How are cracks in rocks at right angles to the surface?

Cracks in rocks at right angles to the surface are typically the result of tensile stresses acting on the rock. These stresses can be caused by factors such as cooling and contraction, unloading and expansion, or tectonic forces. As the rock experiences these stresses, cracks form perpendicular to the direction of the stress, resulting in fractures that are often at right angles to the surface.