Destructive? then this is the instructable for you! This is a simple TNT volcano using command blocks. make sure to make it out of obsidian and keep all valuables away from it. Enjoy!
Step 1: Chute
first you need to make your chute. I suggest using bedrock or obsidian so it doesn't get destroyed.
Step 2: Safety and Coords
If you want to have a lava pit at the bottom of the chute to make it more realistic you'll want to put barriers so the TNT doesn't destroy your beautiful lava pit. Get barriers with the: "/give @p minecraft:Barrier" For the Coordinates place blocks in opposite corners, Press F3 and hold your cursor over the blocks to get the coordinates.
Step 3: Filling.
Get a command block with the command: "/give @p minecraft:Command_block". place it and put the coordinates you gathered inside, add the fill command with: "/fill (Coordinates) (Other Coordinates) minecraft:TNT" make sure it doesn't replace the chute with TNT. Get another command block use the fill command again to replace some of the blocks with redstone blocks. although you can use the summon command and make it summon PrimedTNT if you prefer. Hook it up to a button and Ta da! one working volcano!