A volcanic eruption(喷发) 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 the 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(冰川) of ice up to 12 meters thick. The hot volcano heats up the ice above it, which then forms a layer(层) of water between the glacier and the volcano. This layer of water puts pressure on the volcano, keeping it stable（稳定）. As the water flo