9.1.2012

Volcanoes and geothermal areas

There are five huge calderas in the central North Island of NZ. Calderas are no mountain shaped volcanoes but rather volcanic depressions. When such a volcano erupts (usually quite violently), a vast underground chamber of magma gets emptied. After that those empty chambers often collapse forming a depression which can turn into a lake like for example the Rotorua lake. The first eruption in this area is estimated to have happened 450 000-500 000 years ago, several other eruptions followed. The most recent eruptions was 126 years ago in Tarawera.

For me as a non geologist it is hard to distinguish a “normal” lake from a caldera: It just looks like a lake surrounded by somewhat higher areas. Interesting still to know that you are camping on some type of volcano (or on its margin) which has most possible has a certain cycle of eruptions recurring at intervals of several tens or hundreds of thousands of years. Who knows when the next eruption will be? People here seem to be quite ok with that. At least Taupo and Rotorua are quite normal towns, local centers in an otherwise rather rural sheep and cattle farming area.

More easy to admire for non geologists are the magnificent geothermal areas between Taupo and Rotorua. Geothermal areas are such areas in which heat flows from the hot magma far below the ground to the surface. They can occur in areas of volcanic activities or areas with faults: Rainwater seeps into the ground and gets heated up to several hundred degrees Celsius. Since hot water is less dense than cold water, it needs more space – and has nowhere to go but to the soil or rock surface. It depends on the ground in which form it will come out – as a geyser, as hot vapor in fumaroles, as a hot spring or in form of bubbles in a mud pool. On its way upwards the hot water leaches minerals out of the bedrock which get sedimented on the surface when the water cools down again. Depending on which chemical substances there are in the bedrock, the colours can vary from yellow over green to red and purple. It’s just amazing (and smelly due to all that hydrogen sulphide in the air).

The first place I go is Waiotapu, “Thermal Wonderland” which is referred to be the most colourful geothermal area of NZ. And what should I say .. It is just amazing!
 
“Champagne Pool” a 2000 m2 large spring pool of alkaline chloride water. The orange rim is not only beautiful but also poisonous: It consists of arsenic sulphide.

After a long walk in the geothermal area in Waiotapu, I am tired and it is getting late as well. Time to search for a place to stay for the night .. and why not also a SPA pool? There are a lot of pools filled with geothermal spring water in the area – I guess it’s just fun for most of the tourists to try them and the minerals in them area also said to have healing effects for many skin and rheumatic diseases.
I do not have to search long until I see another sign: Thermal pools. I follow it until I get to heaven. Or let’s call it Waikite valley like people do here.

A hot spring with boiling water discharges into a little creek. Some water of the spring is pumped into a cooling system and from there runs in a series of hot pools you can sit in. And – there is a camping side right next to that SPA place. The deal is – when camping there, you can use the pools the whole day if you wish. Absolutely cool – or actuall HOT! The water temperature in those pools is between 35 and 40 degrees Celsius. You just sit there and enjoy.
Special are also the spring and the creek which flows into a geothermal spring ecosystem (quite rare nowadays and a small conservation area). Some Sphagnum was growing close to the hot river, otherwise a special species of Lycopodium and lots of different ferns.

Geothermal area of Whakarewarewa at the southern end of Rotorua:



Deposits of crystalline sulphur produced by a fumarole.
 Bubbling mud pools

Ei kommentteja:

Lähetä kommentti