Rising from the flat red plains of central Australia, Uluru is one of the most recognisable landforms on Earth. It stands about 348 metres above the surrounding country and measures roughly 9.4 kilometres around its base. Yet what visitors see is only part of the story. Like an iceberg, most of Uluru lies hidden beneath the surface, and the rock itself is far older than almost anything else they will ever touch.

Made from sand

Uluru is made of a type of sandstone called arkose, which contains a large amount of the mineral feldspar as well as quartz. Around 550 million years ago, rain and rivers wore down a nearby mountain range and carried the sand into a low basin, where it piled up in thick layers. Over millions of years the weight of new layers squeezed the sand beneath, and minerals in the groundwater cemented the grains together into solid rock.

Turned on its side

Look closely at Uluru and you will see lines running almost straight up and down its face. These are the original layers of sand, which were laid down flat. Around 400 million years ago, enormous forces inside the Earth folded and tilted the whole region. The layers of Uluru were turned until they stood nearly vertical, at an angle of about 85 degrees. Nearby Kata Tjuta, a group of large domes made of conglomerate rather than sandstone, was tilted by the same events but only by about 15 to 20 degrees.

Why it stands alone

The softer rocks that once surrounded Uluru have slowly been worn away by wind and water over hundreds of millions of years. Uluru's arkose was harder and had few cracks for water to enter, so it survived while the land around it was lowered. A rock left standing above a plain in this way is called an inselberg, from German words meaning 'island mountain'.

Why it is red

Fresh arkose is actually grey. Uluru's famous rusty colour comes from the iron in its minerals. When this iron is exposed to air and water it oxidises, or rusts, forming a thin red coating on the surface. At sunrise and sunset the low light strikes this coating and the rock appears to glow orange and crimson.

More than geology

Uluru lies within Uluru–Kata Tjuta National Park, which is World Heritage listed for both its natural and its cultural values. The Anangu, the Traditional Owners, have lived in this landscape for tens of thousands of years, and the rock's caves, waterholes and markings are tied to their law and stories. In 1985 the Australian Government formally handed the title to the land back to the Anangu, who lease it to the national parks service and manage it jointly. Climbing Uluru, which Anangu had long asked visitors not to do, was permanently closed in October 2019.

To geologists, Uluru is a record of ancient rivers and vanished mountains. To the Anangu, it is a living place. To everyone who sees it, it is unforgettable.