Day 1 - Presented to Sustainable Summits 2016 Simon Cox: New Zealand Mountains Falling Down

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New Zealand Mountains Falling Down
Simon Cox
Principal Scientist, GNS Science

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Atua

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New Perspectives

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Geophysics
301

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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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12. GNS ScienceCox & Barrell (2007)
Southern
Alps

13. GNS ScienceCox et al. 2012 Tectonics 31: doi:10.1029/2011TC003038

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It can be
dangerous
in an active
collision zone!
Aoraki/Mt Cook 1991
12 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 Horo
Dart Valley

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18. GNS ScienceSH6 Pipson Creek, April 2006
Pipson Ck
SH6, 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 Village
Hermitage

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Fan Landforms
6% 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 Road
Ball 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 Avalanches
4% 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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Vampire
Debris
Distinct lobes
300,000 m2

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Source

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Aoraki - Hillary Ridge July 2014
Gardiner Hut

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MCNP
Rock Avalanches

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Rock Avalanches
Slope >50°

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Temperature Effects
Vampire
seismographs

38. 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?

41. 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
Tsunami
Rock avalanche
Dambreak flood
Severe sedimentation
Scenario provided
by 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.660AD
750 million m3
Murchison
Mw7.8 1929
Lake Stanley
18 million m3
Barth 2013 Landslides Hancox et al. 2002 BNZSEE 35(2):59-95

48. GNS SciencePhoto: V. Kennett
Perfect Storm?

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MCNP
Huts

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MCNP
Huts
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)