You cause a 1-foot length of subterranean tunnel to constrict, "locking" it against others who might wish to traverse its length. This spell only affects naturally occurring tunnels or worked tunnels that are surrounded on all sides by unworked, natural, subterranean earth. You can affect any tunnel whose diameter does not exceed 10 feet. A square-sided or rough tunnel can also be affected, as long as its diameter at the point where the spell is cast does not exceed 10 feet. Identifying a tunnel sealed with earth lock (as opposed to a tunnel that just ends) requires a DC 20 Search check.