Bottomless pits are deep, seemingly bottomless holes in the ground. They are often found in areas of geological activity, such as volcanoes or areas of tectonic plate movement. The term 'bottomless pits' can refer to three different types of geological features: abysms (6 letters), CHASMS (6 letters), and ABYSSES (7 letters). Abysms are the deepest of the three, and are usually formed by the collapse of a large cavern. CHASMS are typically formed by erosion, and are usually much shallower than abysms. ABYSSES are the shallowest of the three, and are usually formed by the collapse of a surface layer.