Background The 2018 Hokkaido Eastern Iburi Earthquake triggered serious geodisasters, resulting in several landslides in volcanic soils depending on their geological features. However, there is limited investigation from the geotechnical viewpoint. Considering various volcanic soils are deposited in Hokkaido, Japan, it is crucial to ensure disaster prevention of infrastructures related to volcanic soils. Methods To investigate the degree of weathering, water-retention characteristics, and mechanical properties of the volcanic soil, which triggered landslides during the earthquake, called Ta-d, this study conducted laboratory tests including X-ray diffraction, water-retention, and direct shear tests under various conditions related to a type of Ta-d, saturation condition, and stress dependency. Moreover, the pore pressure of the location where the landslides occurred was monitored for over a year to investigate the effect of rainfall on the previous day of the earthquake on the landslides. Results The laboratory and field monitoring test results showed that Ta-d can be categorized into three types depending on the color and physical properties, which have different degrees of weathering and shear strengths. The water content of Ta-d was high (>100 %) throughout the year, whereas it exhibited a seasonal change due to snowfall, which covered the ground surface. Furthermore, fluctuations caused by the seasonal changes are more significant than those caused by rainfall, which indicated that the rainfall on the previous day of the earthquake was not a primary factor in the occurrence of the landslides Conclusions This study reveals the geotechnical properties of Ta-d, which has not been well known, as comparing with those of other Hokkaido volcanic soils, and gives insights into the significant factors that can potentially cause the earthquake-induced geodisasters.

Short-term N2O emission occurs in relation to snowmelt within seasonally frozen soil. To understand the effects of changing winter climates on the N2O flux, snow cover manipulation experiments are useful. In Japan, snow cover manipulation is practiced by farmers to improve agricultural yield and is executed either by applying a broadcast of blackish agent onto the snow cover, which leads to faster snow-melting thereby extending the crop-growing season, or by snow cover removal/re-accumulation, leading to an enhanced soil frost depth for weed management. Implementation of these practices involves using an amount of fossil fuel, in addition to influencing soil-derived N2O emissions, therefore, the load factors of snow cover management practices per unit area of agricultural field were estimated in this study. Field data including micrometeorological conditions, ground surface flux of N2O, and amount of fossil fuel consumed during machinery operation for management practices, were obtained at two sites in Hokkaido over 2 years (2008-2010). Fuel consumption for the field spreading was found to be unexpectedly small (0.017 Mg CO2 eq ha(-1)). It was therefore suggested that acceleration of snowmelt may have the potential to reduce net greenhouse gas emissions if the agent used is a low-degradable C-rich material, such as charcoal. For soil frost control, the fossil fuel consumption during a set of snow cover removal/re-accumulation (estimated as 0.052 Mg CO2 eq ha(-1)) is discussed, together with the relationship between possible mechanisms causing stimulation of N2O production in frozen soil and inherent large differences in N2O flux among sites.