Wet Tropics geological features, soils and ancient landscapes
The geological foundation of the Wet Tropics has a profound effect on the distribution and types of plants and animals found there.
Rock types determine soil types. Rainfall, plant roots, landslides, river action and other factors break down the rock, particularly where fractures make it more vulnerable.
Soil builds up wherever the rock particles come to rest. Soil types, in turn, determine forest types. Basalt creates the most fertile soil. Granites and metamorphic rocks are more acidic and their soils are less fertile. The most complex and diverse rainforest is found where abundant rain falls on basalt soils in areas of the lowland.
Soils of the Wet Tropics
Soils in the Wet Tropics are predominantly derived from granites and rhyolites, and metamorphic sedimentary rocks. Soil type varies across the region depending on the rock it formed from.
- ridgetops tend to have thin, stony, leached, less fertile soils
- the Atherton Tableland is covered in deep, red basalt soils, which are highly fertile, and
- coastal plains have alluvial soils that can be more than 60 metres deep.
These different soils support a correspondingly wide range of ecosystems, from open woodland on rocky ridges to lush rainforest on the fertile tablelands.
A geological history of the Wet Tropics
Ancient mountain building
The story begins around 420 million years ago, when sediments on the floor of an ancient ocean were compressed by movements in the Earth's crust. These sediments formed the metamorphic rocks that now make up much of the region's mountain ranges. Their folded, layered structure still influences how they weather and break down today.
Granites and volcanics
Between 310 and 260 million years ago, molten magma pushed up into the existing rock and cooled slowly underground, forming granite. Rich in quartz, granite appears light grey to pink and is visible today wherever the rock that once covered it has eroded away.
Around 250 million years ago, volcanic activity produced rocks such as rhyolite. Because these rocks cooled quickly at the surface, they have a distinctive fine texture.
Shaping the modern landscape
Between 100 and 65 million years ago, movements deep within the Earth caused the crust to stretch and fracture. Parts of it sank to form ocean basins and trenches, while other sections lifted, creating the steep escarpment that now runs along Australia's east coast.
From about 7 million years ago, shield volcanoes began spreading basalt lava across the Atherton Tableland. This dense, dark rock weathered over time into the fertile red soils the Tableland is known for today, while later eruptions built the volcanic cones and craters still visible in the landscape.
The break-up of Pangaea—Formation and separation
Around 300 million years ago, the world's landmasses were joined together in a single supercontinent called Pangaea. It began breaking apart around 180 million years ago, during the Permian and Triassic periods—an era when dinosaurs and other reptiles were widespread, and the plant world was dominated by ferns, cycads and conifers.
At the start of the Jurassic period, Pangaea split into two great landmasses: Gondwana in the south, and Laurasia in the north. Gondwana encompassed present-day Antarctica, South America, Africa, Madagascar, Australia and the surrounding regions, while Laurasia included Europe, North America and Asia.
The break-up of Gondwana
From about 140 million years ago, Gondwana itself began to separate. Africa a split away from Australia and South America, Antarctica and India, in a warmer world with higher sea levels—conditions in which the first flowering plants began to appear.
Between 100 and 90 million years ago, Africa separated from Madagascar, India began moving north, and Australia and Antarctica started to drift apart.
By around 65 million years ago, the dinosaurs had become extinct, while the early ancestors of cassowaries were already evolving on a separate path from other birds.
By 50 million years ago, mammals and flowering plants were widespread, rainforests covered much of the global landscape, and plant groups still familiar today—eucalypts, grevilleas and banksias—were evolving.
Around 45 million years ago Australia split from south Antarctica all other continents were approaching something close to their current positions, and India's collision with Laurasian pushed up the Himalayas.
By around 33 million years ago, Tasmania had separated from Antarctica, allowing ocean currents to begin circulating freely around the southern continent. Antarctica cooled sharply, and Australia grew drier as a result.
Finally, between 20 and 15 million years ago, Australia and New Guinea drifted closer to Asia, opening a pathway for some plants and animals to move between the regions.
Geology on display
The Wet Tropics' deep geological history is written into some of its most striking landmarks.
Black Mountain
Black Mountain formed around 260 million years ago from granite that cooled slowly, deep underground. Over time, the rock that once covered it eroded away, exposing the large, fractured boulders visible today. The granite itself is naturally light grey—its dark, almost black appearance comes from a surface layer of algae. Sudden temperature changes can cause the rocks to crack without warning, so it's a landscape best admired from a respectful distance.
Lake Eacham and Lake Barrine
These two lakes occupy volcanic craters known as maars, formed when rising magma met groundwater and triggered explosive steam eruptions. Unlike typical volcanic eruptions, maars eject relatively little material—instead, they leave behind craters with low surrounding rims, which later filled with water to form lakes up to 65 metres deep.
Nearby, Bromfield Swamp and Lynch's Crater are older maars of the same type. Their sediments hold long pollen records that scientists use to reconstruct past environments and climates.
Mount Hypipamee crater
Mount Hypipamee is a rare geological feature called a diatreme, formed when gas rose rapidly through a crack in the Earth and exploded at the surface. The result is a deep, cylindrical pipe with walls around 55 metres high, plunging to a lake about 87 metres deep at its base. It's the only known example of its kind in North Queensland.
Mount Quincan and the Seven Sisters
These volcanic cones formed through explosive eruptions that threw volcanic material into the air. As ash and scoria—a lightweight, gas-filled volcanic rock—built up around each vent, they gradually formed the steep-sided cones that give this landscape its distinctive profile.
Detailed information can be found at here: Rocks, Landscapes and Resources of the Wet Tropics.
Last updated: 13 Oct 2026