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.^[1]

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 ^[2]. 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.

References

This post is based on a question of MikaKaimei on the Faith page.

Jasmine was on bad terms with Lief at the time. The Shadow Lord expertly catered to this feeling by showing Lief up in a bad light. He fabricated the idea that Lief had deliberately kept Faith a secret, fueling the already existing distrust between Jasmine and Lief. For Jasmine the problem also became very urgent because of the imminent death that Faith mentioned. Strong feelings often overwhelm all reason especially when latent feelings are amplified (this is just how human psychologically work). For Jasmine these latent feelings were:
the distrust between her and Lief and the hope/longing to save the slaves. As I said before the Shadowlord magnified the distrust. The Shadowlord also heavily intensified the wish to go to the Shadowlands to save the slaves because Jasmine would now be saving her own sister as well (a member of her familly). Psychologically speaking it makes sense. The story also makes quite a lot of sense (although there are subtle signs that could raise suspicion) as I will explain later.

Firstly, the voice came from the Shadowlands and not from somewhere unknown, Jasmine knew this because Faith told her. Faith also explained that she was born in the Shadowlands while her mother and Doom were captives in the Shadowlands. Third, Doom was seperated from Anna after they were brought to the Shadowlands, he had to fight in the arena and escaped at some point. It is unclear when they got seperated. Therefore it is conceiveable that he did not know Faith was born. Jasmine could have gone to him and ask but she probably knew that he did not know about Faith. For example, Doom never mentioned Faith and would have most likely done so if he had known about her. Also, for Jasmine there was no time to lose because of the urgency and Doom and Lief were not in Del at the time. Jasmine was also on the point of leaving the palace and return to the Forests of Silence, as she wanted to be away from the Palace for some time. This all most likely led to her decision to leave as soon as possible (not waiting for Doom to ask him). 

Now it is possible that Anna got pregnant in the Shadowlands. I believe this is extremely unlikely but possible nevertheless. Of course, Anna could have also become pregnant right before or even up to two months before their capture (women can be unaware of pregnancy the first two months). The books strongly hint at this (see Chapter 4 of Cavern of The Fear). Jasmine was 7 at that point and so Faith would be about 10 (Jasmine is 16 in Deltora Quest 1 and 17 in Deltora Quest 2). Their ages (of Faith and Jasmine) make perfect sense.

As for the signs. A sign of supiscion for an objective observer is: Faith never mentions the name Anna she simply refers to her as 'mother'. Same goes for Doom (father) and even Endon (father friend's). This is because the Shadowlord was not familiar with the names at least the name Anna. It is also questionable how Faith would reach the crystal and how Anna knew about the crystal in the first place (according to Faith, Anna urged her to reach the crystal). It is even stated in Cavern of The Fear that Faith used the crystal multiple times (as she falsely claimed that she had already spoken to Lief). They were slaves in the Shadowlands and therefore should never have access to a such a powerful device or even know about its existence. Jasmine should have considered this things but bear in mind that Jasmine did not know what the crystal was when she first used it. She had know clue that it was normally used by the Shadowlord and its servants exclusively. For alls she knew the crystal was not heavily guarded and the slaves could learn about its existence from sloppy, loquacious guards. Jasmine lacking knowledge of the crystal and given her emotional state probably used above reasoning to justify Faith reaching the crystal. The fact that Faith reached the crystal (a powerful device that slaves clearly should not have access too) may have slipped her mind entirely. Also Jasmine focused on signs that catered to her feelings like Faith falsely claiming that Lief had spoken to her and consequently did not tell Jasmine (thus keeping it a secret and intensifying distrust). Therefore it is conceiveable that she ignored other signs of suspicion even though she is normally quite shrewd.

The Pirra system (the land Pirra, the Pirrans, Pirran Pipe) is characterized by magic. To clarify where this question came from, I was wondering whether the magic of the pipe had an enduring effect, at least for a couple of hours. It is stated that the pipe was played in the morning, at noon and in the evening. This led me to theorize that between those specific times, shadows could still penetrate Pirra.

It is stated in Tales of Deltora that ordinary humans could not enter Pirra because 'powerful magic' barred their way. This could be the magic of the pipe but their are numerous reference in Deltora books that the Pirrans could wield magic as well. Without going into further detail, I have come up with a theory of how the pipe and magic worked.

As mentioned before, Pirrans could use their magic (not the pipe) to protect their land from ordinary humans. This was most likely done by some kind of shutting spell, much like the Torans. However, sorcerers were probably able to penetrate this spell and that is why the pipe was played.

It is obvious that while the pipe is played, all evil is suppressed and temporary powerless. I also believe that the Pirran Pipe somehow reinforced the magic of the Pirrans and Pirra itself. This sounds complicated. So, look at it this way: in my opinion their is some kind of connection between the magic, the land Pirra, the Pirran pipe (specifically its music) and the Pirrans. Obviously the Pirran Pipe plays a pivotal role in this system. However since the origin of the Pipe is unknown, it could be that the Pirran's had created the pipe themselves. Perhaps putting a vast amount of their personal magic in this object. Therefore it is hard to say which factor is specifically paramount with regard to the magic of the Pirra system.

This is all very theoretical but I hope this sparks some sort of discussion.