Earthcache; Blenheim's Boulder Bank (Marlborough) EarthCache
Hidden : 8/4/2016
Difficulty:
3 out of 5
Terrain:
2.5 out of 5

Size: Size: other (other)

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Geocache Description:

This Earthcache has been set to highlight the feature of interest, there is no need to go to the start waypoint for any answers.

Head to the two listed waypoints to appreciate the feature from two different levels. You will find some of the answers to the questions at or near these WPs. Some other information can be found online.
You may log your find as soon as you've sent your answers, no need to wait. I will get in touch if there's any problem.

WAIRAU BOULDER BANK.

One of the more interesting features of the Marlborough landscape is the Wairau Boulder Bank which extends from the White Bluffs in the south of Cloudy Bay to the Wairau River mouth, 8½ kilometres to the north west.

After the last period of glaciation (about 14,000 years ago), as the ice melted, the sea level rose and was at its highest about 6,000 years ago. At that time it intruded into the Wairau Plain to a point west of the Riverlands Cob Cottage forming a deep bay, the shore of which was the sandhills which still stretch across the valley in an arc to Tuamarina.

A strongly flowing flood tide runs north up the Marlborough coast and this carried into the Wairau Bay the gravels which were washed off the end of the White Bluffs. Eventually these gravels were deposited in a strip stretching right across the bay to Tuamarina.

Behind this boulder bank the rivers of the plain dumped their sediments and built up the land until the bay was filled in. North of the Wairau mouth the gravels were pushed continually west forming numerous beach lines to Rarangi while south of the Wairau the boulder bank effectively remained, containing behind it a huge lagoon with swampy edges.

It had taken about five thousand years for the boulder bank to form across the Wairau Bay and the land to fill in behind it. During this time numerous floods and earthquakes added their influence to the continually changing landscape.


History of the Wairau Bar

The Wairau Bar is notable for its rich history. It is the earliest known site of human occupation in New Zealand; home to the first generation of Polynesian migrants, who became known as the Moa Hunter. They were thought to have landed their waka (canoe) more than 800 years ago, settling in a land where birds flourished unchallenged by predators.

The lagoon also provided bountiful kōnae (food basket) of water fowl, seafood and tuna (eel) for these early settlers. The giant flightless bird, the moa, became the Moa Hunters’ primary food source. It is thought to have become extinct around 500 years ago, well before the arrival of European settlers. The Moa Hunter culture was later joined by the fleet Maori in around 1350, who in turn were joined by European whalers and sealers from around the world in the 1800s.

The shallow tidal waters of the Wairau Lagoon with its channels, sand spits and islands, covers approximately 2,400 hectares. Early Polynesians dug long channels to capture fish on the incoming tide and remains of these fish traps are still visible today, evidence of man's early history. The islands are low and flat, ideal for nesting birds such as black swan, black-backed gull and the royal spoonbill.

The Wairau Lagoon is separated from Cloudy Bay and the Pacific Ocean by a boulder bank, an 11 kilometre spit of saucer shaped rocks formed by the isodiametric action of pounding tides and currents. To the south, the White Bluffs soar to a height of 268 metres and at the northern end of the spit lies the tapu (sacred) Moa Hunter burial site.



Formation of the Boulder Bank.

Two main sea currents flow northwards along the east coast of the South Island, the most Southerly of which is the Southland Current. The northern-most flows from the Banks Peninsula to the East Cape of the North Island. This current moves northward any river gravel and debris which is discharged into the sea.

Prior to 5000 Years ago. Prior to 5000 years ago, the sea coast here would have been much further inland, with a bay formation. As gravels from the Awatere River and the eroding White Bluffs were moved northwards by the sea current, they were dumped in the lee of White Bluffs. These gravels began to form the Boulder Bank.

4500 years ago. As the boulder bank continued to extend across 'Wairau Bay', the Wairau River deposited mud and silt on both its northern and southern banks. This gradually filled in the bay, forming the lagoons behind the Boulder Bank and new beach ridges out from the northern cliffs.

800 Years ago.The present position now sees the Lagoons trapped behind the Boulder Bank. The Wairau River flows to sea at its northern tip. A new bay has thus been formed from this process.


Upper questions;


1. The boulder bank to the South (true right) of the Wairau River (mouth) has quite a narrow profile in comparison to the beach to the North, at Rarangi. Why do you think there isn't a boulder bank formed on both sides of the Wairau?


2. Primarily, what factor caused the lagoon behind the boulder bank to double in size in 1855?

3. The largest pool in the lagoon can cover an area in excess of 1500 hectares.
Name 3 different factors that can cause the size of the main lagoon to fluctuate.

4. What is the Maori name for the boulder bank (begins with 'P')

Lower questions;


5. About the changing environment over the years; What do you think it will look like in another 5000 years time, if there is no intervention from mankind?

6. What is the name of the ocean current that is responsible for the creation of the boulder bank?

7. The saucer shaped rocks have been shaped by forces of nature action; In your own words, how do you think they got their even, rounded shape?

Additional Hints (No hints available.)



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