The type of rock and how it's structured affects how glaciers wear it down. In Svalbard, researchers studied metamorphic rocks to see how they get worn by glaciers. They found that on schist, glaciers wear down the rock more when they move in the same direction as the rock's layers. On marble, the rock gets worn more evenly. No matter the type of rock, glaciers wear it down more when the rock's layers are perpendicular to the glacier's movement. The way the rock is naturally formed has a big impact on how glaciers shape it and where holes form underneath the ice.