History of the Misty Mountains Landscape
• The Physiography of the Misty Mountains Region
• Landscape Evolution
• Geology and Vegetation in the Misty Mountains
• Bunya Pines, Remnants of an Ancient Ice Age

The Physiography of the Misty Mountains Region

The Misty Mountain Walking Trail network has been developed atop a rugged and geologically diverse terrain with some striking landform features unmatched elsewhere in the Wet Tropics Bioregion. The terrain can be divided into two physiographic regions, being the Herberton Highland in the west, and the Central Highland, which slopes gradually towards the coastal plain, in the east. The Herberton Highland is formed on acid volcanic rock and comprises the most elevated regions of the walking track system rising to over 1000 metres on the Koolmoon Track. The Central Highland, which has its western limits immediately west of the Cardwell Range, is traversed on the Cannabullen Creek, Cardwell Range and Gorrell Tracks. The Central Highland is a zone of rugged topography with deeply incised gorges, precipitous slopes, and ridgelines that have been etched from granitic, basaltic and metamorphic rock types.

Landscape Evolution

To fully appreciate the evolution of the unique natural features in this landscape, it is necessary to accommodate the vastness of the geological time scale. Around 400 million years ago in a time period known as the Devonian, sediments were deposited off an ancient coastline into the prehistoric Hodgkinson Basin. With time and the pressure of burial, these sediments eventually consolidated to form sedimentary rocks. In the early Carboniferous period, about 40 million years later, sediment accumulation ceased and with movements in the earths crustal plates, the Hodgkinson Basin was compressed and heated. This heat and pressure changed the chemical composition and structure of the sedimentary rocks under a process called metamorphism, and the shales, schists and quartzites of the Hodgkinson formation were created. With continued compression, these rocks were uplifted above sea level, and now form a significant proportion of North Queenslands coastal escarpment. Rocks of the Hodgkinson Formation are most abundant to the east of Downey Creek on the Gorrell Track.

In the late Carboniferous period or around 300 million years ago, an episode of crustal heating created pools of molten lava that ascended into the rocks of the Hodgkinson Formation. This molten magma formed reservoirs, known as "batholiths", at varying levels in the earth's crust. Crustal fractures allowed some of this magma to explosively breach the earths surface. This eruptive activity created a sequence of acid volcanic rocks geologically grouped as Glen Gordon Volcanics, which comprise the remnants of the Herberton Highland. From the magma bodies that cooled slowly in the earths crust, large mineral grains crystallised and gradually solidified into coarse grained rocks known as granites. For over 100 million years, throughout much of the Mesozoic period, the north eastern part of Australia's continent was geologically stable and the major landscape shaping process was erosion. During this time, the granite bodies were gradually exposed, and now form the Cardwell and Walter Hill Ranges which are traversed on the Cardwell Range track.

In the Cretaceous period about 100 million years ago, the eastern portion of Queenslands coastline was fractured when plate movement in the earths crust, opened what is now the Coral Sea Basin. Fragments of crust to the west of the fracture dispersed and were depressed and those to the east were domed and uplifted to form and the highland regions of North Queensland's coastal escarpment. This was a period of greatly accelerated erosion in the catchments of the major river systems and sediment was deposited onto what is now the coastal plain between Innisfail and Tully.

From about 100 million years ago to possibly less than 15000 years ago, a period of volcanic activity occurred on the Atherton Tableland, and numerous volcanic vents formed in the area. During this volcanic episode, sequences of basaltic lava were poured down the deep valleys of the South and the North Johnstone Rivers, Cannabullen and Cochable Creeks, and numerous tributaries such as Downey Creek were back filled during successive surges in volcanic activity. This volcanic activity built up thick sequences of lava that have been measured to be over 200 metres thick in gorge exposures on the North Johnstone River. Lavas were also spilled out across the coastal plain, particularly in the area of the lower Palmerston Highway.

In the time since the river valleys were filled with lava, river courses have incised deep gorges into the basalt, and the thick basalt flow sequences are often exposed along the watercourses. Erosion of these basalt walls is greatly enhanced by the tropical climate which has annual extreme flooding events. The upstream limits of erosion in these basalt filled valleys is often marked by spectacular waterfalls, of which Cannabullen Falls is an excellent example.

Some Interesting Relationships Between Geology and Vegetation

You may notice that the appearance of the rainforest changes in different locations. Many of these differences are related to nutrient availability and soil physical properties which are directly related to the underlying geology. Basaltic soils are nutrient rich and encourage the development of a diverse range of plant life forms including epiphytes and ground ferns, gingers, native bananas, palms, vines and huge banyan figs. These forests are termed complex forests and have an uneven and chaotic appearance due to the merging of many plant layers. Some of the best examples of complex forest on the walking trails are found on the basalt flat of Downey Creek.

Soils formed on rhyolites, granites and most metamorphic rocks are generally nutrient poor with nutrients often stripped through rainfall (leached) or bound up in clays. Rainforests found on these soils generally have a more regular and ordered appearance and lack the luxuriant growth and diversity of complex forests on basalt. The girth sizes of canopy trees tends to be fairly even and the epiphytes and gingers typically found on the ground layer of a complex forest are often absent or rare. These forests are referred to as being of a simple structure These simple rainforest communities are abundant on the Cardwell Range and Koolmoon Tracks.

Bunya Pines, Remnants of an Ancient Ice Age

Pollen records taken from sediment cores in Lynchs Crater on the Atherton Tableland record a complete vegetation history in the area for the past 120 000 years and it is apparent that these are remnants of a forest type that was once considerably more extensive. During the last glacial period that began around 80,000 years ago, rainfall decreased to about half of its present day level and conifer forests expanded hugely at the expense of the floristically diverse rainforests. Conifer forests, composed dominantly of Bunya and Hoop Pine were probably the dominant vegetation community in the area between 80 000 and 40 000 years ago. It is thought that the advent of aboriginal burning may have been the cause of a drastic reduction in the area of the conifer forests between 30 and 40 000 years ago, and eucalypt and casuarina forests became dominant over large areas. At the end of the last glacial period, about 10 000 years ago, rainfall increased dramatically and rainforest communities expanded and rapidly displaced the eucalypt forests. Conifer species could not compete with the rainforest expansion and probably retreated further to the small representations that we see today.

Suggested Further Reading

De Keyser, F., 1964.- Innisfail, Queensland - 1:250 000 Geological Series Explanatory Notes, Bureau of Mineral Resources.

Henderson R. A., & Stephenson P. J., 1980, The Geology and Geophysics of Northeastern Australia, Geological Society of Australia, Queensland Division, Brisbane.

Rainforest Conservation Society of Queensland, 1986 - Tropical Rainforests of North Queensland - Their Conservation Significance, Australian Government Publishing Service, 43 - 58.

This information was collated by David Stanton.

For more information on the history of Misty Mountains, select a link below:
Traditional Owners
Flora & Fauna of Misty Mountains