McLaren Falls

McLaren Falls cascade over a slowly eroding face of welded ignimbrite rock. This rock (belonging to Waiteariki Ignimbrite Formation) was erupted as a gigantic cloud of searing hot gas, pumice, crystals and glass shards that raced across the ground in all directions away from the vent. When the cloud slowed down the solid particles buried the land with tens of metres thickness of still extremely hot ash which welded itself together into this erosion-resistant rock called ignimbrite. This one eruption about 2 million years ago created a huge flat plain which has subsequently been uplifted and tilted to the east to form the Kaimai Ranges. In the west uplift has been along the Hauraki Fault which divides the Kaimai Ranges from the Hauraki Plains. The ignimbrite is tilted down below sea level beneath Tauranga in the east. As the rock cooled and solidified it shrank and cooling cracks formed within it and much of the erosion today is along these cracks which determine the shape of the McLaren Falls.
In the rock around the foot of the falls you will see a number of smooth round holes, 50cm - 1m across. These potholes have been eroded out of the more massive parts of the ignimbrite by small rocks being stirred around and around in the holes by the falling, moving water.

This waterfall looks amazingly different between wet and dry periods. Can you imagine how it looks in full flood with the entire rock face hidden by surging water?
Can you see any of the small rocks in the bottom of the pot holes and are they rough or smooth and round? What would you expect?