A geological trench is formed by a block of crust that is bounded by faults and has sunk compared to its surroundings. Trenches occur as a result of tectonic expansion in weak zones of the earth's crust , always together with tectonic clumps (raised clods of earth).
Sometimes the sedimentary rocks that fill the trenches are harder than the rocks of the adjacent clumps. It can happen that, contrary to expectations, the ditches are carved out as prominent elevations by the erosion , while the clumps form the morphological valleys ( relief reversal ).
- Great African trench
- Upper Rhine Graben