A Passing Stranger...

Comet Panstarrs  - Bottom left at the top edge of the twilight glow

Planets are so predictable, completing lap after lap around the Sun, like a giant sized athletics track.  The Earth in its lane takes 1 year to do a complete circuit - pretty fast, but the real speed demon is the hard baked Mercury at just 88 days.  Jupiter, invariably the brightest object in the sky, is a middle distance runner with an orbital period of just shy of 12 years.  The true distance specialist however is Pluto - one plutonian year, one orbit of the Sun is 248 Earth years.

Then we have the cross country crowd.  Not for them the confines of the athletics track.  We are currently experiencing a visit from a passing stranger - Comet Panstarrs - only discovered in 2011, and with an estimated orbital period of 106,000 years.  We will never see this wanderer again - having made a visit, Panstarrs is off again out into empty space. Linked by the tenuous grasp of gravity, it will be back to visit again, sometime.

Comet Panstarrs (with the Andromeda Galaxy above)

Andromeda Galaxy and Panstarrs

Comet Panstarrs

Foliations or Layers?

Sandstone - Wirral Cheshire

What can be read from the rocks is a very variable thing.  The presence of any sort of lineation across the surface of a rock can imply all sorts of things and the unwary could be caught out by the subtleties.  The brick in a building in Cheshire shown above has two very specific lineations - 1 natural, 1 man made.  Dealing with the man-made first, there are regularly spaced diagonal lines running steeply bottom left to top right.  These are the marks made by whatever instrument (A saw?) cut this block of sandstone to its desired size.  Man made, neither a foliation nor a layer, but the unwary may be taken in by the defined regularity - regularity tends to be the invention of man rather than nature.  The lineations that interest the geoscientist are the less regularly spaced ones that for the most part run in the opposite plane to the saw marks. These are layers and are of varying thickness and colour, and closer inspection will reveal differences in grain size too.  But perhaps the most striking thing about this brick is that the plunge (slant) of the layers undergoes an abrupt change to a less steep angle about two fifths of the way down the brick.  After this the layering seems to gradually peter out.  Like I said, this is nature - it does not feel the need to conform to the human desire for regularity.  The rocks this block came from were sedimentary, and this rock speaks of the ebb and flow of tides and deltas.  These rocks were formed in rivers depositing mainly sand and gravel detrital material in channels to form river terrace deposits during the Triassic Period (252-201 million years ago).  Just in these few inches of rock, the depositional environment seems to have gone from a relatively still tranquil one to a more aggressively tidal one with graded layers stacking in the characteristic herringbone pattern known as cross stratification.  The current would have been from left to right in the top section of the brick.  

Foliated Dalradian rock from Dunkeld, Scotland

So looking at this second piece of rock, layering seems abundantly clear - the exposed and weathered right hand edge seems to give us a clue - the layers can be seen as clear as pages of a book.  Can they though?  Like the one above, this rock was once a sediment.  This rock however has been through process' that the first has not.  Buried, heated, contorted, folded, pressurised, and only now raised back to the surface for our inspection.  It is far older than the previous one and everything it has gone through, including its original deposition is etched into it.  The red arrow indicates the planes of foliation - minerals in the rock have aligned themselves in this plane in response to extreme pressure.  The blue arrow on the other hand indicates the more subtle lineations of the original layers - Barely discernible, but there for all that.  Look long enough and they are apparent.

Garnet Mica Schist - Strath Ardle

This rock has a sort of lineation too.  The lineations flow like silvery glinting  flakes of filo pastry around the rounded raisins of the Garnets.  Don't try eating this though. This rock has been through even more brutal burial, heating and pressure than the previous one.  There are no sedimentary layers left, only foliations, and the minerals themselves have altered, metamorphosed to give it its correct title, into new minerals that are stable in such extreme conditions.  Mica, the shiny flaky mineral is quite common and there were probably some microscopic flakes of it in both the two previous rocks - here it is the dominant mineral.  The other mineral garnet is also a high pressure specialist starting to nucleate in the metamorphic process even before the flakes of mica - hence the mica appearing to have flowed around them.

Cross Stratification in Quartzite

This rock brings us full circle - well sort of.  This is Quartzite - the result of sandstone like in the first photo, being heated and subjected to pressure.  The rock produced is white/grey, very hard, but no longer composed of grains like the sandstone.  It has a slightly sugary texture and close up turns out to be tiny interlocking quartz crystals.  There is often a degree of foliation - a pointer to the direction of pressure, and just occasionally there is what we have here, just feintly visible - cross stratification - a testament to its sedimentary origins.  


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Bendy Rocks

Folded rocks in Glen Gairn, Scotland

Solid as a rock or rock solid are expressions that are all too frequently used, abused and misused. For example describing a premiership football teams back four as a rock solid defence may be stretching the bounds of metaphor to breaking point, but such metaphor is in frequent use on the evening footy shows. And besides, solid as a rock is a bit of a misconception anyway.

Contorted Man 'O' War Gneiss from the lizard Peninsula, Cornwall.  Sample 15cm

The idea of rock being able to bend or flow seems a little counterintuitive, but is it? Solid state flow is something that we have been aware of (even if we could not explain it) for centuries. It has long been noted that stained glass windows (Original ones that is) in ancient country churches are thicker at the bottom than they are at the top. The glass has flowed – admittedly at an extremely slow rate – under the influence of gravity. That example takes place over a period of hundreds of years – over thousands or millions of years, under the influence of gravity, pressure, heat, and other forces such as pulling, stretching and offset lateral pressure, rocks can do the seemingly impossible. The gigantic nappes, folds, and antiform/synform structures observed in the Grampian Highlands of Scotland are classic examples of just this.

An agonizingly contorted pebble of Migmatite from Nigg Bay, near Aberdeen.  Sample 6cm 

So why does rock bend? In short, it's a matter of Competence. The pressure and heat generated by the Grampian Phase (the mountain building episode that produced the original Grampian mountains) did several things including changing the chemical and mineralogical nature of the Dalradian sediments (the bedrock at that time). It also contorted those bedrocks in seemingly impossible ways. Rocks bend as a reaction to pressure because of competency contrast. Competency is a measure of how rocks behave under pressure. Competent rocks are more viscous, maintain their thickness when deforming and may fracture, incompetent rocks are more ductile and will flow more easily. The contrast between the competency of different rock layers dictates how a rock sequence will adjust to applied pressure. In the Grampian Highlands, evidence can be seen of folding on a scale of a few millimetres to metres to a scale of many kilometres.

Microfolds in Dalradian Metasediment from Glen Gairn, Scotland.  Sample 2cm across

At a far smaller scale though, why are even individual mineral grains able to be distorted by these pressures? This question is at the heart of solid state flow, which is in turn a vital part of what keeps the Earth a dynamic living planet. We have all seen pictures, film footage (or maybe even in real life) of molten rock – lava – pouring out of volcanic vents, but this is just the depressurized surface manifestation of a far more significant flow. The rocks of the Earths mantle flow, but they are not molten. The pressure in the mantle is far too great for the rocks to melt. The flow, which results from the intense heat with in the mantle creating convection currents, happens because at those temperatures and pressures, any imperfections in crystalline structures (known as dislocations) allow the material to deform in a plastic manner rather than a brittle manner (as they would under applied pressure at the surface at room temperature). The slow, microscopic, high pressure creep is what keeps the dynamic Earth in operation. 

A Warm Spot

A view of the rugged South Coast of Madeira

Madeira is located 600Km west of Morocco and is the massive shield volcano at the end of hot spot island and sea-mount trail that stretches NE back to the Azores-Gibraltar fracture zone (a probable future plate boundary).  At 5 million years, Madeira is the largest and youngest of the islands and sea-mounts in the trail.  The trail gets progressively older and colder back to the 67 million year old Ormonde Sea-mount SW of Portugal.  There have been no historically documented eruptions, but there is a history of land slippage due to internal movements - an indicator perhaps that this giant may only be sleeping.  Does this fact make Madeira a warm spot rather than a hot spot?

For the uninitiated, a hot spot is were an anomalously hot plume of mantle material (surprisingly termed a mantle plume) rises up through the mantle and pools beneath the crustal plate passing across the top of it.  This results in a linear sequence of islands and sea-mounts at the surface were the plate has passed over it.  Imagine passing a sheet of paper over a candle flame leaving a trail of burns.  In this case, the African plate was corkscrewing in a clockwise direction, passing over the plume and creating the hot spot trail.

South Coast 

Madeira rises to a high of 1861m above sea level, but don't let that fool you.  It continues down to the abyssal plain over 3000m below the waves - It is big.  On land it has been eroded into a spectacularly rugged edifice - the coastal scenery is dominated by imposing sea cliffs (one of which is the 4th highest in Europe) cut by impressive gorges, some of which penetrate all the way into the central massif.

The central Massif from the road to Sao Vincente

Geologically, it is the result of four phases of volcanic out-pouring followed by erosion and remod-elling of the land.  This can be seen quite strikingly at Sao Vincente on the North Coast were eroded and redeposited volcanic materials can be seen covered by more recent lava flows - the new covering the old, so to speak.

The new and the old

Organ Pipes - a section of columner lava formed by thermal contraction as the lava cooled, near Sao Vincente

A result of weathering of volcanic material can be seen all over the island.  The warm, relatively humid climate of Madeira results in the chemical weathering on the underlying volcanic rocks to form an iron and aluminium rich heavy clay soil known as Laterite.  Fields, road cuttings and red running rivers bare witness to this weathering, and it has been going on throughout the islands history, as witnessed by successive layers of laterite topped by lava flows, topped by more laterite, topped by more lava flows, etc.  In the Quinta Grande area, the laterite deposits can be seen with vertical cross cutting volcanic intrusions (Dykes) cutting through them - The dykes are of a more resistant volcanic rock (Hawianite).  Similarly weathering-resistant volcanic bombs (known locally as onion stones due to their concentric layering) can also be found in the laterite - usually exactly were they had landed after having been forcibly ejected from whatever volcanic vent spewed them out.

Laterite

A dyke cross-cutting laterite in a road cutting at Quinta Grande

To the North of the island are a series of caves created as lava tubes.  These were created when a solid crust developed over still flowing lava.  The flow of lava eventually dropped off leaving a long tubular space which was subsequently covered by later lava flows.  These are open to the wondering public and are presented as part of a Disney-esque tourist sideshow.  This is not geology in the raw - it's a well intentioned educational tourist trap that removes any sense of wonder or adventure  from the experience of going into a lava tube.  By hanging back from the crowds on the official tour, I was able to gain a little of the exploratory spirit, but is was immediately removed when the official photographer pounced on me - The image was printed and framed before I had even left the cave!!

Lava Tube at Sao Vincente

In relatively recent times small vents have spewed out copious amounts of volcanic material along the Southern coast.  In the Funchal area, you can see lines of volcanic vents getting progressively older further in land - their output is all around and can be seen on the pebble beaches in and around Funchal.    If you look carefully you may notice little flecks of green in the grey basalt groundmass - sometimes there are larger fragments - xenoliths - little fragments of the mantle, unfractionated, plucked from the Earths mantle and brought to the surface - little bits of the centre of the Earth.

Basalt cobbles on the beach at Lido, Funchal

Funchal from Casa Girau - volcanic cones in the middle and far distance

A small peridotite (Dunite) Xenolith in a  basalt pebble.  Xenolith approx 5mm diameter.

All Over Bar the Dissertation

California Nebula

Well folks.  It's all over bar the dissertation...   I took my last two exams on Wednesday and Thursday, and I'm not too unhappy about the way they went, so I celebrated last night with a trip to California, that is to say The California Nebula...

Techno Techno Techno...

Cygnus area fron Dark Site X

The patience that must once have been required to be an astro photographer is is definitely of the same order of magnitude as the proverbial saint.  Back in the old days for a start, the astro phot had to know one end of a camera from another - now don't get me wrong - an astro phot still has to know one end of a camera from another, but one of the crucial differences between then and now is that back in the day, the astro phot had to get it right first go, by application of skills and knowledge honed with practice.  Today, the same applies, but if you don't like what you've just taken, you can just delete it and start again.   Even today, your choice of camera can have a big impact on your results.  I used to shoot with Olympus, which, while they were great daylight cameras, were far too noisy for astro.  I am now on my second Canon (they control the noise much more effectively) and I cant complain about the results, and the update (a 550d) is am improvement on my previous Canon - an entry level 1000d.  Back in the day your astro phot had to devise ingenious methods of keeping track of the rotation  of the Earth - that way stars were pinpricks of light not streak - no all you have to do is have the right sort of tripod head - aside from setting it up correctly, all the hard work has been done by the R&D departments at various equipment manufacturers.  Back in the day, the astro phot like as not had to spend hours in the darkroom developing his image, using skills that are rapidly disappearing as there are less darkroom spaces available and less companies making the equipment to stock them.  Besides, now there is Photoshop (for the adventurous) and a host of drag and drop, do it all for you image post production applications for the less adventurous.  Who needs a dark room? 

One thing we all need though is more dark sites.  I have already wittered on about dark sites in an earlier post, so I wont bore you now, but if you find a good one, it may be worth keeping it to yourself, taking time to get to know the locals (so they know who the wierdo standing out there in the dark and the freezing cold is).

A Dance on a Volcanoes Edge Part 1

El Tiede from Los Roques Garcia

One goes through life accumulating ambitions, and some of those ambitions will come to fruition, but quite a lot remain unfulfilled. So to tick off an ambition, even at great financial or personal cost is a good thing, and the first time is always the best, even if subsequent occasions have much to recommend them. Since rebooting my geology ambitions, I have harboured the idea that it would be good to see a live volcano. I'd seen British volcanoes (the most recent of which last erupted when the North Atlantic started to rift), but I wanted to seen the real deal. After a difficult summer of Level 2 geoscience (How naive was I? Thinking level 2 was difficult!), I decided a reward for all my hard work was in order and that ticking off a volcano was that reward.

El Tiede is the tallest peak in Spain and an active (if currently slumbering) volcano. It is situated on Tenerife and stands as an imposing presence at the Southern end of the island. Tenerife is one of the Canary Islands and being far from any plate boundaries is and example of a hot spot volcano resulting from a mantle plume – a flow of anomalously hot mantle material flowing up and out from under the western side of the African continental crust. My trip was planned to coincide with Maria getting back from Sudan, so we could have a holiday together, and tick a whole lot of boxes at the same time – volcano, whale watching, Astro stuff, etc.

Accommodation was a small friendly hostel run by an Austrian named Manfred tucked away on the North side of the island. All we had to do in a restaurant was to mention that we were staying at Casa Manfred and free food and drinks would start to appear on our table – It's not what you know, it's who you know.

El Tiede from Casa Manfred

I had toyed with the idea of going up El Tiede in the cable car like a tourist, but it was shut, so our hand was forced. We had applied for and gotten summit passes, which you have to do, but we were going to have to do it the hard way. Luckily, you can gain about three fifths of the required height above sea level in the car, up the gloriously twisty-turny road up to the caldera. Once inside the caldera things level off and you are surrounded by miles of lava fields, with the main cone of El Tiede always present. Off to the left as you drive up the road is the Observatory, high up on the rim of the caldera, in a place were the sweep of the sky is broken only by the looming presence of El Tiede to its south.

The Observatory on the rim of the caldera

From the parking space, the initial walk up the hill crosses a mass of scoria pebbles – this zigzags back and forth through this terrain for a couple of kilometers before starting to level off prior to the first big climb. This climb slogs its way through one of the more recent lava fields – hell on the knees, and starting to gasp for breath. It's a steep climb in a relatively short distance to reach the mountain refuge at Alta Vista. People will often stop there overnight and then get an early morning start to see the sun rise over the summit – not us though we were on a time line we wanted to get to the top for our allotted slot, as determined by our summit pass. A short break for food, water and photographs, and we were back on out way through the next set of lava fields. Although they were less steep, they did seem to go on for ever, and I was discovering by now that I really was no mountain goat.

View from Alta Vista Refuge

At a junction in the path, a left turn took me back towards the top cable car station. This again seemed to take an age to come into view, but once in sight, we were on the finishing straight. At this point I was really expecting to see a little Spanish fellow in a national park employees uniform sitting in a shack ready to stamp my summit pass. The reality could not have been further from the truth – the place was deserted. We probably could have gone up without having a pass at all. The final climb up the smouldering cinder cone is one of the most amazing things I have done. Throughout the steep climb, you are surrounded by gases and steam; Black flows of obsidian snake down the slope; exotic suites of minerals crystallise from the continuously venting gases forming light honeycomb structures; the small of the sulphur dioxide stings the throat and lungs forcing you to breath shallowly and shuffle just a few steps at a time before stopping for a rest.

Eventually, the summit ridge comes into view, and you scramble across a jumble of sulphur laden boulders that make up the rim of the crater. The crater steams and belches gas, but the wind whips it away to join with the clouds that are for the first time marring the view. The realisation that I am dancing on a volcanoes edge is quite intoxicating. Below my feet is a pipeline to the depths of the Earth.

An obsidian flow

Looking north from the summit

The Crater

El Tiede eggs

El Tiede and Roques Garcia