Many people have told us the story about how the earthquake in the 1800's raised the level of the harbour in Porirua from a deep sea harbour to a shallow harbour that now exists. It's really interesting that a good search of the net doesn't yield any information to this nature, but it does tell us a much more interesting story.
Beginning in the late 1850s European settlement in the area had a major impact on the harbours. Forests were cleared a rapid rate. In 1855 the West Wairarapa earthquake, which had a magnitude of 8.2, rocked the settlement. Although it was once thought that the earthquake significantly reduced the floor of the Pauatahanui Harbour arm, research by a geologist has shown that while uplifting has taken place in the past neither the 1848 or 1855 earthquakes lifted the harbour floor. A more plausible explanation for the changes to the shoreline at the head of the Pauatahanui Inlet is the accumulation of silt following the clearance of the surrounding bush. The removal of this protective cover allowed erosion to occur, and many thousands of tonnes of soil were deposited into the harbour. Sea level changes have also had an impact on the harbour.
This deposition of silt has continued over Porirua's development and now poses a serious problem for the Porirua Harbour.
More information can be found here on the Porirua City Council's website.
Taking an image from approximately 1840 by Brees, Samuel Charles, 1810?-1865. [Brees, Samuel Charles] 1810-1865 :Plan shewing the several points of view of the sketches illustrative of the West Coast. [1844 or 1845]. Ref: B-031-036. Alexander Turnbull Library, Wellington, New Zealand. http://natlib.govt.nz/records/23150330
and overlaying a current image on top of this, one can see how far the harbour has been pushed back over the last 170 years.
Next you need to read about deforestation at the following link
In order to log this earth cache you need to do the following
1) Find the sign in the image above and place your hand on the sign and then take a photo of the sign. Please make sure you do not post any background that will give away the location of the sign,
2) Determine how far the water has receeded in the last 170 years from the location of this sign to S41 07.839 E174 50.540.
3) How many meters a year would the soil have moved ? (Assume a straight line for the purpose of the calculation)
4) If deforestation continues they say there will be only 10% of the forests left by when ?
5) Post a short paragraph about what you think Porirua will be like in 20 years time.
I've tried to keep this earth cache simple yet informative and allow people make their own decisions as well as learn a bit about the Porirua history, deforestation and the ability to use your imagination to link the above facts togethers.