Abstract
X-ray stereoradiographical method and phytolith analysis were applied to accumulated tephra and granite profiles in northern Japan, in order to investigate the spread-depth, origin and significance of soil macropores whose form resembles a root system. At the tephra section of Hachinohe Tengudai, soil macropore similar to a root system was extensively found in all stratigraphic units underlying sands which are marine in origin. This type of soil macropore was also predominant, and extended to the deep layers, in tephra sections in the northeastern and southeastern areas of the Iwate Volcano. However, the soil macropore was not present in underlying volcanic debris flow deposits. At the granite profile, the soil macropore was limited to 2m in depth from the top of the granite. In addition, the opal phytolith could be identified in almost all the soil layers where the soil macropore was recognized. The results obtained here supports that the soil pore was derived from subterranean parts of plants, and leads to the inference that volcanic ash soils were formed by successive deposits of airborne volcanic ash and soil formation.
