A power surge aimed at an outgoing wormhole will cause the wormhole to jump, or "arc," to a different destination. The phenomenon first occurred when an unintentional weapons surge to the outgoing gate on P4A-771 caused the wormhole to leap from the default SGC gate to the second Earth stargate in Antarctica.
A power overload can be created deliberately, leaving a recognizable energy signature, and covert NID operatives intentionally overpowered off-world gates to force a return to the beta gate in Utah rather than to the SGC, timing the events to SGC missions to hide the signature energy spike.
When the energy of a black hole prevented the SGC's outgoing wormhole from disconnecting, the explosive force of a shaped charge directed toward the stargate forced the wormhole to disconnect from P3W-451 and arc to another gate on P2A-870, where it could be shut down.
Using this same theory to cause a deliberate wormhole arc, SG-1 attempted to block the Ori supergate by activating a wormhole from a black hole in the Pegasus Galaxy. Because the supergate is designed to dial in from another galaxy, and the energy required to create a stable wormhole is exponentially proportional to the size of the gate, the energy needed for a connection to the supergate far exceeds that of an ordinary stargate. Instead, SG-1 used the Odyssey to deliver a stargate near a black hole in the Pegasus Galaxy while Teal'c deposited a secondary stargate near the supergate in the Milky Way. Once a connection was established, two 26-megaton directed energy shaped charges detonated near the event horizon of the Pegasus gate caused the wormhole to arc from the secondary stargate to the supergate, establishing an indefinite connection with the supergate, powered by the black hole, and preventing the Ori from sending additional warships into the galaxy.
Cross Reference: Beta Stargate, Black Hole, NID Off-World Operation, P3W-451, P4A-771, Stargate, Supergate
Episode Reference: Solitudes, Touchstone, A Matter of Time, The Pegasus Project