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[Urist Da Vinci]

The map shown at the following link is a test of an ice-based superweapon.

http://mkv25.net/dfma/map-10982-bittenpaper

The idea is that when a door is opened via lever, water pressure forces water upwards through "down stairs" carved in the surface in an area with freezing temperatures, encasing enemies in ice. Down stairs don't expose the water on the z-level below to the outside. To reset the weapon, the ice has to be mined into fresh down stairs (beware of ice ceiling cave-in!). The size of my weapon in the test map was limited to the size of the reservoir, which has to be carved out underground to prevent freezing.

I call it a superweapon because, unlike previous ice-based traps, you could build it large enough to span a large area of a map as long as you have a decent hill/mountain for the reservoir. With creative plumbing, you could selectively freeze areas of the surface while leaving other areas open. I was able to instantly kill some migrants with the test weapon. I'm too lazy right now to build the map-spanning version, but I'm planning to do that once the next DF version comes out.

Pros:
- Possible to kill large numbers of creatures on the surface, preserving loot for collection.
- The shape of the effect can be controlled for precise deployment.
- Instant kills once the lever is pulled.
- Can create defensive ice walls for the perfect "shields up!" moment.
- Kills anything except creatures that are made of fire.

Cons:
- Only works in areas with freezing temperatures.
- Miners have to go outside to reset the weapon, exposing them to enemies. If you don't turn the weapon off, the miners will be frozen.
- The weapon has a negative magma quotient.

[Kelenyche]

Ages ago, I watched a video on one of these that worked with a layer of magma pumped under the ice...  Water was at about 3/7 in a long pit that the siege had to walk through to get to the fort, with a cistern of magma under it to keep the water from freezing.  As soon as most or all of the siege was in the water, wading toward the fort, they dropped the magma out from underneath, and the water would freeze instantly.  Then they'd pump the magma back in, melting the ice, and then pump the water into cisterns on the sides of the long pit.  It was pretty amazing.  I wish I wasn't so lazy as to not go looking for the video. 

[tommy521]

Would pumping water in, freezing it, then pumping magma under the ice to melt it work? I've heard that magma will melt ice if above or below a z-level.

EDUT: How do I not notice the ninjas?

[arzzult]

A work around for the need of a large hill/mountain for reservoir is to instead have a reservoir of any size deeper underground and use a pump stack bringing it up into a small hill.

[Mitchewawa]

It's been done. Good trap though.

[Nan]

Good stuff. I couldn't help but build my own. The map I ended up on didn't have much of a hill, it was a mainly flat tundra plain, with a small 1z hill in one corner. The low elevation meant natural water pressure was out of the question. So pump pressure it was.

Initially I had only an array of 6 pumps plunging down into the aquifer, this was enough to freeze large areas of staircases, but it wouldn't freeze them perfectly. Sometimes the water wouldn't be deep enough and would turn into floors instead of walls. While the output would be sufficient to cause massive death and disruption to enemy forces, it wasn't what I was going for. So in the top of the hill I expanded the pumps to a battery of 23 pumps, drawing from a much enlarged 2-z deep reservoir which consisted of the entire hill hollowed out.

The improved output allowed freezing about 350 tiles (an 18x18 area - or a 4 wide wall of ice clear across a 2x2 embark) ice-solid (with a fair amount of spillage to the sides), after that the output started to peter out a bit and there would be voids. Of course 18x18 is more than sufficient for a landmine. And there is nothing stopping me adding another reservoir deeper down, with a "pump stack array" 23 pumps wide. This could easily double the freeze area. Also aquifers seem capable of producing quite a lot of water, and perhaps with a good network of drawage channels (I'm using dug out grids to maximize both water flow and exposed aquifer tiles) and feeder pumps - say 46 pumps feeding the 23 - the pump stack array could possibly operate at full-bore without reservoirs required, making freezing the entire map feasible - although naturally it takes time for the ice to propagate.

For my "final solution" I think I'm going to construct a spiral of ice walls, leading into my fortress entrance. The entire spiral will be boobytrapped with these stairs. When the spiral is full of enemies, a simple pull of the lever will flash freeze the entire spiral and everything in it. My solution to the cave-in problem has been building constructed floors over the freezing areas. However hopefully with high enough ice quality, the natural ice floor will hold itself up - the problem seems to be when intermediate depth ice freezes, it forms a wall without a floor on top. But 7/7 ice produces both wall and floor.

[BigD145]

I could see making a spiral staircase (using ramps) with magma running around the rim and a multi-z-level water reservoir in the center. If it's one tile wide you could add water and then remove magma to freeze and do the reverse to reset. Water would be added universally via 1x1 retracted bridges all up the staircase so little to no movement would occur on the part of invaders. The magma just has to be pulled away from the spiral. Considering you're working in magma and water, just channel away every tile intended to be exposed and rebuild with obsidian, then cut the spiral. ?SCIENCE?

Spoiler (click to show/hide)

Water reservoir in the center, untouched by open air.

Spoiler (click to show/hide)

Sink this sucker into a mountain. Dn'i Great Shaft, anyone?

[Urist Da Vinci]

It seems that some people don't understand how this is different from previous inventions, so I'll list the links that I can find in reverse chronological order:

http://www.bay12forums.com/smf/index.php?topic=92205.msg2616493#msg2616493
Sphalerite's ICEMACHINE (Sept 2011)
-Cavern water naturally flows to freeze invaders that enter a 1-tile-wide hallway in the caverns. Mined to reset.

http://www.bay12forums.com/smf/index.php?topic=71906.msg1758929#msg1758929
Urist Da Vinci's Cold Shoulder (Nov 2010)
-Reservoir water naturally flows to freeze and drown invaders that enter a 3-tile-wide hallway. Mined to reset.

http://www.bay12forums.com/smf/index.php?topic=63346.msg1465467#msg1465467
Scraggletag's Automatically resetting ice trap (August 2010)
-Pumped water freezes invaders that enter a 1-tile-wide hallway. Magma melt reset.

http://www.bay12forums.com/smf/index.php?topic=42210.msg772410#msg772410
http://df.magmawiki.com/index.php/User:Vattic/Orcsicle_maker_Explained
Vattic's Semi-automatic Orcsicle Maker (Sept 2009)
-Pumped water freezes invaders that enter a 3-tile-wide hallway. Magma melt reset.

http://www.bay12forums.com/smf/index.php?topic=15652.60
http://www.mkv25.net/dfma/movie-231-degrinchinator
Vanigo's Degrinchinator (Dec 2007)
-Pumped water freezes invaders that enter a 1-tile-wide hallway. Mined to reset.

There may be more creations, but I can't find them with search.

Would pumping water in, freezing it, then pumping magma under the ice to melt it work? I've heard that magma will melt ice if above or below a z-level.

Yes, but then you need magma plumbing and drains and more levers. The magma has to be constantly moving for the ice to melt. The melting ice moves goblinite into hyperspace, and creates 7/7 water that has to be drained (so it doesn't freeze right away again).

A work around for the need of a large hill/mountain for reservoir is to instead have a reservoir of any size deeper underground and use a pump stack bringing it up into a small hill.

Yes, but the reason I used a reservoir instead of pumps is that the full 7/7 upper level of the reservoir water instantly moves to the target location. The pump method is only as fast as the number of pumps that you have, and can sometimes create ice floors instead of ice walls if it pumps a 1/7 tile.

It's been done. Good trap though.

This hasn't quite been done before. The Prior Art didn't include weapons that hit areas larger than 3-tile-wide hallways underground. I also saw no references to the use of "down stairs" - most people used grates, which would deconstruct if ice forms on them. With creative plumbing, this current idea could be used to ice only parts of the surface that have goblins in them, while leaving the fleeing dwarven caravan unharmed.

...
For my "final solution" I think I'm going to construct a spiral of ice walls, leading into my fortress entrance. The entire spiral will be boobytrapped with these stairs. When the spiral is full of enemies, a simple pull of the lever will flash freeze the entire spiral and everything in it. ...

Awesome, go for it!

I could see making a spiral staircase (using ramps) with magma running around the rim and a multi-z-level water reservoir in the center. If it's one tile wide you could add water and then remove magma to freeze and do the reverse to reset. Water would be added universally via 1x1 retracted bridges all up the staircase so little to no movement would occur on the part of invaders. The magma just has to be pulled away from the spiral. Considering you're working in magma and water, just channel away every tile intended to be exposed and rebuild with obsidian, then cut the spiral. ?SCIENCE?
...

The problem with this idea is that you can't get the magma and water close enough to prevent freezing, and you can't put machine components outside without them having the "Frozen Here" message and failing.