Understanding Volcanic Diversity on the Atherton Tablelands

The Atherton Tablelands in Far North Queensland, Australia, offers a remarkable natural laboratory for understanding volcanic diversity.

For those following, I thought it opportune to demonstrate the types of volcanoes on the Tablelands. This morning I scouted images for this post.

Although there are 65 eruptive centres in the Atherton Basalt Province, most are one of four volcanic types. Prominent examples are found at Hallorans Hill in Atherton, Bones Knob near Tolga, Mt Quincan with nearby Lake Eacham, and Mt Hypipamee - each demonstrating different eruption styles and resulting landforms, despite their close proximity.

Standing at the edge of Atherton township, Hallorans Hill represents a classic shield volcano. Unlike the explosive eruptions many associate with volcanoes, shield volcanoes are formed by relatively gentle effusions of fluid basaltic lava.

Hallorans Hill's smooth, dome-like profile is the result of multiple flows of low-viscosity lava that spread easily across the landscape before cooling. These layered flows created the gentle slopes (typically less than 10 degrees) that give shield volcanoes their distinctive profile—resembling a warrior's shield laid on the ground.

Visitors to the summit lookout can appreciate how this eruption style contributed to the fertile agricultural lands that now characterise the Atherton area.

Near the township of Tolga stands Bones Knob, a shield volcano (1.7 million years ago) with a small crater on the top. It also has a secondary scoria cone (also known as a cinder cone - 1.66 million years ago) to the immediate northwest, seen as a horseshoe structure with cliffs. The lava flow extended 30km to Mareeba with a finger extending to Biboohra.

Scoria cones form when gas-rich magma reaches the surface and expands rapidly, fragmenting the molten rock into small pieces called scoria or cinders. These pieces cool quickly in the air before landing around the vent, building a steep-sided cone of loose material. With its steeper sides (typically 30-40 degrees) and distinctive conical shape, the scoria cone at Bones Knob provides a stark contrast to its shield volcano base.

Mt Quincan , a classic cinder cone, formed as magma interacted with groundwater to produce violent eruptions. These explosions created a prominent crater with a surrounding rim of ejected material. The mountain's irregular shape and deep crater tell the story of these powerful blasts.

Lake Eacham (800m across and 60m deep) represents explosive volcanic features—a maar crater, formed when rising magma encountered groundwater, creating steam-driven explosions that blasted out a deep, wide crater about 9-10,000 years ago.

Unlike the constructive processes that built Hallorans Hill and Bones Knob, Lake Eacham formed primarily through destruction, as explosions excavated a crater that later filled with water to create the crystal-clear spring fed lake we see today.

The dramatic crater walls and depth of Lake Eacham testify to the enormous explosive power that can be generated when magma and water interact.

Located further south in the Tablelands, Mt Hypipamee National Park features one of the region's most unusual volcanic formations—a diatreme pipe. Unlike the other volcanic features we've explored, Mt Hypipamee's crater represents an extreme case of explosive volcanic activity.

The Mt Hypipamee Crater is a near-vertical pipe that was blasted through solid granite by a massive, high-pressure gas explosion. When magma rapidly ascended through the earth's crust, it encountered groundwater, creating a violent steam explosion that literally punched a cylindrical hole through the existing granite.

What makes Mt Hypipamee particularly distinctive is the sheer depth and verticality of its walls—the crater plunges approximately 150 meters down, with near-vertical sides, and contains a small lake about 60 meters below the viewing platform. The circular shape of the crater (roughly 61 meters in diameter) reflects the concentrated, pipe-like nature of the explosive event.

Mt Hypipamee represents volcanic activity at its most explosively focused—more like a volcanic gunshot than a traditional eruption. The surrounding rock shows minimal deformation, as the explosive force was directed vertically rather than laterally.

What makes the Atherton Tablelands fascinating is how these four distinct volcanic styles occurred in such close proximity. This diversity can be attributed to several differing factors including magma composition, ground water interaction, vent conditions and pre-existing geology.

For anyone interested in earth sciences or simply appreciating dramatic landscapes, these four volcanic neighbours provide a window into the powerful forces that continue to shape our planet's surface.