Some
fjords are very deep, well over 1,000 m. Sognefjord in western Norway contains
several basins with almost flat floors, separated by rocky sills. The deepest
section of the fjord is 1,300 m. The floor rises near the mouth to form
a sill with a depth of about 100 m. The bottom of the fjord has a layer
of drift up to 300 m thick. The fjord is 200 km long. As much as 2,000
km3
of rock is thought to have been excavated from Sognefjord
[Andersen and Borns 1994, p. 112].
Many of Norway's lakes have depths comparable to the fjords, and some are apparently extensions of fjords. An Encyclopedia Britannica article states [1960, v 16, p. 546]:
In many cases the low-lying lake near the head of a fjord is separated from sea water by a narrow but steep-sided neck of land which on further subsidence would resemble the submerged sill which is so characteristic of the underwater topography of the fjords.Hornindalsvatnet, the deepest lake in Europe, 514 m deep, area 50 km2, altitude 60 m, lies 10 km beyond Nordfjord. The idea that ice could accomplish such deep erosion is strange enough, but why would it leave rock sills between the basins?
Among the exceptionally deep fjords are the Messier Channel, Chile, 1,288 m, and Skelton Inlet, Antarctica, which reaches a depth of 1,933 m [Flint, 1971, p. 132]. The enormous depth of some fjords suggests they may be too deep to have been carved by ice, because ice would become bouyant where the depth increased, and the erosional capacity required to deepen rock basins would be diminished, although floating ice could perhaps still erode mounds and ridges.
Some of the U-shape profile evident in many fjords is due to landslides and slumping of unconsolidated material from the sides of fjords and because their deeper sections remain partly filled with drift. Terraces of stratified drift may occur in fjords.
Many fjords tend to be controlled by the bedrock structure, and follow the joint patterns and the faults in the surrounding rock, however some are independent of rock structures [Flint, 1971, p. 132].
It is common for fjords to end abruptly. Hanging valleys are characteristic of fjords; some of them have waterfalls. The rock walls of fjords are often polished and striated.
Potholes occur in the fjords in some regions. Hardangerfjord is about 180 km long and is one of the major fjords of western Norway. It has multiple basins separated by sills of bedrock. Whereas in a glacial erosion interpretation we would expect fjords to be deeper near their opening to the sea, the deepest of several rock basins of Hardangerfjord is far inland and has a depth of over 800 m. Potholes occur at several locations in Hardangerfjord, in other valleys in the surrounding region, and in the rocks of the highland above, 1,000 m above sea level. [Holtedahl, 1967].
Skorpo Island is a small island of steep cliffs in Hardangerfjord, about 55 km from its mouth. Abundant potholes of many varieties, large and small, complete and incomplete, occur here. Most are partial cylinders with their lower part complete. The presence of potholes in fjords may be a significant clue to their origin. See: Mystery of Pothole Origins
Since the fjords have not accumulated much debris and most are not being excavated, they must be very young geological features. Syvitski et al wrote [Syvitski et al 1987, p. 3]:
All estuaries are ephemeral geologic features, but fjords are the youngest of all -- products of the general retreat of ice and sea-level fluctuations that have occurred since the last glacial maximum since 17,000 years BP.
The
map at right shows some of the lochs of Scotland. Their origin is realted
to that of fjords, as they have similar features. Loch Ness is one of the
largest of the Scottish lochs with a volume of 7,500 million m3.
For 24 km its bottom lies more than 160 m below sea level. It lies in the
Great Glen fault and is aligned with Loch Oich, Loch Lochy and Loch Linnhe.
Loch Morar in western Scotland is the deepest loch in the British Isles with a maximum depth of 310 m. Its bottom lies 301 m below sea level. Loch Tay is partly controlled by a fault, which corresponds to its deepest section.
Deep, narrow rock basins are unlikely to have been eroded by ice sheets, but point to some very effective mechanism of disintegration controlled by rock structure. This suggests the disintegration was a response to erosion and removal of overburden, initiated within the rock. I suggest the mechanism was the same one which was responsible for the potholes, which are also reported to occur in western Scotland. Gigantic partial potholes with vertical dimensions of 60 to 90 m were reported at a preciptitous rock slope of Glen Nevis [Sissons, 1976, p. 63-64].
Deep erosional basins occur in the Sea of the Hebrides, some containing drift. Sissons wrote [Sissons, 1976, p 48-49]:
Some of the sea-floor basins are far more extensive than any that exist on land. Major basins lie between northern Skye and the mainland, between Mull and Jura, and between Arran and the mainland, each of them occupying several hundred square kilometres ...The rock surface is often very irregular and in several basins lies well below -200 m. The most remarkable feature is a major trench some10 km wide and 100 km long that extends southwestwards from near the island of Rhum. Along almost the whole of the trench rockhead is below -300 m and in one area it is below -380 m. The trench is almost entirely excavated in Mesozoic strata, but the relative weakness of these rocks can only partly help to explain the vast size of the feature.
Andersen, B.G. and H.W. Borns Jr., 1994. The Ice Age World. Scandinavian University Press, Oslo.
Flint, R.F., 1971. Glacial and Quaternary Geology. John Wiley and Sons, New York.
Holtedahl, H., 1967. Notes on the formation of fjord and fjord valleys. Geograf. Ann. 49, Ser. A: 188-203.
Sissons, J.B. 1976. Scotland. Metheun & Co. Ltd., London.
Syvitski, J.P.M, D.C. Burrell, J.M. Skei, 1987. Fjords: Processes and Products, Springer Verlag, NY.
© 1999 by Douglas E. Cox
The Creation Concept