Arkham Horror LCG: In the Clutches of Chaos Mythos Pack - Rules of Play says:

In In the Clutches of Chaos, doom does not accrue at the usual rate. Instead, breaches are made at various locations, marked by resource tokens. When enough breaches have been made a single location, an incursion occurs. An incursion adds doom to its location and causes the breaches to spread, opening rifts in reality at connecting locations. Your goal is to prevent incursions by removing the breaches that cause them, but this can only be done by activating the action abilities on each location. If you do not maintain control over the breaches, you may soon find yourself overwhelmed with Arkham falling into madness. You cannot allow that to happen!