Massive rock outcrops have captivated travelers from around the globe for millennia. Ancient civilizations used distinguishable outcrops as navigation tools and sites of worship and gatherings.
Beautiful landscapes with awe-inspiring mountains like Yosemite and Glacier National Parks are travel destinations for people around the globe.
Devil’s Tower in the Black Hills of northeastern Wyoming was established as the first national monument in the United States in 1906 by President Theodore Roosevelt.
Indigenous people in the area refer to this high-rising structure by various names, including “Bear’s House”, “Bears Lair”, “Aloft on a Rock”, “Tree Rock”, “Great Gray Horn”, and “Brown Buffalo Horn”, depending on the specific tribe.
Standing 867 feet (264 m) from base to summit, this massive tower in the hills of Wyoming is an incredible feature and shrouded in controversy related to its origin.
Sedimentary rocks create the bedrock layers that surround Devil’s Tower. 250-200 million years ago, the landscape that is now northeastern Wyoming was covered by a shallow sea.
Deposition of sand and sediments on the seafloor were cemented and formed several sandstone layers. Iron within the sandstone units oxidized from prolonged contact with the atmosphere, and formed the red, rusted color of the surrounding exposed geologic units.
Uplift during the Paleocene Epoch 56-66 million years ago formed the Rocky Mountains and Black Hills of today.
Prolonged and severe uplift caused dramatic faulting and fracturing of the overlying sandstone bedrock. Fractures in the rocks creates pathways for molten rocks to rise to the surface and form igneous intrusions such as dikes and sills (vertical and horizontal magmatic fissures), volcanoes, or plutons (large bodies of magma that hardened beneath Earth’s surface).
Rocks creating the Devil’s Tower are igneous in nature, meaning they formed from the cooling of molten rocks from inside Earth’s interior.
Specifically, Devil’s Tower is a ‘phonolite porphyry’ that formed 40.5 million years ago. Phonolite referring to a specific type of igneous rock that has an intermediate composition, meaning it has small amounts of silica (sitting in between the extreme classification ends of basalt, which has little to no silica, and rhyolite, which has significant amounts of silica). Porphyry, or porphyritic, meaning the rock cooled slowly still beneath Earth’s surface allowing large crystals to form as the magma hardened.
Arguably the most prominent visual characteristic of Devil’s Tower are the massive, polygonal columns that makeup the tower. Most columns are 5-sided, while some are 4- or 6-sided.
Columns measure upwards of 8 feet in diameter and rise hundreds of feet tall.
Columnar joints are commonly found in cooling igneous rocks and have been widely observed in basaltic rocks.
Columnar joints form from the way magma cools to form igneous rocks. As liquid magma cools, the outer crust hardens and shrinks in volume. Shrinking of the solidifying crust causes the magma surface to crack and form near-perfecr hexagonal columns. The more uniform the material, or how well mixed magma is, the more evenly columns can form.
Rapid cooling of magma is also believed to aid in the formation of columns. Rapid cooling from exposure to air or water may be required.
Once magma hardened to form Devil’s Tower, weathering and erosion of surrounding rock was required to expose it. Igneous rocks generally are resistant to weathering and more likely than typically weaker sandstones to form massive structures.
Millions of years of weathering removed the surrounding sandstones around Devil’s Tower and left the solidified magma exposed.
Though the composition and age of Devil’s Tower is minimally debated, the exact geologic term for this National Landmark still is.
Researchers at the South Dakota School of Mines proposed that Devil’s Tower is the eroded remains of a laccolith: a dome shaped igneous feature fed by a vertical channel.
Others believe that the tower may be a volcanic plug or neck of an extinct volcano. The vertical shaft where magma would have rose to feed a historic volcano could have been filled with magma which hardened over time and left the material to create Devil’s Tower.
Perhaps the most bizarre explanation for Devil’s Tower, and the one with the least amount of evidence, or no evidence besides it’s visual structure, is the petrified remnants of a GIANT tree.
The claim was made that seismic imaging done by the Wyoming parks service found evidence of an extensive ‘root’ system laying beneath Devil’s Tower.
However, there was no real evidence of a supposed root system and this claim is completely false and baseless.
Though proposed by a satirical Facebook post, the claim of a petrified, ancient, giant tree is a prime example to not believe everything that you read on the internet.
The moment I saw the Devil's Tower, I knew I'd seen a similar structure before. In Germany where I'm based, there's a place called Sebnitz. You may find a similar columnar jointing there.