ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

Observation of debris flows and sediment discharge were
executed at three volcanoes: Mount Unzen, Mount Yakedake
in Japan and Mount Merapi in Indonesia where the
lava composition of volcano is similar and the main process
of sediment discharge is the occurrence of boulderly type
debris flow, in order to clarify the effectiveness of eruption
to sediment discharge from volcanic drainage slope. We
found that the rate of sediment discharge and the frequency
of debris flow were different from each other, being
affected by the time after eruption. Geomorphological factors
and hydrological factors are summarized in Table 1.
Comparing the specific amount of sediment transport, a
general relationship is expected in which specific amount
of sediment transport would decrease exponentially with
the time after the last eruption of the volcano. Consideration
of the result in Table and erosion rates in other studies
(Swanson & alii, 1983; Chinen, 1986; Collins et al.,
1986;·Shimokawa & alii, 1987) gives a general expectation,
where the erosion rate of volcanic slope, initially very high
immediately after the eruption, decreases from the magnitude
10 1 - IO'rnm/yr, to l O'mm/yr in less than several years,
and finally approaches IO'rnm/yr in less than a few decades.
This fact recommends us to make response against potential
debris-flow hazard as fast as possible just with the
beginning of a volcanic eruption.
TABLE 1 - Condition of sediment discharge at three volcanic torrents
from 1991 through 1994
Drainage area for the observation site (km')
Mean of annual precipitation (mm)
Year of the last activity of effective eruption
Time after the last effective eruption (years)
Permeability of the slope (em/sec)
Frequency of debris flow (Zyear)
Total volume of sediment discharge 004ml/year)
Erosion rate (rnm/year)
Mt. Yakedake Mt. Merapi Mt. Unzen
Kamikamihori G. Bebeng R Mizunashi R.
0.83
2,600
1962
32
10-210-> 0.7
0.5
6
5
4,500
1984
10
10-210-1 5
20
40
LAFOS SZABO 1, T. SUMNYI K. 2 & ADAM KERTESZ 3
12
3,100
1990-1995
o 10-'10- 5
23
210
175
The effect of crop pattern change on erosion processes of
hillslopes in Hungary
1 University of Agricultural Sciences, H-2103 Godol1o,
p.o. box 303. Hungary
2 University of Horticulture and Food Industry, Villanyitit 29-43,
H-1114 Budapest, Hungary
3 Geographical Research Institute of Hungarian Academy of Sciences,
p.o. box 64, H-1388 Budapest, Hungary
2.3 million hectares are eroded to different extent in Hungary
representing ca. 25 % of the surface of the country.
Mountainous areas underwent a more serious erosion. The
erosion risk is, however, greater in the hilly countries because
of the agricultural activity there. The hills are mostly
covered by brown forest soils developed on loess, loess-
368
like sediments and sand. The area of the original forest has
been continuously diminishing as a consequence of agricultural
activity leading to increasing erosion accompanied
by the degradation of humus manifested in the thickness
of the humus layer, in the quality of humus and in humus
content. As it is well known the best way of combatting
these phenomena is reforestration as a natural biological
tool. Reforestration will also reduce the accumulation of
toxic materials.
The Godollo-Monor hilly country was chosen as a test area
to study the above phenomena and to show the possibilities
of concervation and improvement. Our research was
supported by the «Foundation for soil concervation». This
support is acknowledged here.
ZOLTAN SZALAI
Human impacts on a floodplain ecosystem:
the case of Haros Island, Budapest
Geographical Research Institute, Hungarian Academy of Sciences
p.o. box 64,11-1338 Budapest, Hungary
The Haros Island is a peninsula in the Danube section at
Budapest, near Budateteny, Since the 1950's it has been
closed to the public because of the military barracks established
there. Thus, in the recent past direct human influence
was kept at a moderate level but the impacts of the
nearby industrial and previous forestry activities are still
felt today. The question arises whether there is any relationship
between the microrelief and the soil/vegetation
pattern and how it is manifested in the species composition
of indicator plants under natural and disturbed conditions.
In the Haros Island three subtypes of alluvial soil occur. In
the high-floodplain oxbows calcareous humic alluvial soil
and calcareous humic alluvial soil with double humic horizon
arc found. One metre higher, on the high floodplain
surface there is meadow alluvial soil, indicating transition
from alluvial soils to meadow soils.
The vegetation of the herbaceous and shrub levels displays
similarities to the soil pattern. This is especially clear in the
springtime aspect (in places not affectal by forestry in the
past). In the higher areas youthful deciduous forest prevails
as far as species composition is concerned. In the high
floodplain oxbows plants typical ot high or low floodplain
and of weed associations are present. Affected by forestry
species of willow and weed associations advanced to the
higher areas. In the summer aspect the variation between
the different areas remains but reduces compared to the
early spring aspect. This can be explained by the decrease
in the number of species. The share of the indicator species
showing degradation is higher in the high floodplain
oxbows than on the high floodplain surface as far as cover
and species composition are concerned during the whole
vegetation period.