What Is the Deepest Sinkhole on Earth?

The Deepest Sinkhole on Earth

Xiaozhai Tiankeng in Chongqing, China is the deepest sinkhole on Earth, plunging over 600 meters straight down and spanning 626 by 537 meters at its rim — large enough to swallow several city blocks whole.

Where Is Xiaozhai Tiankeng?

Xiaozhai Tiankeng sits within Wulong Karst National Geology Park in Chongqing Municipality, southwestern China. The name roughly translates to “Heavenly Pit,” and once you understand its scale, the name feels earned. It is not merely a hole in the ground — it is a geological event frozen in stone, the result of 128,000 years of karst limestone slowly dissolving under the pressure of water and time.

What Makes It a “Doubly Nested” Pit?

Unlike a standard sinkhole, Xiaozhai Tiankeng is not a single vertical shaft. It is two stacked bowls — one pit sitting inside another. The upper bowl measures approximately 320 meters deep, and the lower bowl descends a further 300 meters beyond that. This nested structure formed as underground caverns collapsed in successive stages, each failure opening a new chamber below the last. The result is a layered abyss unlike anything else on the planet’s surface.

The Underground River at Its Base

At the bottom of Xiaozhai Tiankeng flows an underground river stretching 8.5 kilometers through the dark beneath the pit floor. This river is part of the broader Difeng cave system, one of the most extensive underground drainage networks in China. Warm, humid air rises from the water below and collides with cooler air near the rim — and the result is something almost surreal: clouds forming entirely inside the sinkhole. The pit generates its own localized weather system, complete with mist, fog banks, and shifting microclimates that vary dramatically between the rim and the floor.

A Hidden Ecosystem Beneath the Surface

Perhaps the most astonishing feature of Xiaozhai Tiankeng is not its depth but what lives inside it. More than 1,000 plant species have been documented growing on ledges and terraces along its walls, thriving in conditions of filtered light and extreme humidity. Scientists have identified rare and endemic species here — organisms that evolved in isolation from the world above, cut off by vertical stone walls hundreds of meters high. The sinkhole functions as a refuge ecosystem, preserving biodiversity that may not exist anywhere else.

Animals have been documented inside as well, including fish adapted to the lightless underground river and birds that nest on protected ledges far below the rim. The microclimatic layering — warmer and wetter at the base, cooler and more temperate near the top — creates multiple distinct habitat zones stacked vertically inside a single geological feature.

How Was It Explored?

Despite its enormous scale and scientific significance, Xiaozhai Tiankeng was not systematically explored until 1994. The sheer verticality of its walls and the depth of its lower bowl made access extraordinarily difficult. Early expeditions required technical rope descents of hundreds of meters just to reach the floor. Even today, large sections of the cave system connected to the pit remain unmapped. There is a genuine possibility that new species — plant, animal, or microbial — are still waiting to be discovered in its depths.

Why Xiaozhai Tiankeng Matters

Xiaozhai Tiankeng is more than a geological record-holder. It is a living demonstration of how isolated environments drive evolutionary divergence, how water shapes stone across geologic time, and how much of Earth’s surface — even dramatic, enormous features — remained unknown to science until very recently. In a world that feels thoroughly documented, a sinkhole that makes its own clouds and shelters species unknown to science is a reminder that Earth still holds secrets.