Through international joint research, a research group led by Associate Professor Stephen Obrochta of Akita University and Professor Yusuke Yokoyama of the University of Tokyo restored the eruption history of Mt. Fuji, which brought volcanic ash to Lake Motosu, and discovered two unknown eruptions.It will be an important achievement in predicting future eruptions and disasters.
The Mt. Fuji area is registered as a World Heritage Site and is visited by 4700 million people from Japan and abroad every year.On the other hand, Mt. Fuji is an active volcano, and prediction of eruptions and the effects and countermeasures of wide-area ash fall are socially important.Since the information available on the ground regarding the timing of past eruptions and the range of ash fall is limited, we collected the strata of Lake Motosu (maximum depth of 121.6 m), where sedimentation continues, and studied the history of volcanic eruptions.
This time, we observed the 4m continuous core sample obtained for the first time in Lake Motosu by combining macroscopic observation and X-ray fluorescence analysis, and investigated the position of volcanic ash.Next, using a total of 30 radiocarbon dating values and two known ash layers, a high-precision graph showing which depth of the core sample hits from the present to how many years ago ( Age model) was created.
As a result, the core sample of Lake Motosu was found to be a continuous record for the past 8 years.Three of the scoria (black porous pyroclastic material) layers sandwiched between the cores can be compared with the Osawa eruption, the Omuro eruption, and the last mountaintop eruption (Kengamine scoria) from the comparison with the research on land. The eruption dates are estimated to be around 3, 1950, and 3042, respectively, starting from 2930.In addition, it was the first time that these volcanic ash were confirmed on Lake Motosu on the windward (west side) side of Mt. Fuji, and it was found that the range of ash fall due to the three eruptions was wider than previously estimated.In addition, two volcanic ash layers that originated from Mt. Fuji but did not correspond to any known eruption of Mt. Fuji were found due to their petrological characteristics, which led to the discovery of two eruptions on the west side of Mt. Fuji.
Paper information:[Quaternary Science Reviews] Mt. Fuji Holocene eruption history reconstructed from proximal lake sediments and high-density radiocarbon dating
