Research Themes

• Determinant of primary succession in post-landslide forests and development of afforestation technique by using nitrogen fixing plant
  Grants-in-Aid for Scientific Research
  01 Apr. 2019 - 31 Mar. 2024
  小林 真, 内海 俊介, 山田 孝, 吉田 俊也
  豪雨などによる山腹崩壊後の森林の生態系機能を効率的に回復させる上では、森林植生を速やかに回復させる植林技術の開発が鍵になる。特に、広範囲で適応可能な山腹崩壊後の植生回復指針を確立するためには、多様な立地環境において発生した山腹崩壊地を対象に、 環境特性にあった植栽樹種を明らかにすることが有効である。山腹崩壊跡地では、しばしば窒素固定植物が植栽された際に高い生存率・成長率を示すことが知られているが、多様な窒素固定植物の中でも、どの樹種が、どのような立地で発生した山腹崩壊跡地への生存に適しているかは明らかにされていない。そこで本年は、前年に多様な立地環境に人工的に作成した15箇所の人工山腹崩壊試験地に植栽していた北海道に自生する2種の窒素固定植物（ヤマハギおよびケヤマハンノキ ）について、その生存率と環境要因の関係を検証した。
  環境条件を調査した結果、15箇所の山腹崩壊跡地では、斜面の斜度が急になるとともに、土壌含水率は低下し、表層土砂の流出量は増加した。一方、斜面の斜度が急になるとともに、エゾシカの発見頻度は低下した。植栽木については、同じ窒素固定植物であっても、ヤマハギとケヤマハンノキでは、ケヤマハンノキの方が山腹崩壊跡地の生存率は高いことがわかった。また、２種間で生存率へ影響する立地環境は異なり、ヤマハギへは土壌の母岩の違いが、ケヤマハンノキへは崩壊地の斜度、土壌の粒径、土壌含水率が影響を及ぼしていた。興味深かったのは、ケヤマハンノキの生存が、斜度が急な立地で生存率が高かったことである。急傾斜地へ植栽したケヤマハンノキが高い生存率を示したことについては、近年増加しているエゾシカによる食害が急傾斜地では起きにくいことが関係していることが考えられた。
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Hokkaido University, 19H02986
• Prediction methods of sediment discharge areas due to slope failures caused by earthquake in volcanic ash deposited areas
  Grants-in-Aid for Scientific Research
  01 Apr. 2019 - 31 Mar. 2022
  YAMADA TAKASHI
  Machine learning was conducted on the slope failures that occurred in Atsuma due to the 2018 Hokkaido Iburi East Earthquake, using pre- and post-earthquake LP data, which revealed that slopes with cracks appearing on the ground in advance were vulnerable and at high risk of slope failure. In addition, groundwater analysis was conducted to reproduce the moisture condition inside the slope at the time of the earthquake. The results suggest that the water retention property of the slip surface and the permeability of the layer below the slip surface are the key points to focus on when identifying slopes in danger of failure. Furthermore, we developed a method to establish a two-dimensional spreading and deposition area for a block sliding surface failure by calculating the reach of the collapsed soil using a rigid body sliding model (the dynamic friction coefficient was measured using field sediment samples) and giving the average value of the collapse width in the transverse direction.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Hokkaido University, 19H02393
• Mechanism of multiple hazard chains and adaptations for rapidly population decline in Japan
  Grants-in-Aid for Scientific Research
  01 Apr. 2018 - 31 Mar. 2021
  Osanai Nobutomo
  In this study, we have organized disaster phenomena that occur in combination with large-scale earthquakes, tsunamis, volcanic eruptions, etc., including water disasters that will be exacerbated by climate change. Furthermore, the survey methods and simulation methods necessary to reduce the damage caused by them were presented. Hokkaido has an aging population and depopulation. It was also necessary to consider how disaster prevention should be in a society with a rapidly declining population in combination with maintaining the vitality of the region. In the future, Japan will not have abundant investment capacity, and complete relocation (migration) will not be easy to ensure safety against various disasters at the relocation destination. In a society with a rapidly declining population relocation destinations may be limited, so "dual life" can be a clue to avoid a crisis and maintain the vitality of the region.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (A), Hokkaido University, 18H03819
• Comprehensive study on the 2018 Hokkaido Eastern Iburi Earthquake and its disaster
  Grants-in-Aid for Scientific Research
  04 Oct. 2018 - 31 Mar. 2019
  Takahashi Hiroaki
  Comprehensive investigation on the 2018 Hokkaido Eastern Iburi earthquake and its disaster was conducted. Mainshock rupture initiated at deepest part and major slip was occurred in 20-30km deep. Multiple simultaneous landslides in Atsuma town was induced by combination of strong ground shaking and weak sliding layer between pyroclastic fall deposit layers. Halloysite cray minerals was discovered in all sliding layers. Simulation suggested landslides might attack residential houses within 6 seconds. Observed peak ground motions in nearby area were larger than common distance attenuation model. Severe wooden house damage in Mukawa town was due to amplified seismic waves due to site effects. Sounding and boring investigation revealed filled low-density volcanic ash and higher groundwater level in liquefaction area. Electricity blackout caused severe damage in social and economic activities of Hokkaido. These scientific outcomes were explained to residents at public briefing session.
  Japan Society for the Promotion of Science, Grant-in-Aid for Special Purposes, Hokkaido University, 18K19952
• Integrated study on the 2015 eruption at the Kuchinoerabujima volcano
  Grants-in-Aid for Scientific Research
  16 Jun. 2015 - 31 Mar. 2016
  Iguchi Masato, KANDA Wataru, MORI Toshiya, GESHI Nobuo, TANAKA Hiroshi, SEKIYA Naoya, KURI Miwa, SAKAMOTO Mayumi, HASHIMOTO Manabu, NAKAO Shigeru, Ohminato Takao, MAKI Norio, ICHIKO Taro, YAMADA Takashi, JITOZONO Takashi, TANADA Toshikazu, TAMEGURI Takeshi, NAKAMICHI Haruhisa, SUZUKI Yujoro, TAKARADA Shinji, MIKI Daisuke, NAKADA Setsuya, KOBAYASHI Tetsuo, YAMAMOTO Keigo, SHINOHARA Hiroshi, NOGAMI Kenji, OZAWA Taku, MIWA Takahiro, NAGAI Masashi, KOYAMA Takao, OHKURA Takahiro
  Discharge rate of volcanic gas, ground inflation, seismicity and geothermal activity successively increased prior to the eruption on May 29, 2015. Degassing and crystallization of magma proceeded at a shallow part beneath the crater. Explosion earthquake of 2014 eruption was larger than 2015 eruption, however eruption volume and intensity of eruption in 2015 was larger. Evacuation experience in 2014 eruption took an important role for evacuation planning and evacuation operation in 2015 eruption. No phenomena to show increase in volcanic activity were detected by instruments installed after the eruption in this project. Evaluation of activity by this project is useful to reduction of restricted zone and decision making for returning.
  Japan Society for the Promotion of Science, Grant-in-Aid for Special Purposes, Kyoto University, 15H05794
• Study on change in hydrological response of catchment to deposition of pyroclastics and occurence of sediment disaster after 2010 eruption of Mt. Merapi in Indonesia
  Grants-in-Aid for Scientific Research
  01 Apr. 2012 - 31 Mar. 2016
  GONDA Yutaka, HOTTA Norifumi, YAMADA Takashi, NUMAMOTO Shinya, MIYATA Shusuke, MIYAMOTO Kuniaki, FUJITA Masaharu
  Field surveys were conducted around Mt. Merapi, where lahars occurred frequently after the 2010 eruption. Results of numerical simulation of lahar inundation conducted by changing combination of data set component and those of field survey were compared. As a result, it was confirmed that the resolution of the DEM is the most important factor to estimate inundation area by lahar simulation and that the peak discharge and total volume of lahar hydrograph at inflow point of numerical simulation is the second most important factor. It was observed that the rain fall intensity causing lahar and magnitude of lahar changes as time passed after the eruption. Therefore, to estimate appropriate magnitude lahar for the lahar inundation simulation, relationship between ground surface condition of the drainage area and runoff ratio of lahar to rainfall should be quantified
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Niigata University, 24404010
• Hydrological observation of subsurface flow spouting from pipe exits in torrent bed material and its triggering rainfall condition for the prediction of debris flow generation
  Grants-in-Aid for Scientific Research
  01 Apr. 2012 - 31 Mar. 2015
  YAMADA TAKASHI, NUMAMOTO Shinya, TSUCHIYA Satoshi, GONDA Yutaka
  Several pipe exits were discovered in the torrent bed material in debris flow generation areas of the Nishinokaito River, Mount Fujiwara ,Mie prefecture, Japan. They were emplaced in a sand and gravel layer between 1.0 and 1.5 m below the surface of the torrent bed material. Gravel supported the internal walls of the pipe exits. Subsurface flows spouted when the rainfall intensity exceeded about 5 to 7 mm in 10 minutes and the soil water index exceeded about 110 mm. Hydrological processes such as subsurface flows spouting from pipe exits and its clogging, subsurface flows spouting at the new pipe exits during heavy rainfall may lead to debris flow generation. The critical rainfall thresholds for them were studied using radial basis function network (RBFN) method.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Mie University, 24310137
• Empirical and analytic study on the influence of forest relating to the scale of slope failure
  Grants-in-Aid for Scientific Research
  2007 - 2008
  HAYASHI Setsuo, YAMADA Takashi
  三重県宮川調査区域と福井県美山調査区域において森林の斜面崩壊抑制機能を明らかにするために, 樹林における崩壊土砂の堆積について調査研究を行った。主要な研究成果は次の2点である。(1)立木の平均胸高直径と崩壊深との関係図において堆積事例と非堆積事例は判別分析により区分される。この傾向は, 両調査区域にみられた傾向である。(2)立木に作用する受働土圧と堆積深との関係より, 堆積可能な胸高直径d_bは崩壊深Dの3/2乗に比例する関係が得られた。
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), Mie University, 19580171
• Storm-induced disturbance on earth surface processes and risk management for sedimentarysystems
  Grants-in-Aid for Scientific Research
  2005 - 2008
  MARUTANI Tomomi, SHUNICHI Kikuchi, MIKIO Kuroki, SEIJI Yanai, TAKASHI Yamada, AKIRA Mano, YUUKI Nakajima, HIDEJI Maita, MASANOBU Kimura, NOBUHIR Ebisu, OSAMU Shimizu
  台風により、倒木、崩壊・土石流などの一次被害から二次・三次被害への連鎖は10年以上から数十年にわたって発生し、一次被害と河床変動や流路変動、浮遊砂流出などの二次被害が、台風被害に起因した連鎖した現象であることがわかった。台風に伴う地表攪乱は、一次被害を森林のマネージメントで軽減することは不可能であるが、二次被害を軽減することはできる。そのために、植林などの生産源対策のみでは無く、流出対策に視点を変えるべきである。また、本来台風による地表攪乱は、土砂流出および浮遊砂流出として大規模な構造体で「溜める」「阻止する」発想から、小規模な構造体で「流す」「緩和する」発想への転換が求められる。
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (A), Hokkaido University, 17208012
• Study on the time variation of sediment discharge after gigantic landslide at volcanic area in south-east Asia
  Grants-in-Aid for Scientific Research
  2005 - 2007
  SASAHARA Katsuo, TAMURA Keiji, YAMADA Takashi, ONDA Yuichi, SHUIN Yasuhiro, TSUCHIYA Satoshi
  In order to examine the mechanism of gigantic landslide occurred at March 26, 2004 in the caldera of Mt Bawakaraeng, South Sulawesi, Indonesia and know the time variation of sediment discharge from deposition of the landslide mass, Field survey and the analysis of satellite images were carried out. The results are as follows.
  (1) Sediment discharge from deposition of Landslide mass was the largest at first year after landslide, then were greatly decreasing at second and third year. This tendency is quite same with the sediment discharge from the pyroclastic deposit just after the volcanic eruption. With the sediment discharge, gully erosion was going to developing at the landslide deposition. At first year, the width and depth of the gully became larger, while width of the gully was still became larger at second and third years. It means that gully side wall was greatly eroded at second and third years.
  (2) The analysis of the route of radioactive tracer was tried in order to know the runout distance of eroded sediment in the Jeneberang River which flows down from Mt Bawakaraeng. But because the amount of sampling of sediment discharge was too small for the radioactive tracer analysis, runout distance of the sediment could not be well made clear. More sampling of discharged sediment is necessary in order to attain the purpose.
  (3) The mechanism of occurrence of landslide was examined by geological and geotechnical methods. The weak laminar at the bottom of the collapsed slope was made clear to be the key of the landslide occurrence. It seemed that the laminar collapsed at first, and whole slope followed to move downward.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Kochi University, 17405003
• Lahar-induced disturbance of naturalresources and recovery from volcanic disaster at the Ruapehu volcano, North Island, New Zealand
  Grants-in-Aid for Scientific Research
  2005 - 2007
  MARUTANI Tomomi, YAMADA Takashi, KIKUCHI Shun-ichi, KUROKI Mikio, KIMURA Masanobu, MAITA Hideji
  Understanding how we can manage a sustainable environment for land resources around volcano must be emphasized for the land management in the world. Both geological features in New Zealand and Japan is very similar and they have a same experiences with disaster on land resources. This program focus on the prediction of lahar-induced disturbance on land resources, such as ecosystem, landscape, local residence area, and life-line instruments. Furthermore the warning system of volcanic hazard and the restoration skill evolved recently can be important. We also have an interest in comparing both lahar-flows occurred at 50years ago and predicted after 2005.
  On 18 March 2007 the summit Crater Lake of Mt. Ruapehu, New Zealand, breached a barrier of tephra emplaced by eruptions in 1995-96, resulting in the rapid release of 1.3 million m3 of water. The flood rapidly bulked by entraining snow, ice, rock debris and alluvium along the steep gorge of the upper Whangaehu River to form a debris flow that then transformed downstream into a hyper-concentrated and then sediment-laden stream flow during its passage to the Tasman Sea 155 km away. No lives were lost' and infrastructural damage was minimal due to a comprehensive warning system developed in the decade before the lahar. A previous break-out lahar in 1953 caused a railway disaster at Tangiwai with the loss of 151 lives. The lahar flowed as a multi-peaked debris flow in the Whangaehu gorge, 7 km downstream of Crater Lake. Automatic lahar measuring equipment, including water level gauges, flow velocity sensors, conductivity samplers and seismographs were installed at key sites along the flow path, and were supplemented by sequential photographs captured by automatic monitoring cameras and observer teams. Flow velocity averaged 30 km/hr and water level rose by 8.2 m in 4 minutes in the gorge. The lahar caused riverbed aggradation in many places and environmental disturbance to the channel regime.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Hokkaido University, 17405002
• 火山噴火の長期予測と災害軽減のための基礎科学
  科学研究費助成事業
  2002 - 2006
  岡田 弘, 中川 光弘, 小山 眞人, 山村 悦夫, 山田 孝, 吉川 肇子, 森 済, 宇井 忠英
  マグマプロセス解析装置の本格稼動で微小精密解析が進み、噴火履歴を正確に復元し,マグマ供給系の構造と噴火プロセスの長期的時間変遷の解明が進んだ。
  高爆発度の道南3火山、対極的な十勝岳三宅島などを対象とした。北海道駒ヶ岳は大噴火後に中小噴火が約五百年続く傾向があり、マグマ供給系の現状と総合すると、現在は活動末期の可能性がある。樽前山も同様であるが、有珠山の活動期は今後も続く可能性が高い。一方、過去約百年間の広域精密地殻変動データの吟味により、有珠山は静穏期に深部マグマの蓄積が、活動期には収縮が認められ、観測による中期予測に駒ヶ岳に続く成果が得られた。
  伊豆大島噴火20周年で「火山危機管理専門家支援サーバ」の野外実働試験が実施された。「火山危機管理担当者訓練のためのシナリオシュミレーション」は、富士山や十勝岳噴火を題材に行政職員、マスメディア、火山専門家などを被験者として実施した.これらの実験により、不確定性の高い現象での科学的判断の多様性と、困難克服の見通しが得られた。
  ハザードマップでは、住民や行政官の危険認識の実態調査を行い、統合型GIS利用の効果を確認した。火山防災の専門用語の問題点を評価し見直し提言を行った。また、火山爆発と関連した土砂災害や火山砂防の課題とその啓発活動のあり方を探った。
  科学者による噴火予測(直前予測・推移予測および終息の判断)と、それぞれの段階における科学的減災助言の実態を解明し、将来の困難に備える指針と必要なツール開発が提言された。また、住民避難や登山規制の解除における科学者の役割が論じられた。
  20世紀に6回発生した噴煙柱が成層圏に達する大規模爆発的噴火の比較研究から、準リアルタイムでどのような物理量が把握でき、減災支援で共有すべき情報はどのようなものかが議論され、過去6回の歴史的成果が次期の大爆発で試されるべきと提言がなされた。
  日本学術振興会, 特定領域研究, 北海道大学, 14080201
• Establishment of watershed conservation methodology based on the prediction of biosphere damage due to fine sediment discharge
  Grants-in-Aid for Scientific Research
  2003 - 2005
  YAMADA Takashi, IRASAWA Michiya, YANAI Seiji, KIKUCHI Shunichi, AKIYAMA Kazuya
  Concentration of solids and organic fine solids in the stream water were measured in a forested catchments where selective-cutting had been carried out. Total fine sediment and organic fine solids concentrations from selective cutting catchments were significantly higher after cutting as compared with those before cutting. The processes underlying land and riparian degradation by quantifying soil erosion and gully growth in slopes adjacent to cropland were examined. The concentration of suspended sediments was consistently higher in cultivated catchments where gully expansion causes 2-3 times more landslides than occur in forested catchments.
  On the basis of these soil erosion and fine sediment discharge situation, erosion velocity equation for cohesive soil was proposed by the newly developed surface shear test equipment and hydraulic model tests.
  Relation between soil surface cohesion of over-saturated layer and water contents at 5 mm depth revealed that as water content increased, soil surface cohesion fell exponentially. Meanwhile, erosion velocity decreased when cohesion increased, however it was increased sharply as the friction velocity increased.
  Sediment discharge prediction method were newly developed on the base of this equation and physical methods of restriction and control of fine sediment discharge for biosphere conservation in watershed were proposed.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), HOKKAIDO UNIVERSITY, 15380098
• Water and sediment delivery process and hazard environment linking with drainage net system and landscape changes in catchments scale
  Grants-in-Aid for Scientific Research
  2000 - 2003
  ARAYA Tohru, NAKASIMA Yuhki, KUROKI Mikio, YAMADA Takashi, MARUTANI Tomomi, MAITA Hideji
  Understanding how the sediment is transported through a catchment is a key issue for food and environmental resources management. Our research project aims to clear the sediment delivery ratios linking with catchment scale, climatic and geological settings and land use in Rim Pacific countries. The sediment production, storage and delivery process in source-to-sink (mountain to sea) sedimentary systems spaced during several square kilometer and thousands square kilometer was examined. The research was conducted in not only Hokkaido to Kyushu in Japan but also New Zealand, Australia and China in Rim Pacific. The result was summarized that the duration and magnitude of sediment storage was determined by catchment scale, averaged catchment slope and rainfall magnitude, and the flow rate and annual volume of suspended sediment were controlled by these factors Adding to it, the flume experimental study available for developing hydrological model ha been done. The influences of sedimentary cascades on riparian and aquatic ecological systems were also examined. The research project managed the international workshop for the source-to-sink sediment transport in catchment scale in Sapporo in 2003, which has invited sediment researchers from Australia, New Zealand, USA, Thailand and Korea. To mitigate and prevent sediment disasters the source-to-sink sedimentary cascades affected by changing catchnment system were successfully cleared in this study.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (A), HOKKAIDO UNIVERSITY, 12306008