AT THE POINT
Location: Degree Confluence 21°S 139°E is in the heart of the Barkly Tableland in western Queensland. A vermin-proof fence runs just to the north of the 139th parallel at this location. A dirt track, which is accessible via the Diamantina Developmental Road to the south, comes within 4 km of the confluence. The remaining distance was traversed by 4WD across country by an expedition of RGSQ members in May 2008. The nearest settlement is the city of Mount Isa, approximately 60 km to the north-east, and located on the eastern edge of Degree Square 21°S 139°E.
Google Image: Big Toby Creek to the south-east of Degree Confluence 21°S 139°E
Landscape: Degree Confluence 21°S 139°E is located in largely flat terrain with an elevation of approximately 285 m. The vegetation community is woodland. Trees are of approx 6-8m height, while bushes and grass tussocks are present. A considerable portion of the ground surface is bare.
Surface alluvial sediments of sand, silt, clay and minor gravel are of Quaternary age. In contrast, the geology of the Mt Isa area is complex and ancient. (Scanned 250K Geology Maps, Geoscience Australia).
Big Toby Creek, 4km to the east, is the closest watercourse to the confluence. It flows into the Goa Creek to the south, and eventually drains into the Georgina River, 90 km to the south-west.
Point Information By: Jo Grant
IN THE DEGREE SQUARE
Climate: The closest representative weather station to the confluence is at Mount Isa, which is 60 km to the north-east of the degree confluence, and has an elevation of 340 m. The station has been recording data since 1966.
The highest temperature recorded was 45.9°C in January 1990, and the lowest was -2.9°C in both July 1984. The highest rainfall in a year was 917.0 mm in 1997, and the lowest was 161.1 mm in 1970. These and other climate statistics for Mount Isa can be found at: Australian Bureau of Meteorology, http://www.bom.gov.au/climate/averages/tables/cw_029127_All.shtml.
Extremes of Nature: Despite the area's inland location, it is still subject to the impact of some cyclones. The database maintained by the Bureau of Meteorology shows that nine cyclones have passed within 200 km of the confluence since 1906, one of which passed within 50 km (TC Jason in 1987). Even distant cyclones bring with them potentially destructive winds and intense rainfall. Cyclone information for this area and all of Australia can be found at the Australian Bureau of Meteorology website, http://www.bom.gov.au/cgi-bin/silo/cyclones.cgi.
Cyclone tracks within 200 km of point 1906 to 2006 (Bureau of Meteorology web site)
Like most places in the Australian tropics, extreme heat is also a danger. Records show that the Mt Isa Station experiences 121 days annually with temperatures 35°C or warmer, 18 days of which reach 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.
The total population of the degree square at the 2011 national Census was 10,683, virtually all of it within that part of Mt Isa that falls within the square. The remainder of the Mt Isa population is located in the 21-140 degree square.
Information: Ken Granger
Climate information: Jo Grant
Edited by: Hayley Freemantle
Geoscience Australia, NATMAP Raster
Geoscience Australia, Scanned 250 K Geology Maps