| Legend |
Category |
Geological Characteristics |
Subject Drainage Area |
 |
Volcanic Rocks |
Mainly consisting of volcanic eject of the Quaternary Period, such as andesitic lava and a layer of pyroclastic materials (with rhyolite, basalt and others), forming alternations of soft and hard strata at many sites. |
Kiyotsu River
Nakatsu River
Shikumi River
Upper Reaches of Aburuma River |
 |
Sedimentary Rocks
of the
Tertiary Period |
Generally consisting of relatively soft rocks with well-developed joints, creating an area of many active slides |
Imokawa River, Middle and Lower Reaches on Left Bank of Aburuma River
Middle and Lower Reaches of ain Channel of Uono River
|
 |
Granite |
Highly weathered hard rocks with well-developed joints and liable to become sand |
Lower Reaches (Matsu River and Hane River) on Left Bank of Aburuma River
Sanashi River
Nobori River
Daigenta River
Upper Reaches of Uono River
|
 |
Mesozoic Formation
Palaeozoic Formation |
Consisting of relatively hard sedimentary rocks, metamorphic rocks (phyllite, etc.) and volcanic rocks (gabbro, etc.) of the Mesozoic and Palaeozoic Eras |
Middle and Lower Reaches on Left Bank of Aburuma River
Mizunashi River
Middle and Upper Reaches of Saguri River
|
 |
Alluvial Formation
of the
Quaternary Period |
Sedimentation area of running down sand, forming flat land, including fans |
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