According to Vishnu Purana and Agni Purana, there are 4 different types of pralaya: Praakritik Pralaya, Naimittik Pralaya, Atyantik Pralaya and Nitya Pralaya.
Praakritik Pralaya, which is of 311,040,000,000,000 solar years duration, occurs after the completion of life of Brahma (i.e. 100 Brahma years = 311 trillion and 40 billion earth years = one day ofVishnu = 1 Parama). After the completion of one Brahma life cycle, the complete dissolution of all the entities (i.e. the Panch Mahaabhoot or Universe) takes place in the eternity (God). Praakritik Pralaya is the time for which Vishnu sleeps. The next morning, he again gives birth to a new Lord Brahma and asks him to create new worldly entities. Noticeably, Praakritik Pralaya and the Life of Brahma are of equal duration.
Naimittika Pralaya, which is of 4,320,000,000 earth years, occurs just after the end of a Kalpa. Also, known as the Night of Brahma, it signifies the end of living world. In Bhagvata Purana, sage Shukdeva told king Parikshit that if Lord Brahma is supposed to be a child (for example), then in a similar way as a child plays with his toys i.e. making various structures from his toys during day and breaking or dismantling them before he goes to sleep at night; Brahma makes the living world during his day (i.e. Kalpa) and destroys it before going to sleep during night (i.e. Naimittika Pralaya). A new living world is created by Brahma, when he wakes up the next day and so on the cycle continues till Praakritik Pralaya. Again, Naimittika Pralaya and Kalpa are of equal duration.
Atyantik Pralaya, also termed as Moksha, is the final deliverance or the attainment of salvation by a jivan (soul) and after that the jivan is never again in the clutches of karma; nor bounded by the tight ropes of Sansaar. It is therefore a variable time span conditioned or determined by the practise of the different kind of Yogas or Prapatti. It is the final immersion of a soul (i.e. aatmaa), thereby completely eliminating its individualism into the eternal almighty (i.e. Parmaatmaa).
Nitya Pralaya, is the sleep or by an extension thereof, Death
Pralaya, in Hindu cosmology, is an aeonic term for Dissolution, which specifies different periods of time during which non activity situation persists, as per different formats or contexts. The word Mahapralaya stands for Great Dissolution. During each pralaya, the lower ten realms (loka) are destroyed , while the higher four realms, including Satya-loka, Tapa-loka, Jana-loka, and Mahar-loka are preserved. During each Mahapralaya, all 14 realms are destroyed.
What happens after Mahapralaya? Bramha, including all other Jeevas get inside Shri Krishna during Mahapralaya only with their Samskaras(leaving all three–gross, subtle and causal bodies!)–then God sleeps for a while—the compassion power(Karuna Shakti) of God wakes him up saying to him that there are infinite number of souls inside him in a ‘pending’ state.
Then God manifests the world as it was with all souls in the status they were before the Mahapralaya, which means, the dogs are dogs and cats are cats. He doesn’t create the existence but rather expresses it—that is what is meant by eternal creation. It’s just divine play without any beginning—beginnings and ends are points for our petty minds to understand.
Sources: Kripaluji Maharaj’s lectures.