Study on uplift and erosion history in the Outer Belt of Southwest Japan

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We found that paleosurfaces are widely distributed in higher elevations and that they are being incised by the Kumano River. The Nakahara River, a tributary of the Kumano River, has knickpoints propagating upstream and undercutting nearby slopes. Dip slopes in particular are destabilized by the undercutting and gravitationally deformed. Most of the tributaries of the Tennokawa River, the upstream portion of the Kumano River, have knickpoints, above which the tributaries are within paleosurfaces. The long river profiles of the tributaries above knickpoints were extended downstream to reconstruct long river profiles of the paleo Tennnokawa River. The reconstructed river bed was about 150 m above the river bed of the current Tennnokawa River. We found a gravel bed on the paleo river bed and dated it 30 ka by cosmogenic nuclide dating. The incision rate of 150 m in 30 ka is very high, suggesting a consistent uplift rate in this area.