Located in Williamstown, this area covers 30 ha and supports rock basalt reef, seagrass beds, intertidal flats, saltmarsh and the largest occurrence of unusual mangroves in Port Phillip Bay.
The Jawbone
This promontory in Williamstown, is known as 'The Jawbone'. It was fenced off from the rest of the world for 110 years by the Merrett Rifle Range and forgotten. It is now considered a haven for coastal and marine life in an amazing mix of geology and fauna. Many adventure seekers now snorkel over the reefs and patches of seagrass of the and look out for Globe Fish. You won’t need to do any snorkelling to explore this Earthcache, just get to know the geology of the site through two easy waypoints.
Filling, excavations, beach nourishment or other engineering works has modified most of the Williamstown foreshore area and this site is the last surviving remnant of very interesting basalt outcrops. These outcrops have become integral to many species of flora and fauna because of the geology of this important site.
The relatively untouched rocky shores support a diverse and abundant range of animal life rarely seen elsewhere in the bay. The presence of large turban shells, limpets and snails is striking. The rock pools boast pretty gardens of green or pink coralline algae. Numerous sea-stars and crabs inhabit the crevices, while shrimps and small fish dart amongst the weeds.
Geological History of Port Phillip Bay
Sea level was about 130 metres lower than it is today in the last glacial period, which ended 18,000 years ago. The Yarra, Werribee, Little and Patterson Rivers, with Kororoit Creek, flowed down what is now the middle of the bay, forming a delta and merging into a larger river, before emptying into Bass Strait. As the ice caps receded 8000 years ago, the sea level rose, flooding the delta and river valleys, forming what is now recognized as Port Phillip Bay.
Port Phillip Bay is the biggest enclosed "sea" in the Southern Hemisphere, 1,950 km2 in area with 264 km of coastline and up to 58 km from north to south and 41 km from east to west. It is separated from Bass Strait by the Bellarine Peninsula on the southwest and Mornington Peninsula on the southeast.
To log this Earthcache, please read two sets of information boards within the reserve and answer the following questions…
The Marine Sanctuary
The sanctuary is significant as a scientific reference area for marine plants and animals. At the published co-ordinates for this Earthcache you will see a board that will help you answer two questions.
1. Why is this unique community of mangroves considered unusual?
2. What tops the basalt outcrops, which occur below the high water line yet above the low water line?
Now for a little walk...
The Point
A short walk away, you will find a boardwalk that will take you out to ‘The Point’ of the Jawbone. Here you will find another board to answer the last question.
3. How many years ago did the lava flow seaward to create the basalt outcrops?
This board has been removed - the council have assured me that it will be replaced soon. If it's not there when you visit, this answer isn't required.
Please e-mail your answers to empiregc@gmail.com before you log your find, logs with no email verification will be deleted as per Earthcache guidelines.
To remember your time at this Earthcache and on the Williamstown foreshore, you can take a photo of yourself and your GPSr standing near the basalt outcrops. This is encouraged but entirely optional.
References:
1. Parks Victoria: Jawbone Reserve
2. Victorian Resources Online (Department of Primary Industries), M3 Williamstown – Shore Platform
3. Friends of Williamstown Wetlands
4. National Marine Discovery Centre
5. Beautiful Altona
