Photo Friday: Some Cypriot Pillow Lava

So, this weeks installment of geologically themed photographs is this almost-perfect cross-section of a pillow lava from Cyprus. I like to buck the geologist cliche of using a hammer for scale, and instead tend to fling whatever I have to hand in the general direction of the outcrop, which works well until you have to jog back to pick up your clipboard/pencil/compass/rucksack. I am a terrible scientist!

Anyway, this lovely little member is part of the Troodos Ophiolite, which makes up the bulk of central Cyprus. Ophiolite is the term used for a portion of oceanic crust that has been thrust upwards, rather than being subducted like the fast majority of the ocean floor. The reasons for this are often complex, but ophiolites offer a wonderful window into the structure of the oceanic crust that would otherwise be impossible to access, even with huge technological advances in drilling. This outcrop represents ancient seafloor, where basaltic lava from seafloor spreading was extruded out to the surface. The hot, exposed lava on the surface of the pillow would have been immediately quenched by the cold seawater, creating a glassy crust. Chemical alteration by circulating fluids and weathering has altered this to pale clay minerals, and this thin layer can clearly be seen on the photo. However, the basalt in the inside of the pillow is relatively insulated from this cold exterior, and therefore cool at a slower rate with time to form crystals. This coarser texture can be seen at the jointed centre of the pillow.

Luckily for us, some lava divers (aka coolest job title EVER!)  in Hawaii have recorded footage of pillow lavas erupting underwater, so we can get a pretty good idea of how this outcrop would have been like 90 odd million years ago. Enjoy!

 

Unconformities – The Sequel

After posting about that lovely unconformity in South Wales, I had a brainwave and a flashback to another unconformity I had seen in the South of France.

Photo Friday: The Power of Nature

For my dissertation, I mapped in the Ardeche, in the South of France, and here’s one of many photos to come. This photo illustrates really well the strength difference of rock when under tension rather than compression. As this sapling has grown into a tree, the pushing forces exerted by the roots have completely fractured the huge sandstone boulder that hosted it. Nature is cool.

On Unconformities and the Birth of Deep Time

An unconformity is a surface that represents a gap in geological time, a period of non-deposition or even erosion of the Earth’s surface. The gap can represent a missing thousand, million or billion years or so, giving a huge insight into the geological processes that have acted on the area.

Angular Unconformity near Friar’s Point on Barry Island. Rucksack and half a PhD student for scale.

As far as lumps of bare rock go, unconformities are pretty cool to look at. This fine example comes from Barry Island in Wales, the home of Gavin and Stacey and not actually an island anymore. The rocks are the base of the photo are 335 million year old bedded Carbonifererous limestones, whereas those at the top of the sequence are 200 million year old Triassic breccias and sandstones.

So what happened in the 135 million years between these two sequences of sediment being laid down?

Photo Friday: Geolo-tea

Yesterday I received quite possibly the best present ever in the whole wide word:

Of course, it’s natural to be jealous….

A Day at Robin Hood’s Bay: Britain’s Other Jurassic Coast

Now, we all know about Dorset’s Jurassic coast, the World Heritage site and quintessentially British landscape. I’m northern, and therefore a bit biased, but I think that our other Jurassic coast here in Yorkshire is wrongfully overlooked.

The Yorkshire Jurassic coast wraps itself around the North York Moors, with Robin Hood’s Bay pretty much bang in the centre of the succession of rocks.

Geological Map of the Yorkshire Coast. Image courtesy of the British Geological Society

Considering Robin Hood was a Nottinghamshire lad, which is a fair way from Yorkshire, it seems a rather obscure choice of name for the small fishing village at the northern end of the bay. However, according to local legend (ahem… Wikipedia) French pirates busy raiding and pillaging the village were accosted by the aforementioned Mr Hood, who then returned the loot to the poor people in the village. At the time of writing, it is unclear as to whether the merry men were involved.

From a viewpoint on the southern headland of the bay, Ravenscar, the geological structure controlling the coastal morphology is obvious, especially at low tide.

Looking north towards the village from Ravenscar

As the sea retreats, a wonderful cross section of the imaginatively named Robin Hood’s Bay dome is exposed. Protected at each end by sandstone headlands of the Staithes Sandstone Formation (~190 Ma), the exposed softer mudstones of the Redcar Mudstone Formation (~200 Ma) have been preferentially eroded to produce the wide arc of the bay we see today. Along with individual strata, known locally as ‘scaurs’ from the Old Norse word for ‘rock’, the cross section also shows a number of radial faults aligned to the centre of the dome. One of these can be seen at the bottom of the photo above.

Hello

Hello, I’m Harriet, a relatively recent geology graduate who loves rocks and writing. It’s only fair that the two should be combined at some point, so here it is! This page is hopefully going to be an amalgamation of my tales and travels in the geosphere, earth science news and probably some cake somewhere along the way. Enjoy!!