Not many topographic features so fulfill that clichéd adjective “breathtaking” as a massive canyon. Ranking the greatest defiles on the planet, though, isn’t easy. Even geologists may disagree on what constitutes a true river gorge versus, say, simply a drainage through mountainous terrain, and the topographic complexity and variety of many canyons makes it challenging to come up with a standard way to measure depth. Do we make different categories based on canyon-forming processes – down-cutting rivers, uplifting mountains, glacial erosion, faulting, etc. – or simply lump all these overgrown gulches together? Regardless of technicalities, the following king-size canyons – some of the very deepest, longest or otherwise superlative on Earth – certainly set themselves apart as head-spinning expressions of geological process.

The upper course of the mighty Brahmaputra River, the Yarlung Tsangpo drops off the Tibetan Plateau and burrows across the High Himalaya through what many geologists accept as the deepest and second-longest canyon in the world: a product of vigorous tectonic uplift and massive rates of erosion. The Yarlung Tsangpo Gorge marks where the river turns south in its “Great Bend,” hooking between a pair of monstrous peaks marking the eastern edge of the Himalaya: 25,531-foot Namcha Barwa and 23,930-foot Gyala Peri. Also called the Yarlung Tsangpo Grand Canyon, this staggering defile stretches more than 300 miles and at its deepest exceeds 19,000 feet.

The Yarlung Tsangpo Gorge comes mirrored on the western side of the Himalaya by the mega-canyon of the Indus River, which also flows parallel to the High Himalaya (northwestward, in this case) and then slices southward to traverse the crest in a dizzying gulf. As the Yarlung Tsangpo Gorge reaches its zenith between Namcha Barwa and Gyala Peri – the eastern reach of the Himalayas – so the Indus Gorge, better than 16,000 feet deep, culminates in the mountain gates of 24,268-foot Haramosh and 26,660-foot Nanga Parbat, two far western Himalayan massifs.

Considered from the surging river level to the highest crowns of surrounding peaks, the Kali Gandaki Gorge in the Nepali Himalaya rivals the Yarlung Tsango in the depth department. The Kali Gandaki River flows between 26,795-foot Dhaulagiri, the seventh highest peak in the world, and 26,545-foot Annapurna, the 10th highest. The difference in elevation between whitewater and these royal summits is more than 18,000 feet.

One of China’s most sublime landscapes encompasses the UNESCO World Heritage Site of the Three Parallel Rivers of Yunnan Protected Areas, where the Salween, Mekong and Jinsha rivers surge through aligned defiles in the Hengduan Mountains. Greatest among these is the Tiger Leaping Gorge, where the Jinsha – the Upper Yangtze – careens between 18,360-foot Jade Dragon Snow Mountain and 17,703-foot Haba Snow Mountain in a tight canyon more than 9,800 feet deep. Why the name? Legend has it a desperate tiger harried by hunters sprang across the great cleft.

The Cotahuasi River makes quite the exit off the Altiplano Plateau in the Central Andes of southwestern Peru: Exceeding 11,000 feet at its maximum relief, Cotohuasi Canyon is the deepest canyon in the Western Hemisphere (and only 30 miles north of one nearly as deep, the more accessible Colca Canyon). Appropriately enough, it’s cruised by a superlative creature: the Andean condor, one of the biggest flying birds on Earth.

A mighty 38,000-square-mile network of canyons – collectively called Barranca del Cobre (or Copper Canyon) – tears into the Sierra Tarahumara of southwestern Chihuahua, ultimately draining out through the Rio Fuerte. Four of the major constituent gorges each exceed 5,500 feet deep; the Barranca Urique reaches 6,135 feet. Homeland of the Tarahumara people (famed for their long-distance running), Copper Canyon also encompasses an impressive ecological tableau given its vertical sweep and subtropical position: from pine forests on the high plateaus to palm groves in the canyon innards.

Between Oxbow Dam and the mouth of the Grande Ronde River, the Snake River roils through one of North America’s deepest and rawest river gorges: Hells Canyon. The brooding, terraced walls and knife-edge divides expose the thick, multilayered basalt flows that compose the heart of the Columbia Plateau – plus older volcanic and sedimentary rocks derived from long-ago island arcs that collided with the leading edge of the North American continent. While the Snake in Hells Canyon lies as much as 5,600 feet below the plateaus of its western (Oregon) rim, the Idaho side opposite rears to the snarled alpine crest of the Seven Devils Mountains, lending a maximum gorge depth of some 8,000 feet.

The Grand Canyon isn’t the largest in the world, though it may well be the best known. Outsized by Himalayan and Andean gorges – not to mention a few North American ones, including the deepest parts of Barrance del Cobre, Hells Canyon and Kings Canyon (another roughly 8,000-footer) in the Southern Sierra – this yawning rimland puncture on the Colorado Plateau nonetheless possesses singular presence: You could argue it's still the "grandest" for sheer aesthetic spectacle. The Colorado River enters the Grand at the mouth of the Little Colorado and exits it at the Grand Wash Cliffs, and within that 277-mile reach the river reveals more than 1.8 billion years of geological backstory in the “layercake” of a fiery-hued defile as much as 6,000 feet deep and up to 18 miles across.

The limestone heights of the Dinaric Alps include a number of awesome canyons, foremost among them the Tara River Gorge: by some measures the deepest in Europe. One of the scenic centerpieces of Durmitor National Park (a UNESCO World Heritage Site), the 50-mile-long canyon reaches 4,300 deep.

Surely in a class of its own among these colossal clefts, the Grand Canyon of Greenland was only described in 2013, despite being up to 2,600 feet deep, six miles wide and on the order of 460 miles long – lengthier than any other canyon on the planet. This Arctic abyss escaped notice so long because it’s tucked under the huge (if diminishing) ice sheet that prevails over most of the island. The subglacial bedrock canyon – which predates the formation of Greenland's frigid roof – drains northward from the interior to the Petermann Glacier, likely shuttling meltwater to the ocean.