Deluge (prehistoric)
Overview
 
In geomorphology
Geomorphology
Geomorphology is the scientific study of landforms and the processes that shape them...

, an outburst flood, which is a type of megaflood, is a high magnitude, low frequency catastrophic flood involving the sudden release of water. During the last deglaciation, numerous glacial lake outburst flood
Glacial lake outburst flood
A glacial lake outburst flood is a type of outburst flood that occurs when the dam containing a glacial lake fails. The dam can consist of glacier ice or a terminal moraine...

s (GLOF) were caused by the collapse of either ice sheets or glaciers that formed the dams of proglacial lakes. Examples of older outburst floods are known from the geological past of the Earth and inferred from geomorphological evidences in Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...

.
Encyclopedia
In geomorphology
Geomorphology
Geomorphology is the scientific study of landforms and the processes that shape them...

, an outburst flood, which is a type of megaflood, is a high magnitude, low frequency catastrophic flood involving the sudden release of water. During the last deglaciation, numerous glacial lake outburst flood
Glacial lake outburst flood
A glacial lake outburst flood is a type of outburst flood that occurs when the dam containing a glacial lake fails. The dam can consist of glacier ice or a terminal moraine...

s (GLOF) were caused by the collapse of either ice sheets or glaciers that formed the dams of proglacial lakes. Examples of older outburst floods are known from the geological past of the Earth and inferred from geomorphological evidences in Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...

. Landslides, lahar
Lahar
A lahar is a type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris, and water. The material flows down from a volcano, typically along a river valley. The term is a shortened version of "berlahar" which originated in the Javanese language of...

s, and volcanic dam
Volcanic dam
A volcanic dam is a type of natural dam produced directly or indirectly by volcanism, which holds or temporarily restricts the flow of surface water in existing streams, like a man-made dam. There are two main types of volcanic dams, those created by the flow of molten lava, and those created by...

s can also block rivers and create lakes, which trigger such floods when the rock or earthen barrier collapses or is eroded. Lakes also form behind glacial moraines, which can collapse and create outburst floods.

Definition and classification

Megafloods are paleofloods (past floods) that involved rates of water flow larger than those in the historical record. They are studied through the sedimentary deposits and the erosional and constructional landform
Landform
A landform or physical feature in the earth sciences and geology sub-fields, comprises a geomorphological unit, and is largely defined by its surface form and location in the landscape, as part of the terrain, and as such, is typically an element of topography...

s that individual megafloods have created. Floods that are known to us through historical descriptions are mostly related to meteorological events, such as heavy rains, rapid melting of snowpacks, or combination of these. In the geological past of the Earth, however, geological research has shown that much larger events have occurred. In the case of outburst floods, such floods are typically linked to the collapse of the barrier forming a lake. They fall in the following classification according to the mechanism responsible:
  • Collapse of glacier dams that impound proglacial lakes (Missoula Floods
    Missoula Floods
    The Missoula Floods refer to the cataclysmic floods that swept periodically across eastern Washington and down the Columbia River Gorge at the end of the last ice age. The glacial flood events have been researched since the 1920s...

    ).
  • Rapid erosion, melting of ice sheets (jökulhlaup
    Jökulhlaup
    A jökulhlaup is a glacial outburst flood. It is an Icelandic term that has been adopted by the English language. It originally referred to the well-known subglacial outburst floods from Vatnajökull, Iceland which are triggered by geothermal heating and occasionally by a volcanic subglacial...

    s).
  • Collapse of earthen barriers (landslides or glacial moraines).
  • Collapse of volcanic dam
    Volcanic dam
    A volcanic dam is a type of natural dam produced directly or indirectly by volcanism, which holds or temporarily restricts the flow of surface water in existing streams, like a man-made dam. There are two main types of volcanic dams, those created by the flow of molten lava, and those created by...

    s created by lava flows, lahars, or pyroclastic flows.
  • Overtopping
    • Lake overtopping (e.g., Lake Bonneville
      Lake Bonneville
      Lake Bonneville was a prehistoric pluvial lake that covered much of North America's Great Basin region. Most of the territory it covered was in present-day Utah, though parts of the lake extended into present-day Idaho and Nevada. Formed about 32,000 years ago, it existed until about 14,500 years...

      ).
    • Ocean spilling over a dividing ridge into a landlocked basin (e.g., Zanclean flood
      Zanclean flood
      The Zanclean flood is a flood theorized to have refilled the Mediterranean Sea 5.33 million years ago, at the beginning of the Zanclean age, between the Miocene and Pliocene, which ended the Messinian salinity crisis...

      , Black Sea flood). A smaller scale example would be the Pantai Remis landslide
      Pantai Remis landslide
      The Pantai Remis landslide occurred on 21 October 1993, near Pantai Remis in Perak, Malaysia. The landslide took place in an abandoned open cast tin mine close to the coast. This area of Malaysia is well known for its tin mining industry...

      .

Outburst flood examples

Examples where evidence for large ancient water flows has been documented or is under scrutiny include:

The Black Sea (around 7,600 years ago)

A rising sea flood, recently disclosed and much-discussed refilling of the freshwater glacial Black Sea
Black Sea
The Black Sea is bounded by Europe, Anatolia and the Caucasus and is ultimately connected to the Atlantic Ocean via the Mediterranean and the Aegean seas and various straits. The Bosphorus strait connects it to the Sea of Marmara, and the strait of the Dardanelles connects that sea to the Aegean...

 with water from the Aegean
Aegean Sea
The Aegean Sea[p] is an elongated embayment of the Mediterranean Sea located between the southern Balkan and Anatolian peninsulas, i.e., between the mainlands of Greece and Turkey. In the north, it is connected to the Marmara Sea and Black Sea by the Dardanelles and Bosporus...

, was described as "a violent rush of salt water into a depressed fresh-water lake in a single catastrophe that has been the inspiration for the flood mythology" (Ryan and Pitman, 1998). The marine incursion, which was caused by the rising level of the Mediterranean, occurred around 7,600 years ago. It remains an active subject of debate among geologists, with subsequent evidence discovered to both support and discredit the existence of the flood, while the theory that it formed the basis for later flood myths is not proven.

The Caspian and Black Seas (around 16,000 years ago)

A theory proposed by Andrey Tchepalyga of the Russian Academy of Sciences
Russian Academy of Sciences
The Russian Academy of Sciences consists of the national academy of Russia and a network of scientific research institutes from across the Russian Federation as well as auxiliary scientific and social units like libraries, publishers and hospitals....

 dates the flooding of the Black Sea basin to an earlier time and from a different cause. According to Tchepalyga, global warming
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...

 beginning from about 16,000 BP caused the melting of the Scandinavia Ice Sheet, resulting in massive river discharge that flowed into the Caspian Sea
Caspian Sea
The Caspian Sea is the largest enclosed body of water on Earth by area, variously classed as the world's largest lake or a full-fledged sea. The sea has a surface area of and a volume of...

, raising it to as much as 50 metres (164 ft) above normal present-day levels. The rise was extremely rapid and the Caspian basin could not contain all the floodwater, which flowed from the northwest coastline of the Caspian Sea, through the Kuma-Manych Depression
Kuma-Manych Depression
The Kuma–Manych Depression , is a geological depression in southwestern Russia that separates the Russian Plain from the Fore-Caucasus...

 and Kerch Strait, over the current eastern coastline of the Sea of Azov
Sea of Azov
The Sea of Azov , known in Classical Antiquity as Lake Maeotis, is a sea on the south of Eastern Europe. It is linked by the narrow Strait of Kerch to the Black Sea to the south and is bounded on the north by Ukraine mainland, on the east by Russia, and on the west by the Ukraine's Crimean...

 into the ancient Black Sea basin. By the end of the Pleistocene this would have raised the level of the Black Sea by some 60 to 70 m (196.9 to 229.7 ft) 20 metres (65.6 ft) below its present-day level, and flooding large areas that were formerly available for settlement or hunting. Tchepalyga suggests this may have formed the basis for legends of the great Deluge.

The English Channel Flood 400,000 BP

Originally there was an isthmus across the Strait of Dover
Strait of Dover
The Strait of Dover or Dover Strait is the strait at the narrowest part of the English Channel. The shortest distance across the strait is from the South Foreland, 6 kilometres northeast of Dover in the county of Kent, England, to Cap Gris Nez, a cape near to Calais in the French of...

. During an earlier glacial maximum, the exit from the North Sea
North Sea
In the southwest, beyond the Straits of Dover, the North Sea becomes the English Channel connecting to the Atlantic Ocean. In the east, it connects to the Baltic Sea via the Skagerrak and Kattegat, narrow straits that separate Denmark from Norway and Sweden respectively...

 was blocked to the north by an ice dam, and the water flowing out of rivers backed up into a vast lake with freshwater glacial melt on the bed of what is now the North Sea. A gently upfolding chalk ridge linking the Weald of Kent
Weald
The Weald is the name given to an area in South East England situated between the parallel chalk escarpments of the North and the South Downs. It should be regarded as three separate parts: the sandstone "High Weald" in the centre; the clay "Low Weald" periphery; and the Greensand Ridge which...

 and Artois
Artois
Artois is a former province of northern France. Its territory has an area of around 4000 km² and a population of about one million. Its principal cities are Arras , Saint-Omer, Lens and Béthune.-Location:...

, perhaps some 30 metres (100 feet) higher than the current sea level, contained the glacial lake
Glacial lake
A glacial lake is a lake with origins in a melted glacier. Near the end of the last glacial period, roughly 10,000 years ago, glaciers began to retreat. A retreating glacier often left behind large deposits of ice in hollows between drumlins or hills. As the ice age ended, these melted to create...

 at the Strait of Dover
Strait of Dover
The Strait of Dover or Dover Strait is the strait at the narrowest part of the English Channel. The shortest distance across the strait is from the South Foreland, 6 kilometres northeast of Dover in the county of Kent, England, to Cap Gris Nez, a cape near to Calais in the French of...

. At a certain time, and apparently more than once, the barrier failed or was overtopped, loosing a catastrophic flood that permanently diverted the Rhine into the English Channel and replacing the "Isthmus of Dover" watershed by a much lower watershed running from East Anglia
East Anglia
East Anglia is a traditional name for a region of eastern England, named after an ancient Anglo-Saxon kingdom, the Kingdom of the East Angles. The Angles took their name from their homeland Angeln, in northern Germany. East Anglia initially consisted of Norfolk and Suffolk, but upon the marriage of...

 east then southeast to the Hook of Holland and (as at modern sea level) separated Britain from the continent of Europe; a sonar
Sonar
Sonar is a technique that uses sound propagation to navigate, communicate with or detect other vessels...

 study of the sea bed of the English Channel published in Nature, July 2007, revealed the discovery of unmistakable marks of a megaflood on the English Channel seabed: deeply-eroded channels and braided features have left the remnants of streamlined islands among deeply gouged channels where the collapse occurred.

Glacial lake outburst floods in North America (15,000 to 8,000 years ago)

In North America, during glacial maximum, there were no Great Lakes
Great Lakes
The Great Lakes are a collection of freshwater lakes located in northeastern North America, on the Canada – United States border. Consisting of Lakes Superior, Michigan, Huron, Erie, and Ontario, they form the largest group of freshwater lakes on Earth by total surface, coming in second by volume...

 as we know them, but "proglacial" (ice-frontage) lakes formed and shifted. They lay in the areas of the modern lakes, but their drainage sometimes passed south, into the Mississippi system, sometimes into the Arctic, or east into the Atlantic. The most famous of these proglacial lakes was Lake Agassiz
Lake Agassiz
Lake Agassiz was an immense glacial lake located in the center of North America. Fed by glacial runoff at the end of the last glacial period, its area was larger than all of the modern Great Lakes combined, and it held more water than contained by all lakes in the world today.-Conception:First...

. A series of floods, as ice-dam configurations failed, created a series of great floods from Lake Agassiz, resulting in massive pulses of freshwater added to the world's oceans.

The Missoula Floods
Missoula Floods
The Missoula Floods refer to the cataclysmic floods that swept periodically across eastern Washington and down the Columbia River Gorge at the end of the last ice age. The glacial flood events have been researched since the 1920s...

 of Washington state were also caused by breaking ice dams, resulting in the Channeled Scablands
Channeled scablands
The Channeled Scablands are a unique geological erosion feature in the U.S. state of Washington. They were created by the cataclysmic Missoula Floods that swept periodically across eastern Washington and down the Columbia River Plateau during the Pleistocene epoch. Geologist J Harlen Bretz coined...

.

Lake Bonneville
Lake Bonneville
Lake Bonneville was a prehistoric pluvial lake that covered much of North America's Great Basin region. Most of the territory it covered was in present-day Utah, though parts of the lake extended into present-day Idaho and Nevada. Formed about 32,000 years ago, it existed until about 14,500 years...

 burst catastrophically in the Bonneville Flood
Bonneville Flood
The Bonneville Flood or Lake Bonneville Flood was a catastrophic flooding event in the previous ice age, which involved massive amounts of water inundating parts of southern Idaho and eastern Washington along the course of the Snake River. Unlike the Missoula Floods, which also occurred during the...

, due to its water overflowing and washing away a sill composed of two opposing alluvial fan
Alluvial fan
An alluvial fan is a fan-shaped deposit formed where a fast flowing stream flattens, slows, and spreads typically at the exit of a canyon onto a flatter plain. A convergence of neighboring alluvial fans into a single apron of deposits against a slope is called a bajada, or compound alluvial...

s which had blocked a gorge. Lake Bonneville was not a glacial lake, but post-glacial climate change determined the lake level and its overflow.

The last of the North American proglacial lakes, north of the present Great Lakes, has been designated Glacial Lake Ojibway
Glacial Lake Ojibway
Glacial Lake Ojibway was a prehistoric lake in what is now Northern Ontario and Quebec in Canada. Ojibway was the last of the great proglacial lakes of the last ice age. Comparable in size to Lake Agassiz , and north of the Great Lakes, it was at its greatest extent c. 8,500 years BP.Lake Ojibway...

 by geologists. It reached its largest volume around 8,500 years ago, when joined with Lake Agassiz. But its outlet was blocked by the great wall of the glaciers and it drained by tributaries, into the Ottawa
Ottawa River
The Ottawa River is a river in the Canadian provinces of Ontario and Quebec. For most of its length, it now defines the border between these two provinces.-Geography:...

 and St. Lawrence Rivers far to the south. About 8,300 to 7,700 years ago, the melting ice dam over Hudson Bay
Hudson Bay
Hudson Bay , sometimes called Hudson's Bay, is a large body of saltwater in northeastern Canada. It drains a very large area, about , that includes parts of Ontario, Quebec, Saskatchewan, Alberta, most of Manitoba, southeastern Nunavut, as well as parts of North Dakota, South Dakota, Minnesota,...

's southernmost extension narrowed to the point where pressure and its buoyancy lifted it free, and the ice-dam failed catastrophically. Lake Ojibway's beach terraces show that it was 250 metres (820.2 ft) above sea level. The volume of Lake Ojibway is commonly estimated to have been about 163,000 cubic kilometres, more than enough water to cover a flattened-out Antarctica with a sheet of water 10 metres (32.8 ft) deep. That volume was added to the world's oceans in a matter of months.

The detailed timing and rates of change after the onset of melting of the great ice-sheets are subjects of continuing study.

There is also a strong possibility that a global climatic change in recent geological time brought about some large deluge. Evidence is mounting from ice-cores in Greenland
Greenland
Greenland is an autonomous country within the Kingdom of Denmark, located between the Arctic and Atlantic Oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for...

 that the switch from a glacial to an inter-glacial period can occur over just a few months, rather than over the centuries that earlier research suggested.

The refilling of the Mediterranean Sea (5.3 million years ago)

A catastrophic flood refilled the Mediterranean Sea 5.3 million years ago, at the beginning of the Zanclean
Zanclean
The Zanclean is the lowest stage or earliest age on the geologic time scale of the Pliocene. It spans the time between 5.332 and 3.6 Ma ± 0.005 Ma . It is preceded by the Messinian age of the Miocene epoch, and followed by the Piacenzian age....

 age that ended the Messinian salinity crisis
Messinian salinity crisis
The Messinian Salinity Crisis, also referred to as the Messinian Event, and in its latest stage as the Lago Mare event, was a geological event during which the Mediterranean Sea went into a cycle of partly or nearly complete desiccation throughout the latter part of the Messinian age of the Miocene...

. The flood occurred when Atlantic waters found their way through the Strait of Gibraltar
Strait of Gibraltar
The Strait of Gibraltar is a narrow strait that connects the Atlantic Ocean to the Mediterranean Sea and separates Spain in Europe from Morocco in Africa. The name comes from Gibraltar, which in turn originates from the Arabic Jebel Tariq , albeit the Arab name for the Strait is Bab el-Zakat or...

 into the desiccated Mediterranean basin
Mediterranean Basin
In biogeography, the Mediterranean Basin refers to the lands around the Mediterranean Sea that have a Mediterranean climate, with mild, rainy winters and hot, dry summers, which supports characteristic Mediterranean forests, woodlands, and scrub vegetation...

, following the Messinian salinity crisis
Messinian salinity crisis
The Messinian Salinity Crisis, also referred to as the Messinian Event, and in its latest stage as the Lago Mare event, was a geological event during which the Mediterranean Sea went into a cycle of partly or nearly complete desiccation throughout the latter part of the Messinian age of the Miocene...

 during which it repeatedly became dry and re-flooded, dated by general consensus to before the emergence of modern humans.

The Mediterranean did not dry out during the most recent glacial maximum. Sea Level during glacial periods within the Pleistocene is estimated to have dropped only about 110 to 120 metres (361 to 394 ft). In contrast, the depth of the Strait of Gibraltar
Strait of Gibraltar
The Strait of Gibraltar is a narrow strait that connects the Atlantic Ocean to the Mediterranean Sea and separates Spain in Europe from Morocco in Africa. The name comes from Gibraltar, which in turn originates from the Arabic Jebel Tariq , albeit the Arab name for the Strait is Bab el-Zakat or...

 where the Atlantic Ocean enters ranges between 300 and 900 m (984.3 and 2,952.8 ft).

See also

  • Altai flood
    Altai flood
    The Altai flood refers to the cataclysmic flood that swept along the Katun River in the Republic of Altai at the end of the last ice age. These glacial lake outburst floods were the result of periodic sudden ruptures of ice dams like those triggering the Missoula flood.-Background:Large glacial...

  • Deluge myth
  • Missoula Floods
    Missoula Floods
    The Missoula Floods refer to the cataclysmic floods that swept periodically across eastern Washington and down the Columbia River Gorge at the end of the last ice age. The glacial flood events have been researched since the 1920s...

     (pleistocene megaflood)
    • Glacial Lake Missoula
      Glacial Lake Missoula
      Glacial Lake Missoula was a prehistoric proglacial lake in western Montana that existed periodically at the end of the last ice age between 15,000 and 13,000 years ago...

    • J Harlen Bretz
      J Harlen Bretz
      J Harlen Bretz was an American geologist, best known for his research that led to the acceptance of the Missoula Floods, and also for his work on caves. He was born to Oliver Joseph Bretz and Rhoda Maria Howlett, farmers in Saranac, Michigan, as the oldest of five children...

  • Outflow channels
    Outflow channels
    Outflow channels is the term used to describe extremely long, wide swathes of scoured ground on Mars, commonly containing the streamlined remnants of pre-existing topography and other linear erosive features indicating sculpting by fluids moving downslope...

  • Zanclean flood
    Zanclean flood
    The Zanclean flood is a flood theorized to have refilled the Mediterranean Sea 5.33 million years ago, at the beginning of the Zanclean age, between the Miocene and Pliocene, which ended the Messinian salinity crisis...


External links

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