glacial valley

On the origins of fjörds (Hubbard 1901)

On the origins of fjörds  (Holtedahl, 1967)

Google Earth image of the fjörd and glacial valley network between Mull and Skye

 

Streetmap view of Loch Sunart, the long E-W trending fjörd north of Mull

Streetmap view of skerries and rock bars at the mouth of Loch Sundart

 

firth of forth

 

Google Earth image of the Sognefjörd, western Norway

 

 

Model long profile of a fjörd. Note the great exaggeration of the height relative to the distance.

 

 

 

 

 

 

 

 

USGS photo of the Hubbard Glacier discharging into Russell Fiord and Disenchantment Bay, Alaska-Yukon

 

 

Fjörd, fjord or fiord

Definition: a glacially deepened valley that has been inundated by a post-glacial rise in sea level

Fjörds are some of the most dramatic landforms of glacial erosion on the surface of the Earth. The deepest fjörds occur where mountain ranges rise abruptly from the coast. A maritime location ensured high rates of snowfall during the cold phases of the Ice Age and consequent high rates of  discharge in coastal glaciers. The relatively warm temperatures and steep gradients allowed the ice to slide rapidly. Ice discharge was channelled into pre-existing and often steep valley systems. This combination of factors led to extraordinary glacial erosion, locally extending hundreds of metres below present sea level.

Like glacial troughs, fjörds have a distinctive three-part long profile.  The upper section of the fjörd falls steeply from shallower valleys which drain interior plateaux.  This trough head may form an abrupt wall at the head of the fjörd.  Typically, the middle section of the fjörd is narrow and steep-sided but often extraordinarily deep. The outer section of the fjörd is often much shallower and more open, with the shores of the fjörd formed by low, ice-moulded rock platforms.  Low islands or skerries may form barriers at the mouth of the fjörd

These changes in valley form are a direct reflection of glacier dynamics. The fjörd system is fed by a series of tributary glaciers from plateau ice caps. The confluence of these glaciers marks the point of accelerating flow of thick and highly erosive ice.  The confluence therefore marks the onset of extreme glacial erosion in the valley.  The maximum erosion takes place in the middle section of the valley where the ice discharge is highest.  Erosion here can extend well below current sea level and allow the formation of one or more deep rock basins.  In the outer fjörd the mountains retreat from the fjörd sides, allowing the ice to flow outwards, slow down and thin, thereby reducing erosion.