Yes it is a massive threat and it has already hit us in the past, around -10 000 BC (so 12k years ago): something rebooted the level of development of civilization, and then the great flood followed, with immediate consequence on or destruction of whatever was built around seas and rivers. And water has this property of washing away all the traces of the past, leaving the survivors unaware of what happened in details, so that the only recorded warning are the ones written in religious texts.