Monday, 1 November 2010

New Zealand ~ land of earthquakes and volcanoes

The recent 7.1 magnitude earthquake in Christchurch highlights the on-going movement of the land we live on.  New Zealand as a land mass came into being as a result of the earth's crust grinding on itself so upheavals are to be expected.  This continuing pressure produces tension which has to be released from time to time - in the form of earthquakes and volcanoes.  It's an element of risk which New Zealanders live with and for the most part ignore.  For long stretches of time things stay put, but from time to time major shifts occur which shake us out of our usual complacency both literally and figuratively.  Just how stable is the land on which our cities are built?  The answer is that it depends how you look at it.

Christchurch and Canterbury:
You can find my earlier article about the Christchurch Earthquake via this link.  The original article has been updated to include several more segments including a recent one about aftershocks.

Dunedin and Otago:
Based on the law of averages Otago is 43 years overdue for an earthquake of the magnitude of about 8, which is greater than the Canterbury one.  You can read more about it in this ODT article of the 18th September: "Quaking in our boots: how prepared is Dunedin?"

Wellington is generally considered the city most vulnerable to earthquakes, a point which seems to be down-played in this article published on 18th Sept 2009.  It's surprising how many Christchurch residents thoughts went to Wellington at the time of the big quake, wondering if it was centred there. 

How about Auckland then?
Although there is no actual volcanic activity there at the moment, New Zealand's largest city is built on an active volcanic field, as described in this article of 20th April 2010.  While eruptions in our lifetime are a 'low probability' these things are not entirely predictable.  Evidence of the last bout of volcanic activity 600 years ago can be seen in Rangitoto Island, the major scenic feature of Auckland's Waitemata Harbour.
     But volcanic threats are not necessarily restricted to local volcanic activity: some years ago when an area of the city's north western motorway was being redeveloped extensive modification was required when over a metre of ancient volcanic ash was discovered dating back to the eruption of the volcano, the remains of which is now Lake Taupo.  This lake is 232 kilometres (144 miles) away to the south.

Living with the potential for volcanic eruption is the subject of this site run by the The Earthquake Commission and the Auckland War Memorial Museum.   
The opening page shows dramatic footage of volcanic eruptions.  Please note that the volcanoes pictured in action are not identified and while some footage may have been filmed in New Zealand, much of it certainly was not.  The website explains that:
Living safely with volcanoes involves a number of approaches. Utilizing the latest monitoring techniques, conducting research, developing thorough and well-rehearsed emergency procedures and putting systems in place to help recover after an eruption are all essential components of helping to stay safe. The Volcanoes website aims to provide details related to all of these crucial issues.
The city of Rotorua in the central North Island is built on an area which provides ample daily evidence of volcanic activity in the form of hot pools and mineral water.  While not all ground is hot or even warm, steam commonly vents through street drains and other holes in the ground.  Photographs of the geothermal activity characteristic of the region can be found in this dramatic slideshow of nearby Waimangu Valley.  It's good to see the photographs identified both by location and the photographers who took them.

The land both in New Zealand and the world as a whole, may seem stable, even fixed, but this is only because of our relatively short lives.

The natural world is in a state of constant change, as is well described in this YouTube clip.  Disappointingly, the commentator's identity is not given.

Here is a brief diagrammatic model of shifting tectonic plates:

There are lots of interesting clips of this topic.  These can be found by exploring related links. 

This third video overview is not included on YouTube and is well worth a look.  In it we can see a construction of how land masses have moved and changed over the last 400 million years, and the possible direction of changes to come over the next 250 million.

So is New Zealand a safe place to live? 
For the most part the answer has to be 'yes' as the movement of our land is usually not noticeable, even if parts of it are constantly moving at the rate of  two to three metres a century!

These movements have given rise to some of the world's most dramatic and beautiful scenery and created the conditions which makes our country the very special and unique place that it is.  To see the slide show of the page linked to above click the Play button on the photograph at the top.

Meanwhile I've been sitting in this hot room while a summery day happens outside.  Time to get a cool drink and go out and enjoy it!

All my articles about the Christchurch earthquakes and aftermath can be found via the page linked to below, or at the upper right of this screen:

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