NZ Herald: We’re a nation built on shifting rock

John Roughan writes in the New Zealand Herald about New Zealand’s geology, and how its landscape came to be.

He explains why the flowing hard rock which makes up the earth’s crust isn’t flat, using the analogy of milk and cream for the two types of rock which rise from the earth’s depths: granite and basalt.

An excerpt: (read in full here)

“Crust, explained Dr Campbell, comes up from the earth’s depths in two forms, granite and basalt. They are the same stuff but different in density, “like milk and cream”, he said.

“Basalt is the milk. It’s heavier and more viscous. It forms most of the ocean floor. Granite is like cream. It is lighter and lumpy. Granite is the continents. The Auckland Museum exhibits lumps of granite and basalt that you can lift. The weight difference is remarkable.

“Milk and cream. The analogy helps many things fall into place. It explains why one plate descends under another, sending up volcanoes of basaltic rock as it heats.

“It might also explain why New Zealand’s plants and birds are unique and there were practically no animals here until humans brought them.”