he used a log as a raft.
I don't thinks so. That way he would have to leave his parents behind. I don't think any log could hold the big sharpteeth and it would be far fetched for them to create something like a raft. Also, we mustn't forget about the swimming sharptooth who prevented the escape of Littlefoot and the others via log.
I suppose there are other possible explanations for how Chomper could leafe the island. Further earthquakes could cause the water to recede (perhaps temporary only before a Tsunami strikes). Sometimes tide patterns can be altered by various circumstances.
However, I think the very idea of getting Chomper from that island could make for a very good, but very difficult story. Imagine this, sharpteeth "food" is running out on the island (Chomper said there wasn't much and with the destruction of the land path there is little chance for a constant supply) and Chomper sends word (via a captured flyer he spares under the condition that the flyer will deliver his message) to Littlefoot and ther others. Now that would be a tough story. On the one hand Littlefoot and his friends couldn't just leave Chomper to his fate on the other hand helping him and his parents would inevitably mean the death of other leafeaters. Could Littlefoot possibly take the responsibility for other dinosaurs sharing his respectively his mother's fate in the first movie? It would be quite a dilema.
