simon cox: new zealand mountains falling down

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New Zealand Mountains Falling Down

Simon CoxPrincipal Scientist, GNS Science

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Atua

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New Perspectives

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Geophysics301

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WEST EASTGeophysics 401

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WEST EAST

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Mountains Presently Growing c. 5 mm/yr

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Contemporary GPS Velocities and Strain Rate

Velocities relative to Australian Plate Max. shear strain rate

Beavan & Haines (2001)Beavan et al. (1999)

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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

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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

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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

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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

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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

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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

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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

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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)