system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does a landfill work? Does it compact and compact or does it just keep piling up until its eventually taller than the buildings around it? Is it ever at risk of bursting or damaging anything around it?
gpt
Modern sanitary/municipal landfills (at least in most of the developed world) are highly engineered structures.  Holes are dug on flat ground or scraped out of the side of a hill, and "cells" are filled with highly compacted waste, ostensibly picked through to remove the worst environmental offenders (things like car batteries, drums of industrial waste, etc.).  Each cell is lined with special barriers designed to last for decades that allow bacteria to thrive and break down most of the waste, while at the same time preventing contact with groundwater and channeling runoff (from rain percolating through the ground) into a collection system for treatment.  Cells are sealed and buried as they fill up, and new ones are opened.  This continues until the landfill is filled, then another barrier is placed on top and the whole thing is covered by a layer of soil.  Sometimes the landfill will be built up higher than the original land, sometimes it's at the same height, but it's not a good idea to leave it as a depression - then water will fill the depression, and a lake over a landfill is a bad idea.  Usually a system to vent gasses produced during decomposition is installed as well - they're largely passive venting systems (think pipes sticking up from the ground that allow lighter than air gasses to vent upwards).  Some systems catch the vented gas and burn it to generate (a small amount) of power.  Properly designed and properly maintained, there's no significant risk of bursting or collapse.