Nikola Tesla called a spark gap a "disruptive discharge."
A disruption is a random series of events effectively creating change, over time, to what would otherwise be a continuous condition of non-change. To an electrically reactive component, such as: an inductor or a capacitor, this randomization of altering electrically reactive activity is as good as rotating an inductor or turning ON and then turning OFF a capacitant, mechanical switch whose two contacts are changing the distance between each other which effectively changes the threshold at which a spark gap (between these two contacts) will form an arc after preionizing this space between these two contacts.
Since power comes from a prime mover, and a prime mover injects change into an (di-)electric, or a magnetic, field, a spark gap - although seemingly stationary - injects the equivalence of motion, namely: change over time, into a neighboring reactive component (such as: an inductor, or a capacitor) and, thus, solves the riddle of what did Tesla mean when he said that he had invented a "solid-state generator (of no moving parts) which would last for five thousand years and possess no prime mover."
This is Tesla's TriMetal Generator which the Ammann brothers have managed to replicate.