Research on the Earth's glaciers found that when the volcanoes under the glaciers start to erupt, they will quickly produce steam streams, explosively penetrate the ice layer, release ash into the upper air, and produce zeolite, sulfide and clay. Recently, people have discovered that these minerals have also been detected on some round flat-topped hills on the surface of Mars, and they are widely and abundantly present. 
The three types of zeolite, sulfide and clay are unique substances that are only produced after volcanic activity under glaciers.
 it is speculated that the early Mars was covered with ice sheets, where there had been more volcanic activities.