", in this paper, means subaerial erosion and also excludes
mass movement. Moreover, special attention is focused on water erosion such as
slope wash, rilling and guliying.
2. Previous studies
Table i demonstrates previous rnain studies of surface erosioR on newly tephra-
covered slopes or catchments. The studies have been reported from several volcanoes: Paricutin (Mexico), Iraz" (Costa Rica), Vulcan (New Guinea), Mt. Usu,
Fernandina (Galtlpagos), and Mt. St. Helens (USA).
Swanson et al. (1983) xeviewed hillslope erosion processes observed at Mt. St.
Helens, Paricutin, Irazd, Vulcan and FernandiRa where detailed and quantitative
studies were done. As a resu}t, they draw the following conclusions. Rates of
Environmental Science, Hol<kaido Vol. 9, No. 1, 1986
138
Table 1. Main $tudies o,f surface erosion on newly tephracoverecl slopes or catchments
Volcano
Reeent eruptive activity
Reference
"' 'vulcall, 'New GtiiilE5 lg37 Ollier and Brown (lg71)
Paricutin,Mexico 1943-1945 Segerstrom(1950>etc.
Iraz6,CostaRica 1963-1965 Waldron(1967)etc.
Fernandina, Galapagos l968 Hendrix (1981>
Usu,Japan 1977-1978 Kadomuraetal.<1978)etc.
St. Helens, USA 1980 Lehre et aL (1983) etc.
superficial erosion from tephra covered slopes iR the viclnity of Mt. St. Helens are
greatly variable in relation to slope gradient, thickRess and texture of tephra, and
lacl< of vegetation and organic debrls. The rate appears to have peaked and declined
during the first rainy season, which was related to such variables as removal of
readily eroded material, exposure of layer of coarse particles and woody material
resistant to erosion, increased infiitration capacity owing to exposure of cearser
deposits and underlying soil. The pattern of a initial hlgh rate of sheet and rill
erosion, followed by a rapid decline, was also reported for other volcanoes.
ColliBs et al. (1983) iR their study on Mt. St. Helens revealed that rapid erosion
occurred on steep, thickly tephra-covered, barren slopes. They stressed an important rele of fallen trees as a erosion-resistant control.
Following the 1943 eruptioRs of Paricutin, standing trees played an important
role for an initiation of rilling by discharging co}lectively the stemflow in the form
of concentrated flow (Segerstrom 1950). In this way, new]y constructed surface,
after a heavy rainfall, was soon cut by rill channe]s, resulting in the occurrence
of small-scale mudflows (Segerstrom 1950, p. 84). Deep gullies cut into, not only
the new tephra, but also the underlying pre-eruption ground surface (Lowdermilk
1947, Segerstrom 1950). "Softening" of landscape through time, for example,
rouRding of gully cllvides, had been evident during the 19-year study period (Segerstrom 1966).
According to Hendrix (1981), no change in gully pattern or size was observed
in a barren area of Isla Fernandina, GalApagos, through successive visits during
1971-1977.
On Iraz" Volcano, removal of new tephra from upper slopes mainly resulted
from the headward and lateral growth of rills and gullies (Waldron 1967). He
estimated that one-third to one-half of the new tephra (ashes) had been removed
from the upper slopes by the end of 1964.
A number of studies of erosion processes following the 1977-1978 eruptions
of Mt. Usu have been undertakeB. Most studies have beeR concerned with debris
and mud fiow occurrences on the outer somma slopes and downvalley (e.g., Kadomura et al. 1978). On the slope of Nishiyama-gawa catchment, research on erosion
processes was conducted by Yamamoto (1984), during 1977-1982, with reference
to ground lowering and to physical properties of the new tephra. He found no
Surface Erosion on Mt. Usu and Other Volcanoes 139
clear relationships between slope gradient and erosion depth. Erosion rate, based
on measurements of erosion pln exposure, was high durlng the period from 1978
to the mid 1979, followed by a subtle change until 1982 (Figure 3); 66 mm average
erosion depth was observed during September 1978 - December 1979, equivaleRt to
54 mmfyr (Yamamoto 1984).
3. Surface erosien on Mt. Usu
1) Ragionalsetting
Mt. Usu is Iocated in the southwestern part of Hokkaido and it faces north
where Toya Caldera Lake which has a 15km diameter is locatecl. The First
Stage eruptions of Mt. Usu which took place August 7-14, 1977 produced thick
tephra (ashes and purnices) (Niida et al. 1980). The Second Stage eruptions oc-
curred intermittently from November 1977 to October 1978, mainly producing
ashes (Niida et al. 1980). The ejecta of the 1977-1978 eruptions amounts to as
much as 9×107 m3 (Katsui et al. 1978 a). The tephra accttmulation, coupled with
notable land deformations, alterecl the erosional regime of the atrio and surrounding
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Map showing isopachs of the newly' lieposited tephra of 19771978 eruptions in the atrio of Mt. Usu (partly modified from
Katsui et al. 1978 a, Niida et aL 1980.)
Solid and dashed lines mean the isopach of the First Stage
(1977) and the Second Stage (1977-1978) tephra, respectively.
Topographic contour as of before the eruptions. Numbers
1-4 denote craters opened during the First Stage eruptions.
Shaded portion is the 4th Crater catchrnent.
Environmental Sclence, Kekkaido Vol. 9, No. 1, 1986
14e
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Figure 2. Geomorphological map of the atrio based on interpretation
of 1: 400e aerial photography taken on 24 September 1981.
1: Cryptodome 2: Knife-edge'ridge-like crest' 3: Rounded crest 4: Col 5: Severely rilled ancl
gullied slope 6: Lightly rilled slope 7: Fault-scarp and flexure including landslide-scarp 8:
Block-covered slope 9: Talus 10:AIIuvial cone and fan consisted chieffy of pumices 11:Fan
and fioor infi11ed by ashes 12: Break in slope 13: Gully (top width }arge: than 6 m) with knick-
point 14:Artificialterraees 15:Landslide 16:Small-scalemudflowIebe 17:Crater 18:Pond
ordepression 19:Road 20:Areadissimulatedbysmol<e Ou:O-Usu(731m> Og:Ogari-yama
(668m) Us:Usu Shinzan (662m) Ku:Ko-Usu (550m) Kb:Kitabyol)ti-yama (633m) 4c: 4th
Crater G:Ginnuma Crater Ro:Ropeway station.
Surface Erosion on Mt. Ustt and Other Volcanoes 141
areas. Rapid surface erosion caused by the agents of rainfall and snow-melting
sculptured the slopes thereafter (e. g., Kadomura et al. 1978, Imagawa 1984, Yamamoto 1984).
In this paper, I discuss aRd evaluate time series of erosion processes in the
atrio where hlgher sediment yield was recorded. I also want to briefiy examine
the effects of erosion control works and vegetation recovery on erosion processes.
Dense forest, composed predominantly of Populus maximoxvic2ii, which covered
the atrio, was completely kilied by the eruptions. The new tephra was more than
lm thick in the atrio; the tephra reached rnore than 4m in thickness in the
vicinity of craters (Fig. 1). In acldition, the artio, except for the northern atrio,
has been out of erosion control works; erosion control works, e. g. terracing, con-
solidation dams, started in 1981 in the northern atrio. The summit atrio, when
compdfEd"WII'i"''th'6' surrouna'iRg areas, is chafacterized by thicker new tephra and
spectacular land deformations. Upheaval and thrust of the U-shaped block, nameiy
the northeastern atyio, resulted in the tilting of the atrio surface by 110. Maximum
upheaval of the new cryptodome (Usu ShiRzan - Ogari-yama rise) reached ca. 180
m. Detailed topographic changes of the atrio duriRg August 1977 - February
1978 are presented in Katsui et al. (1978 b).
Figure 2 dernonstrates the rnain features of geomorphic changes based on an
interpretation of aerial photography taken in September 1981. Following the
upheaval of the new cryptodome, rock fall process formed talus oR the footslopes
of O-Usu, southern {oo￡slope of Ogarl-yama, and western footslope of Usu ShiRzan.
Slopes have been mainly sculptured by sheet wash, rilling and gullying; thus densely
spaced rills and gullies have characterized the atrio. Sediment delivered by such
rilling and gullying formed a}luvlal cones and fans on footslopes and atrio fioor;
lithic fragments as large as O.5-1m in diameter were also transported by gullying
in the northern atrio. Deeply inclsed guiiy network was formed on the U-shaped
block and in a small catchment which drains in Ginnuma Crater. Larger guliies
reached more than 10m wide and more thaR 5m deep. High sediment yield was
caused by such heavy rilling and gullying in the atrio.
The climate of this region belongs to the humid cold temperate zone. The
monthly average temperatures in August and in January are 210C and -40C,
respectively (J.W. A. 1982). Much rain falls in Ju}y, August and September, and
snowfali occurs during the period November - April. The mean annual precipitation durlng the last 29 years has been I030 mm.
2) Ebeosion rate a7zd its relation to slqlt)e g7zidie7it
Sheet wash, rilling and gullying have been the dominant erosion processes in
the atrio; the prevaiiing erosion process has changed from sheet wash and ri]iing
to guliying tltrough time duying 1977-1983 (Chinen and Kadomura in press). Wind
erosion, gelifluction-type soil creep, and small-scale mudflows caused by over-saturation of subsurface layer had a minor effect.
Utilizing erosion pins, 205 in total number, I tried to detect erosion depth in
the atrio during 1982-1984. Sites where the pins were }nsta}led range in gradient
142 Environmental Science, Hokkaido VoL 9, No. 1, 1986
from 40to 330. As aresu}t, ca. 2-4mm of average erosion depth was observed
the period, although the erosion depth was highly variable in space. The
of erosion probably reflected the combined effects of rainsplash, sheetwash,
and gullying. The erosion rate shows the same order of that was obtained
during
amount
rilling
during
the period from the end of 1979 to 1982 by Yamamoto (1984) (Figure 3). Thus
5O-7Ocrn
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.Lashfan
=
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a
w
m
z<
=w
ur
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<J
=
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mm
1977 1978
1979
1980
198Z
1982
zo -20 Deposition
H
co
o
or
o
hi
ta
o
20
40
-------------
Eros±on
----------------
60
80
-------+----i----------------i4
Figure 3.
"---------t--t------t----------------b------------------e
Temporal change in the cumulative mean depth of erosion during
the period from 1978 to 1982 (modified from Yamamoto 1984).
Erosion pins were installed October 1978, on a slope (south-facing,
200-300 in gradient>. All values after the 1978 ash fall have had
4cm of the re-accumulated ash subtracted. The pins used are 65
in total number.
g 2o
MM (4)
:F
11i.li -le "il6' (2i5'(2{i) - ,,t(f{)
o
uat
-20
O 10 20 30
GRADIENT, DEG,
Figure 4･
Relation of erosion depth to slope gradient in inter-rill and inter-
gully areas based on measurements of erosion-pin exposure.
Bars denote 95% confidence range. Values in parentheses above
the bars means number of erosiQn pins. Measurement period:
November 1982-July 1984.
Surface Erosion on Mt. Usu and Other Volcanoes 143
it is indicated that comparativeiy severe slope wash took place soon after the deposition of the new tephra, followed by little erosion until 1984.
Figure 4 indicates the general erosional trend on slopes steeper than 150, while
the depositional trend, though wide-ranged, on lowerslopes gentler than 150. This
relationship obtained from inter-rilJ and inter-gully areas does not entirely parallel
that observed on a slope of Nishiyama-gawa catchment, 1km northwest of the
atrio, by Yamamoto (1984). Although erosion rate was magnified as slope gradient
became steeper ori the slope of Nishiyama-gawa catchment (Yamamoto 1984), the
gentle sites were located only on the crestslope. Consequently, these findings indicate
that the upper slope is subjected to erosion processes while the gentler lowerslope
to deposition processes, and that no clear relationship between erosion depth and
slope gradient is recognizable for slopes steeper than 150.
The 4th Crater catchment (O.21km2), surrounded by the 4th Crater, O-Usu,
Ogari-yama and Usu Shinzan (Fig. 1), represented a high erosion rate at 13.6 cmlyr
when averaged over the first 4-year period (Chinen and Kadomura in press). This
rate can be substituted with the gully erosion rate because gullying contributed
more than 90% by volume to total sediment yield. The extraordinary gully erosion
rate is attributable to faniting, tilting, and base level lowering due to the ￡ormation of the 4th Crater.
In order to examine the relationship between gully density and slope gradient,
a sample area with ca. O.3 km2 was established in the northern atrio. Gully density
in the area was measured on the basis of an interpretation of an aerial photo
taken in September 1981. In addition, a slope map was made by using a topographic map, As a result, higher gully density is recognized on slopes ranging in
gradient from 150 to 300 (Table 2). Field examination indicates that slopes steeper
than 300 are subiected to gravity-governed erosion processes.
'
Table 2. Relation of gully density to slope gradient
in the nortl}ern atrio of Mt. Usu
Gradient, deg.
Area, m2
1
Gu}ly length, m
Gully density, mllOO m2
3500
o
5-10
10-15
15-20
20-30
70400
4600
6.6
99400
7900
8.0
94400
10600
11.2
85100
loeoo
11.8
>30
27400
2700
9.8
5>
o.o
Gradient and area measured on the topographic map (1:2500).
Gully length measured on the aerial photo (1:4000) taken September 1981.
In summary, total slope erosion rate, including both erosion on inter-rill and
inter-gully areas and gully erosion, was generally magnified as slope gradient increased; however, the erosion rate culminated at a s}ope gradient of 150-300.
Environrnental Science, Hokkaldo Vol. 9, No. 1, 1986
144
3) Temporal z,ariation of sediment deliver:y
A sediment budget analysis for the 4th Crater catchment during 1977-1982
revealed that sediment production and yield peaked during 1978-198i and declined
after 1981 (Chinen and Kadomura in press). Although natural erosion processes
have not been observed in the catchment owing to erosion control works after
1982, field examination and measurements of erosion pin-exposure in the atrlo
showed very low eroslon rate after 1982 onwards. Thus it is likely that the erosion
rate ,in the 4th Crater catchment after 1982 was much slower than that during
the 5 post-eruption years, even though the catchment had been prone to natural
conditions.
Active erosion in the 4th Crater catchment terminated in October 1981. However, 17% of the total volume of new tephra was estimated to have been exported
from the catchment whereas 83% remained chiefly on slopes of the catchment by
l982 (Chinen and Kadomura in press>. Cumulative sediment production constantly
iRcreased through time during 1977-1982; nevertheless, the ratio of the voiume
of older tephra to the cumulative sediment production drastically increased during
1978-1982 (Figure 5). This trend is reflected in the ratio of the volume of eroded
new tephra to original total volume of the new tephra, indicating a rapid removal of
the new tephra at the initial stage (Fig. 5). The exponential decline of erosion
rate through time, observed in the 4th Crater catchment, is proportional to the
time series of erosion depth on the slope of Nishiyama-gawa catchment mentioned
before.
M3
(l7)
×lo4
12
Jn
tu
A
>
le
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ut
x
Hn
(16}
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=x
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Figure 5.
'
' ' ''
-
-
.'
--
-t
t-
/"
-x
New tephra
-
t
i .. t-
-t
.t tt
Old
'
" t
" '
- '
'
'
/
t
-
-
tephra
l978 1979
i980 1981
TIME
Time series of sediment production of the new and old tephra in
the 4th Crater catchment on Mt. Usu.
Values in parentheses denote the ratio<%) of the volume of
eroded new tephra to original total volume of the new tephra.
2982
Surface Erosion on Mt. Usu and Other Volcanoes 145
The deceleration of erosion xate over time is probably intrinsic; revegetation
aBd erosion control works have little effect on the rate of superficial erosion of the
new tephra on Mt. Usu. The construction of erosion preventive works might
dece}erate downvalley mass movernent on outer somma slopes (Kadomura et al.
1983a), but field examination and sediment budget analysis in the atrio indicated
that superficial erosion rate had been exponentially decliRing before vegetation
recovery and erosion control works were started in 1982.
The exponential deciine of the erosion ra￡e is probably a result of the forma-
tion of a more permeable, less erodible surface; porous and permeable new pumice
layer and pre-existing organic soll were exposed through rilllng and gullying. Porosity ancl hydraulic conductivity of the surface fine ash layer in Nishiyama-gawa
catchment also increased through time during 1978-1982, resu}ting in less active
occurrence of surface runoff (Yamamoto and Imagawa 1983). This finding supports
the time series of erosion rate described above. Keeping iR line with these trends,
the effective rainfall amount and iRtensity foy sedimene production and yield increased
over time during 1977-1981 (Kadomura et al. 1983b, Chinen and Kadomura in
press>.
4. Comparison of time trend of sediment delivery among newly tepkracovered areas
Swanson et al. (1983) indlcated that rapid decline of erosioR rate was common
to the newly tephya-covered slopes of several active volcanoes such as Mt. St.
Helens, Paricutin, Vulcan, Iraz", and Fernandina. Time-sequential surface erosion
rate observed oR Mt. Usu shows the same trend. Although it is rather diflicult to
compare the decline process of the erosion rate among different areas, because of
various study and environmental conditions involved. Figure 6 demonstrates a more
ecapid decline at Mt. Usu and Mt. St. HeleRs than a￡ Paricutin. Rapid erosion terminated withiR 3 and l year after the latest tephra deposition on Mt. Usu and Mt. St.
i"Ielens, respectively. More iRterestingly, the erosion yate on slopes at Mt. St.
Helens had declined before dense vegetation was established (Swanson et al. 1983).
This finding is comparable to that obtained from the atrio oi Mt. Usu. The
erosion rate in the 4th Crater catchment on Mt. Usu, moreover, had also decliRed
before erosion coRtrol works were done.
Table 3 shows the ratlo of the volurne of removed deposit to that of total
deposit. Only 8% and 17% of the new tephra were removed at Mt. St. Helens
and Mt. Usu, respectively, although the erosion xate had decllned by the end of
each study period;in contrast, nearly 50% of the new tephra was removed at
Paricutin and Irazt't. Deep gully lncisioR brought about a }arge quantity of sediment removal of underlying older tephra in the 4th Crater catchment at Mt. Usu.
However, littie older tephra was mobilized and removed on Mt. St. Helens (Lehre et
al. 1983). which was also the case with Paricutin and Irazt'L Crustal deformation
(faulting aRd tilting) and base level Iowering in the 4th Crater catchment probab}y
contributed to the volumious removal of the older tephra by gullying.
Environmental Science, Hokkaido Vol. 9, No. 1, 1986
146
15
4th Crater catchment,
Mt, Usu
-
IO
at EU
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L EI
M
cx
OM
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ur
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1977I 1978
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1981
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Site Gradient
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(After Swanson et al ., 1983)
Paricutin
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l1":-:dli,hi
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eroslon rate
assuml'ngnoeruption
I nferred
"-----"
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ionrate1940-196
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1940
Figure 6.
l945 l950
]955 1960
(After Segerstromt X961}
Erosion rate as a function of time observed at
Mt. Usu <Chinen and Kadomura in press), Mt,
St. Helens (Swanson et al. 1983), and Paricutin
(Segerstrom 1961>,
Erosion rates on Mts. Usu and St. Helens in
sediment volume per km2 and cm of rainfall.
Surface Erosion on Mt. Usu and Other Volcanoes
Thble 3.
Volcano
147
Removal of new tephra observed at Parlcutin,
Iraza, Vulcan, Mt. St. llelens and Mt. Usu
Deposit Type
Processes
Deposit
Removed
(R9I.g,ent)..
Period of
Record
(yrs>
Paricutin (Mexice)
Airfal,1
Sheet, rill
48
4
Iraz" (Costa Rica)
Airfall
Sheet, rill
30-50
1
Vulcan (New Guinea}
Cindercone
Rill, Gully
Mt. St. Helens <USA)
Airfall
Sheet, Rill
Mt. Usu (Japan)
Airfall
Rill, Gully
5
8
17
2
4
(modifted from Swanson et al. 1983)
In summary, it is indicated that adjustment of slopes to a new erosion-sedimentation regime, caused by a tephra deposition, is rapidly completed. It is also
suggested that erosion control measures will work effectively soon after tlte tephra
deposition. Nevertheless, study methods and site cofiditions are too various to draw
a quantitative conclusion for overall comparative study. For example, sediment
mobilization, sediment yield, and sediment storage generally vary with space and
time. In addition, volcanic activ}ty and lts effect on land surface spatially vary,
resulting in different modes of responses of slope erosion processes to the voicanic
lmpact.
5. Concluding remarks
The summit atrio of Mt. Usu has been subjected to heavy rilling and gullying
since the 1977-1978 eruptions. The xate of sheet wash was magnified as slope
gradient became steeper, although no clear re]ationship between erosion deptlt and
slope gradient was recognized foy slopes steeper than 15e. On the other hand,
higher gully density was recognized on slopes ranging in gradient from 150 to 300
in the northern atrio, Surface erosion rate was variable in space, although slope
erosion rate, as a whole, culminated at a slope of 150-30C.
An extraordinarily high erosion rate (13.6cm!yr) was recorded mainly by
gullying in the 4th Cratey catchment on Mt. Usu when averaged over the 4 posteruption years. However, the active erosion in the catchment termiRated in Otcober 1981, 3 years after the latest ash deposition. Instead of a deceleration of erosion
rate, 83% of the new tephra still remained in the catchment in 1982. The results,
together with field examiRation during 1982-l985, lndicate that surface erosion rate
in the atrio had been deciining before vegetation recovery and eroslon control works
were done.
These findings parallel with that of Swanson et al. (1983), indicatiRg an exponentlal decline of erosion rate over time; this pattern was reported for several
other volcanoes. Consequently, it is suggested that adjustment of slopes and catch-
ments to a new erosion-sedimentation regime is rapidly completed. VoJcanic impacts, study methods and site conditions are, however, too various to draw a quantitative coRciusion for such a comparative study.
Environmental Science, Hokkaido Vol. 9, No. 1, 1986
148
Acknowledgerrtents
I wish to thank Prof. Hiroshi Kadomura, Graduate Schooi of Environmentai
Science, Hokkaido University, for his useful suggestions and constant guidance in
the course of this study. Grateful thanks are due to members of Usu Volcano
Observatory for allowing use of the facilities and field assistance, and to Mr. Hiroshi
Yamamoto, Dr. Toshiaki Imagawa, and Dr. Anne Marguerite Janine Riviere, Graduate School of Environmental Science, Hokkaldo Universjty, for their fruitful
advices and assistance in the field work. I am also grateful to Dr. Frederick J.
Swanson, Pacific Northwest Forest and Range Experiment Station, USDA, for
providing me relevant material and encouragement. Finally I express my appreciation to Miss Deborah Ann Marie Steinhoff, Faculty of Agriculture, Hokkaido University, for her revision of English.
This paper is taken from the Ph. D. thesis: "Post-Eruption Erosion Processes
and Sediment Budget of a Small Catchment on Mt. Usu, Japan" submitted to
Graduate School of Environmental Science, Hokkaido University in March 1986.
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(j):in Japanese
(JE): in Japanese wlth English summary or abstract
(Received 81 Addrch X986)