We often think of “The Great Lakes” as a single place in the middle of North America, straddling the border between Canada and the United States. In fact, even at the very mention, you’re probably already picturing the sprawling, sometimes-frigid expanses of Lakes Superior, Huron, Michigan, Erie, and Ontario. They are an undeniable geographic boon, holding about 21% of the world’s surface fresh water.

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But look across the globe to the heart of the African continent, and you’ll find another collection of massive inland seas: The Great Lakes of Africa (aka The African Great Lakes).

Anchored by the massive Lake Victoria, this network (which also includes Tanganyika, Malawi, Albert, Edward, Kivu, and Turkana) is a completely different geographic behemoth. While they share a name with their North American cousins, the forces that created them, the depths they reach, and the life they sustain couldn’t be more different.

And of course if you’re interested in just one small part of these Great Lakes, be sure to check out my video for the week:

Ice vs. tectonics

The most fundamental difference between the two Great Lake systems is how they were born and the age that are.

Let’s get this out of the way first: the North American Great Lakes are geologic toddlers, born of the last ice age. Roughly 10,000 to 14,000 years ago, as the last Ice Age came to a close, the massive Laurentide Ice Sheet retreated. As this miles-thick glacier scraped across the continent, it gouged deep basins into the earth’s crust. When the ice melted, it filled these basins with fresh water. They are essentially giant, glorious glacial puddles. And what’s crazier is that this all happened while humans roamed the earth. So, in theory, we as a species has known the world before the Great Lakes of North America, and now the world after.

Meanwhile the African Great Lakes are ancient, born of literal earth-shattering tectonic forces. Instead of being carved from above by ice, the African Great Lakes were torn open from below. They lie along the East African Rift, an active continental rift zone where the African tectonic plate is literally splitting in two. As the earth’s crust pulls apart, massive valleys drop down, creating incredibly deep chasms that have filled with water over millions of years.

Now, of course, there is one exception here: Lake Victoria. While lakes like Tanganyika and Malawi are classic “rift lakes”—long, narrow, and plunging deep into the earth’s crust—Lake Victoria is the odd one out. It is the largest lake in Africa by surface area, but it doesn’t sit in a deep rift trench. Instead, it occupies a shallow, saucer-like depression created by the uplifting of the rifts on either side of it. So still connected, but it’s not technically a rift lake.

Now, because of their violent, tectonic origins, the rift lakes of Africa boast statistics that make the North American lakes look like wading pools.

• Depth: Lake Tanganyika is the second-deepest lake in the world (behind Russia’s Lake Baikal), plunging to a incredible depth of 4,820 feet (1,470 meters). To put that in perspective, Lake Superior, the deepest of the North American Great Lakes, reaches a maximum depth of 1,332 feet.

• Volume: Because they are so incredibly deep, the African Great Lakes hold a staggering amount of water. Lake Tanganyika alone holds nearly as much water as all five North American Great Lakes combined.

• Age: While the North American lakes are around 10,000 years old, Lake Tanganyika is estimated to be between 9 and 12 million years old. Lake Malawi is roughly 1 to 2 million years old. So even their “baby” Great Lake is at least a million years older than North America’s.

The evolutionary mixing pot of the world

But here’s the biggest difference between the two.

Because of the immense age and isolation of the African Great Lakes have turned them into some of the most spectacular evolutionary laboratories on the planet, rivaling even the Galapagos Islands.

And because the North American lakes are so young and experienced extreme glacial freezing, they have relatively low levels of what we call “endemism” (or species that are found nowhere else on earth). Most of their fish migrated there from other river systems after the ice melted.

The African Great Lakes, however, have been stable, tropical underwater worlds for millions of years. This allowed a specific family of fish (such as cichlids) to undergo something biologists call adaptive radiation. From just a few ancestral species, thousands of unique, vibrantly colored species evolved, each adapting to highly specific micro-regions within the lakes.

In fact, Lake Malawi alone is home to an estimated 850 to 1,000 distinct species of cichlids. And Lake Victoria, despite a recent near-collapse due to the introduction of the invasive Nile Perch, once housed over 500 endemic cichlid species.

In these lakes, you’ll find fish that have evolved to eat only the scales of other fish, fish that crush snail shells, and fish that incubate their eggs safely inside their own mouths. It is an explosion of biodiversity that simply does not exist in the glacially carved basins of North America.

Both are masterpieces in their own right

To compare the North American and African Great Lakes isn’t to say one is better than the other. Rather, it highlights the incredible, diverse geography of our planet.

In North America, we see the lingering footprint of an ice age that recently shaped our modern landscape. In Africa, we are looking into deep time—staring down into the literal seams of the earth where tectonic plates rip apart, fostering millions of years of uninterrupted and brilliant evolution.

Both systems are “Great.” But they achieved their greatness through entirely different paths.

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