Exploring Australia’s Meteorite Impact Craters: Trekking Into Darwin Crater
In an age where high-resolution satellite imagery is available instantaneously and all the blank spaces of the map labelled “terra incognita” have been filled in, much still remains to be discovered. But this sort of on-the-ground research can offer surprising—and even dangerous—results.
Darwin Crater
Deep inside the Franklin-Gordon Wild Rivers National Park lies a scar from an ancient catastrophe. Roughly 800,000 years ago, a meteorite (or possibly a comet) impacted the land that would become Tasmania, transferring energy equivalent to many nuclear blasts into the local geology. Scorching temperatures crystallised the local rock into an impactite commonly known as Darwin Glass. Close to 11,250 cubic metres of Darwin Glass was thrown into the air and scattered over a circular area totalling 400 square kilometres.
In 1972, road construction south of Queenstown uncovered large amounts of Darwin Glass, including several of the largest specimens yet seen. Mapping its distribution across the Franklin-Gordon Rivers National Park and the West Coast Range Regional Reserve, geologist Dr. Ramsay J Ford discovered the likely origin point: a circular feature 9 km southwest of Mount Darwin. This feature, known as Darwin Crater, is bowl-shaped and 1.2 km in diameter. Frequent rainfall has washed a considerable amount of sediment into the crater basin and the entire area is heavily forested.
Ford accompanied a team that bulldozed a path from the Franklin River Road into the centre of Darwin Crater in 1974. The team drilled cores up to 230m deep in search of diagnostic shock features. These are scars found on rocks that can only be formed at the epicentre of a cataclysmic impact. The most common is the shatter cone—a horse-tail shaped conical feature that can be seen with the naked eye. On a microscopic level, cross-hatch deformations in rock surface and the presence of certain minerals such as Coesite and Stishovite also provide unequivocal proof of an ancient impact. Without the discovery of one of these three geological features, an impact crater remains officially unconfirmed. None were found by Ford’s team in 1974 or by later expeditions (the most recent of which took place in 2007). Despite the wealth of secondary evidence, such as the ubiquitous Darwin Glass, Darwin Crater’s impact origin has yet to be officially confirmed.
Our Goal
Australia is home to 32 confirmed meteorite and comet impacts. A similar number are likely candidates (such as Darwin Crater) but remain unconfirmed. Some craters have important indigenous links while others have provided the scientific community with the evidence needed to make strides in geology and space research. Australia’s ancient geology makes it the best place in the world to study impact craters. Despite this, no one has written a book telling the holistic story. Dr. Paul Dare and I are fixing this.
Paul is a professional pilot and surveyor who invented and spearheaded the development of aerial mapping systems now used globally. For this project, he has adapted his software for use with a drone to create maps more detailed than any seen before.
My primary focus is anthropology—a discipline seldom applied to the study of impact craters. However, several meteorites and comets have impacted Australia during its period of human settlement. Knowledge about these events and their impact on the landscape was encoded in myths and stories that have lasted many thousands of years. Even today, there is still much we can learn from the mythologised eyewitness accounts of the ancient past.
Detailed maps of the majority of Australia’s impact craters simply don’t exist (yet), and no one has visited them all on the ground. We are changing this. Paul and I are embarking on ground-based expeditions to each of Australia’s craters as well as mapping them from the air. We have visited and mapped several craters so far—such as the Lake Acraman impact structure, Gosses Bluff (Tnorala), and the Henbury Crater Field. We found several excellent shatter cones at Gosses Bluff (Tnorala) and completed an aerial survey of Henbury, where broken pieces of the original iron meteorite can still be found. On the outskirts of the Lake Acraman impact structure, we uncovered evidence that buildings were constructed from stones bearing the tell-tale marks of an impact from space. We also completed the first high-definition aerial survey of Boxhole Crater in the Northern Territory. But these expeditions were undertaken in the outback. We had never trekked into a rainforest before, so Darwin Crater posed distinct challenges.
Following in the footsteps of Dr. Ford, we aimed to trek into the centre of the crater and conduct a ground survey. We were also interested in finding out why comparatively few geologists have drilled for geological proof of the crater’s origin.
Before setting out, we reviewed the latest satellite imagery of the terrain, which showed a defined track from Franklin River Road into the crater. This aligned with the “Walking track” shown on the latest available paper map, a 1:25,000 scale topographic map released by TasMap in 1995 (Engineer 3831). We assumed this walking track to be similar to others we had followed in the outback, just with more vegetation. This is what we were equipped for, not for cutting our way through a rainforest. We believed ourselves to be well-prepared, but in the Tasmanian wilderness, things do not always go as you expect.
The Trek
We began the 3km trek from Franklin River Road into Darwin Crater next to a roadside clearing. It was early afternoon, and we expected the ‘walk’ to take roughly an hour each way, giving us plenty of sunlight to conduct a basic survey in the basin. Right at the start, we expected to find a blue sign indicating the trailhead, but it was nowhere to be seen. Here was our first indication that this journey would be more challenging than anticipated.
When Dr. Ford and his team first cut the track through the dense forest in 1974, their heavy machinery left deep tracks. This is what is marked on current maps. Whilst almost entirely overgrown in places, these tracks remain mostly visible. When it rains, as it so often does in a rainforest, water collects in the ruts, turning them into a quagmire.
Sinking to our knees in sucking mud, Paul and I found these sections difficult to traverse, especially while burdened by equipment. This was exacerbated further on, where stands of closely-growing trees had fallen across the track like natural barricades. Nearer the beginning of the track, we crawled under these without substantial difficulty. But the further into the rainforest we went, the more impassable these obstacles became. On several occasions, the stands of trees lying across the track were so thick we could not see the other side. To navigate around them, we struck out into the bush. The track was enveloped by vegetation immediately and we relied upon our senses of direction to get us back. On more than one occasion, we were compelled to fossick around on the other side to identify the track since it had almost entirely been consumed by the rainforest. This was not the sort of trek we had anticipated and entirely a different journey than the one we had planned for.
Roughly two hours into the trek, well over double the time we had allotted, we crested the ridge that lead down into the crater. Here, we lost the track completely. Taking a detour through the bush to navigate around a particularly dense stack of fallen trees, we could not pick up the track on the other side. We chose to move parallel to the track down the ridge in the direction of the crater, hoping to pick it up again at the base.
The ground fell away sharply beneath the ridgeline. The gradient was at least 2:1 and steeper in places. Grasping thin, loosely-entrench trees as we went, our descent was reminiscent of climbing down a long, slippery ladder. A challenge without surveying equipment. But we were virtually at the crater’s edge and determined to push on.
Despite the unforgiving terrain, we reached the basin not long after climbing down from the ridge. The trek had been far tougher than we had expected. But the worst was to come.
The Swamp
Instead of the open space we had seen on the satellite imagery, we encountered a swamp. The vegetation was impenetrable. At ground level, we both sank into festering mud, with water sloshing at our knees. Above the water was an unending tangle of branches. This continued to chest height, and often higher. The gaunt trees were matted with stringy vegetation that obscured vision in all directions. It was impossible to see more than a few metres in any direction. Interspersed amongst the trees were dense patches of cutting grass, further barring the way. The air was thick with the smell of decay and there was little airflow through the trees.
With no sight of the track at all, we followed a succession of streams further into the crater. Thick vegetation forced us to double back frequently and alter our course. Every stride was taxing and before long our bodies were aching with fatigue.
After battling the swamp for some time, we noticed some footprints and, feeling elated that we must be closing in on the original track, followed them. Our hearts sank when we realised not too long after they were our own footprints, and we had inadvertently gone around in a circle. We attempted to backtrack to the base of the ridge, but it was no use. We circled back by accident again.
By this point, we were completely disorientated. The air was heavy with a putrid, rotting stench. Leeches crawled on our skin. Our hands were sliced from cutting grass and we were soaked through. We were totally lost. There was no choice, we had to call off the expedition. In the space of an hour, we had made it less than 100m into a crater 1.2km in diameter.
Although we had a few hours of sunlight left, darkness began to close in in the heart of the swamp. We chose to carve our own path through the vegetation towards the west, knowing that if we missed the track, we could make Franklin River road by nightfall.
We periodically ceased smashing through the bush to check the GPS and compass, but these vital tools proved less than infallible. The swamps’ humidity had allowed water to get inside the housing of our electronic equipment. With a flicker of the screen, both the GPS and compass went dead, and we were on our own.
Getting Out
Doing our best to continue westwards, we cleared the thicker part of the swamp. By chance, I spotted our footprints from earlier and we followed them to the base of the ridge. Without the GPS or compass, our footprints were the best indication we had of the way back to the road. I had made observations on specific plants and animal tracks that crossed our path on the way in and combined with our boot prints, these observations kept us on track during the journey out.
We were immensely relieved when we eventually emerged from the rainforest. When the adrenaline wore off, we suddenly became aware of just how cold, thirsty, hungry, and exhausted we were.
Conclusion
The trek into and out of Darwin Crater was very challenging. Even with considerable preparation and the latest maps, the track was, in places, impossible to follow, making navigation very difficult. We walked, quite literally, in the tracks of the geologists who named Darwin Crater 50 years ago. They failed to confirm its origins then, with the aid of a bulldozer and a team of workers clearing the forest. In its current state, the track into Darwin Crater is scarcely passable for people, let alone heavy machinery. Without significant land clearing, the crater’s impact origin will likely remain unproven.
We never got to do a ground survey, but we did reach Darwin Crater on foot, something few geologists can claim. In the coming months, we plan to return to the crater in a light aircraft and, by combining images in a digital mosaic, create the most detailed map of the crater even seen.
Brad is a Canberra-based writer and explorer with a keen interest in Australia’s ancient past. Working with aerial surveyor and internationally-renowned imagery expert Dr Paul Dare, Brad is in the research phase of writing a book about Australia’s impact craters. They are taking a holistic approach: combining today’s cutting-edge science with the ancient myths of Australia’s first peoples. The book will be equal parts scientific reference, anthropological discussion, surveyor’s report, and cracking tale of discovery.
Online at: https://bradleydare.com/
