It rained so hard in New Zealand that it made a raging river of rocks

And you thought the usual flood of water was scary.

In New Zealand recently, a storm created by former Cyclone Gita ravaged the country, forcing officials to declare a State of Emergency. Apart from damaging property and knocking out electricity, the storm also spawned something unexpected:

A natural phenomenon known as granular flow, or in layman’s terms, a river of rocks.

The granular flow can be seen on video, taken by Donna Field while she was surveying the damage at the Rakaia River in Canterbury. It shows a surge of rocks and boulders cutting across a road, isolating eight farms from a nearby town.

While filming, Field and her son had to shout in order to hear each other due to the noise and strong winds. “It was really loud [and] sounded like when a gravel truck tips all its load, but if you were right underneath it,” she said.

What’s scarier is that, according to Stuff, “it’s an event that has become a regular occurrence for the farmers in the area.”

If a raging river of rocks doesn’t make sense (it really doesn’t), here’s geologist Dave Petley to explain the phenomenon:

“This is a magnificent example of a granular flow. Whilst they appear to be very exotic, granular flows are quite common and have been well-described in the literature. In essence the pebbles behave as particles, allowing behaviour that is akin to that of a fluid.”

It goes without saying that you should never go swimming in one of these, unless you want to have a… hard time staying afloat. Fishing? You’ll only probably catch stonefish. I’ll show myself out now.