When the Martian ice fields warm up in the spring, geysers of gas and dust burst from the frozen surface, spraying darker material into the air. This material is carried by the wind across the ground, forming patterns that mark the direction of the wind when they erupted.
Much of the ice on the surface of Mars is carbon dioxide ice – dry ice – rather than water ice. This ice thaws (or “sublimates”) directly to a gas when heated, bypassing the liquid stage. This process can cause some explosive outbursts in the polar regions on Mars as these gases escape the subsurface through cracks in the top layers of ice.
Image credit: NASA/JPL/University of Arizona