Samon (ripple marks) (砂紋)
Samon (ripple marks) are regular wave-like undulations formed by water and wind currents. Although artificial undulations are also sometimes called samon, the samon usually refer to natural ones. The samon that have been fossilized are called renkon (fossile ripple marks). The word renkon originally included the meaning of samon, but it is used only for fossile ripple marks today. Therefore, the word renkon is sometimes used in place of samon in the academic field.
Samon on the seabed
Samon on the seafloor are also called namiato (wave ripples), sunasazanami (sand ripples), and saren (sand ripples). Low surface waves and limited water depth make only a subtle pattern and do not move ridges. The ridges start moving, however, when different currents come in and waves lapping against the rocky shore cause mass transfer. Wave shape is asymmetrical in shallow seawater, with a gentle and long slope on the seaward side and a steep and short slope on the shoreward side. Waves coming up and down above a certain speed are said to form the whirlpool behind the ridges, thus playing an important role in developing the samon. Seabed photography has recently revealed the presence of samon even in the deep sea at a depth of 1,000 m or more. Studies have been conducted to estimate the speed of water current based on the samon.
Samon on the ground surface
Samon at the surface of the ground is also called fumon (wind-wrought pattern), and usually found in deserts and sand dunes. The size of a sand grain is about 0.7 mm in the seacoast area, and becomes finer to 0.3 mm toward the inland area. In either area, sand starts moving with the wind at a velocity of three meters per second or greater. Height, width, and cycles of the samon depend on the strength and direction of wind, grain size of sand, and other factors. Samon is also found in tidelands and snow-covered areas.
Like samon in the dry landscape garden, most of them are formed for artistic purposes. They are also called hokime (broom marks), and have several types of patterns such as igeta mon (parallel cross pattern), ajiro mon (wickerwork pattern), seigaiha mon (blue ocean wave pattern), uzumaki mon (spiral pattern), and kyokusen mon (curvilinear pattern).