The Onyx River, the longest river in Antarctica, flows in the opposite direction towards the land instead of the sea due to the unique geological characteristics of the region.
Antarctica is home to a vast amount of water, most of which is frozen. As a result, many people believe that rivers do not actually exist on this continent. However, this is not the case. Antarctica does have some flowing rivers, which appear for at least a few months each year. The longest of these is the Onyx River, which is quite unusual.
The semi-permanent Onyx River stretches 32 km. (Photo: Mozgova).
Technically, the Onyx River is a meltwater stream. At 32 km long, it is quite short compared to the 6,650 km long Nile River, but considering the icy landscape it flows through, this length is quite impressive.
The Onyx River is located in the McMurdo Dry Valleys, flowing westward from the terminus of the Wright Lower Glacier into Lake Vanda. This means it flows away from the sea.
This is an example of an endorheic flow – a water system that does not drain into the ocean. The river exists due to a unique geological feature: Glaciers block the entrance to the Wright Valley, causing the Onyx River to flow deeper inland, towards the ice-covered Lake Vanda.
Antarctica has nine meltwater flows like this, but they differ from most other rivers. While rivers like the Amazon and Congo originate from mountainous regions and are formed by many small streams, the Onyx begins to flow when the Wright Lower Glacier melts. Therefore, the Onyx is a semi-permanent river, forming only during the summer in the Southern Hemisphere, when temperatures are high enough to melt the ice.
Rain does not contribute to the flow of the Onyx River because the dry valley rarely receives precipitation, and what does fall sublimates before reaching the river. However, glacier melt often provides enough water to sustain the flow. In recent decades, several flooding events have occurred during particularly warm summers. In 1984, researchers from New Zealand were even able to kayak on this river. With rising temperatures due to climate change, the flow season of the Onyx River is starting earlier and lasting longer, although the amount of flowing water seems to be decreasing.
Not only is it the largest meltwater flow in Antarctica, the Onyx River is also the most ecologically important flow. It has its own unique ecosystem, supporting various microscopic organisms, from tardigrades and nematodes to cyanobacteria and phytoplankton. Algae also bloom abundantly in the Onyx River, even though there are no fish in the river.
