In some cases TNT-Minecarts create a massive crater.

to reproduce:
Build a track with 3 powered and normal rails like in the attachment.
The Minecarts have to be 1 Block apart.
Place at least 14 normal rails in a row.

No Activator Rail needed.

better change gamerule to doTileDrops false (or you get laggs!)

Hit the Button and BOOOOOM. Doomsday

edit:
if you extend the normal rails up to 30 or more: crash