Ihumatao Fossil Forests

In the foreshore that is exposed at low tide, there are very large kauri trunks up to about 2 metres in diameter lying in haphazardly with their lower stumps and roots embedded in a peaty soil. This forest was living when sea levels were lower in an ice age several hundred thousand years ago. At that time Manukau Harbour was a broad forested valley and the coast was tens of kilometers further west. It is thought that the forest died due to a change in environmental conditions such as a rise of the water table. The demise of the trees would have been gradual as one by one they succumbed and fell into the surrounding swamp. The wood of these trees is very well preserved due to being waterlogged. Much later, another forest grew at the same location, over the site of the old kauri forest. This was when sea levels were again much lower during the most recent ice age.
The low cliff of volcanic ash next to the shoreline is the product of explosive eruptions of the nearby Maungataketake volcano that overwhelmed this younger forest 90,000 years ago,

Explore the foreshore to see the kauri trunks lying in peat and sand. The trees caught up in the ash eruption, seen in the low cliff along the edge of the shore, are less well preserved due to not being immersed in water. In places there are hollows where the branches have disappeared to leave only a mould. Look carefully at the peaty layer just below the ash for plant fragments that were lying on the forest floor just before the eruption.