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GNS Science
New Zealand Mountains Falling Down
Simon CoxPrincipal Scientist, GNS Science
GNS Science
Atua
GNS Science
New Perspectives
GNS Science
Geophysics301
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WEST EASTGeophysics 401
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WEST EAST
GNS Science
Mountains Presently Growing c. 5 mm/yr
GNS Science
Contemporary GPS Velocities and Strain Rate
Velocities relative to Australian Plate Max. shear strain rate
Beavan & Haines (2001)Beavan et al. (1999)
GNS Science
NZ in 4 million years….
Buckle up for the ride....?
A cricket pitch of displacement
every 500 years
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After Little 2004
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GNS ScienceCox & Barrell (2007)
Southern Alps
GNS ScienceCox et al. 2012 Tectonics 31: doi:10.1029/2011TC003038
GNS Science
It can be dangerousin an active collision zone!
Aoraki/Mt Cook 199112 million cubic metres
Franz Josef Glacier town
Waiho River
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Temporary storage areas for sediment which evolve and change through time.
Alluvial Fans & Debris Flows
Cass Valley
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Te HoroDart Valley
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GNS ScienceSH6 Pipson Creek, April 2006
Pipson CkSH6, 2006
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Differences in fan type (and hazards) depend largely on whether there is a mechanism for removing sediment from the fan systemAlluvial Fans
1913
Aoraki/Mt Cook VillageHermitage
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Fan Landforms6% of Otago
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Occupying fan landscapes
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Landslides & Lateral Spreading
• Downwasting ice, removes slope support
• Widespread and continued along lateral moraines
• Propagation upwards into bedrock slopes
Ball RoadBall Hut
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Mueller Huts
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Malte Brun Hut Summer 1964-65
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Malte Brun Hut Site 2014
????
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Rock Avalanches4% of MCNP affected by rock avalanches in last ~50 years
22-27° farböschung ‘angle of reach’ common, as low as 16°across snow
Significant recent increase in rate
Allen, Cox, Owens (2011) Landslides 8: 33-48
40-50°>50°
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Beatrice, Nov 2004
When Rockfall gets Bigger
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2008 was a busy year
Vampire Jan 7 & 13
Douglas 18 Feb
Spencer 6-7 Apr
Halcombe 24 Apr
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VampireDebris
Distinct lobes300,000 m2
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Source
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Aoraki - Hillary Ridge July 2014Gardiner Hut
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MCNPRock Avalanches
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Rock AvalanchesSlope >50°
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Temperature Effects
Vampireseismographs
GNS ScienceMcSaveney, Cox & Hancox work in progress
LOCATION Date
Aoraki/Mt Cook 1873
Mt Isobel I c. 1950-55
Mt Isobel II c. 1965
Mt Walter-Green 1972
Mt Vancouver 1974 or 75
Murchison Glacier 25/12/75 *1
Aoraki/Mt Cook 14/12/91
Mt Fletcher I 2/05/92
Mt Fletcher II 16/09/92 *2
Mt Thomson 22/02/96
Mt Adams 6/10/99
Vampire 2003
Mt Beatrice 23/11/04
Vampire 7-13/01/08
Douglas Peak 18/02/08
Mt Spencer 6-7/04/08
Mt Halcombe 24/04/08
Rock Avalanches last 60 years
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Role of De-Glaciation & Accelerated Climate Change?
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Fiordland Earthquake 350 km away, MM III-IV Shaking ~0.4-2.3%g T decay
0.9 ± 0.2 °C over 5
days
Role of Elastic Deformation?
GNS ScienceMcSaveney, Cox & Hancox work in progress
The Seismic Cycle & 330 yr Alpine Fault earthquakes?
NZ earthquake shaking
Rock avalanche frequency
GNS Science
Given the considerable number of spontaneous rock avalanche events, collapses should be widespread when a major earthquake does eventually shake the central Southern Alps.
Hooker Glacier, 1893 Burton Brothers Collection, Te Papa
GNS Science
Alpine Fault
One of the longest, straightest, fastest moving plate boundary transform faults in the world.
•Accommodates 75% of plate motion
• Rapid slip rate of 20-30 mm/year
GNS Science
Earthquakes on the Alpine Fault • Evidence of past
earthquakes preserved in the landscape
• Last ruptured in 1717 A.D.
• ~380 km rupture = Mw8
• Regular Return Interval ~260-400 years (average 329 ± 68 years)
• No major event in past 298 years
• Likelihood ~30% in next 50 years
See Berryman et al. 2012 (Science); Howarth et al. 2012 (Geology) amongst other recent work
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Mw8 Alpine Fault Earthquake scenario
• Synthetic isoseismals (MM intensity) for a MW 8 earthquake
• Southern Alps and Westland = MM IX
(locally X)
• Christchurch & Central Otago MM VI‐VII
• Dunedin = MM V
One possible scenario for a large Alpine Fault earthquake suggested by Tim Davies, Canterbury University
GNS Science
Geomorphic consequences
• Geomorphic impacts of Alpine Fault earthquakes may persist for decades
TsunamiRock avalancheDambreak floodSevere sedimentation
Scenario providedby Prof T. Davies
One possible scenario for a large Alpine Fault earthquake suggested by Tim Davies, Canterbury University
GNS Science
Earthquake Induced Landslides
Cascade Mw?? c.660AD750 million m3
Murchison Mw7.8 1929
Lake Stanley 18 million m3
Barth 2013 Landslides Hancox et al. 2002 BNZSEE 35(2):59-95
GNS SciencePhoto: V. Kennett
Perfect Storm?
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MCNPHuts
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MCNPHuts
Are there are other management options?
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Hazards to consider
GEOLOGICAL• Earthquakes• Rock Avalanches• Rock fall• Landslides• Lateral spreading• Debris flows/floods• Tsunami (lake)
METEOROLOGICAL• Snow Avalanches• Lightening• Hail storm• Wind• Flooding• Geomagnetic storm
WILDFIRE
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Hazardscape
Hazard Assessment:Knee-jerk (± emotion) vs Holistic approaches
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Appropriate Time Scale 10-20 yrs(<< 50 yr Building Code)