Moeraki Boulders, New Zealand

Introduction

The Moeraki Boulders in New Zealand are eye-catching, spherical boulders that look similar to large turtle shells or balls made of rock.

Why Is It Famous?

The Moeraki Boulders are famous because of their unique appearance as they are spherical and sizable. Maori legends say the boulders are eel baskets and gourds that washed ashore when a sailing canoe wrecked.

What’s Nearby?

The boulders are on the Koekohe Beach in New Zealand. You can find this location along the Otago coast.

Geological Description

Formation of the Moeraki Boulders began 60 million years ago when sediments formed on the seafloor. Carbonates accumulated around the core of the sediments. Estimates indicate that some of the biggest boulders required four million years to reach their current size. The largest boulders are more than two meters wide and weigh multiple tons.

The boulders formed in concretions that were on the coastal cliffs. As the shoreline eroded, the cliffs and the boulders slowly appeared along that shore. Geologists have found other similar boulders in the mudstone that will also eventually loosen by erosion and fall on the beach.

Geologists have studied the content of the boulders in great detail, determining that they contain clay, fine silt, and mud. Calcite bonded these elements together with varying degrees of cementation. Each boulder also has an outer ring of calcite. Most boulders feature septaria, or large cracks radiating outward.

There are similar formations in the Hokianga Harbour in the North Island of New Zealand.

Events in Time

A famous sketch of the beach and its boulders in 1848 was completed by W.B.D. Mantell and features more boulders than the beach holds today. You can also find numerous reports and sketches of the boulders from the 1850s.

In Conclusion

The Moeraki Boulders are unique for their spherical shape and prevalence along the beach. They were created via sediment accumulation over millions of years before a receding shoreline exposed them.