New Zealand would be more than 1km underwater if it had the same tectonic "anchor" as Australia pulling it downward, a Kiwi scientist says. Photo / Warren Buckland
New Zealand would be more than 1km underwater if it had the same tectonic "anchor" as Australia pulling it downward, a Kiwi scientist says. Photo / Warren Buckland
New Zealand would be more than 1km underwater if it had the same tectonic "anchor" as Australia pulling it downward.
That's according to a Kiwi scientist whose just-published study has helped answer one of the most fundamental questions about our planet: what determines the level of land.
VictoriaUniversity's Associate Professor Simon Lamb's paper also says that if uncontrolled climate change melted all of Antarctica's ice, East Antarctica would rise up over time to form the world's highest continent.
Lamb, of Victoria's School of Geography, Environment and Earth Science, said it had long been thought the key to land levels was the Earth's crust.
This outermost layer floated on the mantle beneath it like a rocky iceberg, and scientists have generally assumed that, the thicker the crust was, the higher the land rose above sea level.
"But when we put together an accurate picture of the crust in the continents, we were surprised to see there is little relation between the average elevations of the continents and the thickness of the underlying crust."
The reason lay in the fact the crust was just part of the Earth's tectonic plates.
"We realised that beneath the crust the thick tectonic plates also have roots, and these act like an anchor, keeping the elevations relatively low even though the surface of the buoyant crust wants to rise up higher."
Lamb's international team made use of new measurements of the thickness of the tectonic plates, and also worked out the densities of the different rock layers from variations in the strength of gravity.
"It was clear the dense roots of the plates were capable of pulling down the surface of the Earth in exactly the way needed to explain the actual elevations."
For instance, Australia had a relatively thick crust and should be over a kilometre above sea level on average, but it was also part of a very thick tectonic plate.
East Antarctica could eventually spring up 1km above sea level if the ice upon it was melted by uncontrolled climate change. Photo / Nick Golledge
The vast weight of this plate counteracted the tendency for the thicker crust to rise up - and same principle applies to the other continents.
New Zealand, meanwhile, was part of a young continent forming a thin tectonic plate and so most of it has hardly any "anchor" to hold it down.
With the same anchor as Australia, New Zealand would be more than 1km underwater.
The level of the land is determined by both the thickness of the crust and the tectonic plate, Lamb explained.
But over geological time, erosion wore away the crust, tending to keep the land near sea level, whatever the plate's thickness.
"Antarctica, however, has been too cold for large rivers to significantly erode the landscape," he said.
"This way, the crust has been 'protected' from the forces of erosion. Today, the weight of the vast East Antarctic ice sheet is pushing down the underlying bedrock.
"However, if all the ice melts - perhaps due to uncontrolled global warming - the surface of East Antarctica will bounce back over the following 10,000 years or so to form the highest continent of all, about 1km on average above sea level."
The new study, published in the scientific journal G-cubed, is a collaboration between Victoria University, the Earth Observatory of Singapore, and the University of Bremen in Germany.
