Why does gravel remain static in the Nether?

Question

When I traveled to the Nether, I noticed that there was some gravel which didn't seem to be affected by gravity:

When I destroyed one of those blocks, the blocks surrounding it fell down:

So, why does the gravel "stick"?

Answer 1

This phenomenon can be seen with both gravel and sand in any dimension and occurs when the block is spawned by the terrain generator in a place where it would be expected to fall down but does not recognize that it should fall until it receives a block update. The first block to start falling will then trigger block updates for the blocks it touches causing them to fall and trigger block updates for more blocks, until all the blocks that should fall have.

Answer 2

It is a simple block update glitch. Depending on how good your computer is and/or how far your render distance is, spawning in a new world will cause all floating gravity blocks (like sand and gravel) to fall as long as they are near you. If you go far enough away from your spawn, I can almost guarantee they will need a block update. A block update is simply when a block changes. If a block changes next to the floating sand/gravel (such as placing or mining a block) they will fall. Since the Nether is only generated when you first enter, the gravity blocks will not fall. (A simple random bomb thing is used in this manner, having still, non-updated water next to a grass block with a sheep, then when the sheep eats the grass, BLOCK UPDATE and the water begins to flow, breaking a redstone torch, depowering another torch, setting off some TNT. TL;DR Sheep = boom)