25°S 138°E Simpson Desert – Queensland by Degrees

AT THE POINT

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Degree confluence 25°S 138°E, Google Earth

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n

Looking north

w

Looking west

s

Looking south

e

Looking east

Location: Degree Confluence 25°S 138°E is adjacent to, and east of, the Qld-NT border. At this location the border appears unmarked, with no indication on Google Earth of a border track or fence. The site is deep within the Simpson Desert, a vast region in which linear dunes are the main landscape feature. The confluence is on an inter-dune corridor midway between SSE-NNW trending dunes.

There is no direct access to the location. The RGSQ expedition visited the site, travelling the final 13-14 kms across the dune field from base camp on two quad bikes. The nearest settlements are Bedourie and Birdsville, Qld, both about 165 km in a straight line to the ENE and ESE respectively. The RGSQ members travelled to this area from Brisbane in May, 2008.

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Travel on the Hay River Track

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Tough country heading towards the confluence

 

Landscape: Degree Confluence 25°S 138°E is located in an inter-dune corridor, mid way between two linear dunes aligned SSE-NNW, and about 450m apart. These dunes have soft, sandy summits and slopes. Natmap (250K Raster Maps) indicates average height of dunes east of the confluence is 18m, and 10m to the west.

The Google images indicate two important points, namely:

(a) at the area of the confluence much of the dune sand is mobile (active), shifting under the influence of wind, and

(b) much of the vegetation of the wider area has been burnt by wildfire; this exposes the sandy surface and promotes the destabilisation of the dunes by wind (see (a) above).

There is a likelihood that the Google images are some years old, as at the confluence they suggest that there is little vegetation. In contrast, the field photos indicate the presence of low vegetation.

The base of the inter-dune corridors generally are composed of sand rather than being made up of finer sediments of the clay pans and ephemeral lakes found in dune fields elsewhere. There are minor wind ripples on the sand surface between dunes.

There is no drainage pattern at the confluence. The course of the Hay River (usually dry) fades away into the desert's sands about 15km west of the confluence.

The ground surface is mostly bare of vegetation at the confluence. Scattered low bushes are present.

Geological features include Quaternary Aeolian sand, with underlying Cretaceous sedimentaries. (Scanned 250K Geology Maps, Geoscience Australia).

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Google Image: Linear dunes of Simpson Desert at Degree Confluence 25°S 138°E
- burnt area (yellow), unburnt area (darker)

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Google Image: Linear dunes of Simpson Desert at Degree Confluence 25°S 138°E

Point Photo Credits: Paul Feeney, Mary Comer

Point Information Prepared By: Col & Jo Grant

 

IN THE DEGREE SQUARE

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Climate: The closest representative weather station is at Birsdville Police Station, which has an elevation of 47 m.

 

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Year

Mean max
(ºC)

38.8

37.8

35.1

30.3

24.8

21.6

20.8

23.5

28.1

32.1

35.5

37.7

30.5

Mean min
(ºC)

24.2

24.1

21.1

16.2

11.3

7.9

6.6

8.3

12.2

16.1

19.7

22.5

15.8

Mean rain
(mm)

24.7

29.0

16.4

9.5

11.8

10.4

10.9

6.4

5.7

12.1

13.7

16.0

167.2

The hottest temperature recorded was 49.5°C in December 1972, and the lowest was -1.7°C in June and July 1965. The greatest rainfall in a year was 541.8 mm in 1916, and the lowest was 33.2 mm in 1913. These and other climate statistics for Birdsville can be found at: Australian Bureau of Meteorology, http://www.bom.gov.au/climate/averages/tables/cw_038002_All.shtml

Extremes of Nature: The area experiences extreme heat and dryness for much of the year, with Bedourie having an average of 139 days annually with maximum temperatures equal to or over 35°C, and Birdsville having 113. The hottest months in both towns are December to February, all of which experience over 20 days on average with temperatures equal to or over 35°C. Since 1906 there have been no cyclones to pass within 50 km of the degree confluence, but 2 within 200 km (1955, 1976). 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

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Cyclone tracks within 200 km of the confluence, 1906 to 2006 (Bureau of Meteorology web site)

Extreme heat and drought are also a potential dangers. Records show that Birdsville experiences 113 days annually with temperatures over 35°C, 45 of which typically reach 40°C or warmer. 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. With only 23 days on year with any rain and an extremely low average rainfall, the area is also among the driest in Australia.

Today: The population of the degree square is probably zero.



Reference still to come.

Edited by: Hayley Freemantle