Electricity is pulsing through Spain and Portugal again after a massive outage knocked out power in both countries on Monday. So too are questions.

Officials in Spain and Portugal are racing to restore electricity after a huge power outage that grounded flights, paralyzed metro systems, disrupted mobile communications and shut down ATMs, upending the lives of tens of millions of people and turning airports and train stations into campgrounds for stranded travelers

The countries’ top officials were trying to determine the cause of an outage that left tens of millions of people across the Iberian Peninsula without power.