FORMATION PROCESSES OF TAFONI DUE TO SALT WEATHERING

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Tafoni are small hollow, which rock materials composing of the tafoni are removed resulting from weathering. There are observed in arid and coastal regions. It has been thought that the tafoni originate from the wind erosion and the wave action. In this study, formation processes, conditions, and rates of the tafoni are analyzed at north of Matsusima bay (Oku-Matsushima), southwest of Boso Peninsula, and south of Kii Peninsula, based on the annual observation using the data logger.Analyses mainly are carried out for Oku-matsushima, 1) sizes (length, width, and depth) and grain size for the rock meal of the tafoni, 2) production volume of the rock meal, 3) field monitoring of conditions for tafoni formation (rock temperature, water contents of slope, temperature, humidity, insolation, wind direction, etc), 4) rock properties (physical properties, mineral components, dissolution properties).The shape of the tafoni similar to half of the spheroid, and sizes of the tafoni is decrease with distance from beach lines and altitudes. The rock meal mainly product in winter seasons. It was considered that the growth rates of the tafoni are 10ィイD12ィエD1〜10ィイD13ィエD1 year, based on the production volume of the rock meal. Some salt minerals (Halite and Bloedite) are observed in winter season at the inner wall of tafoni showing the dry conditions. As the tafoni develop at the coastal region, these salt minerals are crystallized by adhere of sea splash including ions of NaィイD1+ィエD1, MgィイD12+ィエD1, ClィイD1-ィエD1, and SOィイD24ィエD2ィイD12-ィエD1.