ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

show areas of potential sediment sources for debris flows
or landslides. To verify this hypothesis, a GIS-based geomorphic
mapping from air-photographs and in the field is
used to map the existing debris flow and landslides and to
overlay the results with the reconstructed landsurface as it
was covered by the Egesen-Stadial (Younger Dryas) glacier
in Schoenferwall valley.
KYO]I SAITO
Formation and evolution of alluvial fans in tropical- and
temperate-humid regions
Faculty of Education, Saitama University,
Shimo-okubo, 338 Urawa, Japan
The effects of climatic conditions upon distribution and sizes
of alluvial fans are determined by statistical analyses in
temperate humid Japan and Taiwan, and the tropical humid
Philippines. Data were collected by use of topographic
maps. The results are obtained as follows:
1. Distribution of alluvial fans
The alluvial fans with over 2 km, Qin area are 490 in Japan,
71 in Taiwan, and 129 in the Philippines. Rivers whose
drainage basins are larger than 100 km, Qexist 474 in
Japan, 50 in Taiwan, and 266 in the Philippines. The ratios
of such rivers with fans are 25.90/0 in Japan, 58.00/0 in
Taiwan, and 12.0% in the Philippines.
2. Relationships between development of mountains and
distribution of fans. The development stages of mountains
were estimated, based on variations of relief. Among rivers
with drainage basins more than 100 km, Q ratios of rivers
with fans are 0.0 % in the earliest and early stage that is low
relief energy, 5.7 % in younger-middle one, 22.8 % in older-middle
one, and 47.6 % in later one. Relief ratio is defined
as a divided value of a relative height between an altitude
of a peak and that of a valley mouth by a drainage-basin
length. Relief ratios increase with the advance of the
development stage of mountains. Drainage basins with large
relief ratios have steeper river-bed gradients, and are
apt to make fans to carry larger gravel around valley
mouths. The high percentage 58.0 % of rivers with fans in
Taiwan strongly owe to large relief ratio.
3. Relationships between development of mountains and
evolution of fans. Alluvial fan areas increase with the advance
of the development stage of mountains, specially
from younger-middle to older-middle, and from oldermiddle
to later. Besides, larger fans have been built in the
larger drainage basins in the advance of stage. Mountains
in the older-middle stage with increases in denudation rates
bring existences of fans and larger fans.
4. Relationships between climatic conditions and distribution
of fans. Japan, Taiwan and the Philippines have 470
rivers with drainage basins larger than 200 km', The effects
of five factors upon the existence of fans were calculated
338
by discriminant functions. The five factors are drainage basin
area, intermontane basin area, relief ratio, climatic conditions,
and sedimentary environments. Based on the great
generalized weight and the high frequency in the category
of climatic conditions, it is concluded that the dominating
factor for the distribution of alluvial fans is the climatic
conditions. Sedimentary environments and relief ratios are
also important factors. Climatic conditions were estimated
to exert the greatest influence on the existence and the distribution.
Ratios of rivers with fans to ones whose drainage basin
areas and relief ratios are similar are 12.9% in Hokkaido,
or northern Japan, 47.5 % in the coast of Japan Sea of Central
Japan, 50.0 % in the Pacific side of Central Japan,
13.1 % in West Japan, 66.70/0 in Taiwan, 21.70/0 in the West
Philippines, and 3.8 % in the East Philippines. Debris
supply is rich in Taiwan because of higher precipitation
and larger discharge, as compared with Japan. The debris
product was abundant in Glacial Age in Central Japan to
prevail the periglacial area. Hence, Central Japan had good
conditions for fans in those days. On the contrary, debris
supply was poor owing to the less precipitation even in
Glacial age in Hokkaido, and owing to narrower periglacial
area in West Japan. The reasons have made fewer fans
in these two regions. The fact that the West Philippines
has more suitable conditions than those in Hokkaido and
West Japan indicates that the climatic conditions with dry
and wet seasons are advantage for fans. The most unfavorable
conditions in the East Philippines can be explained
in terms of poor coarse-material production under tropical
climate and perennial rainfall.
5. Relationships between climatic conditions and evolution
of fans. On the basis of equations between drainage
basin areas and fan areas, fan areas in the Philippines are
110 to 1200/0 and those in Taiwan are 120 to 1600/0 as large
as those in Japan. The fans in the tropical Philippines
are small due to poor production of coarse materials as
compared with those in Taiwan, but are large owing to
abundant precipitation and high discharge in comparison
with Japan.
NEIL E. SALISBURY
Seasonal and episodic erosion and mass-wasting in
Dakota badlands
Department of Geography, University of Oklahoma,
Norman OK 73019, U.S.A.
Denudation of the South Dakota badlands involves surface
fluvial detachment and transport (erosion), mass-wasting
(including piping), solution, and removal of sediments by
eolian processes. None of these processes are continuous,
either spatially or temporally, within the study area. Rates
of erosion and sedimentation were measured on badland
slopes and pediments for a period of more than ten years.