Earthquake caused glacier to crumble

By AAP with Carolyn Barry | November 8, 2013

The power of the NZ earthquake has had distant effects, including the carving of a glacier.

WHILE THE FULL IMPACT of the devastating Christchurch earthquake continues to unfold, some interesting environmental effects are being revealed.

Earthquakes are most destructive at the surface of the Earth, where the energy is released as the ground shaking. This means that when the epicentre is close to the surface, there’s not much rock or earth for the tremor to travel through and act as a shock absorber.

Like ripples in a pond, the seismic waves of an earthquake travel out in all directions from a central point. As these waves of energy travel through the Earth, they slow down and lose momentum when they encounter interference – like the Earth’s core, or different layers of rock within tectonic plates.

If there was no interference, waves could travel through the core and arrive on the other side of the world. That’s why it’s no surprise that the Christchurch earthquake could be felt in Dunedin and Queenstown. Or that it caused a 30-million-tonne chunk of ice to break off from the Tasman Glacier, 200 km away in Aoraki/Mount Cook National Park on the west coast of the South Island. The 1.2 km long slab of ice plunged into Tasman Lake.


Tourists observe a giant iceberg that carved off from the Tasman Glacier after the earthquake. (AAP)

Denis Callesen the tourism manager of the Aoraki Mt Cook Alpine Village says he had been expecting the ice to break off for some time, given recent heavy rainfall and La Niña weather conditions, but he had not anticipated that an earthquake would trigger the dramatic event.

A group of tourists on a boat in the lake at the time were walloped by giant 3.5 m waves created by the calving. The ice broke up in the water, forming several icebergs, one 250 m long.
 
This was the third-largest calving to have occurred in the lake in the last 40 years – all three happened within the last two years.

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