Campbell’s Hole Volcanic Dykes EarthCache

Waymarks are listed in www.waymarking.com which is a website operated by Groundspeak, the owners of www.geocaching.com . Whilst www.waymarking.com is operated as a separate entity, your geocaching username and password are the same for waymarking.

The earthcache coordinates given are nominal in that they equate with WMBBCK Campbell's Hole Volcanic Dyke 5 coordinates. You will be investigating the general area of these waymarks, not just the final coordinates.

The geology of the area is similar to that already described for the nearby GC2KWKW Fossil Fence Post and from that cache description, we equally say of Campbell’s Hole

“The geology of the Illawarra may be described by grouping and subgroupings which in order, top to bottom, start at Hawkesbury Sandstone, Narrabeen Group of shales and sandstone, Illawarra Coal Measures including Bong Bong Basalt and Minnamurra Latite, and the Shoalhaven Group including Cambewarra Latite, Budgong Sandstone, Bumbo Latite, (and again) Budgong Sandstone. These rocks are reported as being of the triassic and permian ages with the lower rocks of the earlier permian era. [Reference 1]

"Coal measures" are the number of coal seams known under names such as "Bulli Seam", "Wongawilli Seam" and others at varying depths. Latite is a tough volcanic rock "akin to basalt". [Reference 2] The coal seams and the latites and basalts occur in various layers. The latites in the above listing are a part of the Gerringong Volcanics. The lower levels outcrop at GZ.

Major References:-
1. Fuller L., Mills K.; "Native Trees of Central Illawarra"; Weston & Co. Publishers 1985.
2. Young, R. W., "The Illawarra Escarpment" (1979). Wollongong Studies in Geography. Paper 2. (available as a download from the University of Wollongong Research Online http://ro.uow.edu.au/wollgeo/2/) “

However, the significance of Campbell’s Hole for our purposes lies in a number of volcanic dykes of which five have been waymarked as above. Volcanic dykes represent magmatic intrusion into the sedimentary rock platform. There are quite a number of dykes in rock platforms along the Illawarra coastline, but this group does represent an intense concentration in one local area. Interestingly, the fossilization found on rock platforms to the south (see nearby Earthcaches “Fossil Fence Post” and “Fossillized Gerroa”) seems to be relatively absent in this area.

“The dykes are most easily identified along the coastal rock-platforms and usually consist of fine-grained basaltic rock.”
'The Geology of the South Coast of New South Wales, with Special Reference to the Origin and Relationships of the Igneous Rocks.'
By Ida A. Brown, D.Sc, Linnean Macleay Fellow of the Society in Geology,
[Read 27th September, 1933.] http://biostor.org/reference/67858.text

Each waymark describes a dyke and some of the features of that dyke. You are cordially encouraged to log a visit to each of the waymarks, however this does not count towards the completion of the earthcache. But, the major reference in the waymark variables, the Wollongong 250K Geological Sheet SI5609 2nd edition, accessible via the web link, will prove highly instructive. Included on that sheet (and extremely conveniently for our earthcache!!) are two geological cross-sections which both end very close by.

Your tasks for this earthcache include the following:

1. Between WMBB4F Campbell's Hole Volcanic Dyke 1
and WMBB4G Campbell's Hole Volcanic Dyke 2,
you will find the fault feature in the cliff as shown in the photograph below.

Either walk around to the top and identify the surface feature associated with that fault, or go to the base of the small cliff and obtain GPSr coordinates and then later, open a programme such as “Google Earth”, enter those coordinates and identify the surface feature associated with that fault.

2. In the gallery of
WMBB4G Campbell's Hole Volcanic Dyke 2, there exists a small “cave”. How far in does this opening go? Note that cave entrances of this sort are not so uncommon within four or five kms of this feature. In fact this is a small one.

3. Next to /part of WMBBA7 Campbell's Hole Volcanic Dyke 3 there is a small escarpment. How high is the escarpment where the escarpment meets the cliffline meet? What is the typical width of this dyke? At what angle from north does this dyke lie?

4. In the gallery of WMBBBE Campbell's Hole Volcanic Dyke 4, looking towards the cliffline, you will see a small dyke just to the right of the main dyke. In this small dyke, you will find veins of another rock within the dyke basalt. What colour are they? Does the main dyke penetrate the “cliff” very far? (You will need to climb up on the higher part of the dyke to investigate.)

5. You now reach the last dyke of this series WMBBCK Campbell's Hole Volcanic Dyke 5
Estimate the length of this dyke. Estimate the depth of the pool water where the dyke “travels”.

Please submit answers to these questions after your field visit and email them to me via geocaching .com so that your visit can be verified and a legitimate earthcache visit log can be posted. Please also post a favourite photograph of your visit. Other and specific photographs may be included in the waymarking logs.

WARNINGS:
These dykes are mostly located on exposed rock platforms which are subject to tidal and storm inundation. Do not attempt this earthcache under any conditions except for calm conditions and low tide. If water is flowing off the escarpment near WMBBA7 Campbell's Hole Volcanic Dyke 3 , then completion of this earthcache should be delayed. The GZ of this earthcache is located near deep water with large waves and could be treacherous under adverse conditions. Access to GZ is also across rocks which often have very slippery seaweeds growing on them. Take care with children at all times.

If your starting point for this earthcache is Werri Beach, do not attempt to ford floodwaters from Werri Lagoon when it is open to the sea.