Not much has taken root in the hull of the longboat. After a brief exanimation of the bodies, you think the ice crab has been feeding on them when better prey was unavailable. If it was using the longboat as a home and hunting base, its aura would have kept scavengers away and kept the meat fresh.
The search
The group sets out in the spiral pattern suggested. The portion of the lakebed that is shallower has very little in the way of interesting features and aside from a few schools of fish, your group encounters nothing. The spiral pattern then brings you to where the lakebed dips down deeper. The lake bed down here is more jagged than the smooth bed above. Looking back towards the rise, the group notices a cave opening at the base. As they are taking that in, a bright flash of yellow light comes from the opposite direction. The direction of the flash is easy to pinpoint and it is roughly in the same direction you were going to travel next in your spiral. Whatever caused it though is not yet visible from here.