Eruption of Kilauea

The eruption of Kilauea, an active shield volcano located in the island of Hawaii, in the United States, was an artificially induced volcanic eruption in November 10 of the current Toaru Majutsu no Index timeline. The cause of the eruption was a the deliberate use of powerful explosives from the military device known as Trigger, by members of Trident in order to facilitate their invasion of Hawaii.

Background
Although the reason is still unknown, the top members of GREMLIN, part of their plan is to have Kilauea erupt abnormally. Rather than the characteristic low-viscocity lava flow typical of shield volcano eruptions, such as Kilauea. GREMLIN somehow managed, either with magic or technology to force Kilauea to uncharacteristically erupt explosively, sending massive amounts of ash into the atmosphere.

Planning
To force Kilauea to erupt, GREMLIN chose to use Trigger, a device that was developed by the United States military for the purpose of inducing a controlled eruption of volcanoes. For this purpose, GREMLIN enlists the help of Saronia A. Irivika with the magic to control people. Here, she controls several people in high positions of the United States government in order to research the whereabouts of Trigger, this however did not go unnotice, as Roberto Katze figures it out on his own.

Saronia, Cendrillon, and Olay Blueshake's cooperation was sealed as she was made to believe that the eruption would be used to aid in the invasion of Hawaii, and the eventual transformation of the United States into a theocracy, causing a disruption in the balance between the magic and science side. Needless to say, since the volcano's eruption would serve its purpose to aid in the invasion as well as some lower members of GREMLIN participating, the co-conspirators had no suspicion that they were simply being used.

Discovery of the plans
Roberto Katze (as well as his aide Roseline Krackhart), discover the queer movements of members of his government, which precipitated in him severing ties with government in order to investigate on his own with the Imperial Package. Later, with Kamijou Touma, Accelerator, Hamazura Shiage, Misaka Mikoto, Misaka Worst, Kuroyoru Umidori, and Leivinia Birdway with her magic cabal arriving in Hawaii in order to draw out GREMLIN, they are of course get involved.

After meeting up with Roberto Katze, they determined that GREMLIN is likely trying to obtain Trigger, Here, they conjecture that GREMLIN will be trying to use Trigger on Kilauea, the largest active volcano in the Hawaiian islands, to cause a chain reaction of eruptions of nearby volcanoes on the island of Hawaii (Mauna Loa, Mauna Kea, and Hualalai). This would lead to a catastrophic lost of life (estimated to be around 500,000 by Leivinia). This would also utterly destroy diplomatic relations between other nations and the United States for being unable to prevent the disaster (as many tourist from other countries visit Hawaii every year), and would demand reparations, which the United States could not possibly provide. The plan would be to disrupt the balance between the members of the Science side, the disruption of course would cause the Unites States' economy, and that of the world, to plunge leading to a downward spiral, that would possibly lead to violence between nations.

Prevention attempt of the eruption
With Roberto's help, they determine that the Trigger would be kept in Pearl Harbor. Touma, Accelerator, Mikoto and Leivinia, along with Roberto go to Pearl Harbor to secure Trigger, while Shiage, Umidori and Misaka Worst go to the island of Hawaii, specifically, Volcanoes National Park to set-up a defensive line.

In Pearl Harbor, they discover that Trigger may be in one of the cargo planes, hither, Touma, Mikoto, and Roberto discover that Saronia is there too to retrieve it and a battle ensues over the island of Lanai, culminating in a crash landing on the sea, and both Saronia and Kamijou and company discovering that Trigger wasn't there. Meanwhile, Shiage, Umidori, and Misaka Worst are in one of Kilauea's subsidiary craters, and discover that GREMLIN members have already finished setting up the Trigger. Despite their efforts of destroying some of them, they are forced to evacuate as the volcano erupts.

Eruption
Kilauea erupts explosively, creating an ash plume and sending an unknown amount of ash into the atmosphere, spreading in every direction, which reached even Napali Coast, darkening the sky and was thick enough to prevent aircraft to fly in high altitudes.

Aftermath
Since it did not erupt on the scale as Leivinia predicted, it can be assumed that there were no casualties immediately after due to the eruption. Instead, the eruption was overshadowed by the large scale invasion of the Hawaiian islands by Trident and GREMLIN. The eruption temporarily isolates the Hawaiian islands from any aid from the mainland or Guam, giving Trident an advantage in their ambush on the islands.

The scene would later be revealed that the eruption was the only thing GREMLIN wanted to achieve, explicitly, Kilauea erupting as so to spew smooth volcanic ash. It erupting would be the first complete stage of GREMLIN's plan.