Although practically all of Earth’s human population lives on dry land, our surface is 71% covered by water. Of that water, almost all of it is in the oceans, with just 2.5% of it in the form of fresh, rather than salt, water. Most of Earth’s fresh water is in glaciers, ice caps, and permafrost, and water and ice beneath the surface. Most of the rest, as you might expect, is in the large reservoirs of liquid water on our land masses: Earth’s lakes.
All told, fresh water lakes make up just 0.007% of the total amount of water on Earth, but comprise the overwhelming majority of liquid fresh water on our surface. Most of Earth’s lakes are relatively young, less than 18,000 years old and formed during the end of the last ice age. Only 20 lakes, worldwide, are ancient: more than 1 million years old. But Lake Baikal is not only Earth’s oldest lake, at 25-30 million years of age, but it’s also the largest. Here’s the fascinating science behind it.
Earth’s lakes are the primary location where liquid, surface fresh water is held, but most of them were formed by the retreat of glaciers. The majority of Earth’s fresh water is frozen, in the forms of glaciers and ice caps, and this becomes much more severe during ice ages: where the polar caps grow large and extend down to much more equatorial latitudes than their present locations.
When the ice ages end,
- much of the frozen water melts,
- leading to glaciers carving out paths and causing erosion,
- with glacial melts (and subsequent rainfall and seasonal changes) leading to the formation of lakes (and rivers),
- and subsequent drainage patterns leading to additional lake formation.
For example, the entirety of the Great Lakes, the most prominent fresh water features in North America, are all a result of the drainage of the St. Lawrence River.
Earth experiences ice ages relatively frequently, with interglacial periods separating them on timescales a little greater than every 100,000 years. Almost all of the lakes presently found on Earth’s surface were created during these recent glacial/interglacial period transitions. If a lake was created from these processes, it very likely won’t last very long. The majority of lakes, over long timescales, will wind up filling with sediments deposited from inflowing rivers.
But there are some very prominent exceptions. Not every lake has a river or stream to flow into it, and not every lake was formed as a result of glacial/interglacial cycles and transitions. Rather than living thousands of years and having maximum depths of only a few hundred meters (up to 1,300 feet), there are a few lakes found throughout the world that are ancient and super deep: millions of years old and over a mile (1,600 m) deep.
The ancient lakes found on Earth are few in number, but all have something in common: they’re all found in active rift zones as a consequence of plate tectonics. Wherever two of the plates of Earth’s crust move apart from one another — such as at a divergent plate boundary — a rift valley can begin to form. Over time, the forces of erosion will deepen this rift valley, creating an enormous and deep pit.
What begins as a chasm with two steep, nearly parallel sides eventually widens, filling with sediment from the rift walls or, if the conditions are right, fresh water. Of all the ancient lakes over 1 million years old found on Earth, an enormous 75% of them were formed by this very process, with the exceptions resulting from events like meteor impacts and a volcanic feature.
To look at it from above, Russia’s Lake Baikal appears impressive, but not spectacularly so. Found in southern Siberia, it’s barely half the surface area of Lake Michigan, coming in at #7 among the world’s lakes at a little over 31,000 square kilometers (12,000 square miles).
However, the regions on either side of Lake Baikal are at an extremely high altitudes, with many locations exceeding 2000 meters (nearly 7,000 feet) in elevation. It’s located at exactly a divergent plate boundary, having spread apart so significantly over time that the lake is up to 79 kilometers (49 miles) wide, and has three separate basins to it.
The deepest one — the central basin — goes down to a depth of 1,642 meters (5,387 feet), making it the deepest lake in the world.
How much water does Lake Baikal hold?
If you were to take all of the fresh surface water in the world and add it up, you’d wind up with enough to fill a cube approximately 35 km (22 miles) on each side. This includes all the lakes, rivers, streams, swamps, marshes, living creatures, and even the water in Earth’s atmosphere.
Lake Baikal, which holds more fresh water than any other lake on Earth, is responsible for a whopping 22% of it: over 23,000 cubic kilometers (5,600 cubic miles) worth. It contains double the amount of water found in Lake Superior, five times the amount found in Lake Michigan, and more than all of the North American great lakes combined.
How unique is Lake Baikal?
The bottom of the lake is more than a full kilometer below sea level, but the rift valley that created it goes far deeper. According to research at the University of Alaska, Fairbanks, there are approximately an additional 7,000 meters (23,000 feet) of sediment that have fallen into the rift valley over time, placing the rift floor an incredible 8-to-11 kilometers (5-to-7 miles) beneath the surface. This makes the geological rift that’s home to Lake Baikal the deepest continental rift on planet Earth.
As impressive as these facts are, it’s important to think geologically: this continental rift is both young and active. With every year that goes by, the rift widens by approximately 2.0 centimeters (0.8 inches). There are more than 300 rivers that feed into Lake Baikal, but only one — the Angara River — that drains it.
How pristine is Lake Baikal?
Every other large, high-altitude lake on Earth has, in its geological history, been covered with ice sheets from previous glacial periods. When the glacial periods end, those continental ice sheets ride over them, scouring the lakes.
But not Lake Baikal. Uniquely among these lakes, its sediments show no evidence of these ice sheets riding over them. Instead, deep-drilling core sediments (the deepest bottom of the lake was first reached in the 1990s) show how the climate has varied over nearly 7 million years of recent history. Unusual crystalline solids known as gas hydrates are found within Lake Baikal, making it the world’s only confined fresh water lake to possess them.
How old is Lake Baikal?
Based on the geology of the lake alone — but supported by water and sediment studies — Lake Baikal is estimated to be between 25 and 30 million years old. It is very rare to have a lake on Earth that persists for more than 10 million years (only five are even candidates), and the evidence for Lake Baikal’s old age is overwhelming.
Other very old lakes include Lake Issyk-Kul and Lake Maracaibo, both of which are saltwater lakes rather than fresh water, and both of which have uncertain ages. Kazakhstan’s Lake Zaysan is the only lake that might be older, as substantial evidence dates it to the late Cretaceous, more than 65 million years ago. However, its exact age remains controversial; Lake Baikal is the oldest lake without large uncertainties in its age.
Lake Baikal is not only the largest, deepest, and oldest lake in the world, but houses around 2,000 unique known species of animal that are not found anywhere else on Earth. Although it is protected as a UNESCO World Heritage Site, the average surface temperature of Lake Baikal has risen by 1.5 °C over the past 50 years. Along with chemical pollution in Lake Baikal, this unique ecosystem, left pristine for millions of years, is now changing faster than ever before.
Yet perhaps what’s most remarkable about Lake Baikal is the view it gives us into how Earth evolves with time. The geological processes at work here are the same ones that causes the ancient supercontinent of Pangaea to break up, and resulted in the formations of Earth’s oceans. Perhaps, hundreds of millions of years from now, the rift valley that is now home to Lake Baikal will become a saline body connected to our oceans. It is, by many measures, the greatest lake on our entire planet.
