Large scale frost-fissure polygons are spread at Hokkai-daira plateau, Daisetu volcanic massif, central Hokkaido. In order to ascertain actual frost cracking in the frost-fissures, the authors measured seasonal changes of the width of frost-fissures, ground temperatures and snow cover from September 1984 to September 1985. Main results obtained are as follows; 1. As snow tends to be almost completely blown away by strong wind, snow cover affects the ground temperature only slightly. 2. The annual ground temperature alternations at 1m-depth ranged at least from +0.0_??_1.2°C to -13.6_??_14.8°C, suggesting the existence of permafrost underneath. 3. Horizontal distance changes between the two stakes across frost-fissures from fall 1984 to winter 1985 indicate that the width of frost-fissures increased in winter by 1cm. And frost cracks, about 1cm wide at the surface, occurred by mid-Februauy on the surface of snow and ice which covered or filled in frost-fissures. Therefore, frost-fissure polygons at this site are most likely active. 4. Considering the present climatic conditions of this area, the cross sections of frostfissure and above-mentioned results, we suggest that the frost-fissure polygons at this area are soil-wedge polygons.
Sand ripples formed by waves on a sandy shallow sea bottom are classified into regular parallel ripples, nearshore irregular parallel ripples, diagonal ripples and lunate ripples. They are arranged in this order from offshore to onshore regions. The difference of sand movement mode would probably exist among these ripple types. The purpose of this study is to describe the difference of sand movement on each ripple type in connection with the ripple geometries and the characteristics of wave-induced oscillatory water flows near the sea bottom. Field investigations were performed on a shallow offshore zone at Tatado Beach, Izu Peninsula, Japan (Fig. 1), in July and October 1979. The mode of sand movement was first observed, and then the direction of net sand drift was investigated by use of fluorescent sand composed of four ranges of grain size (i.e., -1-0φ, 0-1φ, 1-2φ, and 2-3φ) with different colors. Wave-induced oscillatory flows were measured using an ultrasonic current meter installed at a height of 36cm above the sea bottom. Three types of sand movement were observed on a rippled bed: Type I: sand movement in traction mode, Type II: sand movement closely relating to vortices formed in ripple troughs, and Type III: sand movement in the form of suspended sand cloud which entirely covers the sea bed. Type I is suitable for coarser sand transport, while Type II sand movement is for finer sand. Type III contributes to the transport of material which can be suspended by the oscillatory water flows. The result of measurement of oscillatory water flows showd that onshore velocity was stronger than offshore velocity on any type of ripples. In such a velocity field, Type I and III give rise to a net onshore sand drift, while Type II produces an offshore net drift due to the existence of vortices. A prevailing sand movement mode is different on ripples with different types. Consequently, the direction of net sand drift for various size of sand grains is different for each type of ripples (Table 2).
The effective cumulative soil temperature in relation to the potential germination of P. densiflora seed was investigated and the results are presented in this study. The laboratory experiment was carried out in the chamber at 5°C, 8°C, 10°C, 15°C, 20°C, 25°C, 30°C and 35°C under both light (3, 000 lx) and dark conditions. The daily germination rate was observed. Initial effective cumulative soil temperature was fixed at 5°C, because the seeds did not germinate at 5°C. From the laboratory experiment at 8°C, 10°C and 15°C, it became obvi ous that, from 75°C•day to 200°C•day (germination period) the P. densiflora seed germinates. Five-day periods of effective cumulative soil temperature, 75°C•day are estimated from the data of the geographical distribution of soil temperature, which is considered to be the beginning of the P. densiflora seed germination in various places. As a consequence, the following facts have been observed (Fig. 4(a)): The first five-day period line of May passes through the southern area of Hokkaido. The first five-day period line of April passes through the Kanto district, Nagano, Gifu, the southern area of Fukui, Tottori Prefectures and Oki Island. That line of March passes through Izu Peninsula, Shizuoka Prefecture, Kui Peninsula, Seto Inland Sea and the central area of Kyushu. The line of February passes through the southern edge of Shikoku and the southern area of Kyushu. Next, the five-day periods of the effective cumulative soil temperature of the ending of the P. densiflora seed germination, that is 200°C•day, are worked out and the results are as follows (Fig. 4(b)): The first five-day period line of June passes through the northeast of Hokkaido. That of May passes through Miyagi, the central area of Yamagata Prefectures and the mountainous area of Jyo-shinetsu. That line of April passes through the south of Honshu, Seto Inland Sea and the central area of Kyushu. The line of March passes through the southern edge of Kui Peninsula, Shikoku and Kyushu. Germination period of P. densiflora seed, that is the period from 75°C•day to 200°C•day, is shorter in northeast Japan compared with that of southwest Japan (Fig. 4(c)). Therefore, there are two deficits in northeast Japan, those are, first the germination time is later and the second the germination period is shorter than in southwest Japan.