Yuki Matsushi

State dependence of climatic instability over the past 720,000 years from Antarctic ice cores and climate modeling

Global cooling in intermediate glacial climate with northern ice sheets preconditions climatic instability with bipolar seesaw. Climatic variabilities on millennial and longer time scales with a bipolar seesaw pattern have been documented in paleoclimatic records, but their frequencies, relationships with mean climatic state, and mechanisms remain unclear. Understanding the processes and sensitivities that underlie these changes will underpin better understanding of the climate system and projections of its future change. We investigate the long-term characteristics of climatic variability using a new ice-core record from Dome Fuji, East Antarctica, combined with an existing long record from the Dome C ice core. Antarctic warming events over the past 720,000 years are most frequent when the Antarctic temperature is slightly below average on orbital time scales, equivalent to an intermediate climate during glacial periods, whereas interglacial and fully glaciated climates are unfavourable for a millennial-scale bipolar seesaw. Numerical experiments using a fully coupled atmosphere-ocean general circulation model with freshwater hosing in the northern North Atlantic showed that climate becomes most unstable in intermediate glacial conditions associated with large changes in sea ice and the Atlantic Meridional Overturning Circulation. Model sensitivity experiments suggest that the prerequisite for the most frequent climate instability with bipolar seesaw pattern during the late Pleistocene era is associated with reduced atmospheric CO2 concentration via global cooling and sea ice formation in the North Atlantic, in addition to extended Northern Hemisphere ice sheets.

Evolution of solution dolines inferred from cosmogenic 36Cl in calcite

Quantification of the development of solution dolines provides important information for understanding the long-term evolution of karst landscapes. This study reports the initial results of an investigation of the long-term denudation rates along the side slopes of a solution doline based on analyses of cosmogenic 36 Cl in calcite. The denudation rates increase in proportion with increasing size of the topographic contributing area, thereby supporting the hypothesis that the rate of surface lowering in carbonate terrains is controlled by water convergence in the epikarst. A simple model based on the empirical correlation between denudation rate and contributing area is successful in explaining the form of several solution dolines located close to the analyzed doline. The model reveals that these solution dolines, which have varying diameters, developed over similar time scales of the order of 10 5 yr.

Evidence of past migration of the ice divide between the Shirase and Sôya drainage basins derived from chemical characteristics of the marginal ice in the Sôya drainage basin, East Antarctica

Ice originating near the inland ice divide of the ice sheet can reappear as marginal ice at the surface near the ice terminal in the ablation area. We have analyzed d 18 O values and ion concentrations of the Skallen, Skarvsnes and Hamna terminal ice sections, located along the estuary line in the Soya drainage basin, East Antarctica. The data suggest that the upper part of the Skallen terminal ice section could have originated from inland precipitation on the Shirase drainage basin during marine isotope stage (MIS) 5e, while the upper part of Skarvsnes and Hamna terminal ice sections could have originated from inland precipitation on the Soya drainage basin. We calculate past elevation maps for the Antarctic ice sheet using the three-dimensional model, SICOPOLIS. This model suggests that the upstream portion of the Soya drainage basin during the glacial period (MIS 2, 3 or 4) was located to the northeast of its present location. A flow history is proposed wherein ice from the inland Shirase drainage area flowed over the present ice-divide line from the Shirase to the Soya drainage basin during the glacial period. The ice in the Soya drainage basin then flowed to the marginal part of the sheet after the ice divide had assumed its present position.

Repeating Seismic Events Indicate Possible Stick-slip Behavior Before the Rausu Landslide†

A precursory sequence of repeating earthquakes was recorded before the Rausu landslide in Hokkaido, Japan on April 24, 2015. There were two seismic sequences with each consisting of very similar waveforms and leading up to significant landslide movements. The nearly-identical waveform shapes indicate similar source locations and mechanisms, so repeated events originated on a particular small area. This sequence is interpreted as stick-slip movement on a small patch leading up to the larger landslide failure. Our observations show that heterogeneous structure, such as asperities on the slip surface, can play an important role in the initiation of landslides, adding a new aspect to the conventional understanding of mechanisms controlling large mass movements.A precursory sequence of repeating earthquakes was recorded before the Rausu landslide in Hokkaido, Japan on April 24, 2015. There were two seismic sequences with each consisting of very similar waveforms and leading up to significant landslide movements. The nearly-identical waveform shapes indicate similar source locations and mechanisms, so repeated events originated on a particular small area. This sequence is interpreted as stick-slip movement on a small patch leading up to the larger landslide failure. Our observations show that heterogeneous structure, such as asperities on the slip surface, can play an important role in the initiation of landslides, adding a new aspect to the conventional understanding of mechanisms controlling large mass movements.

Depth Profile of Radioactivity Induced in the Thick Concrete Shield in EP1 Beam Line at the KEK 12-GeV Proton Synchrotron Facility

Abstract The evaluation of radioactivity induced in the concrete shield is important for the decommissioning of accelerator facilities. Specific activities of gamma-ray emitters of nuclear spallation products and thermal neutron capture products and beta-ray emitters such as tritium and 14C, and 36Cl in the concrete shield along the 12-GeV proton beam line (EP1 beam line, High Energy Accelerator Research Organization) were determined. The depth profiles of the radioactivity of each nuclide in the 6-m-thick concrete shield of the beam lines were compared, and the secondary particles and induced nuclear reactions were discussed.

Seasonal transition of hydrological processes in a slow-moving landslide in a snowy region

Graduate School of Science, Kyoto University, Kyoto, Japan Disaster Prevention Research Institute, Kyoto University, Kyoto, Japan Forest Research and Management Organization, Forestry and Forest Products Research Institute, Tsukuba, Ibaraki, Japan 4 Japan Conservation Engineers & Co., Ltd., Fukushima, Fukushima, Japan Snow and Ice Research Center, National Research Institute for Earth Science and Disaster Resilience, Niigata, Japan Correspondence Hikaru Osawa, Kyoto University, Graduate School of Science, Gokasho, Uji, Kyoto 611‐ 0011, Japan. Email: osawa@scs.dpri.kyoto‐u.ac.jp

Coupling fluvial processes and landslide distribution toward geomorphological hazard assessment: a case study in a transient landscape in Japan

This study quantified the relationship among deep-seated gravitational slope deformations (DGSDs), landslides, and river rejuvenation in the upper reaches of the Kumano River in the Kii Mountains of Japan, an area of frequent bedrock landslides. River profiles and hillslope landforms were examined, and high-resolution digital elevation models (DEMs) were used to identify DGSDs and landslides. Many of the deep-seated landslides were associated with rainstorms in 1889 and 2011. Landslide volumes were related to landslide areas on the basis of 52 deep-seated landslides that failed during the 2011 rainfall, providing basic data for landscape denudation and sediment yield. River rejuvenation occurred stepwise, incising moderate relief paleosurfaces and forming two series of knickpoints and V-shaped inner gorges that are up to 400-m deep. More than 65% of DGSDs and 75% of the landslides were located in association with the incised inner gorges along the peripheries of the paleosurfaces or were entirely contained within the inner gorges. DGSDs and landslides associated with the incised inner valley slopes tended to be larger than those developed within the paleosurfaces and may be long-term transient hillslope responses to river incision. Hillslope undercutting caused by rejuvenated river incision may play an important role in long-term slope stability and distribution of mass movements, and could serve as an indicator of landslide hazard.

Catastrophic Landslides and Their Precursory Deep-Seated Gravitational Slope Deformation Induced by the River Rejuvenation in the Kii Mountains, Central Japan

Slope movements are one of the major processes of denudation as well as erosion and transportation by rivers or glaciers, and many slope movements themselves are induced by river or glacier erosion. We investigated the linkage of river erosion, deep-seated gravitational slope deformation, and catastrophic landslides in the Kii Mountains Japan, where tens of catastrophic large landslides during 1889 Typhoon Totsukawa and 2011 Typhoon Talas occurred. The consequent fatalities were 168 and 56, respectively. The Kii Mountains is underlain by the Cretaceous to Neogene Shimanto accretional complex and has paleosurface remnants at higher elevations. The paleosurfaces have been newly incised by rivers, of which the Kumano River catchment occupies the central part of the Kii Mountains. The new incision of the Kumano River proceeded with the upstream propagation of knickpoints, which developed well-defined convex slope breaks on interfluve slopes. High-resolution DEMs clearly delineated deep-seated gravitational slope deformations, which are characterized by scarps, linear depressions, and bulges, and are aligned along the convex slope breaks, suggesting that they were induced by gravitational instability induced by the erosion undercutting. The catastrophic landslides during the 1889 Typhoon Totsukawa and 2011 Typhoon Talas had been preceded by deep-seated gravitational slope deformation on newly incised inner gorge slopes. Most of the landslides had sliding surfaces along undulating minor faults, probably thrusts, which might have made rock bridges when shearing along preferably oriented parts of the faults occurred. Catastrophic slope failure may occur when those rock bridges are finally fractured.

Sediment-Related Disasters Caused by the Nagano-ken Hokubu Earthquake in the Heavy Snow Season

Mountain slopes covered in deep snow were hit by seismic motions during the Nagano-ken Hokubu Earthquake on March 12, 2011, resulting in avalanches, slope failures, and deep-seated landslides. Sediment-related disasters occurred at places which had geologically weak structures such as faults and fractured rock masses and/or topographical features that were prone to receiving concentrated earthquake acceleration. However, the key characteristic was the interaction between snow cover and sediment-related disasters during and after the earthquake. Fast-moving layers of air and suspended snow particles were also produced when fast debris flows crashed into accumulated snow, destroying peripheral areas along the path of the debris flows. Furthermore, a landslide occurred about 1 month after the earthquake on a slope that was likely to have been loosened by the seismic motions. The numbers of slope failures and landslides were very small compared to the Niigata-ken Chuetsu Earthquake of a similar scale, which was probably attributable to the physical and/or mechanical properties of snow cover.