If you are standing at GZ, you will already know that Norfolk Island lies in the south-west Pacific Ocean approximately 1,676 km from Sydney and at a latitude approximately level with Brisbane. It is 1100 km north-west of Auckland and 965 km south of Noumea.
Norfolk Island has an area of approximately 35 square kilometres and is the largest and only inhabited island in a group of three (Norfolk Island, Nepean Island and Phillip Island).
Climate is warm temperate to subtropical and is generally mild with little variation in diurnal and annual temperatures. The rainfall is generally highest in the winter months and the average annual rainfall is approximately 1,324 mm. High rainfall also occurs in the summer months in association with cyclonic storms and prolonged periods of low rainfall appear to coincide with El-Niño events.
Geologically, the Norfolk Island group is one of a "chain" of volcanic mounts formed after New Zealand/Lord Howe Rise separated from Australia in the Late Cretaceous (about 66 million years ago) then stopped forming the Tasman Sea in the Eocene (about 40 Million years ago) when Australia rapidly separated from Antarctica. The area around Norfolk Island is known as the Norfolk Ridge.
The Norfolk Ridge (which extends nearly 2000 km from New Caledonia to New Zealand) and the Lord Howe Rise are still apart of the Australian continental plate.
Norfolk Island is made up almost entirely of nearly horizontal layers of basaltic lava and inter-bedded tuff from three eruptive episodes between 3.05 and 2.3 million years ago. The pillow lavas and flow-foot breccias, along Norfolk Island’s northern coastline indicate that at the time of these eruptions, sea level was within 10m of the present level.
In the vicinity of GZ, the area around Nepean Island and the coastal rocks of Kingston including Point Hunter and Lime Kilm are not volcanic. These rocks are sandstone. It is thought these were formed in shallow water. Subsequent glaciation and sea level lowering together with weathering has meant that dunes composed of corals and shell grits can be seen in the rocky outcrops around Kingston.
If the initial symmetry typical of volcanic islands is assumed for Norfolk and Phillip Islands then at least two-thirds of the original landmass has been eroded away. The volcanic deposits on the surfaces of both Norfolk and Phillip Islands have been deeply weathered, in many places to a depth of 45 or 50m. Subsequent erosion of this weathered material has formed the Island’s undulating hillsides and deeply dissected valleys.
Norfolk’s steep but relatively stable hillsides reflect an equilibrium between rainfall, surface and subsurface soil porosity and structure, and natural vegetative cover.
Just down the road, you may have passed the first entrance to Headstone Reserve (and you can walk there from here - S 29° 02.667' E 167° 55.289'). Try and visit this spot not far away as well. This is where the headstone is for two soldiers who went fishing and were washed off the rocks and drowned. The creek (Headstone Creek) flows south westerly through the southern reserve. This stream has eroded down to the level of the unweathered basalt close to the coast before it cascades over the cliff about 20 metres above the sea. Look at the small waterfall (about 8m high) that is cutting slowly upstream. Similar effects of smaller streams washing over the cliffs visible from GZ show similar effects, though perhaps not as obvious as this location.
Look around where you are standing now.
The dominant landform in this area around Headstone Reserve is the costal cliffs and headlands. Basalt lava flows under the reserve have been deeply weathered. This has resulted in the formation of rich clay loams on which a dense rainforest grows. The clays are very rich in iron so are sometimes know as ferrosols.
Looking out to the sea, if the conditions are just right, note the powerful left hander that breaks across a rock-reef providing heavy hollow barrels. This break can be the heaviest wave on the island. Basalt seafloor undulations contribute to this interesting wave formation. Wind and the gravitational influence of the Sun and Moon are the major contributors to the swell and tides. Pay particular attention to these two bodies today and note the cardinal directions of their rise and set.
Your earthscience task is to draw your own field sketch of the view from GZ or waterfall area just around the corner (additional waypoint coordinates), which as every good geologist knows must include plenty of SNOT
1. SCALE such as a stick person, Norfolk Island pine tree or other suitable scale item. You may also Snap a picture if you have a camera.
2. NOTES or labels for the iron rich clay loams down to the unweathered basalt.
3. ORIENTATION, which direction you are looking. Your GPSr will show compass direction.
4. TITLE for your field sketch.
Your field sketch should be added to your log, either scanned or photograph. If you have a camera, please try and Snap a picture of the surf break and upload. Please comment on the position of the Sun and Moon in your log and comment on the tide height. Please also comment on what you have learned at this location.
Thanks to and in memory of Billy Twigger who set this type of logging requirement for an earthcache in the Moine Thrust GeoPark in NW Scotland.