Self-destruct is, by definition, the act of destroying oneself or itself. Applied to crafts and other structures, this is either the fruit of a mechanism, or sometimes an accident.
As far as starships, space stations or bases are concerned, a self-destruct mechanism is usually implanted within their power grid, logically consuming a vast amount of the available fuel resources within the main power core(s), in order to provide the most destructive chain reaction possible, in the shortest amount of time. Sometimes, it's preceded by a significant build up, resulting into an overload.
In the case of starships, most of the time they can be controlled from starships, and triggered once proper verification protocols have been passed successfully, but certain systems allow auxiliary control from remote panels throughout the ship or base.
This is a last resort procedure generally used to prevent capture, or to cause as much damage as possible when the ship or base in question is overwhelmed by enemy forces. The resulting effects are generally cataclysmic in regards of the size of the devices.
- Aris Boch's Tel'tak, which was controlled by three delmacs (crystals). The self-destruct mechanism was a security measure in case prisoners would attempt to modify the ship's systems in order to escape. The ship didn't explode as the third crystal was missing. It's unknown if Teal'c certainty about how to disengage the mechanism was due to his knowledge of this particular part of the ship's mechanism, or because he was merely guessing. The later would mean this was likely a modification brought by Boch to his ship. (SG1: "Deadman Switch")
- The Stragoth leader used a self-destruct method to avoid capture and in an attempt to destroy Stargate Command members. (SG1: "Foothold")
- O'Neill (Asgard prototype ship), used to annihilate three pursuing Bilskirnir-class ships crawling with Replicators, while all ships were moving in hyperspace. (SG1: "Small Victories")
- The android clone of Dr. Daniel Jackson, built by Harlan. The copy of Major Samantha Carter tricked the Goa'uld Ja'din into thinking she was activating RoboDaniel's power source, while it set up the self-destruct mechanism, which resulted in the explosion of the remaining artificial body of the Daniel android and the death of the Goa'uld Ja'din. (SG1: "Double Jeopardy")
- Apophis' mothership, activated by Apophis or his Jaffa in order to fight off Replicators before they could stop the reaction. The energized matter shock wave was so powerful that even when taking the Ha'tak (piloted by Jacob Carter) as far as possible away from Apophis' ship (it couldn't be seen on screen anymore), all energy still had to be diverted to shields, which were raised in urgency, to protect the craft and its crew. (SG1: "Enemies")
- Anubis' Ha'tak, kept in standby by the mind of Thor while imprisoned inside the ship's computer. Once the Asgard Commander's mind was removed from the system, the countdown resumed and the Ha'tak was destroyed. (SG1: "Descent")
- The Aurora (Lantean warship), destroyed and vaporized two nearby Wraith cruisers. (SGA: "Aurora")
- A Wraith cruiser, activated by a Wraith Queen but cut off before it exploded. Had it succeeded, the explosion would have cracked the thin sea bed of Lantea, released the magma and destroyed Atlantis as a result. (SGA: "Submersion")
- The Cheyenne Mountain Complex has a self-destruct system that will destroy it in case of an alien foothold situation. It has been activated several times, but always deactivated before going off (with the exception of the Alternate reality). Captain Samantha Carter said it has the force to vaporize the mountain. (SG1: "The Enemy Within")
- The Atlantis expedition set a program to overload the Naquadah generators to destroy the city in the event that it fell to their enemies. This system was not powerful enough to ensure total destruction of all valuable technology in the city, though it is likely that now the city uses Zero Point Modules it will be able to ensure total destruction of itself and likely any attackers orbiting the planet, see below.
Self-destruct being usually and primarily obtained by setting up reactors, it has also been possible to turn independent power sources into bombs of tremendous power, by building up energy for overload (so that even if an energy buffer was present, it couldn't cope with the excess of energy). Such power sources were:
- A portable Naquadah generator Mk-I, capable of liberating an energy worth of 20 kilotons by overloading, according to Dr. Rodney McKay. A similar method was going to be used to destroy the Gadmeer terraformer, by using a model closely similar to the first prototype built by Major Samantha Carter years earlier. (SG1: "Learning Curve", "Scorched Earth") (SGA: "Hide and Seek")
- Zero Point Modules, with varied results, going from estimated star system obliteration, to assured planetary mass scattering, or mere destruction of an Asuran city-ship in orbit of Lantea, displaying the capacity to define a threshold level for the overload of ZPMs. (SG1: "Zero Hour") (SGA: "Critical Mass", "Progeny", "Be All My Sins Remember'd")
We are yet to see other power sources used in such a way.
- The Lantean power core of Project Arcturus, capable of providing the power of 12 Zero Point Modules when working at 50% of max capacity, went out of control and destroyed five sixths of the Doranda system. (SGA: "Trinity")
- Midway space station, destroyed quite by accident, by Dr. Peter Kavanagh when he tried to deactivate one of the Midway Stargates using a boobytrapped system. The Stargates used in the station have survived and a Pegasus Stargate in the Gate bridge was used on Atlantis as the old one was destroyed by the Attero device. (SGA: "Midway", "The Lost Tribe")