[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

1. Introduction Decrease of snow cover has been recently pointed out all over the world, and IPCC (1992) said snow cover area and average temperature in Northern Hemisphere have strong negative correlation. However, Robinson and Frei (1995) compared Northern Hemisphere snow cover area with those of divided 21 areas on Northern Hemisphere continents, and said there are a number of regions whose snow cover area has negative or no correlation as well as strong positive correlation with Northern Hemisphere snow cover area. Thus, this research analyzed regional differences in variations of Northern Hemisphere snow cover from 1966 to 2001 by using satellite data to aim to make the relationship clear between snow cover variations on the earth and climate change such as global warming. 2. Data and Methodology This research used 2 degree grid monthly snow cover frequency data from October, 1966 to June, 2001 processed from 25 equal area grid monthly snow cover data of Northern Hemisphere EASE-Grid Weekly Snow Cover and Sea Ice Extent Version 2 produced by National Snow and Ice Data Center. It used satellite data because ground observation points are primarily clustered near mid-latitude population centers and not representative of the vast rural areas. At first, this research computed monthly snow cover frequency and the standard deviation every year. Then, it does the cluster analysis to the monthly snow cover frequency. It also does the empirical orthographic function to the results of the cluster analysis from October to April, in which several large clusters explain snow cover areas, to analyze regional differences in snow cover. Finally, it analyzes latitudinally monthly snow cover frequency and the standard deviation in Northern Hemisphere and 7 longitude belts. 3. Results 1) Robinson et al. (1993) said reduction of hemispheric snow cover is obvious in spring. However, snow cover frequency shows strong decrease trend in summer such as July and August and no secular variations in spring. 2) Results of the cluster analysis about snow cover variations are classified into 2 periods. One large cluster occupied almost all of snow cover areas in May to September, and several large clusters explain snow cover areas in October to April (Fig. 1). 3) There are both months which have snow cover variation area and no variation area regardless of season, and many snow cover areas, particularly these in the Himalayas and Tibet, show decrease trend in the former months. On the other hand, western North America shows increase trend in a number of months (Fig. 2). 4) Snow cover variations in the Himalayas show contrary trend compared with these in western North America in October to April. Snow cover variations in the Himalayas especially shows contrary trend compared with those in almost all of snow cover areas in December to April (Fig. 3). Thus, snow cover variations in the Himalayas are inharmonious with those in Northern Hemisphere. 5) When monthly average standard deviation of Northern Hemisphere is latitudinally compared with those of 7 longitude belts, seasonal variations in Northern Hemisphere and eastern Eurasia and North America were resemble. Also, seasonal variations in other latitude belts and Northern Hemisphere are not similar. Thus, seasonal variations in Northern Hemisphere show particularly feature of eastern Eurasia and North America.

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

IntroductionRockfall is one of the major geomorphic processes acting on steep mountain slopes. The role of rockfall in the total denudation of mountain slopes is significant in cold areas where vegetation is sparse and frost action is active. Several weathering processes may contribute to rockfall generation in cold mountains. Many studies suggest that rockfall originates from diurnal and seasonal freezing and thawing; some explain deglaciation as a major cause, while some highlights on the thermal stress. Despite such numerous studies, studies focusing on the seasonal difference of rockfall in different slope aspects and altitudes are sparse. This study aims at: describing the rockfall activity in alpine cliff in different slope aspects in relation to the rock temperature and frost wedging in the upper Kanchenjunga valley, northeast corner of Nepal.Research MethodologyRockfalls were observed directly in the field in the east-, west-, north- and south-facing slopes; the exposed bedrock area was calculated from the photographs taken at different seasons. Rock temperatures at 2 cm depth, on the free face at different aspects and altitudes (ranging from 4947 m to 6005 m), were monitored using automatic data loggers. The air temperatures were measured at the altitudes of 4755 m and 6012 m, and precipitation were measured at the altitudes of 4648 m and 5235 m. Freeze-thaw cycles at different altitudes were computed to evaluate the effect of freeze-thaw in rockfall activity. Effect of frost wedging was derived using crack extensometer. Rock samplings were made at the base of each rockfall-counting sites to evaluate the affected geology and, at last, a rockwall retreat rate was calculated using the rockfall number and the average volume of the rocks sampled below the rockwalls at four aspects.Results Results based on rockfall/km2 show distinct difference in rockfall amount in terms of- season, aspect and the time of the day. In the presence of moisture in rock, which varies with season, the magnitude of rockfall activity significantly varies with the change in the ratio of snow-free area to snow-covered area. Different slope aspects show the seasonal difference in temperature and freeze-thaw activities, which are supposed to be the major factors controlling rockfall activity. Monitoring of frost wedging shows the seasonal expansion and contraction of the rocks, i.e., expansion in winter and contraction in dry and rainy seasons. Rockwall retreat rates show significant variations in the different aspects. ConclusionsThe rockfall activity in the Kanchenjunga valley started from the middle of March and reaches maximum during rainy season. This seasonal change in the amount indicates that the activity depends mainly on the seasonal difference of thermal and hydrological regime in the bedrock. Maximum rockfall occurs in the east-facing slope and then in south-, west- and north-facing slopes, respectively. From March to May the maximum rockwall retreat rate was found in the east-facing slope followed by north-, west-, and south-facing slope.

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

This study deals with the geomorphological process of the Borobudur plain in Indonesia, based on whether the eruption of Mt. Merapi in 1016 ruined C. Borobudur directly. We can see that the Borobudur plain has two characteristics types of the geographical features, to make the geomorphological landform classification map. The eastern part of this area is the fluviovolcanic footslope of Mt. Merapi, while the western part is the alluvial plain of the Progo river. So it is certain that mudflood (Lahar and Banjir) from Mt. Merapi has not reach at C. Borobudur. That is, the eruption of Mt. Merapi in 1016 did not ruined C. Borobudur directly.

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract

[in Japanese]

View full abstract