- Last updated:
- 16 Dec 2019
The varied and spectacular scenery of the Sunshine Coast reflects the region’s complex geological origins. The numerous rock types have resulted in varied topography and diverse soils that support different species of plants and animals.
The rocks and landscapes of the region have been formed through a series of uplifts of the ocean floor, movements of the continental crust and associated volcanic activity, metamorphosis (transformation), and finally, long periods of sediment erosion and deposition (accumulation of earth material).
The region's ancient landscape
The oldest rocks formed about 315 million years ago (mya) and most of the rocks of this group are evident in the west of the region. As in much of eastern Australia, the period around 30 mya brought major volcanic activity to the region. The basalt lavas that were produced by these eruptions readily weathered to form the fertile red, chocolate and prairie soils found on the Maleny-Mapleton and Buderim plateaux and other hills in between.
The period between 230-210 mya saw volcanic activity with eruptions; the lavas of these eruptions (the North Arm Volcanics) are believed to have erupted from one or two calderas north of Nambour. The resulting rocks cover a large area in the centre and north of the region, stretching from near Maleny to Coolum, and Kenilworth to north-east of Eumundi. Granite soils, which are relatively coarse and sandy, occur mainly in the west of the region, in small areas near Eumundi. They are only moderately fertile.
Following the eruption of the North Arm Volcanics, an extensive period of erosion resulted in the sedimentary beds known as the Landsborough and Myrtle Creek Sandstones. Generally the resultant soils are of low fertility but in the hills around Nambour, Woombye and Palmwoods some moderately fertile soils have developed as a result of accumulated iron in the soil surface.
Mountains and beaches
The long period of geological stability has resulted in slow but steady erosion of valleys into the basalt landscape and a general lowering of the land surface to expose the volcanic plugs we see today.
The mountains of today’s landscape were formed only around 27 to 26 mya when magma was forced up through the older rocks, possibly filling old volcanic vents (plugs) or subsurface bulges (laccoliths). The southern group of these plugs form the Glass House Mountains, while to the north we see such prominent landmarks like Mt Coolum, which is a laccolith rather than a plug. Mt Peregian is another laccolith while Mt Tinbeerwah is a dyke (narrow body of rock) that intruded (penetrated into other rocks) into the Myrtle Creek Sandstone.
Sediments were deposited, and continue to be, along the stream valleys while mud and sands have accumulated along the coastal shore.
The coastal sand hills and beaches of the Sunshine Coast are the result of deposited quartz sand eroded from granites and sandstones of northern New South Wales. These are washed from mountains to the coast by rivers and carried north by ocean currents. Rocky outcrops such as Caloundra Head and Point Cartwright serve as anchor points or groynes causing sand to collect to their north forming extensive beaches.
Willmot, Warwick, 2007. Rocks and Landscapes of the Sunshine Coast (Revised Second Edition) [PDF 330KB].
Available in council libraries[include7].
- Mary Cairncross Reserve: Glasshouse Mountains Geology[include7]
- Geological Society of Australia (QLD Division)[include7]
- Geoscience Australia[include7]