Origin of Fjords

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Introduction

The Hudson Estuary

Features of Fjords

Fjords and Disintegration Theory

References

Introduction

Fjords are basically estuaries, or valleys drowned by the sea. Similar features with irregular shape and without a U-shaped profile are called a "fjärd" in Sweden. A fjord may be called a "loch", "lough" in Scotland or Ireland. Valleys resembling fjords that are not submerged are common in mountain areas. The usual explanation is that they were eroded by glacial scour. However, many fjords have no glacier. Flint wrote [Flint, 1971, p. 131]:

Many of the strongly glaciated valleys of high-standing coasts underlain by resistant rocks in high latitudes are partly submerged, and constitute fiords. A fiord is a segment of a glaciated trough partly filled by an arm of the sea. It differs from other strongly glaciated valleys only in the fact of submergence. The floors of many though not all fiords contain basins, some of which are both deep and long. As a result many fiords are shallower at their mouths than at some distance inland. Most such basins are believed to be eroded in bedrock, and some are known to be so.

The plausibility of ice erosion is in question. A new approach to the question of fjord origin is possible with the disintegration theory of the drift.

Hudson Estuary

The Hudson estuary in New York has been described as a fjord, and as a drowned river. Beneath the river bed there is a deep bedrock canyon filled with drift and sediments containing organic material. This canyon continues under the sea, cut into the continental shelf, where it becomes a great submarine canyon. The origin of the buried bedrock canyon of the Hudson river is clearly related to the cause of the canyon in the continental shelf, which extends to great depths. Obviously the submarine canyon cannot have been carved by ice.

In my interpretation the canyon of the Hudson River was formed by a mechanism of in situ disintegration along joints or faults, and some of the disintegration product was washed out by fast currents, as the land was raised above the sea. In the steep section of the continental shelf, drift formerly present in the channel was mostly eroded away by currents. Organic sediments accumulated in the estuary since these catastrophic events. Similar mechanisms can account for features of other fjords, that otherwise seem enigmatic.

For the conventional geologic history of the area, see: Overview of New York Geology.

Features of Fjords

Many fjords have a "sill" near the outlet to the ocean, which forms a basin. The presence of sills would have limited the flow of ice from within fjords, so glacial scour would probably have been limited and relatively ineffective. Fjords may have multiple sills and basins.

Map of Sognefjord, NorwaySome 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.

Some lochs of ScotlandThe 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.

Fjords and Disintegration Theory

In this theory, fjords formed by the in situ disintegration mechanism which formed the drift as the continents were raised after the flood. The disintegration process was often controlled by the presence of joints or faults. Uplift of the land caused flood waters to be spilled into the oceans along the coasts. As disintegration occurred, rock was converted to unconsolidated drift. The currents eroded the drift, and exposed fresh rock surfaces to decreased pressure, which were also subject to disintegration. The disintegration and erosion by currents formed deep channels along the coasts.

The process of disintegration was enhanced by continued erosion. This can explain the great depths of fjords, as well as their irregular basins of varying depth, that are problematic in the glacial interpretation. The process of pothole formation, apparently associated with the origin of some fjords, is also characteristic of the disintegration.

Fjords occur in areas where the land rises steeply from the sea. Their origin is associated with differential uplift, erosion by catastrophic currents, and the disintegration mechanism which formed the drift. For more information about the mechanism of disintegration see:

Erosion Aided by Disintegration

References

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.

Related Sites

Fjords - Government of Canada site

For some pictures of fjords, and a conventional interpretation, see: fjords...a web tutorial

Copyright © 1999 by Douglas E. Cox
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