I recorded this some time ago as it's apparent from the version. Ancient debris spawn more close to chunk borders. That's the lines you see in the video. Also they appear more in the y=15 level. These might have changed in the later versions. I didn't devise this method. It's a demonstration. If on a slower computer with low chunk distance, depending on how far you placed the TNTs, you might wanna follow the explosions so the chunks load and the explosions continue happening.