Transcript Giant landslides, topography, and erosion

Giant landslides, topography, and erosion
Korup O. , Clague J.J. , Hermanns R.L. ,
Hewitt K. , Strom A.L. , Weidinger J.T.
Earth and Planetary Science Letters 261 (2007) 578–589
指導教授：董家鈞 老師
報告者：劉正隆
日期：2010/12/16
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Introduction
• Critical hillslope height
• Threshold hillslope angle
𝐾𝐻
𝐸 = 𝐸0 +
[1 − 𝐻 𝐻𝑐 2 ]
𝐸 ：long-term erosion rate
𝐻 ：orogen-scale mean local relief
𝐸0 ：erosion rate due to chemical weathering
𝐾 ：rate constant
𝐻𝑐 ：limiting relief
More stable
More stable
Montgomery and Brandon (2002)
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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 ?
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Topographic controls on erosion rates
𝐾𝐻
𝐸 = 𝐸0 +
1 − 𝐻 𝐻𝑐
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Montgomery and Brandon (2002)
• 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.
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Topographic controls on erosion rates
• Olympic Mountains
- Accretion and erosion → 14 Myr
- High-resolution digital elevation models → 10-m-grid
𝑆 < 25°
𝐸 = 0.04 + 0.02𝑆(𝑅 2 = 0.86)
𝑆 > 25°
𝐸 = −0.70 + 0.05𝑆(𝑅 2 = 0.21)
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Topographic controls on erosion rates
• 𝑆 = 25° → shallow landsliding by debris flows (Campbell,1975)
Sediment flux：
𝐾𝑆
𝑞𝑠 =
1 − 𝑆 𝑆𝑐
Erosion rates：
2
Roering et al. (1999)
𝐾𝑆
𝐸 = 𝐸0 +
1 − 𝑆 𝑆𝑐
2
Montgomery and Brandon (2002)
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Topographic controls on erosion rates
• Mean slope is more strongly influenced by DEM grid size than
mean local relief. (Polidori et al. ,1991)
• High-resolution DEM (10-m-gird)
→ 𝑆 = 4 + 0.014𝐻𝑐 (𝑅 2 = 0.81)
Erosion rates：
𝐾𝑆
𝐸 = 𝐸0 +
1 − 𝑆 𝑆𝑐
2
𝐾𝐻
𝐸 = 𝐸0 +
1 − 𝐻 𝐻𝑐
2
Montgomery and Brandon (2002)
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Topographic controls on erosion rates
𝐾𝐻
𝐸 = 𝐸0 +
1 − 𝐻 𝐻𝑐
2
Montgomery and Brandon (2002)
• 𝐻𝑐 = 1500𝑚 , 𝐸0 = 0.01 𝑚𝑚 𝑦𝑟 (Summerfield,1991)
• 𝐻 → SRTM30 global digital elevation data (~860m)
• H > 300𝑚 → close to Montgomery and Brandon (2002)
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Landslide inventory
• Landslide volumes > 108 𝑚 3
• Over 300 landslides
• Satellite images and digital terrain models
Kamchatka
Caucasus
American
Cordilleras
European Alps
Central America
Pamir Tien Shan
Himalayas
Japan
Papua
New Guinea
Andes
Southern Alps
• Most of the largest landslides are clustered in tectonically
active mountain belts and volcanic arcs.
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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 ?
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Giant landslides and topography
• The topographic relief mainly produced by tectonic uplift and
bedrock incision by glaciers and rivers.
• More than 70% have occurred in terrain with 𝐻 > 1000𝑚.
• More than 50% have occurred in the steepest 15% of these
mountain belts.
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Giant landslides and topography
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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 ?
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Giant landslides in subcritical relief
• Soft rocks
• Extensive low-angle discontinuities
• High rates of fluvial bedrock incision
• Slope loading
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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 ?
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Giant landslides and erosion rates
• Giant landslides are responsible for 5% of the total erosion.
• The contribution of giant landslides to erosion rate (𝐸) increases
nonlinearly with mean local relief (𝐻).
• Giant landslides may be slightly more important contributors to
total erosion in areas of lower mean local relief (𝐻).
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Giant landslides and erosion rates
• 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.
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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 ?
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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.
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Thanks for your attention
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