There’s lots of water in Antarctica, but most of it is frozen. You’d be forgiven, then, for thinking that rivers aren’t really a thing on the continent – however, you’d be mistaken. Antarctica is home to a number of waterways (at least for a few months a year) – the longest of which, called the Onyx River, is a little bit weird.
Technically a meltwater stream, the Onyx River flows for 32 kilometers (20 miles) – it’s nothing compared to the Nile’s 6,650 km (4,130 miles), but considering the icy landscape it cuts through, it’s pretty impressive.
The river is located in Antarctica’s McMurdo Dry Valleys and winds westward from the terminus of the Wright Lower Glacier into Lake Vanda. This, most curiously, means it flows away from the ocean.
An example of endorheic drainage – when land-locked water systems don’t drain into the sea – the river is this way thanks to a geological quirk. Glaciers block the entrance to the Wright Valley, which means the Onyx has no choice but to flow inland, toward the ice-covered Lake Vanda.
Antarctica is home to nine such meltwater streams – but they’re a bit different to most other rivers. While the likes of the Amazon and Congo begin at a mountainous source (or sources), as streams that eventually form a river, the Onyx flows as the Wright Lower Glacier melts. It is therefore semi-permanent, forming only during the Austral summer when temperatures are high enough to thaw the ice.
Rain doesn’t contribute to the streamflow, as it is very rare in the Dry Valleys, and what does fall sublimates before it can make its way into the river. However, the melting glacier generally provides ample water to keep the river flowing – there have been several flood events during particularly warm summers in the past couple of decades and, in 1984, researchers from New Zealand even managed to raft down it.
With temperatures rising thanks to climate change, the Onyx’s flow season is shifting earlier and becoming longer, although the volume of water that courses through it appears to be decreasing.
As well as being the largest of Antarctica’s meltwater streams, the Onyx River is the most ecologically important. Home to its own mini-ecosystem, the river supports a variety of microscopic life, from tardigrades and nematodes to cyanobacteria and phytoplankton. Algae is also known to bloom in its waters, though you’ll find no fish there.
The Onyx may be the longest river in Antarctica, but what’s the longest in the world? Turns out, the answer’s probably more complicated than you think. The same is true for the planet’s oldest river, though it’s largely agreed that that is found in Australia.
