A 190,000-year-old plumbing system
About 190,000 years ago, the Undara shield volcano erupted, unleashing a torrent of basaltic lava across the savanna of North Queensland. This single, massive eruption produced an estimated 23.3 cubic kilometers of molten rock, flowing at a temperature of around 1,200°C. The lava moved at a rate of about 1,000 cubic meters per second, following the paths of ancient, dry riverbeds. One of these flows traveled over 160 kilometers, making it one of the longest lava flows from a single volcano on Earth.
As this river of lava moved, its surface was exposed to the air and began to cool, forming a solid crust. Beneath this insulating roof, the molten interior kept flowing. When the eruption ceased and the last of the liquid rock drained away, it left behind a network of immense, hollow tunnels. Today, more than 70 of these caves have been found. Weaker sections of the tube roofs have collapsed over millennia, creating deep, moist depressions and providing access points into the subterranean world. Some individual caves, like Bayliss Cave, are over a kilometer long, with dimensions reaching 20 meters wide and 10 meters high. This entire system is preserved within Undara Volcanic National Park.