Dykes and other vertical bodies can act as aquicludes within bodies of karst rock. These partitions separate isolated bodies of soluble rock called compartments. Speleogenetically each compartment will behave as a small impounded-karst until the partition becomes breached. Breaches through partitions, portals, allow water, air and biota including humans to pass between sections of caves that were originally isolated.
Osborne, R. Armstrong L..
Partitions, compartments and portals: cave development in internally impounded karst masses.
International Journal of Speleology,
Available at: http://scholarcommons.usf.edu/ijs/vol34/iss1/6