Distribution and formation of tephric-loess dunes in northern and eastern Japan

We studied the genesis of the Esashi, Shiriyazaki, Isozaki-Ajigaura, and Takamagahara dunes and associated blowouts. These dunes are located at the top of coastal cliffs, and they are composed of marine sediments (sand and gravel), which are covered with layers of Japanese loam. We examined pH(NaF) and pH(H2O) of samples from all dunes, and the grain size distributions, total carbon contents, humic properties, and colors (CIE-L*a*b*) of samples from the Esashi and Shiriyazaki dunes. In most samples, pH(NaF), an indicator of active aluminum, was ≥9.5. The grain size distribution in the Esashi and Shiriyazaki dunes was bimodal (with sand and silt-clay peaks), and their color, after removal of organic matter with H2O2, was similar to that of the loam. These findings show that the dunes are composed of marine sediments and loam eroded and reworked by the prevailing winds. Japanese loam is regarded as a kind of tephric loess. Thus, these dunes can be referred the tephric-loess dunes. The physicochemical properties of these tephric-loess dunes are similar to those of Kuroboku soil in that humus accumulation has been enhanced by the presence of active aluminum derived from the admixture of tephric materials.