The island of New Britain, part of Papua New Guinea, lies on the very edge of a tectonic micro-plate, causing the eastern edge of the island to be a volcanic hot spot. (Please see figure 1)
The eastern corner of the island, as it turns out, is in itself one large caldera, with multiple cones rising out of the waters on three sides. (Please see Figure 2) The island itself sports eighteen recognized volcanoes, according to the Smithsonian Institution, ranging from submarine varieties, to calderas, to pyroclastic shields, to complex cones. Papua volcano mythology was documented in a collection of periodical newspaper columns, both translated and edited by Thomas H. Stone. Titled "Folktales from Wantok Newspaper," the book contains two rather large volumes, the dates of the collection running from 1972 to 1997.
The Polynesian "triangle" has an immensely long history, steeped in culture and tradition. Though the myths in my source were, in fact, published works in a local newspaper, the tradition in the area was to pass down stories, mythology in particular, orally (Kirch 2002). As such, most of the myths in the collection had the feel of being spoken. Slightly improper grammar and colloquialisms are abundant with references to local lore that may be otherwise unknown to a reader.
The myth describing the origins of thunder,originally published on March 21, 1973, in the Wantok newspaper, is thought to refer to the New Britain Volcano of the Rabaul Caldera.
"Once there was a short and strong man. He though about going into the forest to find some wild game. He went to many places in the forest and became tired... Suddenly a man…appeared and wanted to kill him. The two of them fought fiercely and they climbed a steep mountain. On top of the mountain was a small house. This house was unusual and belonged to the second man. The man of the forest said "today, you didn't catch any game because I didn't desire it. The man of the forest gave the short man a charmed bow, and with it he was able to kill much game. The next day, he came to find his bow stolen, the only possible culprit his own younger brother. After tracking him down, the two fought for the bow, and the younger brother ran away. When the siblings had held their battle, there was an explosion on the mountain, and so now, when we hear thunder, we know that it is the two brothers fighting again. (Story summarized from Slone's work)
So, it would seem that the brothers fighting caused the mountain to have an eruption, and though one would think that there would be some sort of myth explaining why a mountain was on fire, it appears that an explanation as to the origin of thunder, or what it means, works just fine.
Many stories had been cataloged by Slone (some two thousand of them!) in their original form just as they were passed from parent to child through the years without altering their original spoken feel.
Volcano Myths in Papua New Guinea, specifically on New Britain Island
SpSt 438: Volcanism: A Planetary Process