Faroe Islands -- and a miniature brutalised dendritic drainage pattern

I'm intrigued by the "brutalised" dendritic drainage patterns that we find in glaciated areas which have been subjected to the intense streamflow of large outlet glaciers during some episodes of the Ice Age. These patterns exist where so much flow is concentrated in the main channels that the delicate bits and pieces of the original dendritic river drainage pattern (in other words the smaller tributaries) are simply chopped off. Interfluves or spurs are shortened, and the pattern is greatly simplified.    We can see this in the annotated satellite image above.

In the Faroes almost all of the remaining drainage routes are directed southwards and south-eastwards.  So the main watershed runs very close to, or actually at, the position of this outer coastline.  This is where there are many cliffs over a thousand feet high.   There are a few northward-flowing trough or valley remnants, as we can see on the image, but by and large there has been so much coastal erosion from the west and north that the original landmass of "trap" or horizontal lava flows has been chopped in half.

So there has been intense glacial activity here during pre-Devensian glacial episodes.  These have not, as far as I am aware, been carefully studied in the archipelago.

The other very intriguing thing about these islands is that these "brutalised" patterns and streamlined troughs are really rather small.  The fjords are seldom more than 4 km wide, and more than 20 km long.  The flanking uplands (on the interfluves) are seldom over 400m high.  (The highest peaks lie over 800m asl.)  So these are really miniature fjords or troughs when set alongside those of Norway, Greenland and Arctic Canada.

It is also interesting that if the above map of Devensian glaciation and iceflow directions is correct (I think it comes from a Norwegian research group) then the old trough pattern seems to have had relatively little influence on glacier behaviour around 20,000 years ago.  Indeed, in some places the ice appears to have flowed ACROSS the old troughs rather than along them.  More work is needed on this.

The most spectacular feature of the glaciated landscape as we see it today is the superabundance of cirques and cirque remnants, some of them with basin floors less than 200m above se-level.  How many generations of cirques are there?  Quite possibly several, although there is a preferential orientation of north and north-east -- as we would expect with winds (and snowdrift) from the W and SW, and heavier shading on the N, E and NE flanks of the upland ridges.

Ridges and cirques in the NE part of the archipelago. Norte the old trough pattern.




Cape Enniberg, at the northernmost tip of the archipelago. At 754m high, this is the highest sea cliff in Europe and maybe in the world, depending on how one interprets the mix of natural processes involved in cliff creation! Anyway, to the left there was once a substantial landmass,

now removed by the sea........


Just to get some sort of scale here, the top edge of the Enniberg cliff lies at a far greater altitude than the highest point on Mynydd Preseli (536m).


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More on the glaciation of the islands:

Jørgensen, G., Rasmussen, J., 1986. Glacial striae, roches moutonne´es andice movements in the Faroe Islands. Geological Survey of Denmark; DGU Series.

Pleistocene glacial history of the NW European continental margin

Hans Petter Sejrup, Berit Oline Hjelstuen, K.I. Torbjørn Dahlgren, Haflidi Haflidason, Antoon Kuijpers, Atle Nygard, Daniel Praeg, Martyn S. Stoker, O. Vorren.

Marine and Petroleum Geology 22 (2005) pp 1111–1129

https://www.academia.edu/7463706/Pleistocene_glacial_history_of_the_NW_European_continental_margin?email_work_card=thumbnail

Extract:

Glaciation of the Faroe Islands

Few details are known from the glacial history of theFaroe Islands (Fig. 2a). Nevertheless, pioneering work by Helland (1879) demonstrated that the Faroes once were glaciated. During the Weichselian glaciation the ice cap covered the islands up to at least 700 m above sea level, and extended onto the shelf well beyond the present coastline (Jørgensen and Rasmussen, 1986). The latter authors also concluded that during the Quaternary the Faroe Islands were repeatedly covered by a local ice cap. No foreign erratics have been found, and glacial striations show a radiating pattern from the larger islands. Radiocarbon dating and pollen stratigraphy indicate that glaciers may have been present in the larger valleys until the beginning of the Holocene (Johansen, 1975; Johansen, 1985).  Marine geological studies suggest offshore grounding of the Faroe Islands ice cap down to present water depths of at least 400 m (Waagstein and Rasmussen, 1975). Around the Faroe Islands evidence of glacial reworking of sea bed sediments has been found down to water depths of around 750 m (Kuijpers et al., 1998), whereas seismic sections fromthe northern slope of the Faroe Platform display evidence of glacial reworking of sediments in water depths of up to 900 m (Nielsen and van Weering, 1998). In addition, on the Iceland-Faroe Ridge (Fig. 2a) isolated iceberg ploughmarks are observed down to 960 m water depth (Kuijpers et al.,1998).