The land acts as a defined border to encapsulate the Belt of Deltora and its gems. It is stated that the gems cannot be destroyed and cannot be taken past Deltora’s borders. The land has a grip on the gems and this grip will fasten when the gems near the border. This results in a perceived effect of the gems and/or Belt of Deltora becoming increasingly hot.
Implications of the theory
There are several implication based on this theory
Implications 1: Burn mechanism
Gems become so hot that they burn through anything conveying them expect for the land of Deltora itself. In that case gems will never go beyond a certain border. It is stated in the Isle of the Dead that there is old magic that bonds the gems, land and dragons . This border where the heat gets too much for every organism that carries the gems/Belt might be a specific place with specific coordinates. However, it is also possible that the effects of the heat depend on the organism. In that case some organisms would be able to take the gems further away from the land until the heat overwhelms them. It is still very likely that the heat gets exponentially intense further away from the border otherwise the gems could be taken pretty far away from Deltora given that an appropriate external surface area or container is used.
Implications 2: Role of Magic
Magic could also not be used to transport the gems beyond the border. If that was possible the Shadow Lord would have done so long ago. Telepathy seems the most reasonable choice for such a venture. Most likely the gems would disperse the heat through the magic force and back to the magic wielder. Consequently the heat would become so intense that the wielder is incapacitated and unable to further use magic on the gems.
Potential unresolved questions
Some questions that have less clear answers based on this theory
What if the gems are dropped at the very border. How can they be retrieved?
The most likely explanation is that the gems are slowly pushed back to Deltora by the land itself. This would be the result of the strong bond between the land, gems and dragons.
What if the gems are thrown beyond the border?
Theoretically speaking, the gems could be launched in the air with an extreme force away from the land. As nothing is carrying the gems they would have nothing to burn through to fall back to the land. In that case it seems possible that the gems could end up much further from Deltora than the border at which they would burn through virtually anything. It is still likely that the bond between the land and the gems would prevent them from going much further than the burning border.