Assuming ,at the most conservative level ,that the Tsunami struck immediately before Silappadikaram period,which is unlikely as to reconstruct the Land and take the language to classical level of Silappadikaram would have required at least five thousand years,we can assign the last Tsunami at 14,000 BC. And taking the account of Tamil classics for the duration of each Sangam at ( there is novreason to doubt this as their version about Third Tsunami is validated,
Yet Poompuhar is around 20,000 years old. Tamil Brahmi is older than this,as Cilappadikaram, a Classical Epic of Sangam Era was written, not in Brahmi, but in evolved later Tamil! Archeologists have, in 2013, have catalogued 293 towns belonging to Sangam Era in Vaigai bed! Time we rewrote our History.