Valleuse
Encyclopedia
In the Pays de Caux
, Normandy
, France
a valleuse is a depression in the land surface of the plateau
which permits access to the sea
. On the rest of this coast
, that access is prevented by the height of the chalk
cliff
s.
There are three sorts:
s developed while the water table
was much higher in the chalk than it now is so that a stream
flowed in each of these truncated valleys. It is likely that most of the formation of the valleys in the plateau occurred during cold periods. This region was never covered by an ice cap
but it has been only about 230 kilometres from one. In those circumstances, the conditions will have been tundra
, sometimes verging on periglacial
. When the frozen ground thawed in the spring
, the surface soil was very wet because the melted snow and ground water could not sink into the permafrost
. Any appreciable slope on the surface will have induced slumping and erosion but we have a plateau so the slopes were not originally great.
During the glacial periods, the sea level was low enough to have emptied the English Channel
to the north of the Pays de Caux. The truncated valleys in the chalk, represent the headwaters of streams flowing down to what is now the bottom of the sea. During the interglacial
s the sea eroded the coast and steepened the slope down which they flowed but they will have required ever wetter conditions to keep the water table in the chalk sufficiently high to make the streams flow. In the end, the sea cut the cliff back quicker than the streams cut the valleys downward.
Pays de Caux
The Pays de Caux is an area in Normandy occupying the greater part of the French département of Seine Maritime in Haute-Normandie. It is a chalk plateau to the north of the Seine Estuary and extending to the cliffs on the English Channel coast - its coastline is known as the Côte d'Albâtre...
, Normandy
Normandy
Normandy is a geographical region corresponding to the former Duchy of Normandy. It is in France.The continental territory covers 30,627 km² and forms the preponderant part of Normandy and roughly 5% of the territory of France. It is divided for administrative purposes into two régions:...
, France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
a valleuse is a depression in the land surface of the plateau
Plateau
In geology and earth science, a plateau , also called a high plain or tableland, is an area of highland, usually consisting of relatively flat terrain. A highly eroded plateau is called a dissected plateau...
which permits access to the sea
Sea
A sea generally refers to a large body of salt water, but the term is used in other contexts as well. Most commonly, it means a large expanse of saline water connected with an ocean, and is commonly used as a synonym for ocean...
. On the rest of this coast
Coast
A coastline or seashore is the area where land meets the sea or ocean. A precise line that can be called a coastline cannot be determined due to the dynamic nature of tides. The term "coastal zone" can be used instead, which is a spatial zone where interaction of the sea and land processes occurs...
, that access is prevented by the height of the chalk
Chalk
Chalk is a soft, white, porous sedimentary rock, a form of limestone composed of the mineral calcite. Calcite is calcium carbonate or CaCO3. It forms under reasonably deep marine conditions from the gradual accumulation of minute calcite plates shed from micro-organisms called coccolithophores....
cliff
Cliff
In geography and geology, a cliff is a significant vertical, or near vertical, rock exposure. Cliffs are formed as erosion landforms due to the processes of erosion and weathering that produce them. Cliffs are common on coasts, in mountainous areas, escarpments and along rivers. Cliffs are usually...
s.
There are three sorts:
- living valleuses: natural depressions as at FécampFécampFécamp is a commune in the Seine-Maritime department in the Haute-Normandie region in northern France.-Geography:Fécamp is situated in the valley of the river Valmont, at the heart of the Pays de Caux, on the Albaster Coast...
, YportYportYport is a commune in the Seine-Maritime department in the Haute-Normandie region in northern France. The residents are known as Yportais or Yportaises.-Location:...
and ÉtretatÉtretatÉtretat is a commune in the Seine-Maritime department in the Haute-Normandie region in northern France. It is a tourist and farming town situated c. 32 km northeast of Le Havre, at the junction of the D940, D11 and D139 roads. It's located on the coast of the Pays de Caux area.-The...
. - dead valleuses: to obtain the final access to the beachBeachA beach is a geological landform along the shoreline of an ocean, sea, lake or river. It usually consists of loose particles which are often composed of rock, such as sand, gravel, shingle, pebbles or cobblestones...
it is necessary to set up a stairwayStairwayStairway, staircase, stairwell, flight of stairs, or simply stairs are names for a construction designed to bridge a large vertical distance by dividing it into smaller vertical distances, called steps...
. - perched valleuses: simple depressions in the plateau surface which do not descend far enough to permit access to the beach. Elsewhere, it might be called a hanging valley though it is formed, not by a glacier but by maritime erosionErosionErosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
.
Origins
The word is peculiar to the Pays de Caux but the feature is not, though it shows itself particularly well here. The valleyValley
In geology, a valley or dale is a depression with predominant extent in one direction. A very deep river valley may be called a canyon or gorge.The terms U-shaped and V-shaped are descriptive terms of geography to characterize the form of valleys...
s developed while the water table
Water table
The water table is the level at which the submarine pressure is far from atmospheric pressure. It may be conveniently visualized as the 'surface' of the subsurface materials that are saturated with groundwater in a given vicinity. However, saturated conditions may extend above the water table as...
was much higher in the chalk than it now is so that a stream
Stream
A stream is a body of water with a current, confined within a bed and stream banks. Depending on its locale or certain characteristics, a stream may be referred to as a branch, brook, beck, burn, creek, "crick", gill , kill, lick, rill, river, syke, bayou, rivulet, streamage, wash, run or...
flowed in each of these truncated valleys. It is likely that most of the formation of the valleys in the plateau occurred during cold periods. This region was never covered by an ice cap
Ice cap
An ice cap is an ice mass that covers less than 50 000 km² of land area . Masses of ice covering more than 50 000 km² are termed an ice sheet....
but it has been only about 230 kilometres from one. In those circumstances, the conditions will have been tundra
Tundra
In physical geography, tundra is a biome where the tree growth is hindered by low temperatures and short growing seasons. The term tundra comes through Russian тундра from the Kildin Sami word tūndâr "uplands," "treeless mountain tract." There are three types of tundra: Arctic tundra, alpine...
, sometimes verging on periglacial
Periglacial
Periglacial is an adjective originally referring to places in the edges of glacial areas, but it has later been widely used in geomorphology to describe any place where geomorphic processes related to freezing of water occur...
. When the frozen ground thawed in the spring
Spring (season)
Spring is one of the four temperate seasons, the transition period between winter and summer. Spring and "springtime" refer to the season, and broadly to ideas of rebirth, renewal and regrowth. The specific definition of the exact timing of "spring" varies according to local climate, cultures and...
, the surface soil was very wet because the melted snow and ground water could not sink into the permafrost
Permafrost
In geology, permafrost, cryotic soil or permafrost soil is soil at or below the freezing point of water for two or more years. Ice is not always present, as may be in the case of nonporous bedrock, but it frequently occurs and it may be in amounts exceeding the potential hydraulic saturation of...
. Any appreciable slope on the surface will have induced slumping and erosion but we have a plateau so the slopes were not originally great.
During the glacial periods, the sea level was low enough to have emptied the English Channel
English Channel
The English Channel , often referred to simply as the Channel, is an arm of the Atlantic Ocean that separates southern England from northern France, and joins the North Sea to the Atlantic. It is about long and varies in width from at its widest to in the Strait of Dover...
to the north of the Pays de Caux. The truncated valleys in the chalk, represent the headwaters of streams flowing down to what is now the bottom of the sea. During the interglacial
Interglacial
An Interglacial period is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age...
s the sea eroded the coast and steepened the slope down which they flowed but they will have required ever wetter conditions to keep the water table in the chalk sufficiently high to make the streams flow. In the end, the sea cut the cliff back quicker than the streams cut the valleys downward.