Cyclones bring lots of rain, and with lots of rain comes landslides. But as Cyclone Gita in New Zealand recently showed, nature is full of surprises.
After the storm, a woman named Donna Field captured a terrific example of "granular flow," when rocks start to act like liquids. The area is called Terrible Gully, and when the rocks are flowing with such speed and ferocity, it's easy to see where the name came from.
Granular flow is quite common, says geologist Dave Petley University of Sheffield in an . "In essence the pebbles behave as particles, allowing behavior that is akin to that of a fluid."
Beyond the sheer size of the flow, Petley also points out it's uniformity. He speculates that the rock is " probably ," a rock that is common to New Zealand which has been subjected to significant tectonic shifts over history. Greywacke is New Zealand is estimated to be at least 300 million years old, so getting tossed around in every which way is probably old hat for these rocks.