A Geological Wonder in Tasmania: Devils Kitchen

Tasmania's Geological Wonder: Devil's Kitchen

In the far southeast of Tasmania, the Tasman Sea crashes against sheer cliffs and has sculpted one of its most dramatic artworks: a yawning chasm in the coastline ominously known as Devil's Kitchen. This gaping trench is approximately 60 meters deep, with steep rock walls that plunge to a surging cauldron of frothy blue water. Layer upon layer of ancient rock is exposed in those walls, each stratum telling a story from deep time. These cliffs are made of Permian-age siltstone – sedimentary beds laid down roughly 250 million years ago on the floor of a shallow sea. Over unfathomable eons, geological forces and relentless ocean erosion conspired to transform those marine sediments into the breathtaking natural amphitheatre we see today. What follows is a poetic yet scientific chronicle of Devil's Kitchen: from its primordial origins beneath ice-laden seas, through tectonic upheavals and wave-sculpting, to the awe-inspiring chasm still evolving before our eyes.

During the Permian Period (around 250–270 million years ago), Tasmania lay near the polar reaches of the supercontinent Gondwana, and this region was under a frigid shallow sea. Fine mud, silt, and sand slowly settled to the seafloor, accumulating in thick, flat-lying layers. In that time of ice ages, glaciers extended to the coast and shed icebergs into the ocean; as those floating ice masses melted, they dropped pebbles and stones into the soft seabed. These peculiar dropstones – erratics carried by ice – became embedded in the mud. Even today, geologists can find cobbles and pebbles within the siltstone that do not match the local bedrock, silent evidence of ancient ice rafting. Over millions of years, the continuous rain of sediment compressed the lower layers. Water-rich mud and sand turned to stone, cementing into the grey-brown siltstone that now forms the backbone of the Tasman Peninsula. By the end of the Permian, what had been loose sediment was lithified into solid rock, preserving fossil imprints of marine life and even those glacial dropstones within its strata.

Crucially, these sediments remained relatively undeformed through subsequent ages – the region saw no violent mountain-building to crumple or metamorphose the rock. The Permian beds of the Tasman Peninsula are essentially layered like a giant layer-cake, still lying in gentle, horizontal sheets as they were deposited. This is plainly visible in the cliffs of Devil's Kitchen: one can see the stratification, with lighter and darker bands stacked one atop the other in tidy succession. Each band is a timeline – a chapter of ancient Earth – marked by subtle changes in grain size or mineral content. Some horizons contain coarser sand or gravel (perhaps from a storm or melting iceberg long ago), while others are fine-grained silts that settled in tranquil water. These flat layers would become the raw material for Devil's Kitchen, but it took additional earth forces to prepare the canvas for the sea’s artistry.

Tectonic Uplift and Fractured Stone

After deposition, the ancient sea eventually receded and geological uplift gradually raised these sedimentary rocks above sea level. Over tens of millions of years, the Tasman Peninsula’s bedrock was lifted and exposed as part of the surface of Tasmania. The Permian siltstone, once under an ocean, became dry land—awaiting the day it would meet the sea again. The layers remained level and continuous, indicating the crust here was only gently warped. However, as the land rose and subtle tectonic forces acted, the brittle siltstone responded by developing cracks. Think of a cake that is slowly squeezed or dried out – a network of fractures forms. Likewise, the rock was broken by earth movements, forming a grid of vertical joints in the otherwise horizontal beds. These joints are essentially natural cracks running perpendicular to the layering, often tracing straight lines deep into the rock. They would later serve as crucial pathways for erosion, for they marked points of weakness where water could infiltrate and pry the rock apart.

For long epochs, the siltstone lay in wait. Above ground, it weathered under rain and wind, but the most dramatic sculptor – the ocean – had not yet arrived at Devil's Kitchen. During the last ice age (the Pleistocene), global sea levels were much lower, and the shoreline lay far out on the continental shelf. The site of Devil’s Kitchen was inland, high and dry, probably a forested cliff or hillside not directly touched by waves. This changed when the ice age ended and glacial ice melted worldwide. Around 6,000 years ago, the sea rose to its present level, and the Tasman Sea finally reached these siltstone cliffs. The waves began to attack the base of the bluff, and Devil’s Kitchen’s dramatic transformation was set in motion. In geological terms, this was the moment when a slow story of sedimentation and uplift gave way to a sudden chapter of erosion. The stage was now set for the relentless ocean to exploit every weakness in the rock, using the fractures and bedding planes as lines of attack.

The Sea’s Sculpting Hand: From Cave to Chasm

Once the sea arrived at the foot of the cliffs, the powerful forces of coastal erosion took over. The siltstone may be hard, but the ocean is persistent – each crashing wave can act like a hammer and chisel on the cliffs. Over the millennia since sea levels stabilized, the Tasman Sea has ceaselessly undercut and gnawed at the rocks, exploiting the fractures that latticed the cliffs. The process that formed Devil's Kitchen can be imagined as a sequence of dramatic steps, as the shoreline evolved from an intact cliff into a cave, then an arch, and finally the open chasm we see today:

This is the step-by-step journey of how Devil’s Kitchen was created.

Wave-Cut Notch and Sea Cave Formation: It all began with the waves attacking the base of the cliff. Saltwater, carrying grit and stones, pounded against the rock and cut a notch into the foot of the cliff. The siltstone eroded unevenly, with softer or more fractured sections wearing away faster. Over time, the notch grew into a hollow. The relentless impact of waves, combined with the hydraulic force of water and compressed air thrust into any tiny crack, broke off chunks of rock. A sea cave was born, carved into the cliff along one of the vertical joint lines where the rock was weakest.

Expansion into a Tunnel: Once a cave had opened, each storm and tide could penetrate further. Waves raced into the cavern, trapping air and blasting it against the roof and walls, widening the space. The cave deepened and lengthened into a tunnel that burrowed further inland. Eventually the tunnel may have extended so far that it approached another set of natural fractures or even met the surface at the cliff top. For thousands of years, the ocean scoured this passage, grinding the floor and walls and creating a sea tunnel open at one end to the ocean.

Collapse – Birth of an Arch and Blowhole: No roof lasts forever under such an onslaught. The growing tunnel reached a critical point: a zone of weakness where a major vertical joint intersected the tunnel further inland. The ceiling here thinned as wave shock and the pull of gravity worked together. Finally, the roof collapsed at that fracture line, the rock falling into the churning sea. This collapse opened up a deep pit at the inland end of the tunnel, while the outer part of the tunnel remained intact as a natural bridge. What had been a continuous cave became a coastline archway with a collapsed chamber behind it. (In fact, Tasman Arch – which stands just nearby – is precisely this formation: the seaward half of a tunnel with the landward roof fallen in.) Often, such a collapse can also create a blowhole if a small opening to the surface forms. In this area, the famous Tasman Blowhole formed in a similar way, when the rear of a sea tunnel collapsed to make a shaft where spray erupts.

The Devil’s Kitchen Chasm: If the erosional story continues, even the robust arch will eventually succumb. In the case of Devil’s Kitchen, the process advanced to completion – the remaining arch collapsed entirely, leaving no rock bridge at all, only a gaping gash in the coastline. Devil’s Kitchen, as it stands now, is essentially a former sea cave that has lost its roof from end to end. It is a long, steep-walled trench open to the sky. The surging sea floods in freely, crashing at the base of the cliffs. The name “Devil’s Kitchen” evocatively refers to the violent, boiling motion of waves in this rock cauldron after the “ceiling” was removed.

In summary, Devil’s Kitchen is what remains after a sea cave’s full collapse – it is the final stage of this coastal erosion sequence. In essence, it is Tasman Arch without the arch, a giant rock oven with the lid taken off. If you visit the area today, you can actually see multiple stages of this geologic life-cycle along the coast. Indeed, geologists note that Tasman’s Arch is temporary: “Eventually the arch will collapse and Tasman Arch will become another ‘Devils Kitchen’.”. This dramatic coastline is a gallery of nature’s sculptures in various stages of completion.

Why Devil’s Kitchen Looks the Way It Does Today

Devil’s Kitchen today is a place of raw, elemental beauty shaped by dynamic forces. Its appearance – a rectangular trench with vertical walls – is a direct result of the rock type and the erosional process described above. The rock itself, Permian siltstone, tends to break along flat planes. The cliff faces of Devil’s Kitchen therefore look like stratified walls, with stacked horizontal ledges and shelves corresponding to the original sedimentary bedding. Some layers are a bit harder or thicker and form protruding ribs; others, being softer, have worn back slightly, giving the walls a terraced look. This layer-cake architecture is not only aesthetically striking but also tells us that the rocks are flat-lying and undeformed – a remnant of an ancient sea floor now turned on its side for us to inspect.

At the same time, you can see the vertical fractures (joints) slicing down these walls, the very cracks that guided the formation of the chasm. Where two joint planes intersect with a softer layer, chunks of rock have cleaved away, leaving rectilinear corners and overhangs. In places the geometry of the chasm looks almost too neat and angular, an effect of the rocks breaking along straight joint and bedding planes. It’s a stark, cathedral-like space: nature’s architecture in stone. The Tasman Sea’s waves continue to charge into this chasm at each high tide. With a roar, water strikes the back wall of Devil’s Kitchen and explodes upward and outward. The force of these waves is incredible – with each impact, air is compressed into the cliff’s nooks and crannies, only to expand with explosive force, prying the rock loose bit by bit. Sand and small stones carried by the surf act as abrasives, sandblasting the cliff base. This is how the ocean has eaten its way into the headland, and how it continues to deepen and widen the chasm even now.

During stormy weather, the entire trench becomes a cauldron of churning foam, the "devil’s kitchen" boiling with fury. During calmer seas, one can glimpse the base of the walls, where giant boulders that once were part of the ceiling lie rounded and battered by countless impacts.

Thus, it’s probably clear by now that Devil’s Kitchen is not a static formation – it is still changing today. The same processes that created it have not ceased

What does the future hold for Devil’s Kitchen? Given enough time – on the order of thousands more years – it’s possible that the chasm will widen so much that it simply becomes an open bay or cove carved into the coastline. The cliffs could retreat further inland as the sea continues to erode them. Alternatively, new arches or blowholes might form on the edges of the current formation if parts of the cliff face resist erosion longer than surrounding rock. The exact path is hard to predict, but we can be certain the evolution hasn’t stopped. Eventually, new features will emerge, and today’s Devil’s Kitchen may transform into something different, just as Tasman Arch is fated to collapse one day.

But for now, Devil’s Kitchen remains one of Tasmania’s most awe-inspiring geological wonders. To gaze into the Devil’s Kitchen is to look backward into time, imagining the Permian seas that birthed the rock, and to look forward, realizing that the scene is still being created by natural forces. It is a living laboratory of erosion and a monument to the patience of geological processes.

Here's the video we made on this on the OzGeology YouTube Channel: