Tuesday, 18 December 2007

On the 18th..... at St Andrews!

The GPS tracker is functioning again today and the map (left) shows Mark's location at the end of day 2 in New Zealand. He is approximately two thirds of the way between Dunedin and Christchurch. However, closer inspection of the last fix on the tracker reveals the following...

...and an even closer zoom shows the detail of Mark's last known position..... I bet the locals like to say that they play their golf at St Andrews!

Shortly after leaving Palmerston this morning, Mark would have cycled along this stretch of coastline which, judging by the amount of blue dots (representing the photo layer in Google Earth) is clearly interesting. " Stone globes with unknown origin". Mark may not have had time to investigate but we can and here they are!

They certainly give new meaning to beach balls...
Their location on the beach is the result of marine erosion of the mudstones which underlie the coastal cliffs. As for their almost spherical shape ...... there would appear to be much debate surrounding that! However, if you can cope with the chemistry, there is a pretty detailed explanation here. Or the layman's explanation which I can understand goes something like this.... they were created by a process similar to the formation of oyster pearls, where layers of material cover a central nucleus. For the oyster, this core is an irritating grain of sand. For the boulders, it was a fossil shell, bone fragment, or piece of wood. Lime minerals in the sea accumulated on the core over time, and the concretion grew into perfectly spherical shapes up to three metres in diameter.The original mudstone seabed has since been uplifted to form coastal cliffs. Erosion of the cliffs has released the three tonne captive boulders, which now lie in a haphazard jumble across the beach.

By mid afternoon today, Mark was approaching the border between the region of Otago and Canterbury, the largest of New Zealand's regions. The border follows the the river Waitaki which exhibits some excellent features of braiding.
Braided rivers are made up of a network of small channels separated by temporary islands called eyots. Rivers will often braid if they are carrying a lot of sediment, if their seasonal flow fluctuates and if they are flowing on a very gentle gradient. All of these conditions apply to the Waitaki and to many other braided rivers in South Island New Zealand. Much of the sediment comes from outwash of glaciers in the Southern Alps which is very high in spring and early summer but low in autumn and winter. The view below comes from Flickr and its caption states that is taken looking upstream from the State Highway 1 bridge crossing the river which is the exact location of Mark's crossing of the river today...Beyond the Waitaki lie the Canterbury Plains which I intend to explore tomorrow. However, the last topic for today is yet again the weather! After the hot, dry conditions of Australia, the cool damp weather of summer in South Island is providing Mark with a new challenge. The web diary today actually says that it is windy, overcast and dry and that he is feeling cold. The weather map for tomorrow promises better..By my reckoning, Mark should have a tail wind as any wind will be coming from the south west (this means they will be cool as they have originated in the Southern Ocean). The winds will be very slack. You can tell this because there are hardly any isobars (the black lines) crossing South island. The nearest front (which will have associated cloud and rain is over North Island). We can check tomorrow to see if I'm right!

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