Ancient lake

An ancient lake is a lake that has consistently carried water for more than one million years. Twelve of the 20 ancient lakes have existed for more than 2.6 million years^{[citation needed]}, the full Quaternary period. Ancient lakes continue to persist due to plate tectonics in an active rift zone. This active rift zone creates lakes that are extremely deep and difficult to naturally fill with sediment. Due to the prolonged life of ancient lakes, they serve as models for isolated evolutionary traits and speciation. Most of the world's bodies of water are less than 18,000 years old. There are only 20 ancient lakes over 1 million years old.^[1]

Lake Zaysan in Kazakhstan is one of the oldest lakes in the world.

Lake Baikal is often considered the oldest, as clear evidence shows that it is 25–30 million years old.^[2][3] Lake Zaysan may be even older, of Cretaceous origin and at least 66 million years old^[4] (most likely around 70 million years^[5]), but its exact age is controversial and labeled with some uncertainty.^[6] Another contender for oldest is Lake Maracaibo, estimated to be 20–36 million years old. In ancient times it was indisputably a true lake, but today it is saline and directly connected to the sea, leading many to consider it a large lagoon or bay.^[7]

Ancient lakes vs. younger lakes

There are six major types of lakes (listed below). The majority of lakes dry up as the result of the filling with lacustrine deposits, sediment deposited from a river into a lake over thousands of years. Factors that influence the water level decreasing include fluvial-lacustrine sediment build-up, evaporation, natural drainage, and geophysical processes. Ancient lakes have a prolonged life when compared to younger, more ordinary lakes due to the local active rift zones and subsided sections of land called grabens.

For example, Lake Baikal in Russia, the deepest lake in the world, is an ancient lake created by the Baikal Rift Zone which is 25–30 million years old and 5,387 feet (1,642 m) deep. This is compared to the North American Great Lakes, which were formed by the last glacial period by glacial scouring and the pooling of meltwater which are 14,000 years old and have maximum depths ranging from 200–1,300 feet (60–400 m) deep.

• Rift lakes
• Landslide and ice dam lakes
• Salt lakes
• Oxbow lakes
• Crater lakes
• Glacial lakes
• Subglacial lakes

Importance to evolution

Ancient lakes allow scientists to study the mechanisms of environmental changes over glacial-interglacial timescales. Evolutionary characteristics including sexual selection, adaptive radiation and punctuated equilibrium are studied in ancient lakes due to their prolonged existence and general geographic isolation. Most of the research has been associated with the endemic fauna and diatoms that exist in these isolated lakes, concentrating on Lake Baikal, the Caspian Sea and the African Great Lakes. Information is derived from the associations of the fluvial-lacustrine, fluctuating profundal and evaporative facies.^{[citation needed]}

List of ancient lakes

These are the ancient lakes in the world that have existed for more than 1 million years, excluding the many subglacial lakes whose age is yet to be determined.^[1]

Name	Origin	Type	Age	Area (km2)	Volume (km3)	Depth max	Depth average	Countries	Notes
Lake Pingualuk	meteor impact	fresh, permanent, crater	1.5 million	8		267		Canada
Lake Tahoe	tectonic	fresh, permanent	1–2 million	499	156	505	313	United States
Lake Bosumtwi	meteor impact	soda, permanent, crater	1–2 million	49	2.24	81	45	Ghana
Lake Lanao	volcanic	fresh, permanent	2 million	375		112	60.3	Philippines
Lake Titicaca	tectonic		3 million	8372	893	281	107	Bolivia, Peru
Lake Prespa			1.5-5 million	259	4.8	54	18.7	Albania, Greece, North Macedonia
Lake Ohrid			1.5-5 million	358.18	53.63	286.7	163.71	Albania North Macedonia
Lake Malawi			2–5 million	29600	8400	705	292	Malawi, Mozambique, Tanzania
Lake Hovsgol			2–5 million	2770	381	267	138	Mongolia
Kati Thanda–Lake Eyre		saline, intermittent, endorheic	2.5-5 million	9690	30.1	6	3	Australia
Lake Tanganyika		fresh, permanent	3–6 million	32000	17800	1471	572	Burundi, Congo, Tanzania, Zambia
Caspian Sea		saline, permanent, endorheic	5.5 million	374000	78200	1025	182	Azerbaijan, Iran, Kazakhstan, Russia, Turkmenistan
Aral Sea		saline, permanent	5.5 million	64500	625	67	16	Kazakhstan, Uzbekistan	Formerly the fourth largest lake in the world with an area of 68,000 km2 (26,300 sq mi). By 1997, it had shrunk to 10% of its original size due to water that was diverted in the Soviet Era. It is now split into 4 smaller lakes. As of 2023, the Aral Sea has become mostly desert.
Lake Biwa		fresh, permanent	5–6 million	674	27.5	104	41	Japan
Lake Tule			3–15 million	53	40			United States
Lake Maracaibo		saline, permanent, coastal bay	20+ million	13010	280	60	25.9	Venezuela	Historically it was an ancient lake. Now, it is a large tidal bay/inlet rather than a lake in the traditional sense. It is saline and directly connected to the Caribbean Sea, leading many to consider it a large lagoon or bay.
Lake Baikal		fresh, permanent	25+ million	31500	23000	1741	740	Russia
Issyk-Kul		saline, permanent	25 million	6236	1738	668	270	Kyrgyzstan
Lake Vostok	subglacial	fresh, permanent, subglacial	15–35 million	12500	5400	510	432	Antarctica
Lake Zaysan	tectonic	fresh, permanent	65+ million	5510	53	10	5	Kazakhstan	The construction of the Bukhtarma dam inundated the lake, thus, in some sources, the lake is considered a reservoir.[8]