Alanna Gladstone, a 40-year-old film editor, had landed in Portugal’s capital, Lisbon, on a flight from New York hours before the outage. She checked into her Airbnb and took a nap; by the time she woke up, the technology that the country takes for granted had gone dark.

Power is almost fully restored in Spain and Portugal a day after a major blackout. But many questions remained about what caused one of Europe’s most severe blackouts. Spanish electricity operator Red Eléctrica said that more than 99% of energy demand had been restored by 7 a.

That conclusion has been supported by the operator of Spain’s national grid, Red Eléctrica, which has located where outages began on Monday. Two separate incidents of power outages led to instability in the grid leading to a “breakdown in interconnections with France,” leaving the Iberian grid isolated.