The Biggest Bang in Recorded History...

The Caldera from the Winery

The big bang...

It's the start of everything. Isn't it? Cosmologists would have us believe that about 14 gazzillion years ago, in one very loud instant, we went from nothing to... well if not necessarily everything, at least quite a lot of it. And who knows, they might even be right, but that's not the big bang I'm on about. My big bang is on a rather more human scale – imaginable because it happened within the span of human history. It happened only three and a half thousand years ago – hell from a cosmological perspective, we can still hear the echo!

The airport

The international airport at Santorini is insane! Not in the same way as other airports are insane. Other airports are Machiavellian masterpieces, designed to remove all sense of place and time before flying you to another place and a different time zone. While you await the chance to go through the gate you are bombarded with the opportunity to buy all the things you may have forgotten and lots of things you probably don't need. Once through the gate, the onslaught on your holiday spending money intensifies and the price of a cup of coffee trebles, but the price of Boss by Hugo Boss becomes tax free. The money haemorrhages from your wallet. And as the departure boards change with slumber inducing speeds, you wonder, having gotten up at 4am this morning and being in dire danger of nodding off, if you will have enough time to get to your gate once it has been silently announced...

The caldera from the plane

Santorini international airport is insane because it has none of that! The couple of concourse shops sell local trinkets, Coca Cola and Lays – How quaint. The waiting room were we (about 250 of us) crowded for over an hour on the way back had just about 20 seats – Genius! It is without doubt the straightest stretch of tarmac on the island and can be clearly seen as the plane banks around to approach past the mass of Profitas Ilias – the highest point on the island and one of the few parts that is not volcanic in origin. The plane bumps down and one has to wonder if the pilot only does this as a hobby and his actual area of expertise is dentistry or brick-laying. The runway shuttle bus arrives and so begins the undignified scramble to (a.) get your luggage from the overheads, (b.) get out of the plane, shouldering aside any fellow passengers like a pro-footballer (the American type), and (c.) get a seat on the shuttle bus for that 2 minute journey... For those saddo's and losers who are not prepared to take this affirmative action, there is the indignity of having to stand up on the shuttle bus! Duh!

In the airport, the customs man barely acknowledges my passport or even my presence, and then it's out of the building, into the blazing sun and the chaos of finding our rep. The reps allocate people to buses depending on their eventual destination. It's like being in the middle of one of those epic films with casts of thousands, all of whom are shouting at once – Chaotic, but with a narrative all the same – where are we going to? Perissa – on the inexpensive side of the island. The bus traverses a switchback road through whitewashed villages to to crest of the island with the mass of Profitas Ilias off to the left before similar route down the other side. Whitewashed villages turn dusty and seemingly half finished close up. Vines hunker down close to the volcanic soil. And Venician windmills march across the horizon.

Profitas Ilias from Perissa

Profitas Ilias is a crumpled piece of the basement the oldest rocks on Santorini through which all the volcanic bits burrowed to get to the surface. Looking at it from our destination, Perissa, one can see the curves of tortured meta-sediments and the slashes of the controlling faults. Close up the rocks - marbles, phylites and greywakes speak of their sedimentary origins – they were once seabed, now they are the highest oldest point on the island.

Back to the big bang

So back to that big bang. Three and a half thousand years ago, there was an Island – one of a group of islands called the Cyclides, sited a couple of hundred kilometers behind the Hellenic trench were the African plate descends below the Aegean plate. Back then it had already been the site of several violent episodes of volcanism, creating an island with an inland waterway cutting it off from the volcano in the centre. This was a thriving trading centre at the northern edge of influence of Crete's famous Minoan civilization. All this started to unravel over about 3 weeks to a month in 1650BC when the island was hit by many earthquakes and the volcano started to erupt violently. It sent plumes of smoke, rock and ash into the stratosphere in a so-called Plinian eruption. The ash settled out under gravity, blanketing the island, every road, roof, field. One of the major killers in eruptions is building collapse as ash blankets the roofs of buildings that are not designed to support the extra weight. The final cataclysmic eruption is that big bang I'm talking about. It's arguably the biggest bang in recorded history, and it may have been due to a caldera forming magma chamber collapse... It could have been a Phraetomagmatic explosion due to magmatic interaction with sea water...

The results can be seen all over the island as a thick (up to 60m thick in some places) pale ash layer (photo 4). The ash is mixed with rock fragments, pumice, volcanic bombs and even (as I found) the occasional bit of pottery. From a the water taxi, you can see how soft the ash is were it has been wind eroded into weird castles at the shoreline  and the nutrients provided by the volcanic ash produce good wine producing soils. From the inside of the caldera, the successive layers of ash, pumice and lava can be seen in their magnificence telling a tale of eruptive activity going back over half a million years – The biggest bang in recorded history may be the one that gets talked about, but it was by no means the first.

Ash deposits from the 1645BC eruption

Pumice

Volcanic Bomb

Minoan Pottery (maybe) found buried in the ash deposits

Wind sculpted ash castles 

Ghost towns

There are two ghost towns in Santorini. Akrotiri was the ancient Minoan settlement buried Pompeii style by the ash from the 1645BC eruption. It was a bustling trade centre, frozen in place for over 30 centuries. Unlike Pompeii, there are no bodies, no remains at all. It seems that the the seismic events preceding the eruptive phase was enough to make the population of a thriving town abandon it. Today it is under a climate controlled roof, viewed from carefully placed walkways and viewing points so that the complexity of Minoan culture and the enormity of the disaster which overran it can be appreciated.

The village shop at Akrotiri

The second ghost town is from 30 centuries later. Mesa Gonia (the Corner) suffered a similar set of earth tremors that caused the inhabitants to abandon it completely. Now residents are moving back, renovating and rebuilding, but they are cheek and jowl with houses long abandoned and falling into disrepair, the only people viewing them, the bus loads of tourists. Some of the houses here are actually built into the soft deposits of ash from the 1645BC eruption. The irony is as thick as the ash deposits. 

Craters and Lava domes

Nea Kameni – the current volcanic centre on Santorini is thought to be much smaller that the volcanic peak responsible for the 1645BC eruption. It has appeared on phases and stages since 197BC, with it variously poking it's head above the water in different places at different times before submerging again. The growth of the current shield volcano really took off after 1866 when the Georgios lavas spread out over a wide area. The last eruption was in 1950, but don't be fooled, Nea Kameni is only slumbering. The main crater can be accessed and viewed with ease, lying just south west of the Niki Lava dome.  A tourist path circumnavigates the rim of the crater, and holding ones hand over unassuming holes in the ground near a small cluster of seismic equipment on the south eastern crater rim betrays the heat that is not that far below.  This is the breath of the beast below...  and it's only slumbering...

Lava flows seem to be blocky affairs – the lava was very sticky dacitic, and it emerged like tooth paste, the occasional bomb being blasted pout by the pressures created. This has created a blasted landscape of black, brown and red rock, some coated in dust, others almost glassy smooth, some clearly very dense, others strangely light weight. It's a growing island on which barely anything grows. It's a land of contradictions.

The Main Crater, Nea Kameni

The Niki Lava Dome , Nea Kameni

Sunsets

Santorini is pretty boastful about its sunsets. It is as much about the location as about the actual setting of out nearest star. I have experienced more spectacular combinations of setting sun and appropriately placed clouds and pollution induced colouration in the UK. Try the Isle of Harris off the west coast of Scotland sometime. If you see it from the top of Clisham – Harris' highest peak, it takes some beating. That said, the three sunsets I experiences whilst I was there were not bad efforts. I one I was sat in a cliff top restaurant in the capitol of the island – Fira – with an enormous ice cream and a view out into the caldera before me. A strong gusty wind was whipping the sea surface into little mini tornados amid the surface chop. The view from romantic Oia (pronounced ear) lacks land reference points unless you position yourself very carefully. By about 2 hours before sunset, all the best spots have been taken and in the last half hour or so, there is a frantic scramble, seemingly by every person in town to that end of town. There must be a measurable isostatic adjustment of Santorini every sunset as large portions of the transient population all gather at one end. Does that end go down and the other go up? There's a PHD project there I think. Finally, sunset from a sail boat has everything but land, but who needs land on a sailboat. The company, the food, the Santorini wine (which is rather good by the way), that feel of continuous automatic adjustment of your stance – your sea-legs.

Sunset from Fira

Sunset from Oia

Sunset from the sail boat

Agates

Red Beach is on the shallow side of the island. No caldera view. Just down the hill from the ruins at Akrotiri. The iron rich red rocks of the Therasia Shield outcrop as high loose cliffs above a narrow shingle and sand beach and aquamarine waters. Sun worshipers arrive from the carpark at the Akrotiri end, or from the sea via the frequent water taxis. The water is clear and just the right temperature to cool off in. The general tempo of the place is relax... soak up the sun... have a cool drink... So I wander off in search of treasure! Millenia ago, silica rich fluids seeped through the red rocks, depositing silica in its most common form - quatrz, but with a twist -layer on microscopic layer with slightly different chemical contaminants, forming beautiful, intricate patterns, each one individual, each completely unique – like little tiny faberge eggs - agate. The patient obsessive, can sit in the cool of the water at the surf line and pick slivers and chips of these agates from the shingle – no two of them the same, yet all equally beautiful. I'm one such obsessive.

Red Beach

As the sun drops to the horizon, the sun worshipers start to thin out, leaving only empty coke bottles and plastic wrapping as the echoes of their presence.  The die-hard obsessive sits in the gently lapping surf excavating hand-fulls of shingle for the surf to sort and categorise.  Amid the light absorbent reds, browns and blacks of the volcanic pebbles, the occasional fleck of light reflective quartz shines like a tiny star, yearning to be found, beckoning the obsessive to take it...

Agate

Agate

Agate

Agate

Agate

Agate

Agate

Land of Fire and Ice...

Smokey Bay

The title should read Land of Fire and Ice (and rain, and painfully short days (in Winter), and far too expensive beer prices for nights that are that long, and fantastic, helpful, optimistic people...).  Need I go on?  Five short days is simply not enough - especially when the days are that short!  My post exam (Post degree really) trip was to the the mid-atlantic ridge - the bit, that is, which pokes above the choppy waters of the North Atlantic.

Landing at Keflavik international in the dark the WOW AIR pilot had given us a taster of Icelandic culture even before we arrived - Ladies and Gentlemen, off to the right side of the plane, you can see the Northern Lights - This was about two minutes after the seat belts sign had come on and the trolley-dollies were hustling up and down the plane ensuring that all the seat backs and tray tables were in the upright and locked position.  I was in an isle seat.  It would have been downright rude to clamber across the laps of the quietly spoken and very polite middle aged Icelandic couple next to me, just so I could get my first glimpse of the lights.  They'd seen it all before of course and could not have cared less.


Keflavik was like all airports - seemingly designed by a lunatic with a penchant for mazes.  Back, forth, up a ramp, down an escalator, across a raised platform were others, presumably further along in their attempt to leave the airport, crossed below you at right angles to your direction of travel.  Is there an active competition to make airports as confusing as possible?  That said there's definitely a bit more of a  "Grand Designs" feel to the place than there is at Heathrow.  Use of the dominant local stone  - basalt -  in the build lent it an individuality that is denied most airports.   Reykjavik (norse for smokey bay) initially comes into view as an undulating scattering of 1 - 2 story lights in the otherwise all enveloping darkness of South West Iceland, but it quickly thickens up into something more like a capitol city as the airport bus cruises serenely towards the city centre.  The airport bus service is run with military precision - large buses bring the passengers en mass to the Greyline bus station were they are then split off into smaller mini-buses, the better to negotiate passage around the narrow streets.  The side streets are generally quiet, filled with 2 and 3 story residences, but the main drag - Laugavegur -  in the evening is awash with late shoppers, restaurant goers and barflies, a mass of motion below some of the most tasteful Christmas decorations I have ever seen - Much better than the tacky, usually hollywood movie  inspired ones in London's equivalent Oxford and Regent Streets.

Seeing the Northern Lights was one of my things to get done.  Unfortunately it still is.  I booked onto a guided Northern Lights tour and we were coached out to the middle of nowhere, but apparently a middle of nowhere from where the lights had been seen earlier that evening.  Being an astro-photography bod I had questioned the likelihood of actually seeing anything.  To describe the conditions as patchy was being especially generous.  But the guide seemed convinced by the early evening reports.  They say the waiting is the hardest part, and never has a truer word been said.  Every once in a while, the guide would proclaim that he could see them very feintly on the horizon.  We would look, aim cameras and snap away, and then mutter amongst ourselves about how we wanted some of what he was taking...   One hour turned into two, three and then four before the guide admitted defeat.  Northern Light chasing is a game for the patient and the fervent of heart.  You almost have to believe to be rewarded with a vision.

Icelanders have no choice but to be aware of their unique position geologically speaking.  A trip around Reykjavik during daylight just confirms this connection.  Every building seems to have basalt elements, and were basalt has not actually been used, the design reflects this natural heritage instead - the Cathedral (Hallgrinskirkja) and the concert hall are prime examples.

The columner basalt inspired cathedral Hallgrimskirkja

The hexagonal columns and panes of the concert hall  - Volcanic Glass? 

Traveling in a minibus across an extinct shield volcano (Esja) in the snow was definitely meaningful to me.  The vastness and  flatness of the landscape thereabouts spoke to me of runny lavas erupting effusively like vast running sores in the surface of the earth.  I could appreciate the distinction between this and the general perception of volcanoes as large conical things that go bang in a big way.  I'm not totally convinced that other passengers on the trip around the golden circle were as impressed.  The same applied to the first stop - Thingvellir.  Unless you know more or less what to look for, and more or less how to interpret those things, you may be a little underwhelmed by a place were North America and Europe are moving apart so imperceptibly slowly that the movement can only be detected with specialized equipment.  The edge of the rift upon which we stood spoke volumes to me about rifting, drifting and isostatic subsidence, but some of the comments back at the bus hinted at a feeling of being a little underwhelmed.  Ah well, next stop was the famous Geysir.

Thingvellir - Where continents move apart.

I suspect that even in the warmest summer, Geysir is shrouded in mist.  The heat and damp from below ground envelopes everything.  The town itself seems little more than the hotel (immortalized in Desmond Bagley's book Running Blind), the rest stop, cafe and gift shop and the hydrothermal field itself.  The  actual hydrothermal vent after which the town is named (and indeed all other geysers the world over), does nothing more than burble fitfully.  It has not lived up to its name for many years, and seems to be enjoying a tranquil retirement.  I was told by a twinkly eyed bearded Icelander that for years, people (probably at great personal risk) used to throw rocks down the vent to induce Geysir to blow, but then she just stopped.  This smacks of that rather brainless perception that nature is there for our amusement - apparently nature does not like having rocks shoved down her wind pipe and she's decided not to play anymore.  It would seem that one of the frequent seismic events locally altered the geothermal plumbing system.  Now Geysirs younger brother Stokkur holds centre stage boastfully blowing off on average every 7 - 8 minutes - No rocks are required - no one is allowed near enough.  One of the products of this regularity is that there is lots of flowing water thereabouts and in the winter it turns to sheet ice.  In environment fit for Torville and Dean is created, but the majority of Stokkurs were not so impressed.   Interestingly you can find fossils at Geysir and unlike most fossils, these are not millions of years old, but probably only a matter of a few hundred - perfect calcite copies of plants were the mineral rich waters flowed over them.

Stokkur showing off.  Skating rink in the foreground

Tavertine with very recent plant fossils

By now the day was become increasingly wet and dark.  Gullfoss in the almost dark loses something. Although one cannot argue with the power of the place, the day was becoming a battle with increasing rain, increasing winds and rapidly decreasing light.  The driver stopped in the car park and those of us who dared brave the increasingly bad conditions skated across to the viewing point.  Yes it was very beautiful in its half frozen state, but being honest, I probably could have skipped Geysir in order to see this in slightly better light.  Oh well, It will still be there in the summer.

Gullfoss

When time is short, you end up having to carefully manage it.  The weather was overcast but dry the next day and I took the opportunity to look and see what sort of rocks and minerals I could find in and around Reykjavik.  What the locals must have thought of this nutter scavenging bits of rock from the rough sea defences, who knows.  Whatever they thought, they were too polite to say it.  I was looking for examples of Amygdales - volcanic bubbles into which minerals had crystalized.  There were plenty of them and I managed to identify a reasonable selection of them.

Aragonite

Common Opal

Phillipsite

Pitchstone

A Xenolith

A larger xenolith in the sea defenses.

Olivene Phenocrysts in Vesicular Basalt

The plan had been to go to Iceland for a few days and go on a bunch of organized trips as a sort of recce for a future longer trip with hire car.  As it is I'll have to go again just to actually see some ofmthe things I saw!  The second long trip I did, along the south coast was most note worthy because although we went to a lot of places, due to the fog, low light and driving rain, we did not actually see all that many of them.   At Vik, I had a highly recommended Icelandic Lamb Soup, and I walked on the black sand beach.  A little rooting around in a dune came up with a very fresh bit of Obsidian, and the beach walk produced a rounded sample of the much less common flow banded obsidian.  We also journeyed to Iceland's southern most tip - were columner basalt flows could be glimpsed through the mist.  A trip across the lunar landscape at the base of Katla took us to the Myrdals Jokull glacier.  This still has traces of the ash fall from the 2010 eruption of the next door volcano Eyjafjallajokull, and generally, the poor weather and light conditions made the location seem gloomy and brooding - I have to see it on a sunny day really, but like I said earlier, nature is not there for our amusement and she cant be expected to perform on cue.

Myrdals Jokull Glacier

A giant boulder with glacial striations

Beach pebbles at the southern tip of Iceland

So would I go to Iceland again?  100% Yes I would!  I just scratched the surface.  There are two or three good summer trips worth of material just to cover the obvious things.  The geology is superb, as expected, but more than this, I think the people and their relaxed attitude to life was a real eye-opener.  You never heard the squeal of breaks or the angry honk of a horn.  Cars stop for you if you cross a road, even if you're nowhere near a pedestrian crossing.  Energy is clean and abundant.  And the atmosphere of the place, the vibe, is one of sunny optimism.  My most abiding memory is of a helpful young man at the volcano centre giving me advice the morning after my trip to see the Northern Lights - a trip at which the Northern Lights were conspicuous by their absence.  He said "Pro-tip." I was instantly fascinated - I'd never had someone start a sentence with the word pro-tip.  He went on, "Dont pay for one of these expensive trips, just go out beyond the street lights on the seafront or into a park on a clear night.  You'll see the Northern Lights for free."   Now that's helpful, if a little late.  Why could I not have met him on day one?

Iceland on a sunny winters morning

The Solfar Sun Craft by Jon Gunnar Arnason

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...