So the island seems to have random tides, the tides go in and out randomly. The Island can move, now, we've seen it move through time. Let's say it can also move through space, like, move across the sea (Like a boat).
We all know the island has pockes of electro magnetic energy.
But what if the island isn't a normal island, what if it is a floating island (Like a boat). So what if it is the electro magnetic energy that is repelling against the Earth's magnetic fields, which is what is keeping it afloat.
So in the Afterlife, we see that the Island is underwater. And in the End, we knew MiB wanted to destroy the island by putting out the light. What if by putting out the light, he is turning off the electro magnetism (so there is no magnetic repelling), which makes it sink. So that is why it was underwater in the Afterlife, cos there was no light.
What if the Earthquakes that were on the island were not caused by the earth itself, but because it is floating, it would need something else to shake it. What if the earthquakes are the pockets of electro magnetism repelling with each other, thus, causing the ground to shake. And for the the volcano, what if two pockets of energy are attracted to each other, causing land to be compressed tightly, thus causing some volcanoes, cos the land has gotta go somewhere.
Sorry if this has been theorised before, but I have never heard anyone say this before, so I wanted to share it :)