A volcanic eruption in Iceland has sent ash across northern Europe. Airlines have stopped or changed the flights across the Atlantic Ocean, leaving hundreds of passengers stuck in airports. Grimsvotn is one of the largest and most active volcanoes in Europe. What makes Grimsvotn different is that it lies under a huge glacier of ice up to 12 metres thick. The hot volcano heats up the ice above it, which then forms a layer  of water between glacier and the volcano, keeping it stable. As the water flows out from under the glacier, the pressure lifts. The lava  from the volcano then comes up to the surface. This is exactly what is happening today. Now airlines have to make changes to their flights so as not to fly through the clouds of volcanic ash. According to KLM, one of Europe's biggest airlines, airplanes cannot go under the cloud or over it. Going through the cloud can result in ash getting stuck in the airplane's engines, causing damage to the plane. The eruption has also caused problems for animals in Iceland. The volcano left ash and sharp, glass-like rocks all over the countryside. Farmers are keeping their animals inside to stop them eating ash-covered grass or the sharp objects. What makes Grimsvotn different from other volcanoes?
It is under the sea. Its lava affects the airlines. It is the largest volcano. It is below ice.