1998 Fiscal Year Final Research Report Summary
Mechanism of the change in hillslope hydrology and sediment discharge at volcanoes associated with eruption
| Project/Area Number |
08454133
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Meteorology/Physical oceanography/Hydrology
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| Research Institution | KYOTO UNIVERSITY |
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Principal Investigator |
SUWA Hiroshi Kyoto University, Disas.Prev.Res.Inst., Associate Professor, 防災研究所, 助教授 (00093253)
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| Co-Investigator(Kenkyū-buntansha) |
SAITO Takashi Kyoto University, Disas.Prev.Res.Inst., Research Associate, 防災研究所, 助手 (10225716)
OKUNISHI Kazuo Kyoto University, Disas.Prev.Res.Inst., Professor, 防災研究所, 教授 (30027239)
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| Project Period (FY) |
1996 – 1998
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| Keywords | Volcanic eruption / Volcanic slope / Erosion rate / Yakedake / Mount Unzen / Storm runoff / Debris flow / Runoff coefficient |
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| Research Abstract |
Though the erosion rate of volcanic slope increases abruptly by eruption, it would decrease with time after the termination of eruption. Observation of storm runoff, sediment discharge, debris flows and the field experiments were executed in order to clarify the mechanism of the trend above mentioned ; interaction between hillslope hydrology and topographic evolution. The analysis of the observational and experimental data brought about the following results. The study at Mount Yakedake brought about the following results. Firstly, we found a very fast contribution of subsurface flow to storm runoff. This rapid response of may be brought about by a flow rout of the shallow subsurface network of weed's root. Secondly, the runoff coefficient of a test slope at the headwaters decreased one third from the previous data 18 years ago. This change is controlled by the changes in the microtopography of the slope, the soil structure of the slope surface, and vegetation. The role of them against
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the change was clarified. Thirdly, the erosion rate of the slope decreased to a small value of the order of 1 mm/year. This condition and decrease of debris-flow frequency and magnitude coincide with decrease of runoff coefficient of the slope. The study at Mount Unzen brought about the following results. The decrease of sediment discharge is promoted so far by the fast revegetation in the period after the termination of eruption. Two processes of erosion are working on the slope after the eruption. The major process is erosion at the gully which supplies most of the sediment discharge, while erosion rate at the slope between the gullies is very small which is less than one hundredth or one thousandth of the former. The artificial rainfall experiment using the sample of pyroclastic-flow deposits clarified that the collision of raindrop forms the soil crust in almost any experimental condition to decrease the infiltration capacity of the slope. Two periods of slope erosion are distinguishable. The change in hillslope hydrology and sediment discharge is drastic just after the termination of the eruption whose mechanism was clarified through the rainfall experiments, while the change is gradual during the second period after the first one. The second period leads to the time just before the next eruption. The mechanism of the second period is understood with the revegetation process mentioned above. Less
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Research Products
(18 results)
