Like much of the Mournland’s bizarre terrain, the Glass Plateau remains in flux. The huge upwelling of land reshaped much of southern Cyre around the city of Making, triggering earthquakes for weeks following the Day of Mourning. In 997 YK the tremors began again, and now lava slowly oozes from cracks along the western face of the plateau, like blood seeping from a poorly tended scab. Already inhospitable, the plateau is now almost completely inaccessible on foot from the west. The magma cools into new masses of pale gray glass, and the plateau is slowly growing.
Source: Five Nations
The Glass Plateau is mostly smooth and flat, though jagged spikes and spires jut up from the ground in seemingly random places. The central portion of the highland plain is obsidian, and bursts of fiery light can sometimes be seen in its dark depths. Toward the edges of the plateau, the glass becomes lighter in color and more transparent, appearing almost pale white along the jagged cliffs at the edge. Nothing grows on the plain of glass, and few creatures haunt its jagged peaks and flat expanse.
Source: Rising from the Last War