The tsunami in March 2011 heavily damaged the Pinus thunbergii Parlatore erosion-control coastal forests of northeastern Japan. The restoration is in process but has been challenged by waterlogging resulting from soil compaction of artificial growth bases. In this study, a pot experiment was conducted to elucidate the waterlogging responses of two-year-old P. thunbergii seedlings in terms of waterlogging duration. Three waterlogging durations were set (7 days, 17 days, and 32 days, water table at soil surface) during August, followed by a waterlogging-free recovery period (28 days) in September. In this experiment, the responses of both above- and belowground organs during waterlogging and after the release from waterlogging were elucidated, focusing on parameters, such as transpiration and photosynthesis rates, as well as fine root growth and morphology. As a result, we found that under the conditions of our experiment, if the waterlogging duration is within 17 days, P. thunbergii seedlings can recover physiological activity in about a week; however, if the waterlogging duration is over 32 days, recovery after the release from waterlogging largely varied among seedlings. For the seedlings that could recover, recovery took at least 2 weeks, which required new fine root growth. In cases where the damage was irreversible, seedlings showed an overall decline. These results suggest that it is important to manage the waterlogging conditions so that P. thunbergii seedlings can recover without prolonged negative effects.

Differential frost heave between fine (earthy) and coarse (gravelly) domains was monitored over 10 years (2013-2023) on a mountain-top flat ground subjected to both frequent diurnal and deep seasonal freezing. Monitoring objects include, ground heave, soil temperature down to 55 cm, soil moisture, air temperature, rainfall, and snow depth. The two domains, differing only in the presence of uppermost platy gravel about 1 cm in thickness, undergo frequent diurnal frost heave with about 1-cm-thick needle ice formation. Annual frequency and cumulative amount of frost heave are not significantly different between the two, but the fine domain is slightly more active particularly in spring when the near-surface soil at just above 0 degrees C permits rapid frost penetration. Differential heave mainly occurs as a time lag in the start and peak of heaving, on average, by about 1 h preceded at the fine domain, which tends to concentrate stones to the coarse domain. Frost heave activity shows a large interannual variation, primarily depending on the duration of snow-covered days. Frost heave activity also roughly correlates with annual mean air temperature, possibly reflecting a decrease in snowfall days.

The effect of seismicity in earthquake-prone areas is soil liquefaction. This common geohazard that usually occurs in the world induces fatality damage to buildings and infrastructure. Consequently, preventive effort is required to avoid this condition's harmful effects. Two countries that have outstanding seismic records and soil liquefaction damage histories are Japan and Indonesia. However, liquefaction research in Indonesia is not fully developed yet to assess the liquefaction vulnerability as the mitigation countermeasure as Japan did. This paper aims to generate potential proposals in soil liquefaction research between Indonesia and Japan that will be able to expand in terms of disaster prevention. A bibliometric analysis with Vosviewer was conducted to provide a lot of potential topics in soil liquefaction. Moreover, the research data from the Scopus database was analyzed to list the similarities and differences topics between the two countries. Moreover, comprehensive methods such as empirical, semi-empirical, and computational analysis have been widely mentioned and discussed between the results of the two countries. The results indicate that Indonesia's liquefaction susceptibility analysis should consider Japan's research categories. The research's main contributions are highlighting the many applications of soil vulnerability research in Indonesia and Japan, indicating possible areas of research that have not been explored, and summarizing the exciting possibilities for future research in this subject.