The present report concerns the results of abrasion test of gravels in a Los Angeles type tumbling barrel. The purpose of this study is to test the existence of a deficiency zone in the grain size distribution of deposits observed in the field by Yatsu (1954, 1955), Sundborg (1956), Pettijohn (1957), and Moriyama (1978). A 20-kg gravel sample was taken from riverbed deposits of the Iruma, which forms an alluvial fan in the western part of the Kanto Plain. Sampled gravels were composed of subangular metamorphic sandstone, shale and chert. The abrasion test was stopped periodically and the sample was sieved for particles coarser than 4 φ in order to determine the size distribution. Products of the particles finer than 4 φ were analyzed by the hydrometer method. Roundness of gravels coarser than -1.25 φ was measured using Krumbein's chart. The main results are as follows: A deficiency in particles 0 to 2 φ in diameter appeared clearly, and this “valley” in the size distribution curve became deeper and wider as the abrasion test went on. It seems that particles of 0 to 2 φ and the neighbouring diameters are easily attrited and difficult to produce from progressively rounding gravels. Finally, grain size distribution showed a bimodal curve. The position of the coarse mode around -4 φ hardly shifted during the test. It seems that the coarse gravels were gradually worn down and rounded, producing finer particles of fine sand, silt and clay; they were seldom broken into two particles, rarely producing gravel and coarse sand.
In mid-temperate latitudes, elongate and small ridges are commonly developed on the shore of many inland lakes which are frozen over in winter. Such minor features are formed by ice action and called “ice rampart”. Sediments in the shallow water region are transported onshore and heaped up on the lacustrine shore by the shoreward movement and landing of ice plates to form ice ramparts. During the summer survey of 1982, the author noticed the existence of ice ramparts located on the shore of Lake Kussharo in eastern Hokkaido, Japan (Fig. 1). The purpose of this paper is to describe the distribution, shape, size and internal structure of ice ramparts on the shore of this lake and to discuss the cause of lake ice movement. Two study sites were chosen on the east shore of this lake where a number of ice ramparts were well developed. Using a level, levelling rod and a tape, lacustrine shore topography was surveyed along many traverses in each study site. Observations of the internal structure of ice ramparts were also made. During the period from freeze-up to break-up, observations on the changes in the shore topography of both study sites were made at regular intervals. The distribution of ice ramparts on the whole shore of this lake was investigated. Examination of the survey results indicated that the ice ramparts were developed on the shore in a single or a few rows and were composed of sand and gravel (Figs. 2 and 3). These ice ramparts were normally formed on the whole shore except the location of steeply inclined slope below the water level (Fig. 4). According to many previous studies on the formation of ice ramparts, there are two main causes for the shoreward movement and landing of ice plates: (1) the thermal expansion and contraction of lake ice due to variations in air temperatures; and (2) wind action upon separated ice plates in the spring thaw. The meteorological data at Teshikaga indicate that during the winter season, large and relatively rapid alternations of air temperature below the freezing point frequently occur in the study area, and the snow cover is ordinarily thin in the study area (Figs. 5 and 6). Such intermediate climatic conditions in the study area are favorable for the thermal expansion and contraction of lake ice. Observations on the shoreward movement and landing of ice plates indicated that the ice ramparts on the shore of this lake were mainly formed by the movement of lake ice, which is caused by the thermal expansion and contraction of the ice as described above (Figs. 7 and 8).