Stage One 100 million years ago there was a trench or geo-syncline – Over time it collected sand and mudstone The pressure from he ocean compressed it into sedimentary rock with different layers (showed in drawing
Due to continental drift the Pacific and indo- Australian plates are colliding This collision causes the sand and mudstone in the geo-syncline to squeeze together – This intense pressure changes the sedimentary rock to metamorphic, here it turns to Greywacke This building pressure results in faulting – The faulting causes a rapid uplift, ie Ruahine Range Ruahine Range is referred to as a horst and is still stratified
Moist air is blown off the Tasman Sea and forced upwards which results in… This rainfall hits the Greywacke and gradually erodes it – This erosion is carried by the Tukituki tributaries to the Central Plains region and fertilizes it The high elevation also results in erosion through a frost/freeze process – The effect is scree, or vertical erosion
Stage 3 The continuing plate movement which created the horst has also lead to the fold mountains of the eastern hill country. The new rangitoto and elsthorpe anticline shoulder the atua syncline where the Tukituki river flows.
Stage 4 Folding occurs in the Eastern Hill Country – Location due to younger therefore softer rocks – Bent and lifted due to pressure from the plates colliding 2 Main Anticlines develop – Elsthorpe and New Rangitoto – Tukituki flows along Atua Syncline
Stage 5 The folding from Stage 4 changes the flow of the river Force river to the North-East – Changes river mouth from Kairakau to Haumoana which is further North