Sydney Harbour Bridge EarthCache EarthCache
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The Sydney Harbour Bridge EarthCache
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About this Cache:
This EarthCache is located at Dawes Point Park at the base of one of the most famous landmarks in the world, The Sydney Harbour Bridge. Please take care when using the park and remember the geocaching moto of “leave no trace”. If at any stage the park is closed due to bridge maintenance your welcome to use any of the other three bridge pylons to claim the find. Please do not cross any fences if the park is closed.
About the EarthCache - The Pylons (Granite):
- Granite facing used on pylons & piers: 17,000 cubic metres
- Height of the pylons above sea level: 89 meters
- Rock excavated for the foundations: 122,000 cubic metres
- Concrete used for the bridge: 95,000 cubic metres
The four 89 metre high pylons are made of concrete faced with granite. The fact that the pylons are made from concrete with aesthetic granite is a fact that is usually missed by most people. The foundations for the pylons and four main bearings, which carry the full weight of the main span, were dug to a depth of 12.2 metres and filled with special reinforced high-grade concrete laid in hexagonal formations.
The granite and concrete for the bridge were quarried in Moruya, N.S.W, which is located 300km south of Sydney. The Moruya Quarry, also known as the Government Quarry, opened in 1876 on the northern bank of the Moruya River. Moruya Quarry is of great historic, scientific and archaeological significance because of its links with the international engineering company, Dorman Long, state politicians and the construction of the Sydney Harbour Bridge. From 1925 to 1932, 250 men were employed to produce 18,000 cubic metres of dimension stone, 173,000 blocks and 200,000 yards of crushed stone that was used as aggregate for concrete on the bridge. Nepean sand and Kandos cement were the other components used in the concrete mix
Early in 1925, ninety stonemasons and their families arrived in Moruya from Scotland, along with a few Italians and Australians. A special township, Granitetown, was built to receive them. The regular movement of three steamers carrying the granite to Sydney increased shipping traffic on the Moruya River. As part of the quarry a highly mechanised plant for preparing the stone, a light railway leading to the wharf, and a stone crusher to create aggregate, were built. The masons’ work was so accurate that mortar was scarcely needed. Test assemblies proved the accuracy of the work before shipment to the Bridge. Before loading the masons cut and numbered each stone in order. By 1929, the activity was starting to wind down as the focus shifted to Sydney for the final dressing of the stone and bridge pylons.
Today the Moruya Quarry is still operated by the New South Wales Department of Infrastructure, Planning and Natural Resources.
Granite is a common and widely occurring type of intrusive, felsic, igneous rock . Granite is a very hard, crystalline, and primarily composed of feldspar, quartz accompanied by one or more dark minerals. Granites usually have a medium to coarse grained texture. Granites can be pink to dark gray or even black, depending on their chemistry and mineralogy. Outcrops of granite tend to form tors, and rounded massifs. Granites sometimes occur in circular depressions surrounded by a range of hills, formed by the metamorphic aureole or hornfels.
Mineralogy & Geochemical Origins
Granite is classified coarse grained plutonic rocks (granitoids) and is named according to the percentage of quartz, alkali feldspar (orthoclase, sanidine, or microcline) and plagioclase feldspar. True granite contains both plagioclase and alkali feldspars. When a granitoid is devoid or nearly devoid of plagioclase the rock is referred to as alkali granite. When a granitoid contains <10% orthoclase it is called tonalite; pyroxene and amphibole are common in tonalite. A granite containing both muscovite and biotite micas is called a binary or two-mica granite. Two-mica granites are typically high in potassium and low in plagioclase. The volcanic equivalent of plutonic granite is rhyolite.
Granitoids are a ubiquitous component of the crust. They have crystallized from magmas that have compositions at or near a eutectic point (or a temperature minimum on a cotectic curve). Magmas will evolve to the eutectic because of igneous differentiation, or because they represent low degrees of partial melting.
The composition and origin of the magma which differentiates into granite, leaves certain geochemical and mineral evidence as to what the granite's parental rock was. The final mineralogy, texture and chemical composition of a granite is often distinctive as to its origin. For instance, a granite which is formed from melted sediments may have more alkali feldspar, whereas a granite derived from melted basalt may be richer in plagioclase feldspar. It is on this basis that the modern "alphabet" classification schemes are based.
Diagram Below: QAP Diagram for Plutonic Rocks
Silicon dioxide – 72.0%
Aluminium oxide – 14.4%
Potassium oxide – 4.0%
Sodium oxide – 3.7%
Calcium oxide – 1.8%
Iron(II) oxide – 1.7%
Iron(III) oxide – 1.2%
Magnesium oxide – 0.7%
Titanium dioxide – 0.3%
Phosphorus pentoxide – 0.1%
Manganese(II) oxide – 0.05%
Granite is currently known only on Earth where it forms a major part of continental crust. Granite often occurs as relatively small, less than 100 km² stock masses (stocks) and in batholiths that are often associated with orogenic mountain ranges. Small dikes of granitic composition called aplites are often associated with the margins of granitic intrusions. In some locations very coarse-grained pegmatite masses occur with granite.
Granite has been intruded into the crust of the Earth during all geologic periods, although much of it is of Precambrian age. Granitic rock is widely distributed throughout the continental crust of the Earth and is the most abundant basement rock that underlies the relatively thin sedimentary veneer of the continents. Granite is an igneous rock and is formed from magma. Granitic magma has many potential origins but it must intrude other rocks. Most granite intrusions are emplaced at depth within the crust, usually greater than 1.5 kilometres and up to 50 km depth within thick continental crust. The origin of granite is contentious and has led to varied schemes of classification.
Ascent and emplacement
The ascent and emplacement of large volumes of granite within the upper continental crust is a source of much debate amongst geologists. There is a lack of field evidence for any proposed mechanisms, so hypotheses are predominantly based upon experimental data. There are two major hypotheses for the ascent of magma through the crust:
- Stokes Diapir
- Fracture Propagation
Of these two mechanisms, Stokes diapir was favoured for many years in the absence of a reasonable alternative. The basic idea is that magma will rise through the crust as a single mass through buoyancy. As it rises it heats the wall rocks, causing them to behave as a power-law fluid and thus flow around the pluton allowing it to pass rapidly and without major heat loss. This is entirely feasible in the warm, ductile lower crust where rocks are easily deformed, but runs into problems in the upper crust which is far colder and more brittle. Rocks there do not deform so easily: for magma to rise as a pluton it would expend far too much energy in heating wall rocks, thus cooling and solidifying before reaching higher levels within the crust.
Nowadays fracture propagation is the mechanism preferred by many geologists as it largely eliminates the major problems of moving a huge mass of magma through cold brittle crust. Magma rises instead in small channels along self-propagating dykes which form along new or pre-existing fault systems and networks of active shear zones As these narrow conduits open, the first magma to enter solidifies and provides a form of insulation for later magma. Granitic magma must make room for itself or be intruded into other rocks in order to form an intrusion, and several mechanisms have been proposed to explain how large batholiths have been emplaced:
- Stoping, where the granite cracks the wall rocks and pushes upwards as it removes blocks of the overlying crust.
- Assimilation, where the granite melts its way up into the crust and removes overlying material in this way.
- Inflation, where the granite body inflates under pressure and is injected into position
Most geologists today accept that a combination of these phenomena can be used to explain granite intrusions, and that not all granites can be explained entirely by one or another mechanism.
Granite is a natural source of radiation, like most natural stones. However, some granites have been reported to have higher radioactivity thereby raising some concerns about their safety. Some granites contain around 10 to 20 parts per million of uranium. By contrast, more mafic rocks such as tonalite, gabbro or diorite have 1 to 5 ppm uranium, and limestones and sedimentary rocks usually have equally low amounts. Many large granite plutons are the sources for palaeochannel-hosted or roll front uranium ore deposits, where the uranium washes into the sediments from the granite uplands and associated, often highly radioactive, pegmatites. Granite could be considered a potential natural radiological hazard as, for instance, villages located over granite may be susceptible to higher doses of radiation than other communities.Cellars and basements sunk into soils over granite can become a trap for radon gas, which is formed by the decay of uranium.Radon can also be introduced into houses by wells drilled into granite.
Photo: The final piece of granite being lowered into placed
Granite is the hardest building stone, and due to its hardness, resistance to weathering, capability to take mirror polish, fascinating colors and textural patterns, granite slabs and granite tiles are extremely popular. The principal characteristics of granite also include high load bearing capacity, crushing strength, abrasive strength, amenability to cutting and shaping without secondary flaws, ability to yield thin and large slabs and, above all, durability. Due to highly dense grain, it is impervious to stain. Polished granite slabs and granite tiles have achieved a special status as building stones globally.
The Mohs Scale
The Mohs scale is a system of testing the hardness of a mineral, designed by Friedrich Mohs in 1812. Mohs was a mineralogist from Germany who wanted a simple way of testing the "scratching" ability of each mineral. Mohs based the scale on ten minerals that are all readily available. As the hardest known naturally occurring substance, diamond is at the top of the scale. The hardness of a material is measured against the scale by finding the hardest material that the given material can scratch, and/or the softest material that can scratch the given material.
About the Bridge:
In the late 1700s, Sydney was formed around Sydney Cove and later, as the population grew, it developed around the harbour and its tributaries to the north, west and south. Proposals to join the north and south sides of the harbour with a bridge were first put forward in 1815 by convict architect Francis Greenway.
The possible construction of a bridge became a reality by the early twentieth century, with advances in bridge engineering technology internationally, along with developments in the local manufacture of prefabricated steel and reinforced concrete. The advantage of steel, apart from its cost effectiveness, was that it was durable and malleable enough to span wide tidal bodies of water.
In 1900 the State Government of the day lobbied for the proposed bridge to be built by a private company. To this end, the Minister for Public Works called for a worldwide competition for its design and construction. A design by the Sydney-based engineer Norman Selfe was announced the winner. In 1904, the project was stalled indefinitely when the government changed. On the 24th of November 1922 The Sydney Harbour Bridge Act was passed calling for the construction of a bridge between Dawes Point and Milsons Point. Construction of approaches and pylons commenced in 1924, with the bridge opening on the 19th of March 1932.
Interesting facts about the bridge:
- Length of arch span: 503 metres
- Height of top of arch above sea level: 134 metres
- Number of rivets: Approximately 6,000,000
- Total weight of steelwork: 52,800 tonnes
- Paint required: 272,000 litres
- Approximately 79% of the steel came from Middlesbrough, England,
while the remaining 21% was Australian-made.
To claim this EarthCache you MUST examine the pylons closely and message me the answers to following questions:
Note: You must visit the EarthCache location to claim a find. No back dating of finds are allowed. (e.g) You visited the bridge a few years ago and found an old photo. These finds DO NOT COUNT. You must visit the EarthCache with the intention of finding the EarthCache. I have had to delete logs of people who clearly did not visit the EarthCache and/or perform the required tasks.
There is no need to wait for a confirmation message to log this EarthCache. I read all messages to verify the correct information was sent and will contact you if there are any problems with your answers. Likewise, there is no need to email me photos. Just upload any photos with your log. If both tasks are not completed within a timely manner of logging your cache online your log will be deleted.
1) Where would the granite used on the pylons rate on the Mohs scale? You will need to do further research on the Mohs scale to answer this question.
2) Describe the granite in detail.(Colour, texture, grain size, etc)
3) While exaimaning the granite did you notice any quartz crystals? Using the QAP Diagram (Shown above); Where would this granite rate?
4) Where was a majority of the aggregate for the concrete used on the bridge obtained from? What type of rock was used?
Upload 2 photos with your log.
1) One of yourself &/or group clearly showing your GPS and a pylon close behind you.(Any of the 4 pylons will work)
2) One of yourself &/or group clearly showing your GPS and the entire bridge behind you.
I also encourage you to upload any additional photos taken during your EarthCache find.
You MUST attend the EarthCache location, answer all of the questions and uploaded the required photos to claim a find. Any logs without ALL of these will be deleted.
Permission was granted from the The Sydney Harbour Foreshore Authority to place this EarthCache in Dawes Point Park. Please remember the Geocaching motto of "Leave No Trace".
This page is dedicated to the 16 men who lost their lives in the construction of the Sydney Harbour Bridge.
Addison, Sydney John (1905–1930), boilermaker’s assistant who fell from the arch when he was bolting up a piece of steel.
Campbell, James (1887–1932), foreman rigger, knocked by a derrick crane as he was dismantling scaffolding from the NW Pylon on 6 February 1932. A gust of wind had caught the crane.
Chilvers, James Francis (1877–1931), dogman, was working at the Milsons Point Workshops when a piece of wood knocked him into the water.
Craig, Robert (1863–1926) was a braceman who fell down a ballast heap at Milsons Point.
Edmunds, Alfred (1875–1931) was a Canadian-born labourer who was packing stones when he crushed his thumb. He died from tetanus poisoning 11 days later.
Faulkner, John Alexander (‘Felix’), (1891–1931) was born in Montreal, Canada and the second of the two riggers to die on the job. He was laughing when a huge sliding steel plate almost severed his legs.
Gillon, Frederick (1905–1930) was a rigger who died instantly when a sheerlegs collapsed in Junction Street, North Sydney.
Graham, Robert (1890–1931) was working as a day labourer when a tram knocked him down in Alfred Street, North Sydney.
McKeown, Thomas (1881–1929), an Irish-born rigger who fell from a painting gantry which was suspended from the Bridge’s road deck.
Peterson, Engel August (‘Angel’), (1904–1927), a Swedish born rigger who broke his spine in the Dorman Long workshop and died six months later at the Coast Hospital (aka Pedersen).
Poole, Percy (1897–1927), a quarryman from Moruya, was working in the quarry when a large stone block slid back and killed him instantly.
Shirley, Edward (unknown–1928), married, was working as a carpenter when some scaffolding collapsed on him at the Fitzroy Street Arch, Milsons Point. He died four days later in Royal North Shore Hospital.
Swandells, Nathaniel (1905–1927), ironworker’s assistant, was working in a riveting gang when he fell from an approach pier and died instantly (aka Swondels).
Waters, Henry (1876–1926), dogman and Moruya identity, was riding on a loco-crane at the quarry when the big counterweight jib severed his thigh. He died the next day.
Webb, John Henry (1908–1931) was an English-born painter who fell from a cross-girder when he was working inside one of the south pylons.
Woods, William (1886–1928), a Scottish-born ironworker who fell more than twenty metres from a gantry on the ninth span.
(No hints available.)