DDBM - Mt Climie (Wellington) Traditional Cache

MONITORING TECTONIC MOVEMENT

Continuous Global Positioning System (CGPS) equipment is used by GNS to monitor the crustal deformation occurring in the zone between the Pacific and Australian plates along the east coast of the North Island, an area known as the Hikurangi Margin. Some 60 monitoring stations are being installed between Hicks Bay, Wellington and Wanganui.

To get data that is reliable over a very long time period and to capitalise on the accuracy of the CGPS system (a few millimetres), the monument on which the antenna is mounted must have a very rigid and stable connection to the underlying land mass. Up until around 2005 the monuments were concrete pillars with reinforcing bars glued about 2m deep into rock. This design required good rock at the surface, but at times it was hard to be sure this rock was well connected with the greater land mass. In some areas good rock is hard to find, such as in central Hawke’s Bay where there is a lot of limestone, and the volcanic region where the land is covered by layers of ash. To overcome these limitations a change was made to using a monument design developed in the United States known as the Deep Drilled Braced Monument or DDBM.

A DDBM has the form of a quadropod with the addition of a central vertical leg. It is about 1.6m high. The legs are made of thick-walled stainless steel pipe. Each leg penetrates about 10m into the ground and the bottom 6m are grouted in place. The 4m just below the surface are in a foam rubber casing to isolate the leg from potentially unstable near-surface material. This means the monument foundation is far more likely to be in bedrock that is stable with respect to the surrounding geology.

This is the first trial installation. This has proved to be very successful and only a few changes to the American design and technique were needed. The drilling was done with a purpose-built pneumatic drilling rig, which is light enough to be transported to a site by helicopter.

The cache is a 1 litre snaplock container in a camo bag. At the time of placing it contained a logbook, pen and FTF prize. It is placed a discrete distance away from the actual intallation so as to not interfere with it.

Please NOTE that you must sign the log book for each individual cacher, Finds logged not corresponding with the logbook may be deleted. Please take some time before leaving to ensure that the cache is re-hidden exactly as you found it.

Please observe the usual Safety requirements when venturing out to exposed hill top areas.

• Check the weather forecast before your trip
• Carry warm and waterproof clothing, and enough food and drink for your trip
• Carry sun protection
• Plan your route and tell someone your intentions
• Wear a good pair of boots or walking shoes