Something that struck me when rereading The Great Ordeal was the idea that the Inchoroi actually seem to have used a nuke to soften their original landing (Arkfall):
"Those who witnessed and survived the event claimed that the cataclysmic impact of the Ark somehow preceded the Ark, that the great golden vessel dropped no quicker than an apple into the flash and upheaval of an earlier, far more tumultuous strike."
Dagliash was the second time the Inchoroi detonated a nuclear weapon on the surface of Earwa. As a result, the Nonmen histories may contain a record of nuclear fallout, and radiation poisoning.
The text also mentioned that Arkfall was preceded by the "waxing" of Imburil (the Nail of Heaven) by three years. Are we supposed to think that these events are related?
The fact that it was preceded by the arrival of a new star gives me two hypotheses:
1. The Ark was not itself FTL capable. There is, somewhere in space near Eärwa, an absolutely massive abandoned vessel/station that is the actual FTL device, while the Ark was their living space and warship.
2. Inchoroi FTL is achieved via wormhole. The new star is actually just the star of the Inchoroi's home system seen through it.
Similarly, I have two hypotheses for the greater cataclysm that immediately preceded Arkfall:
1. Orbital bombardment meant to weaken the natives prior to touchdown (I favor this one. Though I doubt it was a nuke. Sounds far too big. Some kind of huge rail gun I'd guess). If this is the case it may well the source of the other crater like mountain ranges (although I also think it's possible the Ark didn't land intact but broke up on the way in, creating the other craters)
2. It's some strange byproduct of Inchoroi FTL and they simply started decelerating too late for whatever reason, causing the place to be bombarded with a ton of exotic energy prior to the Ark itself impacting.