Mass wasting and sediment transfer in New Zealand

1
Mass wasting and sediment transfer in New Zealand
2
Introduction

• Geography
• Climate
• Wind
• Rivers Mountains
• Mass wasting
• Onshore
• Offshore
• Summary

3
Geography Climate

• Mild climate throughout the country.
• Temperature 0 to 30 C
• North Island Subtropical
• South island From cold and wet in the west coast
  to dry and continental to east.
• Rain 500mm to 10,000mm per year

4
Climate summary
5
Westerly winds

• These are strong winds to the North and South of
  the Equator.
• New Zealand is lying between latitudes 35 to 45
  S.
• Zone of strong westerly winds.
• Southern Alps in the way
• Results in particularly high wind speeds to the
  east of these mountains.
• Rates 0.2 tons/ha/year
• Storm events 3000 t/ha.
• Soil erosion
• Farming issues
• Contribute to hillsides erosion
• Dumping sediment into the rivers
• New Zealand is a windy country by world
  standards!

6
Winds Summary
7
Rivers

• There are about 200 rivers in New Zealand
• Occupying 2 of the land
• Longest Rivers
• North Island Waikato - 425km
• South Island Clutha 322km
• These rivers are fast flowing Electrical Power
• Fishing is popular because of clean water in
  major Rivers
• Lakes trapping the sediment
• South Island 15 Mt/year
• North Island 1 Mt/year
• Total Sediments washed out to the coast
• 209 Mt/year split between the two Islands

8
Rivers Suspended sediment load
A combination of Steep slopes, heavy rainfall,
high uplift rates along the eastern side of the
Alpine Fault, and easily eroded schist result in
68 of south Islands sediment yield over 8 land
area.
9
Mountains

• 75 of the land is mountainous or hilly.
• North Island has 1 mountain chain with frequent
  volcanic activity
• Result of plate motion subduction of a plate
• Highest peak Mt. Ruapehu, a voclano 3k
• South Island has different plate motions as two
  plate are smashing into each other
• Formation of southern alps
• 650 km in length
• Mount Aoraki/Cooke Highest peak 3.7Km
• Contain 360 glaciest 29 km in length
• Uplift Erosion 7mm/year

10
Mountains

• 75 of the land is mountainous or hilly.
• North Island has 1 mountain chain with frequent
  volcanic activity
• Result of plate motion subduction of a plate
• Highest peak Mt. Ruapehu, a voclano 3k
• South Island has different plate motions as two
  plate are smashing into each other
• Formation of southern alps
• 650 km in length
• Mount Aoraki/Cooke Highest peak 3.7Km
• Contain 360 glaciest 29 km in length
• Uplift Erosion 7mm/year

11
Mountains Ruapehu
12
Mountains - Aoraki/Cooke
13
Mass WastingAlpine

• Alpine mass wasting
• Terrain made up of hard rock.
• Steep and high slopes
• Mass wasting can range from huge rock avalanches,
  to massive rock slides, rock falls and debris
  flows.
• Can travel great distances in matter of minutes
• Example Mt. Cooke Rock Avalanche
• December 14th, 1991
• 12 million cubic meters (Compare to hope 47
  million cubic meters)
• Travelled 7.5 km at an average speed of 200 km/hr
  
• No damage, no fatalities

14
Mass WastingAlpine

• A seismograph detecting the rock avalanche 60km
  away from the source.

15
Mass WastingLower mountain ranges

• Abbotsford (August 8th, 1979)
• Dunedin suburb of Abbotsford
• Cracks noticed in 1969
• 1979, a water pipe breaks and is unearthed
• Houses slide down
• No fatalities

16
Mass WastingLahar

• Mount Ruapehu (March 18th, 2007)
• Tephra dam burst
• 1.4 million cubic meter of mud, rock, and water
  flowed down on Whangaehu river
• No fatalities, alarm system worked perfectly
• 151 people were killed in 1953 with similar lahar
  flow.

17
Mass WastingHighest Fatality

• Waihi (1846)
• Heavy rain created a landslide
• Landslide blocked the river
• There days later the natural dam broke, carrying
  water and debris down Maori village of Te Rapa
• 60 deaths
• Shores of the lake Taupo

18
Mass WastingGreen Lake

• Largest documented landslide
• 13000 years ago
• Fiordland
• 27 cubic km of material ( 27000 cubic meter)!
• Basically whole chunk of Mountain range collapsed
  into the valley below
• Largest on earth (Onshore)
• Melting of glacier, loosing support?
• 9k mountain section collapsed.

19
Mass WastingOffshore

• Generally a lot bigger in magnitude
• Lubricated by water
• Collapse of thousands cubic meters of seabed.