17°S 146°E Cairns – Queensland by Degrees

 

THE POINT 

Fitzroy from the South

17°S 146°E confluence, Google Earth

 

Location: This confluence point is located off-shore, approximately 7 km south of Fitzroy Island. The point was not visited.

The Landscape: At sea.

Point information and photos: Ken Granger, 2008.

WITHIN THE DEGREE SQUARE

The Country: The landscapes within this degree square range from extensive mud flats and strands of estuarine mangroves to Queensland's two highest mountains, the south peak of Mt Bartle Frere (1622 m ASL) and the central peak of Mt Bellenden Ker (1561 m ASL). It also includes the volcanic landscapes of the Atherton Tablelands as well as the floodplains of the Barron, Mulgrave, Russell and North Johnstone Rivers.

 

The coastal lands, including the lower floodplains, have a gentle topography and are composed largely of alluvium of the Quaternary age (less than 2 million years). In some places around Trinity Inlet these sediments are more than 90 m deep. Trinity Inlet is actually the former estuary of the Mulgrave River. The course of the Mulgrave was altered from its original termination in Trinity Inlet to its current mouth 40 km to the south approximately 15,000 years ago as a result of the eruption of the small volcanic centre known today as Green Hill. Elevations are generally less than 50 m ASL.

Apart from the mangrove communities and some riparian forests, very little natural vegetation remains on these areas as they are now given over either to urban development, sugar cane, pasture or anthropogenic grassland. The most notable fauna in the estuaries are estuarine crocodiles.

Off the coast are several islands and cays. The largest is Fitzroy Island, a continental island composed of Late Permian age (270 to 210 million years) granite. Fitzroy has a maximum elevation of 270 m ASL, that height being reached within 250 m of the water. There are many massive granite tors scattered across the island. Fitzroy vegetation includes mid-height rainforest on the flanks and a low heath on the upper slopes. Fauna noted on and around Fitzroy Island included humpback whales and manta rays off-shore; goannas on shore; and a range of birds including Emerald Dove, Orange Footed Scrubfowl and Grey-headed Robin.

Granite tor on Fitzroy Island (KG, 2008)

Summit of Fitzroy Island (KG, 2008)

Forest on Fitzroy Island (KG, 2003)

Fitzroy Island heath (KG, 2008)

High Island to the south of Fitzroy is also a continental island but has much more ancient geology. It is composed of "gneiss" of Neoproterozoic age (1000 to 545 million years). It carries vegetation similar to that of Fitzroy Island.

Green Island, by contrast, is a coral cay that carries a cover of vine thicket rainforest in the interior, a belt of lower scrubby salt-tolerant shrubs behind the beach and coconut palms along the beach. The coconut palms are believed to have been planted in 1889 to provide a food source for fishermen and stranded sailors. It is the only cay along the length of the Great Barrier Reef that supports such a rich flora. The rich vegetation is largely the result of seeds brought to the island by birds such as the Pied Imperial-pigeon and fertilised by their droppings. Green Island is recorded as being home to some 35 bird species including Osprey and White-breasted Sea Eagle.

Other cays within the square, such as Upolo and Michaelmas, are simple sand cays with very little vegetation at all other than low groundcover plants. The sand cays are nesting rookeries for a range of sea birds such as the Sooty Tern. Surrounding the cays are seagrass beds that support populations of turtles and dugong.

PHOTOS OF THE CAYS WELCOME

The coastal escarpment that runs the length of this square was probably formed from a modified land surface more than 65 million years old. The granite bodies of the various ranges remain the highest points of this land surface because of their greater resistance to erosion.

Around 60 million years ago the eastern part of the continental highland was rifted, leaving a steep eastern slope. This slope has been retreating since then to reach a position close to that of the present about one million years ago. Erosion has occurred most rapidly in the metamorphosed sediments such as the mudstone of Devonian age (410 to 354 million years) that makes up much of the Great Dividing Range through the square, leaving the granite as isolated hills and ranges. These granite bodies, which include Mt Bartle Frere and Mt Bellenden Ker, are of Late Permian age (270 to 260 million years).

The landscape features associated with the escarpment are quite dramatic. The sudden change from the flat and very low-lying land around Trinity Inlet to the slopes of the Isley Hills and Murray Prior Range; and the 922 m high Walsh's Pyramid near Gordonvale, are examples. Walsh's Pyramid is claimed to be the largest free-standing natural pyramid in the world. The Macalister Range to the north of Cairns in places rises to elevations of more than 700 m ASL within a few hundred metres of the sea.

Mt Bartle Frere and forested ridge (KG, 2008)

Macalister Range north of Cairns (KG, 2008)

Trinity Inlet and the Murray Prior Range (KG, 1998)

Murray Prior Range (KG, 2008)

The volcanic landscapes of the Atherton Tableland include the scoria cones of the Seven Sisters and three crater lakes - Lake Barrine and Lake Eacham, both of which have the classic circular shape, and Lake Euramoo with its unusual 'hourglass' shape. The lakes were formed around 23,000 years ago during a period of very active volcanism in Far North Queensland. These features (maars) were formed when rapidly rising magma came into contact with the water table. The resulting explosion of superheated groundwater causing the massive explosions that formed these craters. The basalts of the Tableland date from the Pliocene (5 to 2 million years) and produce some of the richest agricultural land in Queensland.

Seven Sisters near Atherton (KG, 2008)

 

Lake Barrine (KG, 2008)

Lake Eacham (KG, 2008)

Lake Euramoo (KG, 2008)

Typical rainforest canopy Ma-mu Interpretive centre (KG, 2008)


Twin Bull Kauri at Lake Barrine (KG, 2008)

 Bumpy Satinash (KG, 2008)

Red Cedar in vine forest (KG, 2008)

Curtain Fig (KG, 2008)

Bracket fungus on dead log (Judy Granger, 2008)

Orchid and Birds Nest Fern (Judy Granger, 2008)

The vegetation of the escarpment, range and Tableland overlap to a significant degree; the remnant vegetation is now protected in the Wet Tropics World Heritage Area. This area is floristically one of the richest ecosystems in the World with some 3000 plant species from 210 families being represented. They range from massive trees to tiny fungi and delicate orchids. The tallest species such as Hoop Pine (Araucaria cunninghamiana), Bunya Pine (Araucaria bidwillii), Kauri Pine (Agathus robusta and A. microstachya), Black Bean (Castanospermum australe), Black Walnut (Endiandra palmerstonii), Red Cedar (Toona ciliata), Bumpy Satinash (Syzigium cormiflorum) and Flooded Gum (Eucalyptus grandis) were all sought after for commercial logging before the Wet Tropics World Heritage Area was proclaimed and logging ceased. Various species of Ficus including the massive Strangler Fig (Ficus watkinsiana) are also prominent. Two in particular - the Cathedral Fig and the Curtain Fig are so significant that they each have their own national parks! The understory of saplings, seedlings, palms, pandanas, tree ferns, vines and herbs, such as gingers, can be very dense. Orchids and other epiphytes also abound.

The rivers within the degree square carry huge volumes of water. They have sculpted the landscape as they form gorges or deltas.

Barron Falls near Kuranda in the dry season (KG, 2008)


In the rainforest areas tree-dwelling mammals such as Lumholtz's Tree Kangaroos, Feathertail Gliders, Sugar Gliders, Striped Possums and Brushtail Possums make their homes along with a range of both fruit and insect-eating bats. On the forest floor can be found Swamp Wallabies and Red Legged Pademelons together with a wide range of native rodents. In the streams, Platypus can frequently be seen.

The area has a spectacular bird fauna. Some 300 bird species have been recorded in the area with habitats ranging from wetlands and mangroves to mountain rainforests. Amongst these are the migratory Buff-breasted Paradise Kingfisher and its relative, the Little Kingfisher; the ground-feeding Cassowary, Orange-footed Scrubfowl and Bush Stone-curlew; and a wide range of honeyeaters, robins, finches, raptors and pigeons. In the agricultural country around Yungaburra, Brolgas and Sarus Cranes are common. Reptiles range from estuarine crocodiles in coastal areas to a rich fauna of snakes, including Amethystine Python, Red-bellied Black Snake, and numerous species of skinks, dragons and geckos. Frogs are also abundant with tree frogs such as the White-lipped and Green Tree Frogs and the Ornate Burrowing Frog. In the urban and cultivated areas the Cane Toad is a very common feral. Insects abound. Many are spectacular in their size and colouring while others are often very difficult to spot. Butterflies (including swallowtails and birdwings), moths (including the huge Hercules Moth), dragonflies and beetles of many types abound.

Red-bellied Black Snake (KG, 2008)

Blue dragonfly (KG, 2008)

Brown-backed Honeyeater (KG, 2008)

Wedge-tailed Eagle (KG, 2008)

Cruiser butterfly (KG, 2008)

Hercules moth (mounted specimen) (KG, 2008)

The Climate: The altitudinal diversity of the degree square's landscape is reflected in its climatic range. The climate ranges from persistently wet rainforest on the ranges to tropical monsoonal along the coast and Tableland. The climatic averages for Cairns Airport and Mareeba (on the Tableland just outside the square to the west) illustrate the tropical monsoon regime.

Cairns Airport (site 031011) 1941-2008 (elevation 2 m ASL)

 

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Year

Mean max
(ºC)

31.5

31.2

30.5

29.2

27.6

25.9

25.7

26.5

28.0

29.5

30.6

31.4

29.0

Mean min
(ºC)

23.7

23.7

23.0

21.6

19.9

17.8

17.0

17.4

18.6

20.6

22.3

23.4

20.8

Mean rain
(mm)

385.0

449.9

424.8

199.2

91.5

46.8

29.6

27.3

33.8

39.8

91.7

180.0

1994.7

Mareeba QWRC (site 031066) 1952-2008 (elevation 400 m ASL)

 

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Year

Mean max
(ºC)

31.3

30.8

29.8

28.6

27.0

25.4

25.3

26.6

28.1

30.5

32.1

32.0

29.0

Mean min
(ºC)

20.9

21.2

20.0

17.8

15.4

12.3

11.2

11.7

13.5

15.9

18.7

20.2

16.6

Mean rain
(mm)

202.3

242.4

189.1

46.6

22.2

14.7

7.1

6.8

5.2

14.3

53.9

106.0

898.1

The highest temperature recorded in Cairns was 40.5°C in December 1990 while the lowest temperature was 6.2°C in June 1946. Rainfall also varies greatly. The highest total of 3148.8 mm was recorded in 2000 and the lowest total of 721 mm in 2002. In January 1981 the monthly total was 1417.4 mm.

The extremes at Mareeba, some 400 m higher in elevation and only 38 km inland, but on the western side of the Great Dividing Range, show a highest maximum of 40.6°C in November 1990, a record low of 0.4°C in June 1963; a highest rainfall of 1730.2 mm in 1974 and a lowest total of 388.8 mm in 1966.

Unfortunately the BoM web site does not include detailed data for Mt Bellenden Ker, the wettest meteorological station in Australia. It averages 8312 mm of rainfall a year and also holds the annual rainfall record of 12,461 mm of rain in 2000. It has recorded a massive 1140 mm in 24 hours - almost the annual total rainfall for Brisbane in a single day!

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