How do back-arc basins form? View Available Hint(s) How do back-arc basins form? Tensional stresses resulting from slab suction stretch this part of the crust, causing it to thin vertically. Compressional forces bend the sedimentary layers in the back-arc region downward, creating a bowl-like depression. Compressional forces make the back-arc region thicker and denser than the volcanic arc. This higher density causes the back-arc region to sink into a basin shape. The back-arc region subsides into a downwarped basin shape from the added weight of addition of sediment from mass wasting events. A mountain range also forms on the side of the back-arc basin opposite of the volcanic arc, creating a lowland in between the two ranges.