Minecraft wiki entry for Cave, associated text: An entrance to an aquifer from land.
An aquifer boundary, creating an underground lake.
An aquifer meets an ocean.
Magma blocks on the floor of an aquifer, creating bubble columns.
A tiny aquifer, made up of six water sources.
A large aquifer with narrow pillars.
The differing water levels of several aquifers.
An aquifer below Y=0.
A water and a lava aquifer that generated next to each other.
Partially-flooded canyon cave.