Yanger Dryas meteorite
Graham Hancock in Magician of Gods speculated that the Younger Dryas meteorite 12 900 years ago destroyed civilization. He mentioned several up to 2 km fragments of comet and 10 million megatons explosion. The fire and heat were devastating, but perhaps the impact also produced equally destructive flood. He speculated that the heat melted huge amount of ice, and the meltwater, for instance, shaped the landscape of Channeled Scablands. This is an interesting idea and it should be study further with calculations.
How we get 10 million megatons explosion
Comets have very elliptical orbits and they may travel inside the orbit of Mercury and outside the orbit of Pluto. The speeds of comets increase when they approach to the Sun and slows downs when they depart from the Sun. The speed is nearly escape speed from the solar system. The escape speed depends on the distance from the Sun, and at the distance of Earth it is 40 000 m/s. Thus, a comet which crosses the orbit of Earth have speed of about 40 000 m/s.
Earth orbits the Sun with the speed of 30 000 m/s. The simplest assumption is that the orbits of a comet and Earth crosses with the angle of 90 degree. Then the resultant impact speed (according to vector calculus and Pythagoras) is 50 000 m/s. (Earths gravity also accelerates comets, but in these calculations, it can be neglected)
Comets are dirty snowballs. They contains ice, frozen gas, dust, and stones. Thus we can use density of water (1000 kg/m3). A round ice ball with diameter of 2 km have volume of 4 km3 and weight of 4*1012 kg.
The energy of the impact is equal to the kinetic energy (E) of meteorite. In Joules (J) it can be calculated by the following equation:
E = 1/2*m*v2
where m is mass in kg, and v is speed in m/s. When we use mass of 4*1012 kg and speed of 50 000 m/s we get energy of 5*1021 J which is equivalent to 1.2 million megatons TNT.
So, we need 8 fragments in size of 2 km in order to attain about 10 million megatons impact energy. Younger Dryas impact ejecta layer researchers also accept these numbers; Firestone et. al. think 10 million megatons is consistent with the impact ejecta layer, and because there is not found one big crater the hit should be result of multiple smaller fragments which were blocked by ice sheet.
100 000 cubic kilometer of meltwater
The melting energy of ice is 334 000 J/kg. Thus, 10 million megatons ( 4.18*1022 J) can melt 1.25*1017 kg ice, which is about 125 000 km3 water, but we must realize that the amount of actual meltwater is smaller, because all impact energy does not melt ice. Impact creates crater, shock wave, and large amount of heat radiates to the space.
So, Younger Dryas meteorite did not melt more than 100 000 km3 water (I got much smaller amount of meltwater than Graham Hancock presented in his book). 100 000 km3 water rises the sea level only 0.3 m (the area of ocean is 360 million km2). But the plain meltwater was not necessarily crucial, because meteorite impact could liberate already melted water, for instance, blew up the ice dams of glacial lakes.
When the Ice Age turned to end, the 3 km thick ice sheet melted, and during the last 20 000 years the meltwaters more or less gradually raised the sea level 120 m. Several sudden rises, meltwater pulses, have been recognized, but after the Yanger Dryas meteorite (12 900 years ago) there is not found an exceptional rise in sea level www.giss.nasa.gov. This indicates that the Younger Dryas meteorite did not liberate exceptional amount of water. Thus the meltwater flood could be local but not global.
Ocean impact and tsunami
If Yanger Dryas meteorite resulted in the global deluge, in my opinion, the most likely occurrence was that at least one fragment of the comet hit to the ocean and raised a massive wave, tsunami.
Graham Hancock in Magician of Gods speculated that the Younger Dryas meteorite 12 900 years ago destroyed civilization. He mentioned several up to 2 km fragments of comet and 10 million megatons explosion. The fire and heat were devastating, but perhaps the impact also produced equally destructive flood. He speculated that the heat melted huge amount of ice, and the meltwater, for instance, shaped the landscape of Channeled Scablands. This is an interesting idea and it should be study further with calculations.
How we get 10 million megatons explosion
Comets have very elliptical orbits and they may travel inside the orbit of Mercury and outside the orbit of Pluto. The speeds of comets increase when they approach to the Sun and slows downs when they depart from the Sun. The speed is nearly escape speed from the solar system. The escape speed depends on the distance from the Sun, and at the distance of Earth it is 40 000 m/s. Thus, a comet which crosses the orbit of Earth have speed of about 40 000 m/s.
Earth orbits the Sun with the speed of 30 000 m/s. The simplest assumption is that the orbits of a comet and Earth crosses with the angle of 90 degree. Then the resultant impact speed (according to vector calculus and Pythagoras) is 50 000 m/s. (Earths gravity also accelerates comets, but in these calculations, it can be neglected)
Comets are dirty snowballs. They contains ice, frozen gas, dust, and stones. Thus we can use density of water (1000 kg/m3). A round ice ball with diameter of 2 km have volume of 4 km3 and weight of 4*1012 kg.
The energy of the impact is equal to the kinetic energy (E) of meteorite. In Joules (J) it can be calculated by the following equation:
E = 1/2*m*v2
where m is mass in kg, and v is speed in m/s. When we use mass of 4*1012 kg and speed of 50 000 m/s we get energy of 5*1021 J which is equivalent to 1.2 million megatons TNT.
So, we need 8 fragments in size of 2 km in order to attain about 10 million megatons impact energy. Younger Dryas impact ejecta layer researchers also accept these numbers; Firestone et. al. think 10 million megatons is consistent with the impact ejecta layer, and because there is not found one big crater the hit should be result of multiple smaller fragments which were blocked by ice sheet.
100 000 cubic kilometer of meltwater
The melting energy of ice is 334 000 J/kg. Thus, 10 million megatons ( 4.18*1022 J) can melt 1.25*1017 kg ice, which is about 125 000 km3 water, but we must realize that the amount of actual meltwater is smaller, because all impact energy does not melt ice. Impact creates crater, shock wave, and large amount of heat radiates to the space.
So, Younger Dryas meteorite did not melt more than 100 000 km3 water (I got much smaller amount of meltwater than Graham Hancock presented in his book). 100 000 km3 water rises the sea level only 0.3 m (the area of ocean is 360 million km2). But the plain meltwater was not necessarily crucial, because meteorite impact could liberate already melted water, for instance, blew up the ice dams of glacial lakes.
When the Ice Age turned to end, the 3 km thick ice sheet melted, and during the last 20 000 years the meltwaters more or less gradually raised the sea level 120 m. Several sudden rises, meltwater pulses, have been recognized, but after the Yanger Dryas meteorite (12 900 years ago) there is not found an exceptional rise in sea level www.giss.nasa.gov. This indicates that the Younger Dryas meteorite did not liberate exceptional amount of water. Thus the meltwater flood could be local but not global.
Ocean impact and tsunami
If Yanger Dryas meteorite resulted in the global deluge, in my opinion, the most likely occurrence was that at least one fragment of the comet hit to the ocean and raised a massive wave, tsunami.