Raised rock slabs or plates of varying thickness, mostly resulting from the buckling of laminae, plates, and slabs. These forms are generally cracked by tectonic activity, although decreases in lithostatic pressure through unloading, or, more rarely, from surficial expansion of plates caused by intense heat. Smaller plates and slabs may be changed in part through freeze-thaw. A-tents are also known as pop-ups, but Twidale and Bourne (2009) PPG 33, 2, restrict this term to those forms developed instantaneously during earthquakes.