The most famous coal seam fire smolders underneath Centralia, Pennsylvania, but thousands of such underground fires burn all over the world. In the American West, where subterranean coal still burn, ancient conflagrations created the red-inflected landscape we see today.


Gizmodo took a look at the striking phenomenon of underground fires a few months ago, highlighting what is commonly considered the oldest: the 6,000-year-old Burning Mountain fire in Australia.


However, a recent report about the Burning Hills in Utah caught my eye with the incredible statement that "fires in southern Utah might have been burning for millions of years." Could this be true—could this be the oldest fire? No one really knows for sure, and estimates seem to range wildly from decades to millions of years.

For me, even more interesting than finding the longest continuous-burning fire in the world is considering the enduring legacy of ancient fires long since snuffed out. They may not have burned for thousands or even millions of years, but they've made an indelible red mark on the landscapes around us.

Take the Burning Hills of Utah, which are, of course, brick red. Heating from the burning coal has oxidized iron in the rock, giving it its striking color. Even more remarkably, the heat has actually metamorphosed the rock, turning it into what is known as clinker. In some places, the heat is intense enough to actually melt the rock, which then resolidifies as another type of rock altogether, the slag-like paralava.


Geologist Callan Bentley, who also took these photos of clinker in Wyoming, below, has a wonderful explanation at his blog.


This hard, dense clinker doesn't erode as easily as its unmetamorphosed neighbors. Over time, we're thus left with these brick red hills. Repeat this thousands of times over thousands of years, and the topography of the American West is created.

"Much of the landscape of the American West—its mesas and escarpments—is the result of vast, ancient coal fires," wrote Kevin Krajick in Smithsonian Magazine. And underground fires are still burning, too, quietly shaping the landscape of the future. [KLS, Smithsonian Magazine]

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