The Falling Fire of the Smiheim Archipelago

When Wlallert Smiheim first charted the Smiheim Archipelago, there was little out of the ordinary to see. This island group was home to as varied a collection of plants and animals as one would find in a secluded area off the main trade routes as one could find. According to the copiious notes he took, several of the islands had lush foliage and jungle growth and some freshwater streams. If it wasn't so out of the way, it may make a good place to set up a colony. He charted it as he was hired to do, named it after himself since he surmised that his employers would not  mind him doing so for such an unimoportant area of the map, and sailed on into seeming obscurity.
It's not known when things changed, but the next time a ship happened upon the Smiheim Archipelago, it had changed drastically. The KOS Ferret, a cargo ship from the Kingdom of Oprus, had gotten lost in a storm. Once they were able to ascertain their position, they made for the nearest source of land to effect repairs. When they arrived at the Archipelago, they found that most of the islands' lush jungle had been blasted away. They weighed anchor off an island that still had trees and put in for repairs. After the second day of harvesting wood and replenishing food and water stores, the crew looked to the sky and saw a massive, burning, rocky fireball hurtling toward the iislands. Though the fireball did not land on the island they had inhabited, it did land nearby on another island, quickly to be followed by a dozen more.
After the bombardment stopped, they quickly got back to work as to leave the area as swiftly as possible. While they were harvesting, they found evidence that the island they were on had recieved falling rocks as well, but they were much smaller and less destructive. Within three more days they were able to set sail again, and as they put out to sea, they could see another bombrdment of fiery rocks hitting the Archipelgo again, though this time at an island much further away. 
The Captain reported what he had witnessed to the authorities back in Oprus and an investigation team was dispatched  to the area and they concluded that these fiery rocks fall from the sky regularly. Over the course of a month, they observed no less than twenty incidences of these bombardments occuring. Later investigative teams had similar conclusions. As yet, no one has been able to conclusively explain why this occurs, where the rocks come from or why only this island chain. The Oprus authorities have since declared the area a hazard to travelers and no legitimate shipping goes through that area. It is rumored that several pirates and smugglers haveattempted to make the Archipelago a base for their operations, but all have thus far had said bases pulverized by the falling rocks.