指導教授：董家鈞 老師 報告者：劉正隆 日期： 2010/12/16 Giant landslides, topography, and erosion Earth and Planetary Science Letters 261 (2007) 578–589 Korup O., Clague J.J., Hermanns R.L., Hewitt K., Strom A.L., Weidinger J.T. 1

Introduction Critical hillslope height Threshold hillslope angle 2 Montgomery and Brandon (2002) More stable

Key questions What are the relationships between topographic relief and the largest landslides on Earth ? Are these giant slope failures fully explained by hillslope relief ? How do these landslides contribute to relief adjustment and erosion ? 3

Topographic controls on erosion rates Powell(1876) and Gilbert(1877) recognized a strong connection between slope morphology and erosion rates. Ahnert(1970) report a linear relation between erosion rate and mean local relief in mostly tectonically inactive areas. Topographic relief and erosion rates may become decoupled in tectonically active areas. 4 Montgomery and Brandon (2002)

Topographic controls on erosion rates 5

6 Roering et al. (1999) Montgomery and Brandon (2002)

Topographic controls on erosion rates 7 Montgomery and Brandon (2002)

Topographic controls on erosion rates 8 Montgomery and Brandon (2002)

Landslide inventory European Alps Caucasus American Cordilleras Himalayas Pamir Tien Shan Papua New Guinea Southern Alps Kamchatka Japan Central America Andes 9

Key questions What are the relationships between topographic relief and the largest landslides on Earth ? Are these giant slope failures fully explained by hillslope relief ? How do these landslides contribute to relief adjustment and erosion ? 10

Giant landslides and topography 11

Giant landslides and topography 12

Key questions What are the relationships between topographic relief and the largest landslides on Earth ? Are these giant slope failures fully explained by hillslope relief ? How do these landslides contribute to relief adjustment and erosion ? 13

Giant landslides in subcritical relief Soft rocks Extensive low-angle discontinuities High rates of fluvial bedrock incision Slope loading 14

Key questions What are the relationships between topographic relief and the largest landslides on Earth ? Are these giant slope failures fully explained by hillslope relief ? How do these landslides contribute to relief adjustment and erosion ? 15

Giant landslides and erosion rates 16

The volume of individual giant landslides does not increase systematically with mean local relief or erosion rate. High erosion rates may lead to more rapid removal of geomorphic evidence and therefore potential undersampling of previous events. Giant landslides and erosion rates 17

Key questions What are the relationships between topographic relief and the largest landslides on Earth ? Are these giant slope failures fully explained by hillslope relief ? How do these landslides contribute to relief adjustment and erosion ? 18

Conclusions About half of the largest landslides are clustered in tectonically active mountain belts and volcanic arcs where mean local relief and erosion rates are highest. Several giant slope failures are located in areas where mean local relief is below the regional average. The proportional contribution of giant landslides to erosion rates increases nonlinearly with mean local relief. Numerical landscape evolution models that use critical relief thresholds for landsliding may underestimate the contribution to erosion by large events. 19

Thanks for your attention 20