The Huge Super Volcano in Victoria Australia

17 November, 2025
Oz Geology

The Cerberean Caldera: Australia's Forgotten Super Volcano

If I told you that one of Australia’s largest volcanic eruptions—maybe among the largest known in the entire country—happened just northeast of Melbourne, you’d probably think I was joking. But tucked beneath the forests around Marysville, Lake Mountain, and the Rubicon Valley lies a hidden giant: the Cerberean supervolcano, a Devonian monster with a collapsed volcanic crater—or caldera—that spans about 27 kilometres across. Inside that ring, researchers have identified around 900 cubic kilometres of ignimbrite—volcanic ash and pumice welded together into rock—just inside the collapsed caldera. Let that sink in: nine hundred cubic kilometres is enough to bury the entire Greater Melbourne region under a layer of superheated volcanic ash hundreds of metres thick. And that’s only the material preserved inside the crater. The total eruption volume, including material blown far across the ancient landscape, was almost certainly much larger.

*Image depicts the Cerberean Caldera size (Pre-Erosion

*Image depicts the Cerberean Caldera Size (Post-Erosion)

*Image depicts the geological map of the area with Ring Faults highlighted. Ignimbrite layers are depicted as an orange color, and the red color are granites.

This thing was a supervolcano, make no mistake. A full-scale “caldera-forming eruption” capable of collapsing a huge section of crust into an emptied magma chamber and blanketing vast areas of eastern Australia in glowing clouds of pyroclastic fury. And speaking of magma chambers—this wasn’t some little pocket of molten rock hiding under a fault line. The Cerberean supervolcano sat on top of a batholith-scale magma system, built from multiple batches of magma rising and accumulating over millions of years. It was enormous, chemically diverse, and incredibly hot—upwards of 875–940°C for the uppermost rhyolitic melts, and still at least 780°C for the lower ones.

So how did such a monster come to exist here? Why central Victoria? Why then? And how does a volcano grow large enough to literally swallow a piece of the continent as it collapses in on itself? To answer that, we need to peel back the layers of geological time, zoom way out to the scale of continents, and set the stage for one of the most explosive chapters in Australia’s deep-time story.

Long before Victoria ever shook with the fury of the Cerberean super-eruption, the land beneath it was already extraordinary. Central Victoria sits above a block of ancient crust known as the Selwyn Block, which is itself part of a much larger fragment called VanDieland. You can think of VanDieland as essentially Tasmania before Tasmania existed—an exotic microcontinent composed of Proterozoic and early Paleozoic rocks that once drifted independently along the edge of Gondwana. Geological evidence suggests that VanDieland, including what we now call western Tasmania, collided with the margin of eastern Australia sometime around the Late Ordovician to early Silurian, generally placed between 440 and 430 million years ago. When it welded onto the Gondwanan edge, it fundamentally changed the crust beneath what would later become Victoria. Instead of simple continental crust, central Victoria inherited a layered, chaotic, incredibly heterogeneous block of deeply metamorphosed greywackes, volcaniclastic sediments, and rift-related volcanic rocks.

This exotic basement block mattered immensely because it became the raw material for the Cerberean supervolcano. Deep beneath central Victoria, the crust was riddled with ancient sediments that, when heated to sufficiently high temperatures, produced exactly the kind of magma needed for enormous explosive eruptions. These were S-type magmas, formed by melting sedimentary rocks rather than igneous ones. S-type magmas tend to be sticky, silica-rich, water-rich, and dangerously volatile. They are the sort of magmas that erupt as giant pyroclastic flows, rather than as calm, flowing lava.

By the Devonian, central Victoria had been through hundreds of millions of years of tectonic chaos. Subduction zones had opened and closed. Volcanic arcs had come and gone. Rifting had pulled the crust apart only for compression to push it back together again. This constant tectonic switching created faults, fractures, and weaknesses throughout the crust. But more importantly, it thickened the crust and trapped heat. Thick crust behaves like a giant slow cooker, particularly when new hot magma from the mantle keeps intruding from below.

And intrude it did. Instead of one enormous, uniform pulse of basaltic magma rising into the crust, the Selwyn Block was repeatedly injected by many thinner sills and sheets of mafic magma. These small intrusions behaved like a long series of blowtorches heating the basement rocks. Each intrusion roasted the local crust, melted part of it, and allowed tiny pockets of granitic magma to form. Over millions of years, these pockets migrated upward, merged, mingled, and slowly grew into massive bodies of melt.

*Image depicts the batholith size magma chamber of the Cerberean Caldera. The yellow circles indicate volatiles in the melt.

The important thing here is that the crust was not melted evenly. Because VanDieland was a patchwork of different sediments and volcanic rocks, each region of melting produced magma with a slightly different composition. Some areas melted greywacke more completely, others melted mudstone, and others melted volcaniclastic rocks rich in iron and magnesium. This is why the Cerberean eruptive units—the Rubicon Ignimbrite, its high- and low-aluminium variations, and the Lake Mountain Ignimbrite—are chemically distinct from one another. They were not born from the same melt, but from different pockets of crust that melted at different times. By the time these pockets had risen into a single larger chamber, the magma body had become a marbled mixture of slightly different magma batches. This heterogeneity is one of the signature features of supervolcano systems.

As the magma chamber beneath central Victoria grew, a huge dome of hot, ductile crust began to balloon upward. The pressure inside the chamber increased. Water dissolved in the melt built up. Temperatures remained brutally high. The magma became saturated with volatiles—water vapour, carbon dioxide, and other gases that dramatically increase the explosiveness of silicic magmas. The stage was set for a cataclysm.

The eruption likely began with a deep failure in the magma chamber. Perhaps a fresh injection of hotter magma from below destabilised the chamber roof. Perhaps pressure built up along a pre-existing weakness. Whatever the trigger, the chamber ruptured violently. A point explosion sent shock waves through the crust. Ring fractures propagated outward in a near-perfect circle, thirty kilometres across, slicing the crust with terrifying speed. These fractures opened pathways for magma to rush to the surface.

The first pulses of magma erupted explosively, forming towering eruption columns. The high-Al Rubicon Ignimbrite came first, filling the early caldera basin with pyroclastic deposits. As the eruption intensified, the magma feeding the vent changed slightly, reflecting the transition from one batch of melt to another. The low-Al Rubicon Ignimbrite followed, even larger and more voluminous than the first. The eruption drove pyroclastic density currents—avalanches of incandescent ash, pumice, and gas—outward at hurricane-like speeds. These flows consumed everything in their path, flattening the Devonian landscape and leaving behind a smothering blanket of hot volcanic debris.

*Image depicts the Rubicon Ignimbrite outcrops today (The first erupted layer that was largely buried by the Lake Mountain Ignimbrite.

*Image depicts the Lake Mountain Ignimbrite layer.

As the eruption continued, the composition of the magma shifted again, indicating that deeper, slightly more mafic parts of the chamber were now being tapped. This transition gave rise to the Lake Mountain Ignimbrite, a rhyodacitic unit representing the final and most voluminous phase of the eruption. The Lake Mountain Ignimbrite would eventually make up the bulk of the 900 cubic kilometres of material preserved inside the caldera.

But the most dramatic part of the whole sequence was the collapse. As the magma chamber emptied, the roof above it lost support. The central block of crust—kilometres thick—began to slump and sink into the void. This sinking was not gentle. It was catastrophic. The ground collapsed along the ring fractures in a cauldron-style subsidence event, dragging the surface downwards like the lid of a pot falling into boiling soup. The collapse, in turn, triggered more magma to erupt. The eruption fed the collapse, and the collapse fed the eruption.

The result was a vast caldera, rimmed by ring faults and filled with a sea of ignimbrite. If you could travel back in time, you would see fountains of ash darkening the sky, pyroclastic flows racing across a barren wasteland, and the Earth literally caving in upon itself. The Cerberean eruption would have been one of the most violent geological events ever to take place on Australian soil. And even though hundreds of millions of years have passed, the ghost of that catastrophe is still visible today. If you open a satellite map and zoom in on the region between Marysville, Lake Mountain, Cambarville, and the Rubicon Valley, you can trace the faint but unmistakable curve of the caldera rim. The landscape forms a subtle, giant circle—its arc picked out by ridge lines, valley orientations, and the distribution of volcanic rocks. It’s not obvious to the untrained eye, but once you know what you’re looking for, the 27-kilometre-wide outline snaps into focus like a fingerprint from deep time. The caldera is still there—quiet, forested, eroded, but undeniably present—etched into the high country like the scar of a wound the Earth inflicted upon itself.

When the eruption finally ended, the caldera remained active for some time. Magma continued to intrude beneath it, but instead of exploding at the surface, it cooled slowly underground. These late-stage intrusions crystallised into granodiorite, forming many of the granite outcrops now seen in the Marysville region. Over the next several million years, erosion, uplift, folding, and sedimentation slowly obscured the caldera. Forests grew. Rivers carved through the ignimbrites. The violent past sank beneath a peaceful landscape.

Yet the evidence remains. Lake Mountain owes part of its topography to thick accumulations of ignimbrite. Boulders and cuttings along roads between Marysville and the high country expose welded tuffs, glassy volcanic rocks, and granodiorites that once pulsed with heat. The Rubicon Valley preserves relics of pyroclastic flows that were once hundreds of degrees hot.

What makes Cerberean so fascinating is its context. This was not a one-off oddity. During the Late Devonian, central Victoria experienced widespread magmatism. From Mount Macedon to the Dandenong Ranges. Calderas erupted across the region. The crust was extraordinarily fertile for melt generation. The Selwyn Block supplied sedimentary source material ready to melt. Continuous injections of mafic magma kept temperatures high. Faulting and extension provided pathways for magma ascent. This was the perfect storm for giant silicic eruptions. Cerberean was simply the biggest expression of this magmatic province.

*Image depicts the Macedon Ranges Ignimbrite layer.

*Image depicts the Dandenong Ranges Ignimbrite layer.

The presence of VanDieland beneath Victoria was crucial. Without that exotic fragment of thickened, heterogenous crust, the region would not have had the chemical richness required to feed such massive magma chambers. Tasmania’s ancient rocks provided the fuel. When VanDieland welded onto the mainland around 430 million years ago, it carried with it a geological legacy that would one day erupt in spectacular fashion.

Today, the landscape above the Cerberean caldera is quiet and peaceful. Alpine ash forests cover the slopes. Hikers walk trails that follow ancient fault lines without knowing it. Beneath their feet lies the memory of a supervolcano, preserved in silent stone. The region looks serene, but the rocks tell a different story. They tell of a time when the ground trembled, when the Earth roared, when the sky filled with darkness, and when an entire piece of crust collapsed into a sea of magma.

Understanding Cerberean is not just about studying an ancient eruption. It is about recognising that Australia, often seen as a geologically quiet continent, has a deep-time history every bit as dramatic as Yellowstone or Toba or Taupo. The Cerberean supervolcano is one of the greatest geological stories on the continent—hidden, forgotten, but vast in scale and astonishing in power.

If you walk the forests of Marysville and Lake Mountain with that in mind, the land suddenly feels different. Every granite boulder becomes a remnant of a cooling magma chamber. Every roadside cutting becomes a window into an inferno that once raged with unimaginable force. And the tranquillity of the landscape becomes even more remarkable when you realise that beneath the trees lies the shattered heart of a supervolcano.