Who painted the rock? EarthCache
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The terrain is an old disused quarry on the ocean’s edge with basalt stones of varying sizes scattered over the site. The walk from the carpark to this cache is about 10 -15 minutes, the terrain flat until you climb some larger boulders to stand on cache.
In 1876 the growing coastal township of Kiama completed its harbour contributing to the development of a basalt quarrying industry. Other factors that assisted in the development of the basalt quarrying industry was the growth in tramways, roads and railways that used the crushed basalt. After decades of removing Bombo quarry, the site where the Earthcache is located, became an almost wasteland of bare earth and basalt columns. Construction of a sewage treatment on the site added to its starkness. However, geologically it bared opened the opportunity to discover what laid beneath the original landscape. Now a days its starkness and interesting basalt columns feature regularly as a backdrop in automobile commercials and television reality shows. The geological feature that is scattered around the site is a number of volcanic dykes. The comment that people make upon seeing a dyke for the first time is that it looks as though someone has painted a dark stripe over the rock face. So what is a dyke? In simple terms a dyke is a thin layer of intrusive igneous rock. Dykes are mainly vertical intrusive bodies that occupy a fracture in the surrounding older rock. Dykes are the most important magma transportation system on Earth. The dykes scattered around the Bombo site are small in comparison to larger ones on the planet especially those at located at oceanic spreading ridges. Dykes also occur singly or in great swarms. Their size varies dependent on the extent of the fracture.
The educational task for this Earthcache is to measure the dyke’s width and length (the dyke may vary slightly in width along its length so an average is sufficient). A long tape measure rather than a ruler will make the task easier. Accompanying the measurements should be a photo of your GPS placed on the dyke showing the colour difference of the dyke and surrounding older rock.
To access the quarry follow the signs to Bombo beach and park in the northern end carpark. From the carpark walk in a north easterly direction over the disused quarry site (The site is public space and if you have a dog it’s an off leash area where your companion can run to its hearts content).
There are two lookout points over the quarry. Those lookout points are S34° 38.933 E150° 51.875 & S34° 38.945 E150° 51.905 accessed by parking at the southern end of Cliff Drive, Kiama Downs. Note the signs near the lookout points warning of dangerous cliff edges. While this is not part of the Earthcache the local area contains one other Earthcache and a significant number of geocaches. So make a day of it and enjoy the variety of caching opportunities as well as the splendid region of Kiama.
Before heading out to locate the Dyke familiarize yourself with the following geological terms. In doing so you will gain a better understanding/appreciation of the rock cycle.
Find the meaning of - magma, lava, igneous, intrusive igneous rocks, fractures in rocks, dykes that occur singly or swarms (many images on the internet), oceanic spreading ridges.
Additional Hints
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