Indian Mythology/Legends/Pralaya

What it is?
Pralaya essentially describes the destruction of Universe that took place in the past and will take place in future. It also describes the time between two consecutive Pralayas and has excellent account of time-keeping in Hindu Mythology.

When?
After every completion of 100 year cycle of Bramha, Pralay (also known as Maha-Pralay) takes place.
 * 1 Year = 360 days (as per Hindu Calendar)
 * 1 Yuga = 1 Lakh years (100, 000 years)
 * There are 4 Yuga : Satyug, Treta, Dwapar and Kali (each one having 100,000 years)
 * 4 Yugas = 1 Dev-Yuga (which is equivalent to 4 * 100,000 = 400,000 years)
 * 71 Dev-Yuga = 1 manvantar (that is, 28,400,000 years)
 * 28 Manvantar = 1 day of Bramha (which is, 795,200,000 years)
 * 100 years of Bramha = (360 * 100 * 795200000 = 28,627,200,000,000 years)

Restoration of Hindu astronomical calculations

Following the restoration of Hindu astronomy by Sri Yukteswar in 1894 the astronomical figures quoted above are deemed to have come about through a misunderstanding occurring during the last descending Kali Yuga. Referring to the works of Manu Sri Yukteswar quotes

"Four thousands of years, they say, is the Krita Yuga (Satya Yuga or the "Golden Age" of the world). Its morning twilight has just as many hundreds, and its period of evening dusk is of the same length (i.e., 400 + 4000 + 400 = 4800). In the other three ages, with their morning and evening twilights, the thousands and the hundreds decrease by one (i.e., 300 + 3000 + 300 = 3600; etc) That fourfold cycle comprising 12,000 years is called an Age of the Gods. The sum of a thousand divine ages constitutes one day of Brahma; and of the same length is its night."

Sri Yukteswar, the teacher of Paramahamsa Yogananda, explains that the Yugas described represent the descending cycle of the Yugas which is complemented by an ascending cycle. In this way the descending Kali Yuga, of 1200 years, including its dawn and evening twilights, precedes an ascending Kali Yuga with the meeting place of those two ages as being the depth of the cycle and the greatest distance the Solar system moves to from the centre of mental virtue he identifies as Brahma. The entire cycle takes 24,000 years during which time the Solar System moves towards and way from this centre of mental virtue with the Golden Age composed of two Satya yugas, one ascending and one descending, comprising a total of 9,600 years or more than one third of the entire cycle. Sri Yukteswar places the depth of the cycle, the period of greatest ignorance or least mental virtue, in 499 AD, and himself writing in 1894 as being at the end of the ascending dawn of the Dwapara Yuga, meaning that in 2009 we are 110 years into the ascending Dwapara age proper.

Sri Yukteswar, The Holy Science, Introduction pp 7-17, Self Realisation Fellowship, 1990

How?
At the time of Pralay, the energy residing in all the living beings unite at a single place. Brilliance of Sun increases by many many magnitudes and this generate extreme heat. The heat causes huge fires and it devours everything, all the living beings die. Only ashes remain in the Universe. Then the Supreme Wind (Vaayu) gathers these ashes in one place. Afterwards the Supreme Rains start and it drowns everything.

Who says so?
Only one Rishi - Markandeya Rishi - has seen and survived the Maha-Pralay. He watched the Maha-Pralay and survived it because he is Immortal. After this event, there was water everywhere and nothing else. He felt terribly lonely after the Maha-Pralay and he went to Bramha and made prayers and pleaded to have just one Darshan of Him. Granted the request, he saw a leaf of Pipal tree floating in the water and on that leaf he saw a human infant playing happily with its thumb. When the infant saw Rishi, the infant said, "Bal Markandeya. (Ed.: Generally, elders call a kid as "Bal" which means "Son") hope you are fine!". The Rishi was astonished as the infant addressed him as "son". Slightly angered, he replied, "My age is few lakhs of years, and still you are addressing me as 'son'? Who are you?!"

On this, the infant laughed aloud and replied, "I have seen and survived innumerable such Maha-Pralayas! Your father was blessed with an Immortal son, hence you survived this Maha-Pralay. I am known as Bal-Mukund and I am the creator and destroyer of this Universe. Now I leave it to you to disseminate this story." and the infant disappeared.