Pouawa Beach Tsunami Deposits?

This outcrop was discovered by an emergency manager from Gisborne and identified as a tsunami deposit by scientists at GNS Science. The almost horizontal layering of well sorted particles, with very low angle cross bedding and graded bedding (layers where the particle sizes decrease upwards) indicates that the deposit was laid down by currents of moving water, but not the turbulent back and forth flow of beach waves. The incorporation of shells and larger rock fragments within the deposit are also a clue that the sediment was sourced from the sea bed. Please note that GNS Science researchers have identified this as likely to be a tsunami deposit, but o get absolute confirmation they would want to look at the microfossils, map the extent of the deposit, and rule out other explanations. Currently it is a "field-based" assessment that a tsunami is the most likely agent of deposition for these layers.

At the time of the tsunami, the coast would likely have been a kilometre or more further out than its present position right beside the outcrop. This explains the relatively steady, but surging flow of water that is indicated by the cross cut, laminated appearance of the deposit.

The rocky shelf at the base of the sandy cliff is the remains of a wave-cut platform that is being eroded away. This platform is at a higher elevation (about 1 metre) than the rocky shore platform at present sea level. Shells embedded in this rock outcrop have been dated at the same age as the shells in the sand layers. This suggests the possibility that the wave-cut platform was uplifted by the very same earthquake that caused the tsunami. They are both about 1600 years old.

Walk along the shoreline below the layby and look for a place where the sea has eroded a vertical section through the layered sand. Erosion changes the nature of these outcrops in big storms so you might find sections that look different from the photos. Sometimes the sand outcrop has collapsed, and you may need to scrape away with a trowel to expose a clean section. See if you can find the upper and lower boundary of the layered section, where it meets the less sorted dune sands (without obvious layering) that it is sandwiched between. Estimate or measure the thickness of the deposit and try to identify some of the sedimentary features described above.