1. Fjord Formation in Norway Holtedahl, 1967
Lauren Thompson

2. What is a fjord?
Deep glaciated valleys that have been eroded adjacent to coastlines and are now occupied by marine waters following deglaciation and eustatic sea level rise

3. Previous Fjord Formation Theory
JW Gregory (1913): Fjords are of tectonic origin, influence of glaciers negligible
Pointed to connection between Tertiary dislocations and development of fjords
Pattern of pre-glacial valleys is coincident with tectonic lines (axes of folds, joints, and contacts of geological formations)
Shows fluvial erosion and glacial erosion tectonically controlled
-He pointed to the causal connection between the Tertiary dislocations and the development of fjords, and as late as in 1927 described Hebridean fjords as being due to the "rending of the crust during and after the Alpine earth movements and to the subsequent gaping of the fissures during the Pliocene uplift of the British area”
-The presence of well developed, typical fjords along the westcoast of Norway is a natural consequence of the oblique Tertiary uplift of the Norwegian landmass. The rejuvenation caused increased fluvial erosion, especially active on the slopes facing the ocean, this resulting in more or less deeply cut preglacial valleys.

4. Tectonics in Norway
Seismic investigations off west coast and south coast of Norway conducted to look at young Cenozoic dislocations on continental shelf
Sediment with primary wave velocity of 2 km/s and thickness of 800 m overlying sediment with velocity of 3.25 km/s and thickness of m
Strong indication of fault line or fault zone running offshore and parallel to coast
Does not prove that fjords form primarily from tectonics

5. Glacial Influence on Fjord Formation
Now accepted that glaciers have major significance on formation of fjords
Fluvial erosion has also been important
Focus one two major Norwegian fjords

6. Hardangerfjord and Sognefjord

7. Similarities Extend far into the country Both deep and narrow
Surrounded by high mountains inland and low land near the coast
Extensive tributary fjords found in inner parts
Extend km
Sognefjord has a max depth of 1308 m and Hardangerfjord about 900 m
Average width of 5 km

8. Differences Hardangerfjord
Direction of fjord coincides with main structures that run northeast and southwest
Oriented along boundary between Precambrian complex to southeast and Cambro-Silurian schistose rocks to northwest
Close connection with fractures
The direction of the Hardangerfjord coincides to a great extent with the main Caledonian structures which run north-east and south-west, and the fjord has a situation very much along the boundary between the Precambrian complex to the south-east and the Cambro-Silurian schistose rocks to the north-west. No doubt its situation on the eastern flank of the downfolded Precambrian basement is of importance.

10. Differences Sognefjord Cuts through parts of northwestern gneiss area
Crosses over fold trough to the east
Also a relationship between fracture systems and trend of main fjord
Fracture systems have guided erosion
The Sognefjord cuts through parts of the north-western gneiss area with south-west and north-east structures, mainly of Caledonian origin, and then penetrates the Caledonian fold trough in the east. There is no obvious relationship between the east-west trend of the Sognefjord and the fold pattern, with the exception of some of the branches in the inner parts of the main fjord. There is, however, as in the Hardangerfjord, a relationship between fracture systems and the trend of the main fjord and its branches, and these fracture systems have played an important role in guiding erosion. A very marked north-south fracture pattern is present at the mouth of the fjord, being especially well developed in the Devonian rock complex, and a similar northsouth trend is also characteristic in the outer part of the Hardangerfjord.

13. Longitudinal Profile: Sognefjord
Increases evenly in depth to the west
Passes gradually into a central basin with depths of m
Floor rises rapidly
Sinks gently with a threshold depth of 150 m

15. Longitudinal Profile: Hardangerfjord
Several basins; innermost is deepest
Basins further out have floors situated at decreasing depths
Basins separated by thresholds
Irregularity indicates rocky nature

17. Thresholds
Thresholds at mouths of fjords: one of strongest indicators of glacial origin
Location of thresholds related to sounds, valleys, and lowland
Locations where ice able to spread out, meaning it had a less erosive effect
Explain differences between longitudinal profiles
Sognefjord: ice constricted to about 30 km from coast
Hardangerfjord: connection between location of thresholds and location of sounds
Sognefjord: Ice constricted to narrow channel in homogenous gneissic rocks to an area 30 km from the coast where spreading was suddenly possible through sounds and valleys
Hardangerfjord: more varied geological conditions which cause variation in the width of the fjord
There is a connection between the location of thresholds and location of sounds which have acted as “escape routes” for main-fjord glaciers. Threshold at a very narrow part further inland can be attributed to the widening of the fjord basin

18. Glacial Erosion Conclusion
Present depth conditions of fjords a result of glacial erosion
Influenced by thickness of glaciers
Greatest in inner parts where confluence took place
Least in outer parts where diffluence occurred

19. Subglacial Fluvial Erosion
Subglacially flowing water has significantly contributed to erosion
Often neglected
Evidence: glaciofluival material found in form of silts and clays, or coarser materials as eskers and outwash accumulations
Subglacial streams or possibly water-sheet drainage under hydrostatic pressure

20. Fossli Area of Hardangerfjord
From head of fjord, valley continues south as lake basin
Mabodal valley branches off towards east as v-shaped valley with steep walls
Terminates in a vertical valley head
River dashes down in single fall
Top of cliff, river continues in broad, open valley
From the head of the Hardangerfjord at Eidfjord, the valley continues southwards as a lake basin. South of the lake, the Mabodal valley branches off towards the east as a winding, open v-shaped valley, whose inner part narrows to a gorge with very steep walls, which terminate in a vertical valley head 235 m high. From the southern wall the river Bjoreia dashes down in a single fall of 147 m. At the top of the cliff the river continues in a broad, open and shallow valley with gentle slopes

21. Contribution of Glacial Meltwater
Subglacial fluvial erosion very important in formation of Mabodal valley
“Dry” canyon evidence for this
Canyon incised m into rocky surface
Giant potholes m high
Subglacial fluvial erosion most likely explanation
Current river gorge incised in a surface with a dip perpendicular to trend  superimposed
Superimposed: having a course not adjusted to the structure of the rocks presently undergoing erosion but determined by a prior erosion cycle
-The “dry” canyon is a tributary to the present river gorge and joins it at a point where the Bjoreia river cuts through the sloping rocky hillside just above main waterfall
-Incised m into the rocky surface, with vertical walls, continues in the south eastern direction where it ends in a few steps with steep valley ends
-As a result of weathering, canyon walls rough and bottom covered in talus
At some points, the wall is fresh and polished and giant potholes are seen m high
Clearly eroded by running water because the position of the canyon and potholes on the divide cannot be explained by subaerial streams
Another piece of evidence is the fact that the present river gorge between the junction of the dry canyon and the main waterfall is incised in a sloping surface, with a dip perpendicular to its trend

22. Erosion of Glacial Meltwater vs Current River
Subglacial meltwater was extremely powerful agent of erosion
Eroding effect of present river since ice left has been very small
The subglacially formed tributary canyon and present river meet at almost the same level
River would have lowered bed by actively eroding away material, leaving dry tributary canyon hanging
So we know that the current river has not contributed much to eroding the canyon

23. Outwash
Subglacial meltwater streams are apparent due to the large accumulations of glaciofluvial material that has accumulated as an outwash delta at the head of the fjord
Present as raised terraces with maximum thicknesses of 100 m

24. Flamsdal Area Flam valley: tributary to Sognefjord
Sharply cuts into a mountainous area with heights of m
Ends abruptly in steep wall
Cirque-like valley head
Step-like longitudinal profile
U-formed shape
Canyons with potholes common
The Flam valley is a fjord-valley that sharply cuts into a mountainous area with heights of m and ends abruptly in a steep wall
It has a cirque like valley head, step-like longitudinal profile and U-formed shape, which all point to glacial erosion
Canyons are common: usually narrow and fringed with potholes

25. Flam Valley Major canyon forming present river channel
Present river runs in very narrow gorge
Position not in deepest part of valley, but on sloping side --> superimposed
There is a system of canyons, with a major canyon now forming the present river channel, and tributary canyons, which on the whole do not carry streams at the present time. At Berekvam the present river runs in a very narrow gorge, 30 m deep and less than 2 m broad at its narrowest part, and has a position, not in the deepest part of the valley, but on the sloping side, suggesting that it is superimposed

26. Longitudinal Profile Step-like profile
Stoss and lee topography  ice movement downstream
Steps connected to vertical fractures
Semicylindrical giant potholes
Glacial meltwater moved between vertical walls and ice, forming channel
The valley floor has a step-like longitudinal profile
Stoss and lee topography indicates ice movement downstream in a northerly direction
The steps are closely connected to the occurrence of vertical fractures and have steep and sometimes overhanging walls and show surfaces with fluvial erosional forms, like well-developed giant potholes
Glacial meltwater must have moved in channels between vertical rocky walls and ice
These channels have formed a system, some with direction towards the central part of the valley, others along the steep side walls

27. Furuberget Series of fluvial erosional features present
Furuberget: a riegel with a step on its northern side leading down to broad and flat lower part of the Flam valley
Current river runs in narrow gorge through riegel
Riegel: a low transverse rock ridge on the floor of a glaciated valley commonly situated at the down- valley end of the flat
Potholes common inn these canyons, and most show glacial striae
Glacial meltwater had a considerable erosional effect on the valley floor
The glacial fluvial erosion in the Flam valley is believed to be caused by a system of subglacial streams probably under hydrostatic pressure

28. Evidence for Glacial Fluvial Erosion
Remains of canyons, only one wall exists
Giant potholes showing striations
Giant potholes at fjord-head close to present sea level
Narrow channels  stream concentrated and ice-pressure present against rocky wall, indicating thick glacier
Glacial fluvial erosion in the Flam valley is believed to be caused by a system of subglacial streams, most likely under hydrostatic pressure
There are remains of canyons of which only one wall exists, the other having been formed by ice
Giant potholes show striations and are at fjord head close to present sea level
Narrow channels mean the stream must have been concentrated and the ice-pressure must have been present against rocky wall, indicating a thick glacier

29. Conclusion Depth of fjords depends on thickness of the glacier
Deepest in inner parts of fjord where confluence takes place
Subglacial fluvial erosion by meltwater under high hydrostatic pressure was a large contributor to formation of fjords and fjord valleys
Still unknown to what degree