Lava Cave Formation


Auckland, New Zealand’s largest city, is home to a unique geological feature – lava caves. These caves owe their existence to the volcanic activity that shaped the region over 200,000+ years. These eruptions produced vast amounts of basaltic lava, which flowed across the landscape, creating a network of volcanic conduits and tubes.

The formation of Auckland’s lava caves begins with the eruption of lava from the region’s numerous volcanic vents. As this molten rock flows across the landscape, the exposed surface rapidly cools and solidifies, creating a hardened crust. However, the lava beneath this insulating layer continues to flow, carving a channel within the surrounding rock.

This continuous flow of lava within the insulated channel prevents the complete solidification of the interior, forming what is known as a lava tube. These tubes can extend for hundreds of meters, their dimensions dictated by the viscosity and volume of the lava flow.

Examples of lava caves being formed


As the eruption subsides and the lava supply diminishes, the remaining molten rock gradually drains from the lava tube, leaving behind a hollow cavity – the lava cave. The solidified outer crust of the lava flow, having served as a protective shell, now stands as the ceiling and walls of the newly formed cave. Subsequent lava flows may infiltrate pre-existing lava caves, thereby altering their morphology.

The size and shape of these caves vary considerably. Some are narrow passages, barely wide enough for a person to crawl through, while others are spacious chambers with high ceilings and multiple levels. The internal features of these caves are equally diverse, with smooth, undulating walls, arched ceilings, and occasional lava stalactites and stalagmites formed by the dripping and cooling of residual lava.

Over time, erosion can play a role in shaping the caves, widening and deepening them through the action of water and other environmental factors.

The known age range of accessible lava caves in Auckland spans from approximately 60,000 to 70,000 years for the oldest, while the youngest documented caves are just 600 years old.

Examples of long-cooled lava caves in Auckland