As I’m sure you’re aware, rivers usually combine together to make larger and larger rivers until they reach the sea.
However, there are some exceptions: rivers do sometimes split up and flow in separate directions.
These splits are called “bifurcations” (bi” meaning “two”, and “furcations” being the forks). They happen most often when rivers are close to the sea, which forms deltas. These separate branches then reach the sea soon after.
These branches can also happen inland, where they will usually re-join again to form a river island.
However, in very rare occasions these branches can go off in totally different directions, and even into separate oceans.
The same phenomenon can also happen with lakes, where a lake may have 2 outflow rivers that head in very different directions.
Here’s a little image showing 4 different types of bifurcation:
The Casiquiare Canal
Perhaps the best example of a river bifurcation that links two different river systems can be found in South America.
The Amazon River system is the largest in the world, and, by a peculiar quirk of geography, it connects to the Orinoco river which is, by water volume, the 4th largest river system in the world. The Casiquiare Canal is a natural river that flows out of the Orinoco River and into the Rio Negro, a major tributary of the Amazon. It’s large enough that small boats can travel between the two river systems.
This leads us to an interesting question:
When a river splits and branches reach the sea soon-after, this creates a delta island. The largest delta island in the world is Marajó in Brazil, in the Amazon delta. You can actually see it on the right of my map above. At 40,100 km², it is considered the 35th largest island on Earth.
So what about the “bifurcation island” created by the splitting of the Orinoco River into the Casiquiare? If a delta island is considered an island, surely this whole north-eastern region of South America should also be considered one? Like a delta island, it is surrounded entirely by sea and rivers. As an area of land separate from a continent, permanently and entirely surrounded by water, it seems to fit every definition of an island I can find.
At around 1,700,000km², this would make the “Casiquiare island” the second largest island on Earth, behind Greenland.
But wait, there’s more! The Casiquiare Island is by no means the only example of a bifurcation island on the planet.
There is one in Europe too:
The Hase River
Near the source of the Hase River in Germany, a small portion of the water flows east and becomes the Else River. Most of the Hase flows west and into the Ems, while the Else flows east and into the Weser. These rivers reach the sea around 90 km apart. This means there is a roughly 14,500 km² region of Germany that is entirely surrounded by natural rivers and the sea. This Bifurcation island is larger than Cyprus, and could be considered the 8th or 9th largest island in Europe.
However, to find the biggest bifurcation islands, we need to look at North America, a continent riddled with bifurcating lakes and rivers.
There are at least 4 places in the USA where a water system naturally splits in 2 directions and reaches the sea very far apart, and coincidentally, they all connect together. This effectively creates a vast system of connected rivers, that flow into 3 separate oceans.
Committee’s Punch Bowl
The bizarrely named “Committee’s Punch Bowl” is a lake in western Canada which lies exactly on the so-called “Great Divide”. This is the hydrological divide between the areas that drain west of the Rocky Mountains and into the Pacific Ocean, and the areas that drain east of the Rockies into the Arctic and Atlantic Oceans. Most lakes only have one river flowing out of them, but the Committee’s Punch Bowl is rare in that it has two. Even more unusually, these rivers flow in opposite directions and eventually into separate oceans.
To the west, the Woad River flows into the Kinbasket Lake, out of which flows the Columbia River, which eventually reaches the Pacific Ocean.
Meanwhile to the east, the Whirlpool River flows to the Athabasca River. The water passes though several other lakes and rivers before joining the Mackenzie River (the longest river in Canada), which flows into the Arctic Ocean.
These rivers cut off a huge area of North America, including much of western Canada and all of Alaska, totalling an area of about 3,600,000 km², larger than Greenland (the current largest-island record holder).
But Committee’s Punch Bowl isn’t the only bifurcation lake that drains into the Arctic via the Mackenzie River:
Wollaston Lake
Wollaston Lake in Saskatchewan, Canada, also has two outflows. To the northwest, Fond du Lac River takes 10% of the outflow to the Mackenzie River and into the Atlantic. To the northeast of the lake, the Cochrane River takes the other 90% of the water from the lake which eventually reaches the Churchill River, and finally empties into the Hudson Bay. This creates another bifurcation island north of Wollaston lake with an area of about 2 million km² .
Divide Creek
Heading back into the Rockies, not far south of Committee’s Punch Bowl and also along the Great Divide, we have a river aptly named “Divide Creek”. Divide Creek is a small stream that (you guessed it) divides into two separate streams: one flowing west, the other east.
The west branch flows in the Kicking Horse River, joins the Columbia River and then to the Pacific Ocean. The east branch flows into the Bow River, which reaches Hudson Bay via the Saskatchewan River and Nelson River. The island created by this bifurcation and the Wollaston Lake system has an area of about 790,000 km² .
The eastern branch of this system actually has its own bifurcation: a river called the Echimamish flows out of the Nelson River and into the Hayes River, which then winds across Manitoba for 600km before reaching the Hudson Bay very close to the Nelson River estuary.
The Parting of the Waters
Nearly 1000km further down the Great Divide we have another river which splits in two. The river is named “North Two Ocean Creek”. In a swampy patch of Wyoming woodland, the river bifurcates into two branches, named Pacific Creek and Atlantic Creek.
To the west, the Pacific Creek flows into the Snake River, which is the largest tributary of the Columbia River.
Atlantic creek flows into the Yellowstone River, then the Missouri. The Missouri is the largest tributary of the Mississippi River, which flows into the Gulf of Mexico (part of the Atlantic Ocean).
The Mississippi river itself splits about 400km before reaching the sea, with 30% of the water flowing down the Atchafalaya River.
The Parting of the Waters creates the largest natural bifurcation island I can find: over 7,300,000 km². This is more than 3 times the size of Greenland (currently considered the largest island), and almost as large as Australia (the smallest continental landmass).
The real largest islands in the world
So, there we have it: there is a secret giant island in North America that includes more than a third the area of the USA and Canada.
The new, corrected list of largest islands in the world, including bifurcation islands, is as follows:
- Parting of the Waters Bifurcation Island: 7,300,000 km²
- Committee’s Punch Bowl Bifurcation Island: 3,600,000 km²
- Greenland: 2,130,000 km²
- Wollaston Lake Bifurcation Island: 2,000,000 km²
- Casiquiare Bifurcation Island: 1,700,000 km²
- Divide Creek Bifurcation Island: 790,000 km²
- New Guinea: 786,000 km²
I expect you all to correct your encyclopaedias as soon as you get a chance. Although it might be best to wait until someone can give these new islands better names. “Committee’s Punch Bowl Bifurcation Island” is admittedly a bit of a mouthful.
Thank you for your time,
Starkey
Bonus: here’s a minimalist version of that North America map:
Bonus bonus: some other bifurcations from around the world:
- The Wayambo River in Suriname splits into two streams. The western one flows into the Nickerie River, and the Eastern one to the Coppename River. Both of these rivers flow into the Atlantic Ocean. They can be seen on my Casiquiare map, as a bifurcation island within a bifurcation island.
- Isa Lake in Wyoming is only about 120km north of the Parting of the Waters, and similarly drains both west and east. However, it only does this during the spring, when meltwaters cause its eastern edge to overflow.
- The Nerodimka in Kosovo flows into the Aegean and Black seas. I didn’t end up including it in the article because it is thought that the split was likely artificially constructed in the 14th century, but I did make a map for it if anyone is interested.
- The Gatun Lake in Panama drains into the Atlantic and Pacific, however this is also artificial. The lake forms part of the Panama Canal.
- Lake Okeechobee in Florida is a trifurcation lake, with three separate outflows. This is artificial.
- The Danube Sinkhole is an unusual case of a vertical bifurcation: some of the water of the upper Danube River drains though the riverbed and into a system of caves. This water eventually ends up in the Rhine, which flows north into the North Sea. The rest of the Danube continues on east to the Black Sea. Since part of this system is underground, even I won’t stretch the definition of “island” so far as to include most of western and southern Europe. Still, interesting stuff!