1. Land of lava and strata

2.  Gondwana land – ancient southern super- continent (break up in the early Jurassic about 184 Mya)  Great thickness of sand and mudstone deposited off the eastern edge  Sediments slowly metamorphosed into hard grey sandstone and mudstone (greywacke)  An upheaval event raised this new land mass above sea level, forming mountain ranges - ancestral New Zealand

4.  These mountains were eroded down and the sea advanced  By about 30 mya, NZ consisted of a few scattered islands  About 25 mya, two large tectonic plates of the earth’s outer crust started impacting and sliding past each other  The country split along the alpine fault  The Pacific plate began subducting under the Australian plate.

7.  Volcanic activity in the Northland area under the sea.  The Auckland area subsided to become a deep marine basin.  For 5-6 mill yrs material from a chain of volcanoes along the western side of Northland eroded and began filling the basin – the Waitemata basin.  Volcanic eruptions ceased about 15 mill yr ago in Northland

8.  The Waitemata basin was filled with sand and mud layers (Waitemata strata)  Volcanic vents then began to form in South Auckland  Sand began to build along Auckland’s West Coast  0.15 mill yrs ago, basaltic lava began erupting in Central Auckland within a 20km radius of the City centre  There were 50+ small volcanic cones and craters.

9. Waitemata strata of volcanic andesitic ash and sedimentary rocks Overlaid with more recent volcanic sandstone, rhyolitic ash and scoria REFERENCE Homer,Moore,Ker mode.(2000) Lava & Strata.p4, Inst.GNS

10.  Rangitoto island is the youngest 600 years ago (just “yesterday”)  Field trip  At Takapuna beach North end the main geological feature is lava flows  At South end are outcrops showing sandstone and mudstone strata of the Waitemata series

11.  Homer,L, Moore,P and Kermode,L (2000) Monograph Lava and Strata. Institute of Geological & Nuclear Sciences