How Was Angel Falls Formed? The Geology Explained

Angel Falls formed because a river flowing across the summit of Auyán-tepui, a vast table-top mountain in southeastern Venezuela, reaches the edge of a cliff made of extraordinarily old and resistant sandstone and plunges nearly a kilometer to the jungle below. That cliff exists because roughly two billion years of erosion stripped away softer surrounding rock while the hard, flat-lying sandstone of the tepui held firm. The result is a free-falling waterfall about 979 meters tall, the highest uninterrupted drop on Earth, cascading off a geological formation so ancient it predates complex life itself.

The Guiana Shield and the Oldest Rock on the Continent

To understand Angel Falls, you have to start with what sits underneath it. The waterfall is perched on the Guiana Shield, a massive slab of ancient crust that forms the northern core of the South American continent. The Shield is the northern part of the Amazonian Craton, separated from its southern counterpart, the Brazilian Shield, by the Amazon basin.¹ Cratons are the stable, ancient hearts of continents, and this one has been sitting more or less in place for over a billion years. Its basement is made of Precambrian crystalline rock, the kind of hard igneous and metamorphic material that forms when continents are still being assembled from volcanic arcs and colliding landmasses.

On top of that crystalline basement sits a thick cap of much younger (though still unimaginably old) sedimentary rock. This cap is what builds the tepuis, and it is where the story of Angel Falls really begins.

The Roraima Supergroup and How the Rock Formed

The rock that makes up Auyán-tepui and the other tepuis of the Guiana Highlands belongs to a geological unit called the Roraima Supergroup. These are Paleoproterozoic sedimentary rocks, deposited roughly 1.7 to 1.9 billion years ago, when the area looked nothing like the jungle-covered highlands it is today.¹ Back then, the region was a low-lying basin at the edge of the growing Amazonian Craton, gradually being filled with sediment washed off the surrounding highlands by rivers and flash floods.

The Roraima Supergroup is composed of three main rock types: conglomerates (essentially cemented gravel), sandstones, and mudstones interbedded with thinner sandstone layers. These were deposited in a range of environments, including alluvial fans, braided stream channels and deltas, lakes, and open sandy flats.² You can picture it as a series of landscapes cycling between braided rivers dumping gravel and sand across a broad floodplain, standing lakes accumulating finer mud, and dry expanses where wind reworked sand into dune-like deposits.

Over time, these sediments were buried, compressed, and cemented into stone. The sandstones in particular were hardened into quartzites and tough arenites, rocks where grains of quartz are locked together so tightly they resist erosion far better than most sedimentary formations. The original deposit accumulated to a thickness of several kilometers in places, creating the raw material for the tepuis that would emerge much later.

How Erosion Carved the Tepuis

The tepuis are not mountains in the usual sense. They were not pushed up by tectonic collision or volcanic eruption. Instead, they are erosional remnants, the leftovers of a once-continuous sedimentary plateau that has been slowly eaten away over hundreds of millions of years. Imagine a thick layer cake of sandstone stretching across the entire Guiana Shield. Rivers, rain, and chemical weathering have been gnawing at that cake since at least the Mesozoic era, carving it into isolated mesas separated by deep valleys.

Auyán-tepui, the particular mesa that hosts Angel Falls, is one of the largest of these remnants. Its summit covers roughly 700 square kilometers, and its cliffs rise vertically for hundreds of meters above the surrounding lowland forest. The reason the cliffs are so steep is that the sandstone layers lie almost perfectly flat, the way they were originally deposited. When erosion attacks flat-lying resistant rock from the sides, it tends to produce vertical faces rather than gentle slopes, because blocks break off cleanly along fractures and bedding planes rather than crumbling gradually.

The tepuis are sometimes described as islands in the sky, and that description captures their geological reality well. Each one is a fragment of a former supercontinent-scale sedimentary basin, isolated by the relentless removal of everything around it. The process is still happening. The cliffs of Auyán-tepui are still retreating, grain by grain and block by block, but the rock is so resistant that the pace is glacially slow.

Why Some Layers Resist and Others Do Not

The dramatic cliff face over which Angel Falls plunges is not uniform rock. Field studies on tepuis show that the sandstones of the Roraima Supergroup, while all broadly similar in composition, vary in how well they resist weathering depending on their internal structure. Fine-grained arenites that were deposited in aeolian (wind-blown) conditions and later compacted into flat, featureless beds are considerably harder than arenites containing cross-bedding, the angled internal layering left by ancient dunes or ripples.³

Research on neighboring Akopán Tepui found that the cross-bedded layers retain higher porosity, meaning more tiny pore spaces between grains. Water can seep into those pores and work on the rock from the inside, loosening grains and gradually creating depressions, overhangs, and even small caves in the cliff face. Flat-bedded or structureless layers above and below remain tighter and harder.³ This selective weathering is what gives the tepui cliff faces their distinctive sculpted, pockmarked appearance rather than a featureless wall. It also contributes to the undercut overhangs visible behind Angel Falls itself, where water has been exploiting softer layers for millennia.

The interplay matters for the waterfall because it determines the cliff profile. If every layer eroded at the same rate, you would get a gradually receding slope rather than a sheer vertical face. Because harder layers cap softer ones, the cliff maintains its steepness even as blocks collapse from the weaker zones below. This is the same mechanism that sustains waterfalls in layered sedimentary rock worldwide, but on the tepuis, the effect is amplified by the extreme thickness of the hard sandstone layers and the enormous timescales involved.

Water on the Summit and the Birth of the Falls

Auyán-tepui receives an enormous amount of rainfall. The Guiana Highlands sit in a belt of tropical convective rainfall, and the tepui summits, rising above 2,000 meters in some areas, act as condensation targets for moisture-laden air moving inland from the Atlantic. Annual rainfall on the summits often exceeds three to four meters per year, several times the average for most temperate cities.

All that water has to go somewhere. Because the sandstone summit is not perfectly impermeable, some of it infiltrates through fractures and pores, feeding underground drainage systems. But much of it collects into surface streams that flow across the relatively flat summit until they reach the edge. Angel Falls is fed by one such summit stream, the Río Gauja (sometimes called Río Churún at different points). The river is modest by most standards, not a thundering torrent, and during the dry season, it can thin to a wispy ribbon. During the wet season, the falls swell dramatically.

The actual plunge happens where the Río Gauja reaches a fracture-controlled cliff edge on the north face of Auyán-tepui. The main uninterrupted drop is about 807 meters, after which the water hits a steep slope and cascades an additional 170 or so meters to the base. Because the drop is so long and the stream volume relatively modest, much of the water atomizes into mist before reaching the bottom, especially during drier months. On a windy day, the lower portion of the falls can appear to simply dissolve into air.

Why Fractures Matter

The exact location of Angel Falls on Auyán-tepui is not random. The cliff face where the water goes over the edge is controlled by a system of vertical fractures, or joints, in the sandstone. These joints are planes of weakness that formed in the rock long after deposition, likely in response to regional tectonic stresses, unloading as overlying rock was eroded away, or both. Where two or more joint sets intersect, the rock breaks away more easily, creating the deep re-entrant alcoves and vertical faces characteristic of tepui cliff edges.

The river channel on the summit also follows fracture zones. Water naturally finds and widens cracks, so over time the drainage pattern on top of Auyán-tepui has been guided by the underlying joint geometry. The stream that feeds Angel Falls flows along a fracture-controlled valley to the cliff edge, and the cliff itself is a fracture face. Without that particular joint set running in the right orientation at the right spot, the water might have found a different exit point, producing a different waterfall or draining underground entirely.

This is a general principle for waterfalls on flat-topped plateaus. The location is almost always structurally controlled by faults, joints, or contacts between rock types, rather than being a purely random feature of the landscape.

Caves and Sinkholes on the Summit

One of the more surprising features of the tepui summits is the presence of cave systems and massive sinkholes, features you would normally associate with limestone landscapes rather than sandstone. Geologists studying cave systems on Venezuelan tepuis, including the enormous systems on nearby Churí-tepui, found that these caves did not form primarily through the dissolution of quartz, as was once assumed. Instead, the dominant processes are mechanical erosion of poorly cemented layers and the chemical breakdown of feldspar and mica minerals in certain rock types, a process called lateritization. Quartz dissolution, where it occurs at all, plays only a minor role.⁴

This matters for understanding Angel Falls because the same processes that create caves and sinkholes on tepui summits also affect how water drains across the summit. If the rock were perfectly solid, all rainfall would run off the surface and feed waterfalls. In reality, a substantial amount of water disappears underground through fractures and cave passages, re-emerging from springs lower on the cliff face or at the tepui’s base. The balance between surface runoff and underground drainage determines how much water actually reaches the falls at any given time, and it is part of why the falls can vary so dramatically in volume between seasons.

The existence of these underground drainage systems also means the tepui summits are slowly being hollowed out from within. Sinkholes on Sarisariñama tepui, a neighboring mesa, are hundreds of meters wide and deep, with isolated rainforest ecosystems at their bottoms.⁵ Auyán-tepui has its own network of internal voids, though less spectacularly visible from above. Over geological time, this internal erosion may eventually undermine cliff edges and redirect drainage, changing or even eliminating waterfalls as the landscape evolves.

Why Angel Falls Is Uniquely Tall

The world has plenty of waterfalls, so what makes Angel Falls so much taller than the rest? The answer is a combination of factors that rarely line up elsewhere. First, the Roraima Supergroup sandstone is exceptionally thick, stacking to over two kilometers in places. That gives the tepui cliffs enormous vertical extent to work with. Second, the rock is hard and uniform enough to maintain near-vertical faces over hundreds of meters without collapsing into rubble slopes. Third, the flat-lying bedding means the cliff does not step back in terraces the way a waterfall over tilted rock layers would. And fourth, the summit is high enough and wet enough to support a perennial stream that reaches the cliff edge with enough volume to be visible.

Most tall waterfalls around the world form where glacial valleys create U-shaped cliffs, or where lava flows create basalt escarpments. Those settings rarely produce single vertical drops exceeding 300 to 500 meters. The tepui setting is geologically unusual: an ancient, hard, flat-lying sedimentary cap on a stable craton, in a wet tropical climate that provides plenty of water but not enough to erode the cliff rapidly. The same conditions that make Angel Falls possible also explain why the other tall waterfalls in the region, like Kukenán Falls on the neighboring tepui, are found in the same geological context. This is not a one-off freak of nature. It is a landscape type that reliably produces extreme waterfalls wherever the geometry cooperates.

The Biological World the Geology Created

The geological isolation of the tepui summits has had a striking biological consequence. Because these flat-topped mountains have been cut off from each other and from the surrounding lowlands for tens of millions of years, their summit ecosystems have evolved in near-total isolation. Each tepui harbors species of plants, amphibians, and insects found nowhere else on Earth. The sandstone substrate, which is nutrient-poor and acidic, creates boggy, nutrient-starved soils that support carnivorous plants, specialized orchids, and stunted shrubs rather than the lush forest of the valleys below.

For Angel Falls specifically, the mist zone at the base of the waterfall creates its own microhabitat. The constant spray sustains a band of moisture-loving vegetation that extends well beyond what the local rainfall alone would support. The waterfall is not just a geological feature but an ecological engine, redistributing water from the summit to the valley floor in a way that shapes the plant and animal communities for hundreds of meters around its base.

The tepuis were famously the inspiration for Arthur Conan Doyle’s 1912 novel The Lost World, in which explorers discover dinosaurs living atop an isolated plateau in South America. The real biology is less dramatic but arguably more interesting: rather than preserving ancient life, the tepuis generated entirely new species through long isolation on ancient rock. The geological processes that formed Angel Falls, the deposition of sandstone, the hardening of the rock, the slow erosion of everything around it, also created one of the most unusual evolutionary laboratories on the planet.