On the Cause of the Subsurface Cold Air Circulation at Debris Accumulated Slopes

Abstract

Even in summer, the cold air, lower than average annual temperature by 10°C, is exhausted from underground through spaces within debris at the sites called “Fuketsu”.At the Fuketsu, the subsurface air circulation occurs. In winter, the air is inhaled from lower part of a slope, and exhausted at upper part of a slope. During this kind of the air circulation, the debris is frozen to even 50 m depth. In summer, the air circulation is reversed. The inhaled air is cooled to almost annual average temperature before arriving frozen debris. Due to these processes, debris remaines to be frozen untill autumn and this is the reason why the exhausted air in summer is abnormally cold.The common ground condition of the “Fuketsu” is studied by relative comparison of 20 samples, and the result is as follows.1) Snow covered districts in winter.2) North facing slopes.3) Abundantly debris accumulated slopes in front of steep scarps, gigantic landslide area is favorable to this condition.