http://www.gns.cri.nz/Home/Our-Science/Earth-Science/Plate-Tectonics/NZ-plate-boundary
Becuase of these volcanic eruptions, young volcanic rock are not unusual on the island. The island nation is constantly growing from the formation of new rocks on top of the old sediments that rest just off the shores. The earthquakes which often shake the nation also do erode mountains and cause more debris to fall into the shallow seas off shore. These constant natural activities make New Zealand unstable but also contribute to its natural beauty. The nation is almost a throwback to ancient Earth where earthquakes and volcanoes where constantly reshaping the surface. This makes New Zealand like no other place on earth. New Zealand lies on what is known as the Ring of Fire. This is a circular area in the pacific where volcanoes are quite common and active.