Tafoni are cave-like structures distributed on a rock surface, and they are interpreted to be formed as a result of salt weathering. We studied the distribution of tafoni on the coasts of the Noto Peninsula, and identified many of them on sea cliffs composed of Miocene volcanic rocks in the western, northwestern, and northern coasts. We created red relief image maps from DEM (Digital Elevation Model) data obtained from a laser scan survey in the western coast, where these features are abundant. The maps revealed detailed topographic features of the sea cliffs and tafoni. We also studied the relationship between rock strength and tafoni distribution through Schmidt rebound tests. Tafoni are distributed widely over these cliffs, and their distribution and shapes are constrained by bedding planes and cracks. Most of them are range in diameter from dozens of centimeters to several meters. Single tafoni display elliptical, rectangular, and spindle shapes, whereas combined tafoni display gourd-like and amoebic shapes. They tend to be elongated sideways, increasing their size by growth along lateral structures or by connecting with each other. Schmidt rebound tests show that the strength of inner parts of the tafoni is generally greater than that of the other parts, although the surfaces of inner parts are weakened by salt weathering.

The authors investigated the relationship between distributions of faults and deep seated landslides. Therefore, it was found that deep seated landslides occur at the areas where the density of faults is low. When the number of faults is less, the scale of faults is bigger. Further, fracture surfaces distribution of inland earthquakes caused by active faults indicate the following. When the length of faults is longer, the fracture surface exists in the deeper and the deep weathered zone is formed more easily. When the density of faults is lower, the fracture surface exists in the deeper and the deep weathered zone is formed more easily. Therefore, it is considered that the risk of deep seated landslides increases.

Characteristics of salt weathering and wave erosion and their effects on the wavecut bench in Iwami-tatamigaura are discussed through geomorphological investigations. The wave-cut bench is part of the Middle Miocene Tougane Formation and is made up of fine- to medium-grained sandstone. The sandstone layer includes nodules which are described as an oblate ellipsoid with height, major axis and minor axis of around 30, 50 and 40 cm, respectively. The nodules are thought to be the sandstone concreted by the precipitation of calcium component from fossils of marine organisms. The concretions are now exposed on the surface of the wave-cut bench. Tafoni, which are formed by salt weathering of rock, develop on the surface of the concretions. The size of concretions and the depths of tafoni were measured to evaluate the effects of salt weathering and wave erosion on concretions around the wave-cut bench. The measurements revealed that the effects of salt weathering and wave erosion on the wave-cut bench vary regionally although the appearance of the entire wavecut bench is homogeneous. The aspect ratio, which is defined as the ratio between the minor axis of the concretions and the major axis, reflects the effect of wave erosion on the topography of concretions. Mean ratio is the smallest (0.79) in a part of the bench where waves with the largest energy approach, and is the largest (0.90) in the leastaffected part. Direction of the major axis of the concretions corresponds well to that of the direction of wave propagation from the sea. Salt weathering occurs everywhere around the bench if the surface of the concretions dries. However, the surface with tafoni is easily removed or exfoliated by waves in a region where the effect of wave erosion is large. Therefore, the largest mean depth of tafoni (ca. 2.0 cm) is found in areas where wave energy is low, and the smallest tafoni (ca. 1.5 cm) are found in areas with the highest wave energy. This suggests that both wave erosion and salt weathering control the topography of the concretions. The effect of salt weathering is dominant if the effect of wave erosion is small. The processes may affect not only the concretion topography but also in the general development of the wave-cut bench.

Typhoon 26 attacked Izu-Oshima Island on 16 October, 2013 and caused many shallow landslides. After this storm event, to understand the effect of the infiltration process on the shallow landslides, we investigated the physical properties of slope materials and subsequently observed the responses of subsurface water to later rainstorms at a shallow landslide site. The alternation of tephra and loess layers within a depth of 2.5 m overlays the basaltic spatter and lava around the investigated shallow landslide site. The slip surface of the shallow landslide was found in a tephra layer (the so-called Y1.0 which was deposited in 1777-1780). Undisturbed slope materials were collected at a head scarp of the shallow landslide. The particle diameter of the Y1.0 tephra layer corresponded mostly with that of sand (70%) and had a hydraulic conductivity of approximately 10^－3 cm/s with a high gravitational drainage capacity (5-10%). The particle diameter of the loess layer within a depth of 115 cm corresponded mostly with that of clay (50%) and had a hydraulic conductivity of 10^－5 cm/s and a high water retention capacity (50-55% within the field capacity). During a rainfall event with a total rainfall of more than 150 mm, a positive pressure head was observed both in the loess layer with the low hydraulic conductivity and in the bottom of the Y1.0 tephra layer above the loess layer. Statistical analysis based on the records of subsurface-water responses in rainfall events showed a linear relationship between the maximum pore water pressure and an antecedent precipitation index with a half-life of 4 hours.