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A valley step (german: Talstufe or ''Talschwelle'') is a prominent change in the longitudinal slope of a 
Such basin forms, with an abrupt beginning, often appear as marked steps, which may separate the flatter sections of the valley. Large steps were often formed where the erosion forces of the glacier that once filled the valley were suddenly increased, for instance, when large glaciers merged. They are then referred to as confluence steps. Similar steps are formed when moving sheets of ice merge into glacial streams, which can intensify surface scouring of the rocks ('' exaration''). If these valley steps are close to the upper end of a valley, they are also referred to as a valley head or trough head; otherwise, they subdivide the course of the valley into often very distinct individual valley sections, with gentler and broader hollows alternating, chain-like, with and narrow intermediate valleys or gorges. In the interior of mountain ranges, these valleys dictate the structure of settlements, and may result in isolated communities that are difficult to access.
Side valleys, which rise high above the valley floor in a trough valley, also join the main valley at a marked step in the terrain, the stream descending over the valley wall of the main valley. This is referred to as a
Stefan Rasemann: ''Geomorphometrische Struktur eines mesoskaligen alpinen Geosystems. Kapitel 2.3: Reliefformen des Hochgebirges.''
Dissertation Rheinische Friedrich–Wilhelms–Universität Bonn, 2003, p. 77 (pdf data; 3,95 MB) {{Glaciers Glacial landforms
A valley step (german: Talstufe or ''Talschwelle'') is a prominent change in the longitudinal slope of a valley
A valley is an elongated low area often running between hills or mountains, which will typically contain a river or stream running from one end to the other. Most valleys are formed by erosion of the land surface by rivers or streams ove ...
, mainly in trough valleys formed by glacier
A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires distinguishing features, such as ...
s.
Typically, a valley formed by glaciers has a series of basins with intervening steps formed by the locally varying erosion
Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is dis ...
depths of valley glaciers. After the ice melts, this initially becomes a sequence of lakes with intermediate rapids or waterfall
A waterfall is a point in a river or stream where water flows over a vertical drop or a series of steep drops. Waterfalls also occur where meltwater drops over the edge of a tabular iceberg or ice shelf.
Waterfalls can be formed in severa ...
s. The transportation of gravels, erosion and sedimentation
Sedimentation is the deposition of sediments. It takes place when particles in suspension settle out of the fluid in which they are entrained and come to rest against a barrier. This is due to their motion through the fluid in response to the ...
processes in the streams lead to the formation of sequences of flat valley bottoms and gorges.
Such basin forms, with an abrupt beginning, often appear as marked steps, which may separate the flatter sections of the valley. Large steps were often formed where the erosion forces of the glacier that once filled the valley were suddenly increased, for instance, when large glaciers merged. They are then referred to as confluence steps. Similar steps are formed when moving sheets of ice merge into glacial streams, which can intensify surface scouring of the rocks ('' exaration''). If these valley steps are close to the upper end of a valley, they are also referred to as a valley head or trough head; otherwise, they subdivide the course of the valley into often very distinct individual valley sections, with gentler and broader hollows alternating, chain-like, with and narrow intermediate valleys or gorges. In the interior of mountain ranges, these valleys dictate the structure of settlements, and may result in isolated communities that are difficult to access.
Side valleys, which rise high above the valley floor in a trough valley, also join the main valley at a marked step in the terrain, the stream descending over the valley wall of the main valley. This is referred to as a hanging valley
A valley is an elongated low area often running between hills or mountains, which will typically contain a river or stream running from one end to the other. Most valleys are formed by erosion of the land surface by rivers or streams over ...
, and the step is seen geomorphologically as the valley wall of the main valley, so it is not a valley stage in the narrow sense described above. Borderline cases are, for example, cirques, which typically form basins in which there is often a lake which either drains periodically over the valley threshold or seeps entirely into the subsoil.
Valley steps may also have existed before the glaciation of mountainous terrain or may be formed without the aid of glacial processes, typically due to varying erosion resistance of the rock, or due to active faults. These are then only accentuated by glacial and / or fluvial erosion
In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluviogl ...
. Examples of this are the ''tobel'' valleys in sandstones or, often only underground, draining troughs in the limestone, where the valley step is formed by downward erosion.
Valleys that were formed without the aid of glaciers are often found in the area of cuesta
A cuesta (from Spanish ''cuesta'' "slope") is a hill or ridge with a gentle slope on one side, and a steep slope on the other. In geology the term is more specifically applied to a ridge where a harder sedimentary rock overlies a softer laye ...
s. These can then also create a very characteristic structure of a river course in its lower reaches on the broad plains and form a significant obstacle to navigation
Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: land navigation, ...
.
Literature
Stefan Rasemann: ''Geomorphometrische Struktur eines mesoskaligen alpinen Geosystems. Kapitel 2.3: Reliefformen des Hochgebirges.''
Dissertation Rheinische Friedrich–Wilhelms–Universität Bonn, 2003, p. 77 (pdf data; 3,95 MB) {{Glaciers Glacial landforms