AT THE POINT
Location: This confluence point is located on a working property, Chatsworth, and is to the south of the Phosphate Hill mine, after which the degree square is named. The site is in north-west Queensland, in the Swift Hills area, and while the confluence itself is unmarked, a GPS was used to find the exact location. Well-graded dirt tracks following powerlines came within 1 km of the point, and the last part of the journey was made on foot. The closest settlement is The Monument, 27 km to the north-west of the point. The site was visited at mid afternoon by a party of RGSQ members travelling in four 4WD vehicles from Brisbane in June, 2009. The point falls within Cloncurry Shire.
Prickly plant at the degree confluence
Landscape: Elevation at the degree confluence is 243 m, and the view shows a predominantly flat terrain, excepting the low Swift Hills on the eastern horizon. The surface at the point is largely covered by grass, along with a few scrubs (height to 3 m), and some isolated trees. The vegetation is denser in nearby gullies and creeks, and especially to the south, along the course of Middle Creek, where trees reached a height of 5 m. No animals were sighted at the point, although some tracks were evident.
Sandy red soil with some gravel constitutes the surface material at the point. This is on top of a base of Cainozoic alluvium such as sand, silt, and gravel. The Swift Hills visible a few kilometres to the south-east are comprised of limestone Lower Ordovician age (488 to 472 million years).
The closest watercourse is Middle Creek, less than one km to west and south, although the main drainage of the area is the Burke River, which is 16 km to the east, and part of the Lake Eyre Basin. Numerous waterholes and bores are also found in nearby countryside.
Point information and photos: Paul Feeney, Mary Comer, Jo Grant, Mary Nowill
WITHIN THE DEGREE SQUARE
The Country: The country within the degree square slopes from north to south. Elevations range from around 400 m in the Standish and Selwyn Ranges to 150 m where the Burke River leaves the square. The geology is much more complex in the northern half of the square than in the south. In the north there is a mixture of granite, schist, siltstone, limestone, quartzite and arenite all of Statherian age (1800 to 1600 million years). These areas are separated in places by the Quaternary age (less than 1.6 million years) alluvium of the drainage channels. In the south, by contrast, are large areas of Early Ordovician age (488 to 470 million years) limestone and Early Cretaceous age (146 to 100 million years) mudstone and siltstone interspersed with areas of Cainozoic age (less than 65 million years) and Quaternary age (less than 1.6 million years) sand plain and riverine alluvium.
The main drainage is the Burke River and its tributaries such as Wills Creek and Mort River that flow to Lake Eyre. These streams run only during periods of heavy rain and for much of the time are restricted to occasional deeper pools or billabongs.
Burke River landscapes
Vegetation across the square includes large areas of Mitchell Grass grassland and areas of wattle scrub. Along the water courses are narrow bands of riparian forest with Coolibah and River Red Gum the main trees.
Cattle grazing is the dominant land use. There are several mines in the square.
Climate: The climate of the area is classified as hot grassland with a winter drought. The Bureau of Meteorology climate station at Boulia, about 100 km to the south, provides representative statistics.
Boulia Airport (038003) 1886 to 2009 (elevation 162 m ASL)
The highest temperature ever recorded at Boulia was 48.3°C in February 1915 while the lowest temperature was -1.4°C in August 1906. Rainfalls also vary greatly. The highest total of 798.6 mm was recorded in 1950 and the lowest total of 24.1 mm in 1905.
Extremes of Nature: In spite of its inland location, the cyclone database maintained by the Bureau of Meteorology contains the tracks of eight cyclones that have tracked within 200 km of the confluence point in the 101 years between 1906 and 2007. Of these only two passed within 50 km of the point. They were: an unnamed cyclone in March 1918 and an unnamed cyclone of January 1951. Most cyclones that impact on the area have degraded to tropical lows, however, they all bring torrential rain that produces extensive flooding over a wide area that can last several weeks.
Cyclone tracks that passed within 200 km of the point since 1906 (Bureau of Meteorology web site)
The area experiences on averages around 20 thunder days a year. The more severe thunderstorms can produce intense rainfall and localised flash flooding, destructive winds (including tornadoes) and lightning strikes that can spark bushfires if there is sufficient fuel to sustain spread.
Floods in the Burke River and its tributaries are not frequent but when they do occur they can spread over a wide area and have significant velocities. They can close roads and isolate properties for lengthy periods.
Flood debris in Kolan Creek near Phosphate Hill mine
Extreme heat is also a serious issue. The climate records for Boulia show that on average (over 119 years of records) the area experiences 138 days a year with temperatures over 35°C and 46 days a year with temperatures over 40°C. Such extreme temperatures can cause heat stroke and death if appropriate measures are not taken such as avoiding strenuous physical effort, keeping as cool as possible and drinking lots of water. Heat waves kill more people in Australia than all other natural hazards combined.
Drought is probably the most destructive of all hazards. This area has suffered severe drought on many occasions, the most notable being the 'Federation Drought' between 1900 and 1905, 1925, the mid-1960s and again in the early 2000s. During drought periods blowing sand can reduce visibility significantly.
The National Earthquake Database maintained by Geoscience Australia contains no earthquake epicentres within the degree square.
The Indigenous Story: The land within the degree square is the traditional country of the Yalarrnga people.
MORE INFORMATION WELCOME
European Exploration and Settlement: The First Europeans to pass through the square made up the ill-fated Burke and Wills expedition of 1859-60.
The country in the square was opened up for cattle grazing. The railway line to Townsville reached Dajarra in 1916 and by the 1920s Dajarra boasted the largest cattle yards in world. It is said that more cattle was shipped out from Dajarra than the US state of Texas. Mobs were driven to that railhead from as far away as Western Australia for transportation by rail to the east coast.
MORE INFORMATION WELCOME
The total population of the degree square at the 2011 national Census was 677.
The surge in the male population at the 2001 census reflects the developmental stage of the Phosphate Hill mine. The overall decline in population probably reflects the difficulties experienced by the cattle industry during a lengthy drought. Changes in the census collection boundaries would also have had an influence in the numbers deemed to be within the degree square.
The Phosphate Hill mine and ammonium phosphate production facility is the most significant economic activity in the square. Phosphate rock is mined at the site and sulphuric acid produced from the gas emissions at the Mt Isa copper smelter are shipped to the mine where the acid is reacted with the phosphate rock to create phosphoric acid. This is then combined with liquid ammonia to produce fertiliser that is then shipped to Townsville by rail.
Cattle grazing remains important across the square. Chatsworth Station is typical of the runs in this part of Queensland.
Infrastructure within the square includes a well established network of public and private roads and the rail link to the main Mt Isa to Townsville rail line. There are several station airstrips within the square. The underground Ballera-Mount Isa Gas Pipeline passes just to the west of the point.
About two thirds of the square lies within Cloncurry Shire with the southern third is within Boulia Shire. Tere are no national parks within the square.
Compilers: Jo Grant with additional material by Ken Granger, 2009
Edited by: Hayley Freemantle
References: various web sites including local governments and Bureau of Meteorology.
Queensland Museum, 2003: Discovery guide to Outback Queensland, Queensland Museum, Brisbane.