Arthur’s Seat, Edinburgh

Edinburgh recently held a volcanology conference (VMSG), which is quite fitting seen as an ancient volcanic complex can be found at the centre of Edinburgh! The following photos are just a few photos from a  trip up Arthur’s seat whilst at VMSG…

Edinburgh from  Arthur's seat
Edinburgh from Arthur’s seat. This ancient volcano  existed around 350 million years ago in a period know as the Carboniferous.
Columnar jointing above the road on Arthur's Seat
Columnar jointing above the road on Arthur’s Seat. This feature forms when the the molten rock cools causing it to fracture in a regular pattern. The intersection of these fractures forms the polygonal columns. They are a common feature found in igneous rocks worldwide.
Columnar jointing above the road on Arthur's Seat
More columnar jointing above the road on Arthur’s Seat…
Arthur's Seat at sunset
Arthur’s Seat at sunset. I think this area is currently closed due to rockfall.
View from Arthur's seat at sunset
View from Arthur’s seat at sunset
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Oil Shale Experiment

Another stop on the trip to Scotland involved looking at the oil shale’s exposed beneath the Forth Road Bridge.

The Forth Bridge
The Forth Bridge

Unfortunately the tide was in meaning we couldn’t look at the outcrops we had intended to, but we did get to see some of the sand produced from these rocks.

The black sand here is fragments of the oil shale. Unfortunately the tide was in so we couldn't see the actual outcrop.
The black sand here is fragments of the oil shale. Unfortunately the tide was in so we couldn’t see the actual outcrop.
Oil shale sand beneath the Forth Bridge
Oil shale sand beneath the Forth Bridge

If you take some of this black sand and heat it up (we used a candle), it is possible to release the hydrocarbons in the rock. Nothing particularly scientific, but its a fun experiment to determine if the rock contains abundant hydrocarbons!

Heating up the oil shale
Heating up the oil shale
Smelling the hydrocarbons released from the oil shale
Smelling the hydrocarbons released from the oil shale

Hutton’s Unconformity at Siccar Point

In Geology an unconformity is a surface separating two rock types of different ages from one another. An unconformity represents a period of erosion or non-deposition in the sedimentary record, i.e. a gap or hiatus where we have no record of what happened.

Hutton's Unconformity at Siccar Point
Hutton’s Unconformity at Siccar Point

One such unconformity is Hutton’s Unconformity. The confusing part is that the name Hutton’s Unconformity is the name given to several unconformities identified by the famous 18th century Scottish geologist James Hutton. On a recent fieldtrip to Scotland we visited Hutton’s Unconformity at Siccar Point, but other unconformities identified by James Hutton can be found on Arran and near Jedburgh.

Hutton's Unconformity at Siccar Point
Hutton’s Unconformity at Siccar Point

When sediments (fragments of previous rocks) are deposited (settle before becoming a rock) they form layers of progressively younger material burying the older material. If a sedimentary rock is the correct way up the further up the rock you go the younger (closest to present day) it is.

At Siccar point we can see two distinct units rock, with the layers of rock (bedding or strata) in the upper and lower units being at different orientations from one another. This means that before the second (upper) unit was deposited the lower (older) unit was tilted and eroded, producing a gap in the geological record.

Sign at Siccar Point
Sign at Siccar Point

Unconformities are crucial to our current understanding of geology. They paved the way for us to consider deep time, that is essentially an appreciation of the fact it has taken a very long, yet quantifiable length of time for the rocks we observe around us to have reached their current situation.  For the rocks here at Siccar point that means; deposition of the older sediments, tilting of the older sediments, erosion, then the deposition of the younger sediments on top. This order of processes cannot possibly happen quickly!

Sign at Siccar Point
Sign at Siccar Point

Unconformities have also been used as evidence that the mechanisms governing the production of these rocks (and the universe) have, and always will operate in an assumption  known as uniformitarianism. Uniformitarianism is a counter (and more accepted view) than the opposing catastrophism, which implies that the Earth was created in a series of sudden short lived events.

View from Siccar Point
View from Siccar Point

An ancient ocean floor in the Alps?

After the adventures in Italy and Switzerland it was time to start the fieldwork part of my trip in Briancon. Part of this involved a visit to the Chenaillet Ophiolite in the French/Italian Alps.

Looking north with the large pillow lavas outcrop in the foreground
Looking north from the Chenaillet Ophiolite

Some Basics

To think about what an ophiolite is we first need to go back to some basic geology…

The outer layer of the Earth is made up of numerous large pieces which can move relative to one another in a theory known as plate tectonics, we use this to explain many of the phenomenon that we observe on the Earth. There are two types of crust making up the outer layer of the Earth; so called oceanic and continental crust. Oceanic crust is thinner, yet denser than continental crust.

This animation gives some idea of how a mid-ocean ridge may look and function but I'm not entirely convinced. http://upload.wikimedia.org/wikipedia/commons/c/c0/Mid-ocean_ridge_topography.gif
This animation gives some idea of how a mid-ocean ridge may look and function but I’m not entirely convinced…
http://upload.wikimedia.org/wikipedia/commons/c/c0/Mid-ocean_ridge_topography.gif

Oceanic crust is created at Mid ocean ridges. These are essentially underwater volcanic mountain chains where the erupted material produces new crust. They mark the boundary between different plates, and are referred to as a divergent boundary as the plates are moving away from one another.

http://en.wikipedia.org/wiki/File:Earth_seafloor_crust_age_1996.gif
Ages of the ocean floor. Oceanic crust is created at the Mid-ocean ridges and destroyed at subduction zones, because of this the crust closest to the mid-ocean ridges is youngest and the oldest is found closest to the edges of the Oceans. http://en.wikipedia.org/wiki/File:Earth_seafloor_crust_age_1996.gif

The difference in density between different crustal units is crucial to allow a process called subduction to take place. Subduction occurs when two plates move towards each other and the denser of the two goes underneath the less dense plate. Subduction zones are the opposite of mid-ocean ridges in that they are a convergent boundary, meaning that the plates move towards one another. As a result of subduction oceanic crust is essentially destroyed, as it is sent back down into the Earth.

Looking out over the Chenaillet Ophiolite in the Franch–Italian Alps. The blue areas of scree represent weathered outcrops of the serpentinised peridotite.
Looking out over the Chenaillet Ophiolite in the Franch–Italian Alps. The blue areas of scree represent weathered outcrops of the serpentinised peridotite.

When we observe rocks which have the characteristics of the oceanic crust on top of continental crust we call these abnormalities ‘ophiolites‘. The word Ophiolite apparently literally translates to ‘snake rock‘ referring to the similar aesthetics of the rocks found in ophiolites and snake skin. Ophiolites have taught us a lot about oceanic crust and tectonics but there is a catch; if normal oceanic crust is subducted back into the Earth then for ophiolites to have been preserved must mean that they do not represent “standard” oceanic crust.

So oceanic crust is created at mid ocean ridges and destroyed at subduction zones, but how did we end up with a segment of oceanic crust high up in the French Alps? Why was this segment of oceanic crust not subducted?

How do we know that the rocks here in the Alps are in fact oceanic crust?

Firstly, we have got abundant outcrops of Peridotite. Peridotite is a ultramafic igneous rock (contains less than 45% silica and solidified from melted rock). Peridotite is the main rock type in the upper mantle and it wouldn’t just form here, it needs to have been produced elsewhere and put here.

A small fragment of the serpentinised peridotite
A small fragment of the serpentinised peridotite

Another major piece of evidence is that the peridotite has undergone a process known as serpentinisation. This is a chemical reaction which occurs through contact with sea water, and has produced many of the minerals in the fragment shown above.

Angular fragments of serpentinised peridotite incorporated into a carbonate
Angular fragments of serpentinised peridotite incorporated into a carbonate rock

The photo above shows that some of the peridotite has been reworked and incorporated into sedimentary rocks (rocks made up of fragments of older rocks). The darker parts are the peridotite and the lighter surrounding material is limestone. Limestone of this type is produced under the sea which is further evidence towards the oceanic origin of these rocks.

Pillow lavas
A spectacular outcrop of Pillow lavas

Finally at the Chenaillet Ophiolite we observe large outcrops of pillow lavas. Pilow lavas are volcanic rocks which were produced underwater, providing further evidence towards the oceanic nature of these rocks.

How did these rocks get here?

These observations of rocks which seem out of place confused early geologists, and it wasn’t until the theory of plate tectonics was established that these suits of rocks were understood to represent small fragments of the oceans attached to the continents.

The process of ophiolite emplacement is termed obduction, and is defined as the overthrusting of oceanic material on top of continental.  Obduction occurs at convergent tectonic boundaries (i.e. where two plates are moving towards one another), this explains why we often find ophiolites incorporated into the mountain chains produced at these boundaries.

Numerous mechanisms have been proposed to explain why obduction occurs rather than the expected subduction but they often struggle to be applied to all cases. It is therefore generally regarded that there is no singular mechanism responsible for all ophiolite occurances, and that more work is required to understand the formation of ophiolites…

Alpine bound

When I was first offered the opportunity to head out to Briançon in the French Alps for fieldwork in September I immediately jumped at the idea. I love fieldwork, especially in places like the Alps! It got even better when I found out that I could add a climbing trip on as it made no difference to the university if I flew out a week early, then returned a few days late.

Well organised kit whilst packing tonight
Well organised kit whilst packing tonight

So anyway I doubt I’ll be posting too regularly whilst I’m out and about but I can promise a combination of interesting climbing and geology posts from this trip on my return:)

Shaftoe Bouldering

Headed up to Shaftoe in Northumberland on Tuesday evening trying to make the most out of the decent weather and light evenings as the nights start to draw in.

Pete on Soft Centre, Shaftoe
Pete on Soft Centre
Me on Sloper masterclass, Shaftoe
Me on Sloper Masterclass

The rock at Shafoe climbs quite differently to other venues in Northumberland in that its much more rough than the sandstone found at places like Bowden Doors and Kyloe (in and out). Its still a sandstone but with a definite feel of grit about it, similar to the rock at places like The Slipstones down in Yorkshire.The rock on the problems generally has brilliant friction and is of good quality, quite different from the much finer, softer sandstone found at nearby Corby’s

The coarse fluvial Sandstone at Shaftoe
The coarse fluvial Sandstone at Shaftoe

In terms of the geology of this rougher sandstone is believed to be a fluvial deposit. This means that it is a sedimentary rock produced by a river, and is slightly younger than the Fell Sandstone which makes up Bowden and Kyloe.

Pete on Hound Dog, Shaftoe
Pete on Hound Dog
Me on Soft Centre, Shaftoe
Me on Soft Centre

Dykes on the beach

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.

Beach on the way back from climbing on Gogarth
Beach on the way back from climbing on Gogarth

The main rock type here is a metamorphic rock (picture below) known as a gneiss with abundant mafic intrusions cutting it perpendicular to the coastline.

Foliation in the Gneiss which the mafic dykes intrude
Foliation in the Gneiss which the mafic dykes intrude

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.

One of the larger intrusions observable on the beach
One of the larger intrusions observable on the beach

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.

Small offshoot of the dykes
Small offshoot of the dykes

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.

Not sure what makes this pattern in the intrusions? Maybe contraction during cooling?
This pattern was observable on some of the dykes, but I’m not sure what causes it!  Maybe contraction during cooling?

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 😉

A glacier in Helsinki?

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…

Example of striations near Helsinki
Example of glacial striations near Helsinki

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!

Geography of Finland Wikipedia Page

Flutes and fossils: Trowbarrow

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.

Climbing on the main wall, Trowbarrow, UK
Climbing on the main wall, Trowbarrow, UK

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…

Coral Sea (VS), Trowbarrow Quarry, Lancashire
Looking down onto Coral Sea (VS), Trowbarrow Quarry, Lancashire

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.

Fluting at the top of Trowbarrow Quarry, Lancashire, UK
Fluting at the top of Trowbarrow Quarry, Lancashire, UK

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!).

Fluting at the top of Trowbarrow Quarry, Lancashire, UK
Fluting at the top of Trowbarrow Quarry, Lancashire, UK

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!

UKC Trowbarrow Logbook Page