{"id":2905,"date":"2021-09-23T10:34:06","date_gmt":"2021-09-22T22:34:06","guid":{"rendered":"http:\/\/blogs.lincoln.ac.nz\/gis\/?p=2905"},"modified":"2023-05-07T00:40:31","modified_gmt":"2023-05-07T00:40:31","slug":"nga-purakau-o-te-whenua-kaitorete-spit","status":"publish","type":"post","link":"https:\/\/blogs.lincoln.ac.nz\/gis\/nga-purakau-o-te-whenua-kaitorete-spit\/","title":{"rendered":"Ng\u0101 P\u016br\u0101kau o Te Whenua – Kaitorete Spit"},"content":{"rendered":"

Satellite images, DEMs and hillshades are used to help tell the story of Kaitorete Spit and Te Waihora\/Lake Ellesmere.\u00a0\u00a0Thanks to\u00a0Lloyd Carpenter for guidance on this post’s title, roughly translating to “A Landscape Story”.\u00a0\u00a0Ng\u0101 mihi e hoa!
\n<\/em><\/p>\n

Oh great…\u00a0 Yet another featureless, boring Canterbury vista…(nice day, though)<\/p>\n

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You could certainly be forgiven for thinking this!\u00a0 We’re on the Little River Rail Trail looking roughly southeast.\u00a0 Te Waihora and Kaitorete Spit<\/a> are\u00a0just over our right shoulder and parts of Banks Peninsula are visible to the left.\u00a0 But I would argue that we’re right in the middle of a fascinating, geomorphic story here – it’s just that it’s not very apparent from where we stand.<\/p>\n

Satellite imagery and aerial photographs give us unique perspectives on the world. They are\u00a0full of things that may not look look like much on a human scale, but take on very different meaning when viewed from higher altitudes.\u00a0 Increasingly, LiDAR <\/a>is doing the same.\u00a0 Here are a few examples to get us started.<\/p>\n

This might just look like a wind blown high desert at ground level:<\/p>\n

\"\"<\/a>
https:\/\/www.cheapflights.com\/news\/archaeological-travels-nazca-lines<\/em><\/span><\/figcaption><\/figure>\n

but when viewed from altitude (~500 m), well,\u00a0the Nazca Lines<\/a> are pretty amazing:<\/p>\n

\"\"<\/a>
https:\/\/www.cheapflights.com\/news\/archaeological-travels-nazca-lines<\/em><\/span><\/figcaption><\/figure>\n

Switching continents, here’s a view from the ground somewhere in the Mauritania:<\/p>\n

\"\"<\/a>
By Clemens Schmillen – Own work, CC BY-SA 4.0, https:\/\/commons.wikimedia.org\/w\/index.php?curid=86877213<\/em><\/span><\/figcaption><\/figure>\n

But just look at it from an altitude of around 100 km:<\/p>\n

\"\"<\/a><\/p>\n

This is the so-called Eye of the Sahara<\/a>, known as the\u00a0Richat Structure<\/a>\u00a0to geology geeks.\u00a0 Once thought of as an impact crater from an asteroid, it’s now believed to be the eroded remnants of a geological dome, sort of like a ginormous Moeraki Boulder<\/a> being eroded away from above.<\/p>\n

We are like the fleas on the elephant’s back, never quite getting the big picture from our squat perspective.\u00a0 And we don’t have to go too far to see some similar things in our little part of Aotearoa.<\/p>\n

Flying in and out of Christchurch, one can’t help but notice the patterns like these on\u00a0the south\u00a0side of the Waimakariri (at least I can’t), reminders of the meanderings of the river before the days of stopbanks:<\/p>\n

\"\"<\/a><\/p>\n

(The whole of Canterbury Plains has basically\u00a0been\u00a0river bed at one point or another so one needn’t go far to see these patterns.)<\/em><\/p>\n

Here’s another one.\u00a0 Let’s start with the view from the ground:<\/p>\n

\"\"<\/a><\/p>\n

Move along folks, nothing to see here.\u00a0 We’re looking northwest just off highway\u00a075 on the way to Little River (at the blue dot below).\u00a0 Wairewa\/Lake Forsyth is at our back and Te Waihora\/Lake Ellesmere is not far away to the west.<\/p>\n

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Let’s jump 3,000\u00a0metres up:<\/p>\n

\"\"<\/a><\/p>\n

What’s with those lines on the ground?\u00a0 They weren’t particularly noticeable at ground level but are much more apparent from above.\u00a0 Wet versus dry soil?\u00a0 Tracks from the centre pivot?\u00a0 Are they real?\u00a0 By that, I mean are they more than just coloured areas on the ground from cropping perhaps?\u00a0 Let’s use some data to check it out.<\/p>\n

Here’s a hillshade<\/a> layer derived from 1 m LiDAR<\/a> data:<\/p>\n

\"\"<\/a><\/p>\n

Going by the hillshade, these features are real enough that their slightly higher elevations are sufficient to create simulated shadows.\u00a0 Querying the elevation data, these ridges certainly look real.\u00a0 Using the Profile tool I can whip up an elevation profile chart:<\/p>\n

\"\"<\/p>\n

(On this profile north is at the left, south to the right.)<\/p>\n

And this isn’t the only place these occur.\u00a0 Moving north and west, we see some interesting shelf-like arcs in Birdlings Valley (note that the curving state highway is clearly visible in the data to the left):<\/p>\n

\"\"<\/a><\/p>\n

Looking east from the highway, here’s what that area looks:<\/p>\n

\"\"<\/a><\/p>\n

And a profile:<\/p>\n

\"\"<\/p>\n

Doesn’t look like much but that tree-covered ridge is\u00a0close to five metres high!\u00a0 And on the inside of Kaitorete Spit, some even crazier, arc-like patterns:<\/p>\n

\"\"<\/p>\n

(The blue dot shows where the picture at the start of this post was taken.)<\/p>\n

And real enough to be picked up by the hillshade:<\/p>\n

\"\"<\/a><\/p>\n

But here’s what that area looks like at ground level from the rail trail (looking west):<\/p>\n

\"\"<\/p>\n

Not much to see.\u00a0 Taking a wider and higher angle we can start to see a bigger picture emerge with all sorts of lines and patterns:<\/p>\n

\"\"<\/a><\/p>\n

These patterns aren’t new and they have been studied before.\u00a0 A 1970 thesis by John Armon mapped these lines and ridges:<\/p>\n

\"\"<\/a>This figure was adapted from Armon, 1970 by Soons et al., 1997.\u00a0\u00a0<\/em><\/span><\/p>\n

These features are all quite real and tell a story, a geomorphic story, about the formation of Te Waihora and the Kaitorete Spit – the two go hand in hand,\u00a0echoes <\/a>of their shared history.\u00a0 To get the full story we need to go back in time a bit, about 8,000 years.<\/p>\n

Disclaimer: I’m not a geomorphologist (nor do I play one on television<\/a>) and have relied heavily on some good chats with Peter Almond and papers from Jane Soons and Jamie Shulmeister for what follows.<\/em><\/p>\n

Back in the day, what is now Te Waihora\u00a0was an open bay, something like this (please excuse the modern features on the basemap):<\/p>\n

\"\"<\/a>Approximate coastline\u00a0\u00a0early Holocene (adapted from Armon, 1970)<\/em><\/span><\/p>\n

Eroded shingle from the Southern Alps\u00a0was carried\u00a0down to the sea bythe Rakaia and Rangitata Rivers, ending up in the ocean where it was exposed to the Southland Current, which runs southwest to northeast along the coast.\u00a0 Most of this sediment started migrating north along the coast, transported along by\u00a0longshore drift<\/a>.\u00a0 This started building a gravel spit moving gradually to the northeast:<\/p>\n

\"\"<\/a><\/p>\n

Spits like this are long and thin with a rounded head shaped by wave action, (see, for example, the Brighton Spi<\/a>t, or the Boulder Bank<\/a> in Nelson).\u00a0 We see a similar shape at Southshore where the local current moves north to south:<\/p>\n

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Slowly, the spit grew closer to Banks Peninsula:<\/p>\n

\"\"<\/a><\/p>\n

As it grew, it left behind the swirling hooked ridges we saw in the image above:<\/p>\n

\"\"<\/a><\/p>\n

Once contact was made with Banks Peninsula, the longshore drift sediment continued to flow, gradually filling in the bays and building the beach ridges we saw above at Birdlings Valley and a few other locations, but also filling in the valleys and depositing sediment towards the south.<\/p>\n

But that’s not the end of the story, no, because at a point in time around 700 to 1,000 years ago (Soons et al., 1997), the Waimakariri shifted (avulsed) to a new bed and flowed into what was the relatively newish Te Waihora lagoon, likely breaching the spit close to the current state highway and maintaining an opening to the sea.<\/p>\n

\"\"<\/p>\n

As braided rivers are wont do, it later avulsed again, heading north to its current bed where the stopbanks now have it locked in.\u00a0 This significantly reduced outflows through the spit, which was then able to reattach itself to the peninsula, permanently this time.\u00a0 Longshore drift continued to relentlessly transport sediment which slowly built up and out, pushing the coastline further south:<\/p>\n

\"\"<\/a><\/p>\n

And\u00a0forming the Kaitorete Spit as we know it today:<\/p>\n

\"\"<\/a><\/p>\n

And so, with time, we come to the current configuration of the Kaitorete Spit and Te Waihora as we know it today.\u00a0 In the process, Te Roto o Wairewa\/Lake Forsyth was also created as the shingle built up and cut off its connection to the sea.\u00a0 But as recently as the 1830s, waka and whaleboats were able to enter Wairewa from the sea (see Soons, 1998 for more thorough detail on this), meaning that Wairewa as a lake is quite a young feature.\u00a0\u00a0As sediment steams along the coast, the shoreline has gradually reoriented itself along an almost east-west line but currently doesn’t seem to changing much (an interesting question in itself!\u00a0 \u00a0Where’s all that shingle going now?).<\/p>\n

As most of the coastal geomorphologists will have been muttering under their breath, Kaitorete shouldn’t really be called a spit once the Waimak shifted and the reconnection to the peninsula.\u00a0 The proper term would be barrier beach but the name Spit has stuck, and I suspect most geomorphologists wince when they hear that.<\/p>\n

It’s a fascinating geomorphic story, methinks, and hopefully you’ve seen how available spatial data help us understand how it unfolded.\u00a0 The use of imagery and hillshades (plus some elevation profiles) have helped to tell this story, bolstered by field data and some hard mahi.\u00a0 And I guess it highlights yet another great thing about living in Aotearoa – everywhere you look, there’s an interesting story the landscape has to tell us.<\/p>\n

C<\/p>\n

Aside: I wanted to get a sense of any meaning or story behind “Kaitorete” for this post…it proved to be quite a challenge.\u00a0 With Lloyd’s help, the best we were able to do by way of translation was \u00a0“eat parakeet”\u00a0and also ‘”distress cry of parakeet” by\u00a0Taylor (1944)<\/a>\u00a0(similar in\u00a0Fletcher, 1929<\/a>) but also as “eat while fleeing” by White (1887)<\/a>.\u00a0 The Te Waihora Co-governance site tells us<\/a> that ”\u00a0Its ancestral name, K\u0101 Poupou a Te Rakihouia denotes the function of the spit \u2013 which is similar to that of an eel weir, guiding eels into the mouth of the hinaki (eel trap). In this case, the eels are guided to the Taumutu area where the k\u014dumu (eel channels) are constructed to catch migrating eels.”\u00a0 Place names are important but not always straightforward.<\/em><\/p>\n

References<\/p>\n

Armon, J. 1970.\u00a0 Recent shorelines between Banks Peninsula and Coopers Lagoon.\u00a0 Unpublished master’s thesis. University of Canterbury<\/p>\n

Soons, J., J. Shulmeister and S. Holt.\u00a0 1997.\u00a0 The Holocene evolution of a well nourished gravelly barrier and lagoon complex, Kaitorete “Spit”, Canterbury, New Zealand.\u00a0 Marine Geology<\/em> 138:69-90.<\/p>\n

Soons, J. 1998.\u00a0 Recent coastal change in Canterbury – the case of Lake Forsyth\/Wairewa.\u00a0 New Zealand Geographer<\/em> 54(1):7-14.<\/p>\n","protected":false},"excerpt":{"rendered":"

Satellite images, DEMs and hillshades are used to help tell the story of Kaitorete Spit and Te Waihora\/Lake Ellesmere.\u00a0\u00a0Thanks to\u00a0Lloyd Carpenter for guidance on this post’s title, roughly translating to “A Landscape Story”.\u00a0\u00a0Ng\u0101 mihi e hoa! Oh great…\u00a0 Yet another featureless, boring Canterbury vista…(nice day, though) You could certainly be forgiven for thinking this!\u00a0 We’re […]<\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-2905","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-json\/wp\/v2\/posts\/2905","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-json\/wp\/v2\/comments?post=2905"}],"version-history":[{"count":1,"href":"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-json\/wp\/v2\/posts\/2905\/revisions"}],"predecessor-version":[{"id":4008,"href":"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-json\/wp\/v2\/posts\/2905\/revisions\/4008"}],"wp:attachment":[{"href":"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-json\/wp\/v2\/media?parent=2905"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-json\/wp\/v2\/categories?post=2905"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.lincoln.ac.nz\/gis\/wp-json\/wp\/v2\/tags?post=2905"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}