Atosanupuri Volcano is one of the active volcanoes, located in the Akan-Shiretoko Volcanic Chain, eastern Hokkaido. Tephro-stratigraphic and tephro-chronologic studies were conducted on two drill cores and new outcrops around the volcano to reveal a recent history of the explosive eruptions. Widespread tephra layers, such as the 10th century B-Tm tephra, and the 2.7 cal. ka BP Ta-c2 tephra were distinguished by the geochemical composition of volcanic glass. In addition, ¹⁴C ages of organic samples underlying the eruption deposits were obtained. Using these data, we identified seven phreatic eruption deposits, At-ph1 to At-ph7, overlying the T-c2 tephra; these include the previously described At-a and At-b tephras. At-ph7 yields the oldest ¹⁴C calibrated age (2.5-2.7 cal. ka), and the deposition ages of At-ph6 to At-ph1 range from cal. AD 554 to 1678. At-ph4 (At-b) is the thickest phreatic ejecta, with a volume of ~3 × 10⁶ m³. Five phreatic eruptions occurred from Atosanupuri Volcano between 1,500 and 1,000 cal. BP. The youngest eruption, At-ph1 (At-a) occurred at 300 ~ 400 cal. BP, which might be documented in historical records.

Once the volcano erupted, fallen ash accumulated on the ground flew easily even by slight rainfall and generated lahar, which sometimes caused disaster. Therefore, certain criteria are required to evaluate the possibility of lahar after the eruption. It is, however, not well understood under which process or conditions lahar were occurred in the past. For the purpose of future volcanic disaster prevention, we reviewed the historical records of the lahar in japan related to phreatic or phreatomagmatic eruption. Totally 60 records were investigated, and the process of the lahar could be classified into 12 patterns. The most frequent type was secondary lahar （triggered by rain） and the next was primary lahar （induced by hydrothermal water）. According to the research of rainfall records on four volcanoes, initial secondary lahar may be produced particularly when the rainfall rate was approximately 11-35 mm/hour which was maximum experienced hourly rainfall after the eruption.

A phreatic eruption occurred from Ontake Volcano (3067 m a.s.l.) on September 27, 2014 (at 11:52 a.m.), resulting in the distribution of diluted volcanic ash over an area extending eastward. Details of ash fall distribution were determined using a questionnaire survey of observations in Nagano, Yamanashi, Gunma prefectures, and Tokyo Metropolis, together with data from other published research. Results indicate that trace amounts of ash (<1 g/m²) were deposited over a widespread area in mid-south Nagano Prefecture and northwestern Yamanashi Prefecture. The deposition pattern was particularly wide to the south of the ash fall axis, especially in the Ina basin (from Ina City to Iida City), located between the Kiso and Akaishi mountains. This indicates that the deposition of trace amounts of ash is affected not only by prevailing wind direction, but also by local topographic effects on surface winds. The effect of surface winds on the distribution of ash fall has previously been reported for magmatic eruptions from Asama and Sakurajima volcanoes, in addition to being a feature of the phreatic eruption from Ontake Volcano. Therefore, it can be assumed to be a factor commonly affecting fine-grained ash falls.

Japan Meteorological Agency reported that the mode of eruptions of Shindake Volcano in 2014 and 2015 was phreatomagmatic or magmatic, which generated high-velocity pyroclastic flows. This interpretation is based on the presence of fresh glass shards in the tephra deposits. However, the glass shards were non-vesiculated, and their groundmass were almost crystalline, hence they are regarded to have originated from consolidated intrusive bodies in the shallow vent.

Similar examples of ejecta were reported from the violent eruptions of Shindake Volcano in the 20th century. The representative sample consisted of high-temperature large volcanic jointed blocks erupted on 22 June 1966. The eruptions caused a forest fire, indicating high-temperature, probably more than 400 degrees Celsius. They have been interpreted as ejected blocks from a dike in shallow vent. Many explosive eruptions from Shindake Volcano in historical time have generated pyroclastic materials of the same origin. The 2015 eruption clouds, spouted out directly from the crater and flowed down the slope with high speed (>100 km/h), should be classified as a blast.

We conducted an organic carbon analysis of flood sediments from the 2003 typhoon no. 10 off Hidaka, southern Hokkaido. Flood-induced sediments from the river mouth, inner shelf, outer shelf, and upper slope are rich in terrigenous organic carbon. Four years after the typhoon, flood sediments were found preserved in a topographic depression on the inner shelf, within an area protected from waves and currents. Stratigraphic variations in terrigenous organic carbon ratios in flood sediments from the depression reflect changes in river discharge with rainfall during the flood. Our results indicate that terrigenous material from the river mouth was continuously supplied and deposited on the shelf. These stratigraphic variations in the terrigenous organic carbon ratio could be significant in ongoing attempts to discriminate flood sediments from ancient turbidite successions.

We performed U-Pb dating on detrital zircons from sedimentary rocks (e.g., sandstone and tuff) of the Kuruma Group in central Japan. The youngest ages are from sandstone of the Jogodani and Gamaharazawa formations, which yields ages of 187.7±1.2 Ma and 189.4±0.9 Ma, respectively. These formations are located in the stratigraphically lowermost part of the Kuruma Group. In addition, vitric tuff within the Kitamatadani Formation, which conformably overlies the Jogodani Formation, yields weighted mean zircon ages of 187.0±1.6 Ma and 186.3±1.3 Ma. Previous studies reported upper Pliensbachian ammonites from the Teradani Formation in the stratigraphically lower part of the Kuruma Group, providing strong evidence that the lower part of the Kuruma Group, from the Jogodani Formation to the Teradani Formation, was deposited in the Pliensbachian (191.4 Ma to 183.7 Ma), and that the Jogodani Formation is correlated to the Gamaharazawa Formation. As the lower part of the Kuruma Group is up to several thousand meters thick, it is inferred to have formed during a period of rapid sedimentation in the Pliensbachian.