Major Geological Landmarks Around the World.
A collection of real, famous landmarks, each explained through processes already covered elsewhere on the site — the same idea as the Mountain Ranges and Grand Canyon pages, applied to a wider, more visually varied set of places.
### GIANT'S CAUSEWAY (Northern Ireland)
What it is: Roughly 40,000 interlocking, mostly hexagonal basalt columns stepping down a coastline into the North Atlantic.
How it formed: A volcanic fissure eruption around 60 million years ago released a thick basalt lava flow (see the Basalt rock page). As that thick lava cooled slowly and evenly, it contracted — and cracked, the same way drying mud cracks into a network of shapes, just underground and in three dimensions. Because the cooling happened uniformly from the surface downward, those cracks organized themselves into strikingly regular, mostly six-sided columns — a process called columnar jointing.
Worth knowing: the columns you can walk on are only the exposed tip; the same basalt flow continues well beyond what's visible at the surface.
### DEVILS TOWER (Wyoming, USA)
What it is: A single, dramatic, steep-sided rock tower rising abruptly from the surrounding land, covered in the same striking columnar jointing as Giant's Causeway.
How it formed: Same physical process as Giant's Causeway — contraction cracking as molten rock cooled — but a genuinely different setting: Devils Tower is made of an intrusive igneous rock (it cooled slowly underground, the same broad category as granite on this site, rather than erupting at the surface like Giant's Causeway's basalt). Erosion has since worn away the softer surrounding rock that used to bury it, leaving the harder intrusion standing exposed and alone.
Worth knowing, honestly: geologists don't fully agree on the exact original shape of the intrusion that became Devils Tower — several competing theories exist. What is agreed on is the columnar jointing mechanism itself, and that it's a genuinely rare formation to find in this kind of rock; columnar jointing is far more commonly seen in basalt. A good real-world pairing with Giant's Causeway to show the same physics — slow, even cooling and contraction — playing out in two completely different settings, extrusive versus intrusive.
### ULURU (Northern Territory, Australia)
What it is: A massive, isolated sandstone monolith rising from an otherwise flat landscape — most of its bulk actually continues underground.
How it formed: Around 550 million years ago, erosion of a newly-uplifted ancient mountain range shed huge volumes of coarse, feldspar-rich sand into a nearby basin, which became arkose — a variety of sandstone (see the Sandstone rock page) — as it was buried and cemented. A later mountain-building event, the Alice Springs Orogeny, compressed and folded the region, tilting Uluru's originally horizontal layers until they stand nearly vertical — visible today as the parallel ridges and grooves running up its face. Hundreds of millions of years of erosion then stripped away the surrounding, softer rock, leaving Uluru standing alone as what's called an inselberg — a resistant remnant that survived erosion that removed everything around it.
Worth knowing: part of why Uluru resisted erosion so well is chemical, not just structural — the rock has few of the internal cracks and fractures that let water penetrate and break weaker rock apart.
### WHITE CLIFFS OF DOVER (England)
What it is: Already covered in depth on the Chalk rock page — a dramatic, world-famous exposure of the same soft, white, microscopic-plankton-derived rock described there. Included here as a cross-reference, not a separate write-up, since the Chalk page already tells the full story.
### PAMUKKALE (Turkey)
What it is: Brilliant white, terraced pools cascading down a hillside — the name means "cotton castle" in Turkish.
How it formed: Hot spring water (see the Geysers & Hot Springs page), rich in dissolved calcium carbonate from the rock it passed through underground, reaches the surface and cools. As it cools and the water evaporates, it can no longer hold as much dissolved mineral — so the calcium carbonate precipitates back out as solid travertine, the same basic chemistry as Limestone's page, just happening rapidly at the surface rather than slowly on an ancient seafloor. Layer after layer of travertine builds the terraces over time, as the mineral-rich water continues flowing and depositing.
### ANTELOPE CANYON (Arizona, USA)
What it is: A narrow, smoothly-sculpted slot canyon with flowing, wave-like walls, carved into Navajo Sandstone.
How it formed: Primarily flash flooding — infrequent but powerful desert rainstorms send fast-moving water surging through what starts as a narrow crack in the sandstone, and that forceful, turbulent flow, repeated over centuries, is what carves the smooth, swirling shapes rather than the sharper edges typical of most canyons. Windblown sand abrasion (see Deserts & Sand Dunes) also plays a supporting role in smoothing the walls between flood events.
### ZHANGYE DANXIA (China)
What it is: Dramatically striped, multicolored hills and ridges — bands of red, orange, yellow, and green running across the landscape.
How it formed: The colorful layers are sandstone and siltstone (see those rock pages), originally deposited over millions of years with varying mineral content — different iron and trace mineral concentrations in each layer produced different colors as the sediment oxidized. Later tectonic uplift tilted and folded these layers, and erosion has since carved into them, exposing the tilted, multicolored bands at the surface. This style of colorful, eroded sedimentary landscape is called a Danxia landform, and similar (though usually less vivid) formations exist elsewhere, including in the American Southwest.
### BRYCE CANYON HOODOOS (Utah, USA)
What it is: Thousands of tall, thin, oddly-shaped rock spires, called hoodoos, packed densely into a series of natural amphitheaters.
How it formed: Bryce Canyon's rock (mostly limestone and siltstone, see those rock pages) is broken by a dense network of vertical cracks. Water repeatedly seeps into those cracks, freezes, and expands — frost-wedging, a form of mechanical weathering — gradually widening the cracks into narrow walls, then into isolated columns. Because the rock layers aren't uniformly hard, softer layers erode faster than harder ones, leaving the harder, more resistant caps that give many hoodoos their distinctive mushroom-like, top-heavy silhouette.
(New terms this collection introduces — columnar jointing, hoodoo, inselberg, travertine — are in the main Glossary.)