Pacific Ring of Fire

The Pacific Ring of Fire is a chain of volcanoes on Earth, running along the coastline of the various continents bordered by the Pacific Ocean. As it is a notoriously geologically unstable region that is home to over 75% of the world's volcanic eruptions, the Decepticons have taken a stab at exploiting it more than once.

The Battle of the Star Gate
In the late 1990s, Starscream hatched a plan to generate energy by stimulating the tectonic plates that form the Japan Trench, part of the Pacific Ring of Fire. Striking a deal with the Japanese Prime Minister that kept their activities secret from the Autobots in exchange for non-aggression, the Decepticons had Rumble and Frenzy use their pile drivers in the trench, creating a series of earthquakes that yielded an impressive amount of energon cubes. Unfortunately for the villains, the Autobots got wise to their scheme when Japan's Professor Ōnishi realized that none of the earthquakes were being preceded by natural phenomena known as "earthquake clouds", suggesting they were being artificially generated. The Autobots arrived to battle the Decepticons, at which point Megatron had Rumble and Frenzy kick off the most devastating quake yet. Although severe damaged resulted, Hound was able to stop the quake when he ventured into the trench's depths and used his holograms to take down Rumble and Frenzy.

The Headmasters cartoon
In 2011, Decepticon emperor Scorponok schemed to put the Pacific Ring of Fire to much more destructive use, planting a series of plasma energy bombs in strategic locations all along it with the intent of tearing the planet apart. After Scorponok had planted several devices, including one in Alaska, the Autobots' human ally Spike Witwicky detected the pattern in the villain's movements, and the Autobots were able to use it to track him down to the Kamchatka Peninsula. In the battle that resulted, the power-drained Fortress Maximus was hurled into a volcano by Scorponok, but the lava only succeeded in re-energizing him, allowing him to defeat Scorponok by perforating his weak spot with the Master Sword.

The Decepticons subsequently fled Earth, leaving the Autobots to deal safely with the explosives they had left behind. Chromedome and Hardhead were in the process of removing a set of five bombs when a volcanic tremor started the explosives' timer, and they had to race the bombs into space to save the Earth from their devastating detonation.