Wednesday, 19 December 2007

Canterbury Plains

I am quite looking forward to the American leg. At the moment with Mark being 13 hours ahead, I just settle down to do today's posting and find that Mark is already well into tomorrow! It's now the 20th in New Zealand and Mark is heading out of Christchurch. We haven't got there yet but we're about to......

Mark's route today (or yesterday depending on your time zone!) took him across the Canterbury Plains. You can see them clearly on this map - the large lowland area to the east of the Southern Alps which stretches in an arc around Christchurch. They are, according to one source, an area of braided rivers and pastoral perfection between the Southern Alps and the Pacific Ocean. As flat as a billiard table, the plains are a remarkable sight from the air - a patchwork of agricultural activity that ranges from grazing grass and wheat to herbs and sunflowers. The area produces more than 80% of New Zealand's grains, crops and seeds.The Canterbury Plains are formed from the alluvial shingle fans of several large rivers - the Waimakariri, Rakaia, Selwyn and Rangitata. Above... an aerial view of this intensively farmed region which, despite Mark's experiences so far, is actually quite dry, receiving only about 650mm of rain in a year. This is due to its position in the rainshadow of the Southern Alps which act as a barrier to the north westerly prevailing winds. Amidst the green patchwork there are many of the pivot irrigation circles which we have seen in so many countries along Mark's route. In the Canterbury plains, some of these areas are simply irrigated to produce better grazing as in this image which shows a segment of one circle with many grazing cattle. (You will have to take my word for it as they do not show up clearly on the lower res images of the blog). In the absence of obvious field boundaries, I assume that grazing is controlled by electric fences.

Interesting though the farming on the Canterbury Plains may be, it is the physical landscape and in particular the wonderful braided rivers which really caught my attention as Mark cycled through. First today was the Rakaia river ... The two bridges crossing the Rakaia River, at the township of Rakaia are New Zealand's longest road and rail bridges respectively. The bridges are some 1750 metres in length and the road bridge carries the main A1 highway along which Mark cycled today. A bit of 'manoeuvering' on Google Earth managed to produce this image looking up stream from the bridges. As mentioned in yesterday's posting, one of the reasons why rivers braid relates to the sediment load they are carrying. Rivers like the Rakaia carry huge volumes of sediment which has been washed out of the glaciers in the Southern Alps. Following the Rakaia back to the mountains, we can even 'find' the glaciers which are the source of its water.....

Some 30 miles east of the Rakaia, and again crossed by Mark's route earlier today, is the Rangitata river which exhibits similarly astounding braiding and a floodplain which is almost 'carved' into the farmland.
These rivers have really caught my attention - not least because until this week I had no idea that there were such good examples of braided rivers in New Zealand. The only other examples of rivers like this which I have seen are in Iceland. Here's one above which I photographed a couple of years ago. As a geographer, I find it very 'reassuring' to find features like this replicated all over the world!

The other interesting feature of the physical landscape along Mark's route today is the area just south of Christchurch. The circular peninsula is Banks peninsula and comprises the eroded remnants of two shield volcanoes. West of this is the Ellesmere lagoon lake and Kaitorete spit formed by longshore transport of beach material by the waves. The spit forms a barrier to the sea and creates the shallow, sheltered lagoon which is Lake Ellesmere. This first photo shows a view across the lagoon from inland and the second (below) shows a view from the lagoon of the Southern Alps some 50 miles away. Mark overnighted on the 19th in Christchurch , viewed here with the backdrop of the Southern Alps. And finally.... here's a bit of video of a train journey across the Canterbury plains which shows the Rakaia river crossing

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