Friday, June 12, 2015

Mystery explosions solved - does long dead volcano become alive again??

Friday, June 12, 2015
oldbearnews editor

As you know - we had a rather large earthquake in Christchurch and that February  shake did do some decent damage to the area.  As you probably also know - Christchurch is the largest city in the South Island of New Zealand, and the country's third-most populous urban area. It lies one third of the way down the South Island's east coast,   just north of Banks Peninsula (ok so that part is the important part here).  wohooo
Banks Peninsula forms the most prominent volcanic feature of the South Island. Geologically speaking, the peninsula comprises the eroded remnants of two large composite shield volcanoes (Lyttelton formed first, then Akaroa), and the smaller Mt Herbert Volcanic Group. These formed due to intraplate volcanism between approximately eleven and eight million years ago (Miocene) on a continental crust. The peninsula formed initially as offshore islands, with the volcanoes reaching to about 1,500 m above sea level. Two dominant craters formed Lyttelton and Akaroa Harbours. The portion of crater rim lying between Lyttelton Harbour and Christchurch city forms the Port Hills.  Actually Banks Peninsula comprises 15 volcanic vents/cones - not 3. These have not been active for 6 million years and the subduction zone and 'hot spot' that made their creation possible has long since moved away - much like the Hawaiian chain islands of extinct volcanoes.  So they say . . . . .
So naturally when we had the 6.2 earthquake one of the most often questions asked was: is the volcano coming alive again?!  Common consensus  until that point in time was - no chance - it is extinct  and has been so for some long time. 

Further our GNS scientists here in NZ have tested the hot springs around Banks Peninsula post-quakes.  The chemical composition of that water is not that which would indicate volcanic activity/source.  The massive amount of liquefaction and earthquakes that Christchurch has experienced has caused changes in our water table and natural spring levels but again nothing indicating volcanic activity or presence of magma. 

See this link and read the story there:

However in the last few months there have been "mystery explosions" and deep rolling boom sounds recorded in the eastern part of town.  The hot springs tested - have also  been noted to be - well - hotter.

Further - I lost count how many aftershocks we have experienced since Feb 2011 but it is fair to say it is in excess of 3000.

So guess what was observed today - urm - yesterday??  One gigantic enormous steam-cloud being spewed forth from the crater rim, rising vertically  several hundred meters before it flattened  out.  Steam - which means water had to be heated by magma and find its way up and out.   It was a impressive sight for sure!
I tried to ring the local Geonet people who intially did take my call - but then laughed this off - and hung up.  Subsequent phone calls were ignored.  I think they may have put me on a barred list.  Sighs
Luckily for me - I had my camera with the long lens with me at the time, so was able to take urm - 'an evidence - photo'.  

Leaving work later in the afternoon and taking another look - by then the steam had dissipated - so I guess the volcano run out of - urm - steam?? Or was it puff??
Either way -  Banks Peninsula may be declared as dead volcanoes, now I am not so sure anymore . . . . .

Have fun

 bear print

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