Tuesday the 19th of June, after weeks of cold and rain, the weather was good enough for a trip into the woods near my home in Vänge. The idea of making a geology trip of my own had struck me long ago, but that day was the day when I had nothing else that I needed to do, and the weather was favourable. I hoped to be able to find some interesting features, both as a form of repetition, and generally for fun. Of course, I had no idea of how much there was to discover, and how fun it actually would be!
The woods in Vänge are extensive, so I could not explore everything (which means there is much more left for other days!). Therefore, I decided to, as the first trip, take a safe route: there is a 2.5 km long walking path (which by the way is also used for skiing in winter), which I chose to follow.
From where I live, there is a short walk through the forest before you get to the actual beginning of the large path. Already shortly upon entering the minor trail, there lie, before my feet, a rock exposure with clear glacial striations – small furrows carved out as rocks carried by an advancing glacier grind against the exposed rock surface. These are typical signs of glaciers, and their direction shows how the glacier moved.
These furrows are emphasised by the green plants that grow in them. (Or maybe that is mud and dirt…)
A bit further along the small path, a familiar colour on my left beckoned. A spot of light pink on a boulder. Could it be pegmatite?
It was surrounded by plants growing on the rock, but a patch was exposed, and on looking closer, it was clearly pegmatite – a very large-grained rock, composed largely of pink potassium feldspar and light, translucent quartz minerals. I though pegmatite was a fairly uncommon rock type, at least in Sweden, but when I looked around, there was even more pegmatite nearby. I even found a large boulder that was half made up of pegmatite!
And over there! Among the greenery, a very pink pegmatite piece pointed out.
Oh my! There’s pegmatite everywhere! This came as a real surprise, actually, and I began to wonder if there would be even more farther into the forest.
However, stumbling upon this cool rock diverted my attention from that.
It has been split in three larger chunks, and I doubt that it has been caused by anything but frost wedging (water in its pores freezing and thus expanding so that the rock is wedged apart), probably connected to the Ice Age. It seems as if this rock has been cleaved in two separate events, the first one splitting the original rock in two, and the next breaking that piece that was closest to me when I took the photos. That’s just an idea, but it if you look at the planes through which the rock is cut, you can see that one extends across the entire rock length, while the other cuts from one side to the larger cleft, but not beyond. This can be explained by separate frost wedging events.
Hihi! It feels like playing a real geologist, walking around and trying to explain weird things I come upon.
When I could see the beginning of the main path, I could see something else next to it.
A small, funny-looking rock hill, with parallel cracks, slightly tilted to the right. Curious. It was probably formed by some tectonic process, and I did not care to think too much about what exactly that could have been, but instead climbed up to see if I could find anything else on top.
I was quite disappointed not to find anything at all, but when I went to the ledge and looked down, there was a small bird, sitting in a nest! It looked back up at me, worried, it seemed, so I backed away to let it be, and kept searching around for something else of interest. But when that failed, and my curiosity over the bird, and the desire to catch at least one photo of it having grown stronger and stronger, I could not resist returning, slowly and carefully, not to frighten it. But that failed. I got scared and flew away, leaving its nest, with five turquoise eggs in it.
I took a quick photo of the nest, and took my leave, not to torment the poor bird any more, and let it return to its nest with calm.
The first hundred metres of the large trail were uninteresting. I saw a bunch of uprooted trees, probably by wind (windthrow), and recalled that our soil teacher had said that uprooted trees are excellent opportunities to look at the soil profile or quaternary deposits below the surface without needing to dig a hole. I went there to check, just because… As expected, I had no idea what quaternary deposit was there (I hardly know any such besides till…): it was black and rather fine, mixed with small rock fragments and plant litter. Later, I thought that perhaps that was the top layers of a soil profile – where partially decayed plant matter mixes with inorganic rock particles. The dark colour hints toward a high organic content, and it does seem to be a mix of muddy substance and dead plant matter.
The next picture was taken for the purpose of showing a typical sight in Swedish forests – at least very common in this one – namely medium-sized, angular rock blocks scattered across the ground, characteristic of glacier-affected land. A glacier is the only transport medium strong enough to readily carry such heavy objects, except powerful storms; however, the angularity of the rocks shows that they have been carried by glaciers, since water and wind tend to make the edges rounder.
But, when I look at this picture, it seems almost magical, like something out of a fairy tale. So I would rather show it for its beauty.
And, speaking of magical pictures, this is what lay before me next.
It felt as if taken right out of a Walking With Dinosaurs scene. Barring a few angiosperm (flowering plant) bushes, this was as close to my idea of a Jurassic forest (i.e. from the time of the dinosaurs), with plenty of short ferns covering the ground and all conifers rising above them.
I was completely compelled to film a short panorama clip of this place.
All it lacked was a flock of small dinosaurs running around the bushes and the distant sound of vast sauropod herds by the forest margin.
The next site was a curious one. A bit away from the main trail, there was a small deforestation patch. However, not all trees had fallen to the hands of man.
A handful of them had been windthrown. But what caught my attention was how surprisingly thin the lump of roots and root-bound soil was.
It is as if the roots did not go deeper than a few decimetres below the surface, but spread out sideways instead. First, I though about cacti, which grow their roots in a similar fashion in order to cover as large a surface area as possible, to absorb more rain; the heat means that water rarely percolates deep into the soil in deserts, so there is no point in having roots digging down. But this forest is hardly as dry as a desert, so there must be another reason for this peculiar root pattern.
My next idea came from the pool of water where the tree had once stood. Perhaps the groundwater was very superficial in this area. In that case, there would be little need to penetrate deeply into the soil – unless for the purpose of anchoring steadily into the ground, but this area was probably sheltered from wind by the sheer mass of trees; when humans removed the vegetation surrounding them, their shallow roots could not hold against strong winds, which could explain why the trees fell.
If you have been following this blog, you might recall from the excursion to Uppland that there is a certain yellow flower with a cumbersome name (alternate-leaved golden saxifrage) that is commonly associated with superficial groundwater. The patch was literally teeming with small yellow flowers!
But, they were not the one.
Close, so close.
Well, not finding that flower cannot exclude the presence of superficial groundwater, since the plant pollen must have reached that area for the plant to even appear. Still, I did not find the conclusive support I needed to prove to myself that I knew what I was doing, that I could play nature detective. I had to leave this mystery unsolved.
Not far away, I found an odd rock to divert my thoughts.
That loose piece was as if it had been peeled off the big rock like a fruit shell. I had never seen anything like it…
… until I walked a few more steps and found this:
I was quite amazed – this was something completely new, something I had no idea could happen with non-sedimentary rocks (i.e. rocks that do not usually form in layers).
From there, I carried on for a while, until I saw a rocky hill to my left.
No question what that pink rock was: more pegmatite!
I went up the hill to search for some more, or perhaps something else of fun. I found neither; the only thing of note were some pretty impressive cracks in two rock chunks.
They could be results of intrusion (recall from the excursion to Väddö) where the intruding material was more easily eroded than the surrounding rock, and therefore vanished entirely long before the host rock.
I could not find much pegmatite on this hill, but standing there and looking over to the other side of the road, I saw a long length of large, exposed pink rocks. I made a short panorama clip here too.
Of course, I had to make sure it was pegmatite, so I went over there to get a close view.
Yup, pegmatite indeed! At least, I am quite sure…
To my right was a funny-looking cave opening.
However, I did not dare to linger to examine it more closely, due to the eerie figure standing on top of it.
A demon of some sort, no doubt. And it was not happy at all.
I took my leave instantly.
I think I had not walked through half the path yet, so there was much more left to discover! Unfortunately, either my attention slipped, or the sites of note were more sparse from here, but the walking distance between the following places was almost doubled compared to before.
My quest for pegmatite was laid to rest, being sure that at least this forest has plenty of that rock. However, another question still rang inside my head, re-evoked when finding another uprooted tree with shallow roots, again with a pool of water at its feet.
All it did was to make my head itch again. Apparently, it was not a feature of that deforested area way back, but something appearing throughout the forest. Because, I did find even more of these – even a pair where one had fallen on top of the other.
Here, there was little water at its feet, probably just having dried out.
I grabbed a stick and poked around in the soft mud.
Down a few centimetres – around five – the stick hit solid bedrock. This should have been a complete eureka moment, but I only figured out as much as that the superficial bedrock explained why the roots did not go deep: they could not penetrate the hard rock, and where forced to grow laterally. Interesting, I thought.
On I went, with a few distractions, among them lazy trees…
… and another magic-like scene with ferns growing in a shallow inward dome on a large rock, looking almost like a nest of eggs – or a nest of fern plants.
Then, I found even more fallen trees.
With plenty of water this time.
The whole grass patch was inundated!
Now, that eureka moment came: there was so much water because of the solid bedrock below! Aha! Everything began to fit in place now: the roots could not penetrate the rock, nor could the rainwater (it had been raining hard for days before)! Hard winds fell those trees whose roots were not deep enough to provide proper anchoring.
I passed a giant anthill along the way.
After that, I heard the lovely sound of running water. On both sides of the path. Woah. I looked around and saw that water was actually flowing from a pool on one side of the path, through the path, out to the pool on the other side. This might sound crazy, but I filmed this. I mean, while I'm playing nature photographer, I might as well play nature filmer as well.
Later, I found a crinoid stalk on the ground. Hehe…
Not far away, I learned that old rocks also have wrinkles.
This was essentially the end of the truly fun bits. I went on to find a few glacial striations, both curved and criss-crossed ones, showing that glaciers can turn direction…
… but that was not much fun…
Still, this day had gone marvellously well, and I had found more than I could ever have imagined. It did indeed spur my will to go on more explorations alone, to see what else is out there! If you just take your time, look around, both close and far away, I’m sure you will find something wherever you go!
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