On Thursday a volcanic eruption in Iceland melted a glacier causing severe floods and spread ash across northern Europe bringing chaos to air travel. About 800 people have been forced to evacuate their homes, and airports in 23 European countries have grounded more than 63,000 flights stranding thousands of travelers. Scientists warn that if these eruptions last for an extended period of time, there is a risk they could melt other glaciers that now cap the nearby Katla volcano, allowing it to blow its top and potentially pump enough ash into the atmosphere to lower temperatures worldwide.