I had pretty much forgotten about this amongst everything else but I still think this is worth posting. On the way back from doing Dream of White Horses on Gogarth (2 weeks ago) we decided to have a quick stop on the beach and found some interesting geology to look at. From just a few simple observations on this beach some really key geological principles can be demonstrated.
An intrusion is when molten rock is injected into another rock and the word ‘mafic‘ refers to the composition of the intrusion. Here I am using mafic to describe an igneous rock which is dark coloured and with crystals too small to identify, but its actual definition is a silicate mineral (contains the elements silicon and oxygen) which is rich in the elements magnesium and iron. A metamorphic rock is a rock which was previously another type of rock which has been physically/chemically altered through increased pressure and temperatures in the Earth.
The patterns we can see in the gneiss (second photo down) are known as foliations. These are a planar feature caused by pressure forcing the minerals in the rock to align in a preferred plane.
This simple observation of the dykes on this beach also demonstrates a crucial geological principle, so called ‘cross-cutting relationships‘. The principle of cross-cutting relationships states that the geologic feature which cuts another geological feature is the younger of the two features. Geologists use observations like this to build up the sequence of events (relative ages as opposed to absolute ages) that led to the particular setup which we observe. From this we can reliably say (with no need for dating techniques!) that the dykes here are younger than the metamorphic rocks they intrude. This concept of relative dating was noted as early on as 1795 when James Hutton published his ‘Theory of the Earth‘, and is not just limited to intrusions, it can be applied to a whole array of geological features such as faults or erosional surfaces.
I would imagine most of the beaches this side of Anglesey have things of interest. If you find yourself passing by might be worth a quick look 😉
Whilst on holiday in Finland last year we visited an Island not far from the centre of Helsinki and found some interesting things to look at…
The linear features here are called striations and have been gouged into this rock. They are caused by the movement of a glacier over the bedrock, through the process of abrasion. Abrasion is a term used to describe when fragments of rock captured by a moving glacier are pressed onto the surface of the underlying rock. As the glacier drags these rock fragments along lines are scraped into the rock. Striations are a common feature of glaciated landscapes and are just one of many features glaciers can produce.
Striations such as these along with other glacial landforms can help us to reconstruct the dynamics of past glaciers, and help us understand more about modern glaciers. The presence of glacial landforms where we no longer have glaciers (such as here in Helsinki) demonstrates how the environment can change over time.
If you find glacial landscapes interesting you may find Rock Paper Glacier! blog to be of interest.
This example near Helskinki really does show us that even in built up areas we can still observe the influence of the forces that shaped the landscape around us!
Before heading off to North Wales last week I went to Trowbarrow quarry in Lancashire for a quick climb and poke about but haven’t had time to post about it.
This disused quarry is a geological SSSI with lots of high quality (and some crap!) climbing on offer. One of the most prominent geological features at Trowbarrow is the near vertical nature of the bedding planes. We can see this on the photo of the main wall where the routes follow cracks along the bedding. Other interesting geological features at Trowbarrow worth seeking out include; faults, folds, fossils and apparent paleo-karst.
The photo of the main wall above is actually one from a few years ago but it hasn’t changed much, except some people say that the entire right hand side of the main wall is rotating causing the cracks to widen? The climbs on the righthand side of the main wall are looking a little ‘unstable’ but I’m sure people can make their own judgements about whether to climb them…
Like many of the climbs at Trowbarrow Coral Sea (photo above) follows the bedding plane, and as the name would suggest numerous fossils are observable all the way up.
Another feature at Trowbarrow is Fluting. This is a common feature on limestone and is caused by differential weathering and erosion. It can be observed at Trowbarrow at the top of Assagai wall, where it forms the spectacular finish to Assagai (good sling runner in the flutes!).
In terms of the climbing the obvious mid grade classics Jean Jeanie(VS 4c), Coral Sea (VS 4c) and Assagai (HVS 5a) are certainly worth a look. Polish can be a bit of a problem at Trowbarrow (especially on Jean Jeanie!) but generally the climbing is really good quality!
Apologies for the multiple posts today but there’s lots to post about since returning from Wales!
I hadn’t climbed on Lower Pen Trwyn (LPT) before but would certainly go back. In terms of the Climbing LPT has some really good routes across the grades and has the feel of sport climbing elsewhere in Europe, especially if the sun is out! Could The Orme be the Welsh answer to Kalymnos?
The approach is pretty simple (steep start) with some good geology to maintain interest on the way in. The following photos and thoughts are by no means an exhaustive study, and were captured in a passing by type manner with the intention of inspiring climbers to look around them on the way in to LPT.
Presumably the sediments above the limestone are relatively recent, and are sourced from the limestone above on the Orme? This short transportation distance however does surely not provide a satisfactory explanation as to why there is such rapid variation observable in roundness and sorting between beds?
Climbing wise Under the Boardwalk stands out as a real classic of the crag, proving to be a tricky little number requiring a sustained effort right till the end, but the crag contains abundant quality climbs. At the far right end there are several ‘easier’ sport routes in the F6a(ish) range with Beauty is Only and Skin Game being good fun.
Oh and remember that LPT is tidal, and accessible apart from about three hours either side of high tide. Its also worth noting that the 1st bolt on most climbs is pretty high (due to the tides).
I have always loved the Welsh slate (in terms of climbing and geology) so no trip to North Wales would have been complete without a substantial amount of time spent here. This is not intended as a in depth review of either the geology or the climbing, more like a few photos, words and thoughts. A really great article on the climbing can be found on UKC.
So what is slate? Slate is a metamorphic rock (meaning that it was previously another rock which was heated up and pressurised without melting causing physical and chemical changes). The rock which made up the slate previously was probably a fine grained sedimentary rock (such as a shale).
Good things about climbing on Welsh slate:
Quick drying: this is wales we are talking about so it will rain and with some routes climbable only 15mins after a shower it can save a damp days climbing!
The cotton plants here show how wet this ground normally is, but the prolonged heat wave a few weeks ago has really dried the ground out! This has however made walking here a lot easier.
By studying modern examples of features such as desiccation cracks, when we observe fossilised desiccation cracks in the geological record we can infer things about the environment they formed in.
I spoke to my friend Suzy who’s PhD is on damage to peat and she told me that the photo of the desiccation cracks demonstrates that the peat in this area is not in a good condition. She told me that peat can be up to 95% water and adequate vegetation can prevent the effects of extreme weather causing damage such as this.