Tesserae exhibit the effects of eons of compression and tensional deformation. Grabens are indicative of tensional forces and crustal stretching. There are two hypotheses in the mechanism of the trench formation&colon; tensional and compressional. Around 1989, a theory of formation by tensional fracturing was proposed. They develop in response to tensional tectonics due to rifting of an existing island arc. Once tensional forces cease, subsidence continues due to cooling. However, no unambiguous evidence for tensional faults occurs in the Bach quadrangle. Lava flooding and thermal or tensional stress fractures are two causes of graben formation. A spreading apart of the surface causes tensional forces. By convention the compressional quadrants are colour-filled and the tensional left white. Horst and graben structures indicate tensional forces and crustal stretching. When oceanic plates diverge, tensional stress causes fractures to occur in the lithosphere. In the Western Cordillera however, tensional faulting facilitated the occurrence of voluminous volcanism. Tensional activity has been dominant along the down-dip edge along the 1942 rupture zone. The tensional load of drawing the train (draft force) is carried by the coupling system.