Norwegian Geology: Adeene Among the Giants / by Adeene Denton

Important disclaimer: many books have been written about each of these topics! My posts are not intended to be comprehensive, nor the decisive work in any of these areas. It would be incredibly presumptuous of me to claim otherwise. These blog posts exist to be educational, factual, and entertaining.

Now that I've gotten that disclaimer out of the way, welcome to the Norwegian geology blog post! This post is targeted at both people relatively familiar with geology and those who are not - hopefully no one finds this too pedantic.

The Basics

I wasn't sure what to expect from Norwegian geology, because most of what I knew about Scandinavian geology prior to this trip concerned the Fennoscandian Shield, containing really old rocks but not actually containing much of Norway.  My basic Norwegian rock knowledge consisted of this: fjords exist.... and also there are mountains running the length of the country? And lots of past glaciations. As geologists, we rarely go in-depth into the geology of a country besides the one we live in - there's so much to tackle just in the US that looking elsewhere isn't really a priority to teach students (I agree with this decision by way - tackling all the mountain ranges of the world in-depth would've fried my poor young brain). I didn't learn much of anything about the geology of Europe from my classes at all, which meant that before and during my trip I was doing a lot of geology catch-up at very basic level.  I was a European geology rookie! ...I kind of still am.

So, how old are the rocks of Norway? The answer is: old overall, but definitely not as old as Sweden and Finland's rocks (i.e., the Fennoscandian Shield). So by Scandinavian standards? Quite young, actually. I use this solidly unhelpful description because, like any country, Norway's rocks have a range of ages which makes it difficult for me to give one solid number. The oldest rocks are in Sør-Varanger in the large Arctic Province of Finnmark and are 2.9 billion years old, but these make up a relatively small portion of the rocks in the country as a whole. These older rocks tend to be gneisses and granites, which is typical and what we would expect.  Norway is actually covered in granites of various ages - it's most famous granites tend to be much younger.  The Iddefjord and Larvikite granites, which formed ~925 and 292 mya respectively, have been quarried for hundreds of years, paving some of the most famous streets in the world. This is a source of pride and I am told you should Google it.

 Vastly simplified geologic map of Norway. 

Vastly simplified geologic map of Norway. 

Many of these granites formed during the compression and uplift associated with large orogenic belts, which left large and small plutons cooling across the country.  The Trans-Scandinavian Intrusive Belt (TIB), a 1400-km-long belt of plutonic material, is by far the largest of these plutonic features (and is alternately reffered to as a series of batholiths or as plutons depending on the literature).  The TIB formed between 1.8 and 1.65 billion years ago, and in the intervening years the northern sections were largely covered by sheets of material overthrust by the massive Caledonian orogeny.  Most of the exposed sections of the TIB in Norway are referred to as "windows," because they let us see beneath the otherwise impenetrable layers of the Caledonian nappes.

Speaking of the Caledonian, it's time we got into it. The impressive mountain range that forms the spine of the nation was formed around 500 million years ago in an event known as the Caledonian orogeny. With this orogeny, Norway as we understand it today came into being, drawn out of the ocean by the force of two massive continents driving themselves into each other.  As I flew from Oslo to Bodø, the mountains were unmistakable - glaciated, wintry, and forbidding even in early June.  The ancient collision of Laurentia and Baltica thrust huge sheets of metamorphosed oceanic crust tens of kilometers onto dry land, covering up large sections of older rock, and creating massive folds in other sections.  The Caledonides are broken into smaller mountain ranges by intermingling fjords and valleys running east-west (perpendicular) – a typical valley consists steep granite cliffsides abruptly descending into water that has stretched far inland from the Atlantic. While they have been substantially eroded since their initial formation, they remain imposing, powerful, and a natural barrier both to outsiders and anyone wishing to travel across them.

 Simplified geologic map of Scandinavia: Blue = exposed sections of the Transcandinavian Intrusive Belt. Green = Caledonian Orogeny.

Simplified geologic map of Scandinavia: Blue = exposed sections of the Transcandinavian Intrusive Belt. Green = Caledonian Orogeny.

Norway's younger rocks are also very important, both to the formation of the coastline and the country's livelihood - the massive sequences of organic-rich muds deposited in the late Jurassic (161-146 mya) during massive rifting along the coastline became hugely profitable oil and gas reservoirs in the present day. Rifting is rarely a simple process, and in the case of Norway multiple small, shallow basins formed - perfect for the deposition of organic material. For those who may be unfamiliar, petroleum is currently Norway's biggest industry, and as of a survey done in 2004 (it's kind of old but it's the best I got) it was the world's third largest exporter of oil and gas.  It's not something many of us hear about in the US, but the entire continental shelf off of Norway contains the same late Jurassic formation known to be a formidable source rock.  However, the main thing I noticed is that most sedimentary deposits in Norway are confined to the continental shelf - I saw nothing approaching a sedimentary rock in either the north or central parts of the country.  Metamorphic and volcanic (mostly plutonic) rocks dominate, which gives both the mountains and the coast a complex character.

In summary: Norway is a complex, fascinating country geologically. When I visited, I didn't really know what I was in for.  It has a rich history of being at the forefront of many continental collisions as well as rifts - the Caledonian orogeny and the opening of the Atlantic ocean come to mind - and thus is a country of immense topographic highs and lows, and very little flat land.

Wish I could get more specific about what the geology is like? You're in luck - that what's I'm going to do next!

Lofoten

I spent a large portion of my time in Norway on the islands of Lofoten, an Arctic archipelago in the Norwegian county of Nordland.  Loften is considered to be a window into the Norwegian basement, and as such the rocks are much younger than those typically seen in the Caledonides. In geologic literature, "Lofoten Wall" defines the islands as a chain of older Precambrian massifs stretching 160 km into the cold north Atlantic.  The islands were uplifted in local crustal extension after the Caledonian Orogeny, and are defined by fault planes that run NE/SW. As seen in the figure below, these fault planes form the straits and fjords that dominate inter- and intra-island geography.

 Geologic map of Lofoten and Vesterålen. Apologies for the lack of English, but a lot of the rock terms are fairly self-explanatory.

Geologic map of Lofoten and Vesterålen. Apologies for the lack of English, but a lot of the rock terms are fairly self-explanatory.

Rocks in the Lofoten Archipelago range from 2.10 to 1.79 Gy, which makes them much older than the rocks of the Caledonian orogeny in mainland Norway.  It’s a mix of older feldspathic gneisses and the younger Lødingen granite, whose composition (charnockite and mangerite for those wondering who are versed in granite types) indicates formation deep in the lower crust.  There are also pockets of less mature plutonic rocks, namely types of gabbro and anorthosite.  While some of the rocks predate it, Lofoten is typically attributed to be one of the remaining exposed sections of the northern part of the Trans-Scandinavian Intrusive Belt.  In addition to being referred to as the "Lofoten Wall," the literature also terms the islands the "Lofoten Window" looking beneath the Caledonian nappes.

As I moved from Sorvagen to Reine, climbing up and down the ridged backs of the fjords, I was surrounded by mostly granite similar to that seen in Central Texas, but also banded gneiss with massive chunks of biotite.  The Lofoten geologic map lumps gneiss and granite together in the southern islands, but granite appears to dominate, particularly in the lower elevations.  Lofoten is famous for its sheer peaks (as seen below) and its correspondingly amazing climbing – these slick, massive granite peaks plunging straight into the water make incredibly tempting targets, but are actually quite difficult to climb.  There’s not many trails in Lofoten, nor are there large Chamonix-like towns to get you by on gear if you screwed up and didn’t bring what you need.  I've seen LOTS of mountains in my time as a geologist - and these are really different. Maybe it's the fact that they literally start at sea level and climb relentlessly upwards. Maybe it's the utter lack of any trees or animals as I climbed them.  The mountains have clearly won over the encroach of living creatures, though the consistent landslide deposits everywhere suggests that they're not as immortal as they look.

 The iconic mountain Reinebringen above the fishing village of Reine, voted prettiest village in the world back in the 1970s. It's still true, I'd say.

The iconic mountain Reinebringen above the fishing village of Reine, voted prettiest village in the world back in the 1970s. It's still true, I'd say.

Glaciations

Scandinavia is famous for being the locus of one of the thickest ice sheets during the Last Glacial Maximum – so, how many glaciations has Norway had?  Well, the answer is actually up for debate (but it’s a lot).  Most previous scholarship has defined four major glaciations, but it really depends on how a scientist defines the time between advances and retreats to say whether a glaciation is “significant.”  All we can really do is approximate the extent of a glaciation, and try to look beneath any overprinting by more recent events.  While the Caledonian orogeny is certainly the event that birthed modern Norway, glaciers and ice sheets are what shaped the country and have given it the unique look that all of us recognize – fjords, cirques, and thin, curving mountain peaks (arêtes).  This shit is iconic.

 That's some iconic shit right there. In all seriousness, look at how vertical the walls of this valley are, and how neatly the water bisects it. 

That's some iconic shit right there. In all seriousness, look at how vertical the walls of this valley are, and how neatly the water bisects it. 

Lofoten, where I spent most of my time, was relatively untouched by glaciers – the mountains are too low to have mountain glaciers, and only the biggest, thickest ice sheets advanced out to the continental shelf.  There are hints of glacial activity – striations, mostly – but overall the primary source of weathering is and has been physical and chemical erosion, culminating in numerous rock falls and landslides along the flanks of the mountains. Lofoten's fjords, which are undeniably impressive, are the result of motion and preferential erosion along fault planes and sustained physical and chemical deterioration of the granite islands rather than having a predominately glacial origin (and as such, are not really fjords at all).  This is not to say they are untouched glacially; however, glaciations have not dominated Lofoten's history, and it remains a pristine example of lower crustal development without much alteration.

I also spent four days in Møre og Romsdal based in the city of Molde, however, which is much farther south - where glaciers have had a much larger influence.  The fjords of Møre og Romsdal are huge, and clearly glacial in origin; the U-shaped valleys and the depth of fjords have to be seen to be believed.  There are no slopes to the valley walls as they meet the water - they remain near-vertical until they disappear beneath the clear blue of the water.  The islands of the region's intricate coast are all surging whalebacks of granite, smoothed out by the glacial grindstone. The Moldefjorden, the fjord I saw out my window each morning, is a 20-km (12 mile) branch of an even larger fjord (the Romsdalsfjorden) - so big it was hard to conceptualize, even for a geologist, the scale of glacial forces at work.  It hurts my brain to think about that much ice - but the landscape's origins are obvious and inescapable.  The islands in the Moldefjorden are long and thin, stretching in the path of the glacier's flow in an undeniable directional indicator.

 The Geirangerfjord, one of the most famous fjords in Norway.  Not pictured: the thousands of caravans filled with tourists.

The Geirangerfjord, one of the most famous fjords in Norway.  Not pictured: the thousands of caravans filled with tourists.

Norway's glacial history is just as varied (and interesting!) as its geological history.  I visited two different locations on the same coastline, and saw two very different stories of coastal evolution, with different levels of glacial impact.  This result, while far from being surprising, further supports the knowledge that glaciers and ice sheets do not just shape the topography - the topography shapes glacial flow patterns as well, and over longer glacial cycles the two can create a feedback loop.  Mostly what I'm saying here is I want detailed bathymetric maps, not that anyone will give me any. The system of branching fjords is absolutely fascinating, and tracing flow lines and the history of ice sheet retreat after the Last Glacial Maximum is the work of a lifetime.  Not that I'll get to do it, but I still find it absolutely fascinating, and I recommend looking into the literature if you get a chance. 

In Conclusion

What did we learn today? Well, hopefully something, despite the very short length of this post relative to the immensity of its subject.  I learned that I can write almost 2000 words on something and still feel like I've not said nearly enough.  While the Norway today doesn't look like it should have such mountainous terrain since its coastline is a passive rather than an active margin and thus it has no active tectonics to speak of, it has sustained a rich history of volcanism and orogeny to rival the big mountain belts of the present.  I would highly recommend taking a look for yourself.

Do you want to read more? Check out Norway: The Making of a Land (I. B. Ramberg et al., 2008), which offers more than 600 pages of detailed geologic history and excellent diagrams, with clearly marked chapters running chronologically through the geologic timescale. It can be difficult to wrap your mind around the locations as they jump around the country, so keep a map of Norway handy so you can process your journey. It's a great book! 

 If you're still here, thanks for sticking with this truly massive blog post! I hope you enjoyed learning about the geology of Norway. Please feel free to message me with comments and suggestions for my next blog posts.  See you soon with the history and culture post!