As volcanic ash rains down over northern Europe, the World Health Organization is warning Europeans to stay indoors. It started Wednesday, when a volcano beneath the Eyjafjallajokull glacier in Iceland erupted, spewing up hot gases and ice chunks the size of houses. Those living nearby were evacuated because of flash floods. WHO spokesperson David Epstein says the resulting ash cloud is potentially dangerous for people, because if inhaled, it could cause respiratory problems.
On Friday, about 28,000 flights were cancelled in Europe—more than twice as many as were cancelled on Thursday. The International Air Transport Association says those cancellations are costing a whopping $200 million a day. Some flights may resume on Saturday morning.