What’s the biggest rock in the world? Well, it depends on how you define a rock. But without stepping too far into a geological, philosophical, and linguistic minefield, there are several colossal contenders for the title, including a bunch in the Aussie Outback.
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For many, Uluru (also known as Ayers Rock) is the undisputed title holder. This sandstone giant rises from the wonderfully empty, gloriously red heart of Central Australia, towering 348 meters (1,142 feet) above the surrounding plain and stretching 9.4 kilometers (5.8 miles) around its base.
It looks like a giant red brick that’s been plonked in the orangey desert, leaving a bold impression that makes it one of Australia’s iconic sights.
The story of Uluru begins around 550 million years ago when the entire region was covered by a sea. Sand and mud fell to the bottom of the seabed, eventually turning into solid rock. The sea vanished 400 million years ago, leaving the rock exposed to wind, rain, and temperatures that eroded away the softer rock, sculpting it into the form we see today.
Mount Augustus is another big rock, although technically a monocline.
But travel more than 1,000 kilometers (620 miles) north of Perth into the wild interior of Western Australia, and you’ll find a potential challenger: Mount Augustus. It stands approximately 860 meters (2,820 feet) above the surrounding plain and covers at covers an area of 4,795 hectares (11,850 acres), making it more than twice the size of Uluru.
Geologically speaking, however, Mount Augustus is a very different beast. It’s the world’s largest monocline, defined as a massive fold in the Earth’s crust where rock layers bend upward on one side, like a rug pushed against a wall. Rather than a single block, it’s a vast structure made up of many folded layers laid down over immense stretches of geological time.
This is where Uluru might take the edge. Defined as a monolith, Uluru is a relatively uniform mass of rock. Although it’s also composed of layers of sandstone, the layers belong to one continuous formation and could be considered more akin to a single rock.
Giant Rock, with pickup truck for scale.
This distinction explains why any old mountain can’t claim the crown of the world’s largest rock. Mountains and many other rocky formations are more like a geological Frankenstein’s monster: odd layers of rock, soil, and volcanic material piled, pushed, and folded together over millions of years like patchwork.
If you’re looking for something more concrete, so to speak, the US is home to the largest freestanding boulder in the world: the aptly named Giant Rock in California’s Mojave Desert, covering 5,800 square feet of ground and is seven stories high. It is, as its name suggests, just a free-standing giant rock, albeit with a surprisingly colorful backstory involving desert mysticism, UFO cults, and hermits.
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