If a huge amount of tnt erupts at the same time, water and lava do not flow, they just stop. As tnt bursts they catch up quickly. If there is something not clearly explained in the video link for download file .mp4 (google drive 183mb)

https://drive.google.com/open?id=1PRZ4xbHrE2IqnAqyqQChmTfpFaujiCTZ    < delete the floor on click on this

i used google translator