The same hotspot in Earth's mantle that feeds Iceland's active volcanoes has been playing a trick on the scientists who are trying to measure how much ice is melting on nearby Greenland.According to a new study in the journal Science Advances, the hotspot softened the mantle rock beneath Greenland in a way that ultimately distorted their calculations for ice loss in the Greenland ice sheet. This caused them to underestimate the melting by about 20 gigatons (20 billion metric tons) per year.