It’s true! Icelandic volcano Eyjafjallajokull hit the skids in April of 2010, throwing out such a monstrous ash cloud that flights across northern and western Europe were grounded for almost a week. While thousands of people were trying to figure out how the hell to get home, the rest of the planet was trying to figure out how the hell to pronounce the name of this damn volcano.
There’s something beautiful about a woman’s rage (not counting the tarts from Geordie Shore) and in no better way is this sentiment illustrated than by Mother Nature’s ire. As terrifying as it is to be at ground zero, from a safe distance, natural disasters are incredibly awe-inspiring and angry volcanoes deserve a top spot for making people go “ooooh” and “aaaaah” and “oh shit…”
Volcanoes are literal pathways from the Earth’s fiery guts to its crusty exterior. But the channels available for the molten rock and gas that spew forth are far too narrow to satisfy the sheer volume of indigestion within and the result is an immense build-up of pressure. The release of this pressure includes, but is not limited to, violent sprays of lava, devastating pyroclastic flows, stratospheric columns of volcanic ash, electrical storms, scalding gas and dust and Hiroshima-type explosions that not only dislocate millions of tonnes of solid rock, but have been reported to be audible many thousands of kilometres away from the point of origin.
Volcanoes have the potential to send species to extinction, yet at the very same time, they nourish the biosphere in an appreciable radius around them (volcanic ash is highly fertile). Volcanoes are magnificent and a wonderful example of how the surface of our planet is in a constant state of dynamism.
Where Not To Go On Summer Vacation
Volcanoes typically form at the convergent and divergent boundaries between the enormous shifting tectonic plates that comprise the Earth’s crust (see gorgeous image above). It is here that the seams of the Earth permit plumes of its molten interior to travel towards the surface. But as it was mentioned, the surface-bound transport of this material is anything but a six-lane highway. It’s more like a gravelly, pothole-ridden country road. The gas and molten rock that are trying to get from A to B encounter rigid rock and the cracks they exploit along their journey are incredibly narrow. A build-up of pressure results in a potentially explosive situation, so that when something finally gives, the results are disastrous for the local biology: human habitation included.
Volcanoes also form over features called “hot spots”, which don’t necessarily occur near plate tectonic boundaries (see diagram below). The Hawaiian Islands – all of them formed by volcanic activity in the middle of the Pacific Plate – are a prime example of this.
There are several scientific theories that seek to explain what hot spots are and a popular one is that they are upwelling intrusions of molten material (mantle plumes) that originate at the boundary between the Earth’s core and mantle. The exact depth of this varies, but the Hawaiian hot spot is estimated to be 3,000 km deep. That’s 9,842,520 ft. for those of you in ‘Merica.
Volcano Classification
There’s more to volcanology than your stock standard angry Earth pimple. Volcanoes come in many shapes, sizes and compositions. What happens at the surface – what we see and experience when volcanoes awake from their slumber – is dependent on a suite of factors and an especially important one is the composition of the magma that is trying to escape the lithified constraints of the crust.
Lava Composition
Rock that is rich in silicates tends to form chunky, viscous slow-moving magma. This subset of liquid rock is in no hurry to go anywhere and tends to contribute to terrible congestion. It also has the particularly nasty habit of trapping gas, which is why things can get explosive. Since Hawaii is no stranger to seismic activity, its inhabitants have coined a word for this particular magma and it’s pāhoehoe.
At the other end of the spectrum, you get magma that doesn’t contain a lot of silicates, but is rather rich in ferrous (iron) compounds. This magma – ʻAʻa, pronounced “ah ah” – get’s extremely hot and tends to flow hard and fast. If you’ll excuse the crass analogy, the difference between pāhoehoe and ʻAʻa is much like the difference between constipation and Delhi belly.
Both, however, are extremely uncomfortable.
Magma isn’t, of course, one or the other. There is a vast spectrum of mineral compositions between, but by understanding the difference between one extreme and the other, we can begin to understand how different kinds of volcanoes are formed.
Cone, Shield and Stratovolcanoes
If there’s one thing to be said for geologists, it’s that they don’t mess around with terminology. The name bestowed upon a volcano is as transparent as a wet T-shirt.
Cone (Cinder) Volcanoes
Cone volcanoes, also known as cinder cones, generally consist of a hill that can be anywhere from 30 meters (98 ft.) to 400 (1,312 ft.) meters in height. Formed from the eruption of materials that are riddled with gas, crystals and a hodgepodge of fragmented rock. To see an example of this kind of volcano, put on your sombrero, crack open the tequila and get on a plane to New Mexico. There, you will find a spectacular volcanic field called Caja Del Rio, which comprises more than 60 cone volcanoes. If the prospect of New Mexico doesn’t appeal, you can always bum a lift on the next scientific mission to Mars or the moon, both of which are believed to feature this type of volcano.
Shield Volcanoes
Shield volcanoes have a much broader profile than cone volcanoes and, as the name suggests, are shaped like shields. Bet you didn’t see that one coming. These beasts are formed from the eruption of very runny lava that tends to escape the Earth’s crust before causing too much mayhem as a result of a build-up of pressure. Shield volcanoes are, by comparison, the placid elderly aunt of volcanoes and are most commonly found at oceanic tectonic boundaries. Oceanic plates aren’t usually rich in silicates, which explains why the magma produced here is more felsic in composition, hence its lower viscosity. Skjaldbreiður in Iceland (say that three times fast) is an example of a shield volcano. The Hawaiian Islands, which have formed almost smack bang in the middle of the Pacific Plate over a “hot spot,” are also shield volcanoes.
Stratovolcanoes
Stratovolcanoes, or composite volcanoes, are the tri-polar member of the volcanic family. They look like your typical volcano but actually consist of alternating layers of different kinds of erupted material as the above diagram depicts. Stratovolcanoes produce a range of eruptions depending upon their mood and these include chunky cinders, choking ash and molten rock (lava). One of the best known (and least loved) of these volcanoes is Mount Vesuvius, which is located in Stromboli, Italy. This one was responsible for the notorious levelling of the cities of Pompeii and Herculaneum in AD 79, killing 16,000 people. It is estimated that Mount Vesuvius released 100,000 times the energy liberated by the Hiroshima bomb.
Volcanic Hazards
When volcanoes become active, a number of things can happen, none of them good if you’re fond of life. One of the most devastating of these consequences is ash. You wouldn’t think so… ash is soft and white. How on Earth could it possibly inconvenience you the way a searing hot lake of lava might? Stratovolcanoes are especially fond of explosive eruptions, which send voluminous clouds of ash into the atmosphere and cascading down their slopes.
This ash, however, isn’t the kind you find in your barbeque pit after a night of camping, beer and sing-a-longs. It’s mixed with gas that is hot enough to disassociate your atoms. These eruptions send roiling clouds of gas, dust, ash and other debris down the mountain, which devastate anything organic in their path, leaving behind a scene that looks like a bomb went off in a cocaine factory.
Extinct, Dormant and Active Volcanoes: The Good, the Bad and the Ugly
Volcanoes are dangerous creatures. So an apt analogy for the popular classifications of these geological features would be your mother. When she has a gin and tonic in her hand (dormant), you may want to make plans for the evening. When she’s 10 G&T’s down (active), it’s time to execute those plans and get the hell out of the house. When she’s passed out on the couch (extinct), it’s safe to come home, although my recommendation to you would be to move out your childhood home and get yourself an education.
Extinct volcanoes, such as the Netherland’s Zuidwal and Shiprock volcanoes, are no longer considered to be active at all because they don’t have a supply of magma. They also have no documented history of indigestion. Dormant volcanoes, on the other hand, are known to have erupted at some stage in recent history. They may be quiet, but that doesn’t mean they can’t suddenly awaken. Mount Vesuvius (Gulf of Naples) was a purring kitten before it went psycho in AD 79, as was Mount Pinatubo (Philippines) prior to its epic tantrum in 1991. The latter is now considered an active volcano, which is one that has exhibited recent activity and is therefore a potential hazard to all within its vicinity.
Krakatoa
If you’ve ever had a fight with Mexican food and lost (who hasn’t?) then integrating “Krakatoa” into your vocabulary is a wonderful idea if you need help explaining exactly what just happened to you to the flat mate who is next in line for the bathroom. You may not be absolved for your sins, but it’ll get you a laugh or two.
Krakatoa is a first class example of what happens when Mother Nature gets really cross and decides to let off a bomb that makes Hiroshima look like a fart. In 1883, the build-up of pressure under the Earth’s crust between the islands of Sumatra and Java in the Sunda Strait was so immense that it caused an apocalyptic-sized explosion, sending a once much bigger island into the stratosphere.
The Krakatoa eruption was reported to have been heard almost 5,000 km away (the loudest sound ever made in recorded history) and the resultant shock waves sent barograph needles oscillating violently off the page. Over 36,000 people were killed by the eruption: if not by the devastating pyroclastic flows and falling debris, then by the tsunamis that followed. The dust catapulted into the atmosphere caused stunning sunsets around the world for months after the eruption.
Too bad colour photography wasn’t in vogue in the 19th Century.
Class Dismissed: Your Take-Home Message
If you ever needed to respect the fact that we are just not in control of our natural environment, then stand next to an active volcano. From lakes of lava and earthquakes that shake the foundations of your stick hut to falling debris and scalding hot pyroclastic flows that choke the biosphere, volcanoes are creatures to be respected, studied and understood. If ever there were an item to put on your bucket list, it would be to stand next to an active volcano and feel the heat of Earth’s exterior lap at your cheeks. Just make sure you’ve ticked off the rest of those bucket list items before you do so…
For those who struggle with gastric reflux, indigestion and heart burn, the Earth provides some comforting empathy. Check out these three AMAZING videos of volcanoes wreaking havoc upon the local biology:
Volcanic Eruption in Papua New Guinea
Video Source: “Volcanic Eruption in Papua New Guinea” by Phil McNamara and uploaded to the YouTube Channel at http://www.youtube.com/watch?v=2XlDa3WxVJ0
This intense clip was captured on August 29th, 2014, when Mount Tavurvur on Papua New Guinea finally blew its lid, sending an incredible shockwave into the atmosphere and into the ocean vessel the filmmaker was riding!
Pyroclastic Flow Followed by Series of Tornados (Sweet Jesus!)
Video Source: “Pyroclastic Flow Followed by Series of Tornados” uploaded by Photovolcanica on YouTube channel http://www.youtube.com/watch?v=tzbIdE51jcg
In this amazing science video, the pyroclastic flow off Mount Sinabung volcano (North Sumatra, Indonesia) leaves behind a trail of superheated material, which then generates incredibly strong convection currents. These begin spinning vertically due to the speed with which the air is rising and the result is like salt in the wound of an already decimated landscape: TORNADOS!
Nature’s Fireworks: The Five Most Spectacular Volcanic Eruptions of Recent Years
Video Source: “Nature’s Fireworks: The Five Most Spectacular Volcanic Eruptions of Recent Years” uploaded by Zoomin.TV Science on YouTube channel http://www.youtube.com/watch?v=R15iePGcFYE
The title pretty much gives away the content of the film, so go ahead and enjoy these five catastrophically seismic events! It’s a visual feast.
Welcome back to this, the second instalment of our foray into the field of plate tectonics in which we seek to understand how the giant bumping and grinding shards of crust that make up the surface of our planet have helped to shape it, create it, destroy it and give Hollywood directors endless material for disaster movies. In Part 1, we began our journey with a look at convergent boundaries – where two tectonics plates come together causing a fender bender of such epic proportions that it has resulted in some of the highest (Himalayas) and deepest (Mariana’s Trench) topographical features on Earth.
We discussed the difference between continental collisions (where two continental plates crash into each other) and subduction zones (where one denser oceanic plate gets “pushed” underneath a lighter, crustier plate). Both are characterised by plates that are slowly, yet inexorably colliding into each other and both result in some totally awesome environmental features, such as soaring mountain ranges, plummeting ocean floors, city-shattering earthquakes and volcanoes with monstrous cases of indigestion.
In this week’s blog, we’ll take a look at the other boundary types and what kind of geological party one might expect to find there…
2. Divergent Boundaries: When Two Plates Pull Apart
At the opposite end of a plate’s convergent boundary, one tends to find a divergent boundary. Here, the prodigious convection currents in the Earth’s asthenosphere (the squishy onion layer beneath the crusty lithosphere) serve to wrench the two plates apart. This exposes the bubbly mess of searing molten rock beneath. For the same reason you want to sew your butt cheeks together when you have a really bad case of “Delhi Belly”, this runny mess of lithic indigestion explodes out from between the plates causing all sort of fun for the neighbouring wildlife.
There are typically two geological features one finds at divergent plate boundaries and just as was the case with tectonic convergence, the resultant landscape depends very much on whether the plates pulling apart make up the continents or the ocean floor.
Mid-Oceanic Ridges
When the separation occurs between two oceanic plates, as is the case with the African and South American plate (in the southern Atlantic basin) and the Eurasian and North American plates (in the northern Atlantic basin), you get a mid-oceanic ridge, which doesn’t really look like Ronn Moss posing in the exquisite turquoise waters of some tropic paradise. No, mid-oceanic ridges are a lot bigger, a lot more ripped and far more complex, although perhaps not as emotionally so… and definitely not as annoyingly successful with the ladies.
Two plates can’t get away with divorce without some serious repercussions. For one, the divergent motion of the plates releases a whole lot of pressure on the underlying asthenosphere. It subsequently melts in relief, releasing a surface-bound flood of molten rock known as magma, or at least until it actually reaches the Earth’s surface, at which point it becomes known as lava.
Don’t ask me why geologists have to make things so complicated.
This lava cools and solidifies upon contact with the atmosphere or, in the case of mid-ocean ridges, the overlying water, forming blocky solid structures of igneous rock. Over time, the release of magma from the divergent motion of the plates forms wave after wave of new ground in a process referred to as “seafloor spreading”. This all explains why the age of the rock closest to a plate boundary is younger than the rock as little as 100 metres away! Cool, huh?
Some of the attractions one might expect to see on a routine exploration of a mid-oceanic ridge include deep gorges and valleys and formidable submarine mountain ranges that are, in height, taller than Mount Everest. When you’re not “oohing” and “aahing” at the fantastic topography, you can “ugh” at the local wildlife.
This sexy sock-face with nipples for eyes is actually a Deep-sea Pompeii worm, which typically hangs out near the hydrothermal vent chimneys found along marine divergent boundaries. This large sea squishy enjoys black smokers, long walks along the trench and its ambient environment close to boiling point. Hydrothermal Vent Eelpout fish, Giant Tubeworm and the Hydrothermal Squat Lobster are more examples of wildlife that find boiling water totally amenable. In fact, there is a whole community of specialised critters that have become adapted to life in close proximity to blistering, incandescent volcanic vents.
Rift Valleys
When tectonic divergence occurs between two continental plates, rift valleys can form. East Africa provides us with a beautiful example of this in the shockingly named “East Africa Rift Valley.” I mean, how left field can you get? Here, the splitting apart of the Somalia and Arabian portion of the African plate has caused the ground to sink in a complex series of fault lines. The resultant synclines (fancy geology speak for “valley” or “dip”) can become filled with water, as is the case with Lake Malawi, Lake Tanganyika and Lake Victoria… some of the oldest, deepest and largest lakes in the world.
“Hold on,” you say. You’ve referred back to the map of the world’s major tectonic plates and there isn’t a plate boundary anywhere near East Africa.
“How observant you are!” I exclaim saccharinely…
The Africa plate is in the process of splitting into two, like a giant amoeba or your mother’s personality when she drinks too much gin. The plate to the east of the Rift Valley is the Somali Plate and the one to the west is the Nubian or Arabian Plate (check out the diagram below). These two crusty offspring are referred to as “protoplates” or “subplates”.
What other exciting attractions do rift valleys have to offer us other than very old, very large and very deep lakes? Seismic activity of course, which includes all manner of fire, brimstone, earthquakes and highly specialized organisms that have adapted to the heat and the strange chemical environment found around aquatic volcanic vents.
3. Transform Boundaries: Where Two Plates Rub Together
We’ve looked at convergent and divergent plate boundaries, but what happens along the peripheries of the plate if the “front” is having a head-on collision and the “back” is being torn asunder?
If your guess was a great idea for a blue film, I commend you on your filthy mind. However, “transform fault” was more along the lines of what I looking for.
Transform boundaries are characterised by two plates grinding past each other. Since jagged rock rarely slides easily past jagged rock, this fault line tends to be the source of much rocking and rolling in the Earth’s crust. Every now and then – which is painfully slowly in geological time – one plate gets snagged on the other and they are brought to a strained halt. The pressure mounts as the one plate tries in vain to move on, but is held back emotionally by the other, until, in a sudden Earth-shattering shudder, they become unsnagged, sending the plates shooting past each other.
This is precisely why transform faults are notorious for causing earthquakes. One of the best-known examples of such a boundary is California’s San Andreas Fault (image below), which is currently – as we speak – being torn asunder by the divergent motion of the North American and Pacific plate.
San Andreas fault is also testament to just how stupid humans can be… building a massive city on a fundamentally unstable Earth foundation is a disaster movie begging to be scripted and cast with slack-jawed hunky men and big-breasted, blue-eyed blondes. Although, if you are a film director and find yourself being inspired by this, please consider casting me as the clip-board wielding, surprisingly young, yet double PhD-educated science floozy! I may not have blonde hair, but you know what they say…
You can easily sleep with a blonde, but a brunette will keep you up all night long.
Mila Kunis is scientific evidence of this fact.
The disturbing reality about San Andreas fault is that it’s been 107 years since a major earthquake has occurred, which means that all these long years, the pressure between the plates has been building. Sure, there has been a smattering of decent earthquakes in between the 1906 San Francisco event and the present day – the most recent being the 6.0 magnitude Parkfield earthquake of 2004.
Don’t get me wrong, a 6.0 magnitude will leave your martini shaken and not stirred, but according to the latest Uniform California Earthquake Rupture Forecast (kind of like a weather forecast, but for earthquakes), California has a 99.7% chance of experiencing a larger than 6.7 magnitude earthquake in the next 30 years! I.e. you can bank on it.
It gets worse: the chance that this earthquake could achieve a magnitude of 7.5 or more is a frightening 46%. This may seem like a paltry percentage at first, but if your tandem buddy had to suddenly turned to you on a sky dive and tell you there was a 46% chance the parachute wouldn’t unfurl, you’d most definitely soil your undergarments. You can bank on that, too.
Could the next “Big One” finally send San Francisco into sliding into the sea? Is “Frisco” about to become the next city of Atlanta?
Who can say? Only time… and the underlying tectonic plates. Not Enya.
Class Dismissed: Your Take-Home Message
Plate tectonics play an incredible large-scale role in shaping the surface of our planet. Of course there is a myriad of smaller scale (both spatially and temporally speaking) factors that mould the mountains you climb over, the oceans you swim across and the valleys you… bungee jump across?… to be with the one you love.
But, plate tectonics are the daddy of global scale change and transformation.
Be in awe!
So very in awe…
Is it possible for something that’s spherical to have a physical end or beginning? A ball just keeps going on and on and on and on. No matter how many times you turn it, you never get to any definitive beginning or end. Where does an egg start and where does it end? With the chicken or the egg or the chicken or the egg or the chicken?
Well, in spite of its spherical shape, planet Earth has many beginnings and endings and they are found at the boundaries of the colossal shifting plates that comprise its surface! Plate tectonics account for many of the soaring and plummeting landscapes on our planet and it explains a host of our most frightening natural disasters, from spewing volcanoes to shuddering earthquakes. It builds beautiful fertile islands in the middle of vast ocean expanses while ripping the ocean floor apart elsewhere, forming trenches in excess of 10 kilometres deep. Understanding plate tectonics is key to understanding our planet and its dynamic surface, which, as stable as it seems under our feet, is in reality anything but.
The Earth’s Surface is Divided into Plates
The Earth’s outermost crusty layer is known as the lithosphere (lithos meaning “stone” in Greek) and it can be likened to a giant shell that has been broken into large, rigid interlocking pieces (refer to the image below). These pieces sit upon the warmer and more malleable asthenosphere and basically bumble their time away by colliding into each other, pulling apart and rubbing against each other. They also, you know, support the entire biodiversity of planet Earth in their spare time.
Meet Planet Earth’s tectonic plates: Americans and Canadians get the North American Plate, Europeans and Asians get the Eurasian Plate and the penguins get the Antarctic Plate… EVERYONE gets a plate!
The asthenosphere, which is fluid-like and warmer and more pliable than the outer crusty lithosphere, promotes the migration of the Earth’s tectonic plates. Prodigious convention currents of heat and molten magma travel from the bowels of the planet to its surface, compelling these giant puzzle pieces to move. Just like Tree Ents from “the Lord of the Rings” and the cogs in your brain after a heavy night out, these motions are frightfully slow. Some plate boundaries, such as the Mid-Atlantic Ridge, move as fast as your fingernails grow, which is approximately 1 to 4 cm per year. Doesn’t exactly make for riveting viewing, does it?
But over time, patience wins out against the resistance of solid rock and the results are as creative as they are destructive.
The Three Plate Boundary Types
All of the plates that make up the lithosphere are in constant motion thanks to the giant hot and moist “visco-elastic” asthenosphere upon which they sit. Hot and moist. If you’ll refer back to the map above, you’ll notice that every plate fits snugly into another, much like a giant jigsaw puzzle. Since each plate is in constant motion, one can definitely assume that it’s where they meet – at the plate boundaries – where the party’s at.
The picture below shows us the direction of motion of each of Earth’s tectonic plates. At any given time, one periphery of a plate is wrenching away from another. At the opposite end of the plate, there is a violent collision going on, while the sides are causing iniquitous mayhem as they rub lasciviously against each other. And as the more, erm, experienced will know… friction leads to all sorts of seismic events.
Map indicating the direction of motion of Earth’s tectonic plates. The red ‘teeth’ indicate where two plates are colliding, which, as we shall find out momentarily, has resulted in the formation of the magnificent Himalayan mountain range (continental collision) and Mariana’s trench (subduction zone). The first is home to the highest viewpoint on Earth (although you might kill yourself getting there) and the second, the very deepest point in Earth’s crust (although, again, you might kill yourself getting there).
1. Convergent Boundaries: When Two Plates Collide
If you drove your car at the rate of fingernail growth into a brick wall, you would have no idea what would happen because you would have gotten out long ago to use the toilet and get married (probably in that order). But hypothetically speaking, in the absence of arseholes to use and arseholes to marry, you’d probably discover that nothing very much would happen in a collision between a brick wall and your car moving at the rate of fingernail growth. Why? Because you’re going too slowly!
BUT! Substitute your car with a billion tonne megalith and that brick wall would be cement dust in… oh a few million years or so!
The convergent boundaries of Earth’s plates result in the formation all sorts of interesting topographical features. Two colliding plates can either become a subduction zone (where one plate – usually the denser one – plummets beneath the other one), or it can become a collision zone. The plate boundaries that are home to continental soil tend to opt for the latter, while the plate boundaries that are home to ocean soil, the former.
Continental Collisions
The coolest example of a continental fender bender on Earth has got to be the Himalayan mountain range, which is home to the world’s highest, most hostile and most abundantly body-strewn slopes. This formidable mountain range is the product of two continental tectonic plates (the Indian and Eurasian plate) crashing together and forcing each other to crumple and buckle into soaring mountain peaks and plummeting mountain valleys. There are more than 100 mountain peaks in the Himalayas that smash the 7,000 m (23,000 ft.) altitude mark. Mount Everest, the range’s and world’s largest mountain, comes in at 8,848 m… a staggering 29,029 ft. above sea level.
Typical and totally average view on a hike through the Himalayas
Subduction Zones
When two plates collide and the one happens to be heavier and denser than the other, it typically gets forced beneath the less dense plate. Imagine Paris Hilton gets into a fight with Natalie Portman. Who would come out on top? My vote would be on the substantially less dense (and Harvard degree-wielding) Miss Portman.
This kind of active plate boundary is known as a subduction zone and it can form deep-sea trenches that plunge for kilometres into the ocean floor, as well as yawningly vast abyssal plains that are home to a plethora of deep-sea squishies, only a fraction of which have had the pleasure of joining our taxonomy system. The remaining majority have not yet been discovered or named, although one did feature very briefly in the Pixar animated film, Finding Nemo.
The vertical antithesis of the Himalayas is Mariana’s Trench, a deep gash in Earth’s crust in the Mid-Pacific, directly east of Southeast Asia (refer to the map above). Here, the Pacific plate smashes into the Philippine Sea Plate and the former, which is composed of denser, more metal-rich rock than the crusty, silty continental latter, gets forced downwards. There are examples of mid-ocean trenches all over the world, but at 11,000 m (36,070 ft.), Mariana’s Trench is the very deepest. Not even an inverted Mount Everest could fill this gash.
That is a huge gash.
But wait, there’s more! One plate does not simply get sucked underneath another without the appropriate ceremony! Deep-sea trenches are very good and all, but we want fire and brimstone!
I’m so glad you asked…
The Ring of FIRE!
When one tectonic plate plummets beneath another, it faces the fiery wrath of the Earth’s immensely pressured mantle. This heat causes the hydrous (water-containing) minerals within the plate’s rock to release their moisture. Since water acts to lower the melting temperature, the mantle overlying the subducting plate melts (surprise!), sending plumes of magma towards the Earth’s surface.
These pockets of molten rock tend to become trapped underneath the crusty rock making up the lithosphere, where the pressure builds up. Eventually, all hell breaks loose and you get a volcanic eruption. This can occur either on the ocean floor or on land surface. Sub-aquatic volcanism tends to result in the formation of fiery, volcano-strewn islands, such as the Pacific Ring of Fire. Terrestrial volcanism tends to result in Pierce Brosnan being a hero and other awesome feats such as pyroclastic flows, earthquakes and village-bound lava lakes.
As long as the Earth’s tectonic plates are mobile, subduction will remain an ongoing process. The denser plate is continuously consumed by the continental plate, sending plume after plume of magma to the Earth’s surface, fuelling the ingoing wrath of these lithic pimples.
Stay Tuned for Part Two!
Want to find out what happens when a billion billion tonne slab of rock rubs against another billion billion tonne slab of rock? Things get seismic.
Stay tuned for next week’s blog instalment – Plate Tectonics: the Ends (and Beginnings) of the Earth, Part 2.
Wander Woman Thea 