White IslandBy Roger Childs

There are plenty of advantages in living in a remote part of the planet. New Zealand has been far away from the theatres of conflict in the two World Wars and the Japanese never got this far south in 1942. We also don’t have any land borders with other countries, and because we are a set of islands, we have a huge Exclusive Economic Zone for harvesting resources.

However, the country does have some major location disadvantages:

  • situated in the “Roaring Forties”
  • sitting on the Pacific “Ring of Fire”
  • surrounded by sea, with direct ocean access from the tropics and Antarctica.

The last few days have seen the country affected by four natural hazards related to these disadvantages – high winds, torrential rain, flooding and a volcanic eruption. Once again these have underlined our vulnerability to the forces of nature.

Forces beyond our control

Southern Alps rainfallBeing located in the forties latitudes surrounded by water, New Zealand often gets strong winds off the Tasman Sea, and from the oceans north and south. Our weather generally moves from west to east, and winds coming off the sea rise rapidly over the Southern Alps and the lower mountain ranges of the North Island. As the moist air rises, it condenses and there is often very heavy orographical rain. This explains why the wettest parts of New Zealand are Fiordland and the West Coast.

However, heavy rain may result from fronts moving up the country from the south-west, and much of the flooding in South and Mid Canterbury and North Otago late last week was caused by this process. Torrential downpours may also come from tropical cyclones moving south-east.

Interacting tectonic plates

Our hazardous environment is compounded by New Zealand’s location on the edges of two of the Earth’s crustal plates. The Australian and Pacific Plates are sliding past each other, very slowly, and this accounts for earthquakes and volcanoes. Nelson was once attached to Central Otago, but over millions of years the region has slid along the plate boundary to its present location. It is now on its way to Taranaki!

NZ EEZBelow the plates molten rock (magma) helps to move them along and occasionally through fissures (faults) in the rock above, magma reaches the surface as volcanoes. In the past this has occurred in Northland, Auckland, Taranaki, the Central North Island, Banks Peninsula and Port Chalmers. Today it happens on the Volcanic Plateau and White Island. 

These are dangerous places, but people still want to walk the Tongariro Crossing and land on White Island. Occasionally this can be disastrous as it was on Monday.