The living Earth: Rocks, plumes and hot spots. Part I

An Earth model made from living rock

The Earth is alive. Well, not really. At least it is not life as we know it. Appropriately, the origin of this expression – slightly rephrased from the original Star Trek series – is from the second-most-famous non-human in existence, Spock, referring to a living rock. It is only a small step for humankind to apply it to an entire planet.

(What Spock actually said was ‘there is no life, other than the accountable human residents of this colony beneath the surface. At least, no life as we know it.’ In another episode Spock comments about a strange creature ‘It is not life as we know or understand it. Yet it is obviously alive’. The version that is always quoted is in reality from the 1986 song Star Trekkin’. But I digress.)

To be considered ‘alive’ an organism needs to meet some requirements (as defined by the powers-that-be): the ability to adapt to the environment, to respond to stimuli, to actively regulate its internal conditions, to produce energy by metabolism, to grow and reproduce. The Earth doesn’t do any of this. It is big enough not to have to worry about it. But speed up time, and you can see the Earth come to life. Continents drift, collide and separate; oceans grow and wane; mountains rise and fall. Volcanoes sprout, grow and die. Plates subduct, refresh the Earth inside and the enriched mantle resurfaces as new oceanic crust. This is the Earth breathing – if you can imagine breathing solid rock. There is a rhythm to the Earth. It dances to an inner beat.

Where there is a beat, there is a heart. This story is about the search for the Earth’s heart.

Bare bones

To find the heart, we need to look below the surface. From the outside to the core, our surgical cut reveals the crust (and/or lithosphere, if you prefer), the upper mantle, the lower mantle, the outer core and the inner core. Each has a different role to play.

The iron core acts as the Earth’s skeleton. It consists of two parts, a solid, stable inner core and a liquid outer core in which the liquid moves around in huge convecting bubbles. As a byproduct these bubbles create the Earth’s magnetic field, which immunizes us from space weather. This protective role can perhaps be compared to that of bone marrow. Of course it consists of iron and is outside rather than inside the solid part, but you get the idea. Apart from breeding the magnetic field, the core does not affect us: like our skeleton, it stays inside to provide stability.

(The inner core is not entirely uniform. There are hints that the composition slowly changes with depth. This is sometimes described as a separate innermost core, but this seems to overstate things as there is no obvious transition layer.)

Beyond the core lies the mantle, the main body of the Earth which ferries the heat from the centre to the surface. It consists of rock rather than iron. At the bottom of the mantle lies a thin region (no more than 150 km thick) named the D″ (pronounced D-double-prime) layer which encases the core. Blame mathematics for the strange name. Originally the entire mantle was called the D layer. When seismology showed the mantle to have subdivisions, the geo-mathematicians called these D, D′ (D-prime) and D″ (D-double-prime). The first two are now known as the upper and lower mantle, but no one wanted the last (tiny) layer and so its name survived. The D″ layer belongs to the mantle but the precise composition is unknown. It has been suggested to be partly melted, or to have an iron-enriched composition, or to be a denser phase of perovskite (found in the lower mantle) called post-perovskite. Seismology shows that D″ layer is variable both in thickness and in properties; in a way it is almost similar in structure to the crust of the Earth with valleys and mountains and different rocks. This is the most mysterious, and least studied, of all the layers of the Earth. I am not sure which body part to compare it to! Perhaps the equally mysterious but controlling amygdala will do. Or may be this gives it too much credit, and it is more like our coccyx in looking interesting but not doing anything useful. We’ll come back the mantle, as it is the main topic of this post.

Beyond the mantle lies the crust, which separates into the asthenosphere (a thin lubrication layer on which the crust can move), the oceanic crust and the continental crust. The oceanic crust is slightly processed mantle material with some external pollution such as water, carbon and shipwrecks. The continental crust is low-density flotsam which resolutely stays on top and therefore is well-placed to carry our cities – you might call the continents the Earth’s warts. In some places the crust is stacked, with continental crust lying on top of an oceanic crust, but most locations have either oceanic plates (with oceans, obviously) or continental plates (which can still be partially submerged). Continental crust is a passive on-looker in the rhythm of the Earth and is of little interest to us apart from providing a good place to call home; only the oceanic crust is invited to the inner party.

Mantle shapes

The part of the mantle that isn’t the D″ layer (i.e. almost all of it) consists of two parts, the lower mantle and the upper mantle. They differ in the structure of their rock. Both consist mostly of magnesium-silicates (peridotites), but the elements are arranged in different mineral structures. At the top of the mantle it forms olivine, which becomes compressed into ringwoodite a bit deeper in the upper mantle, into bridgmanite (and related minerals) in the upper part of the lower mantle and to perovskite in the deeper part of the lower mantle. If you now feel a bit lost in the nomenclature, join the club. Geology is even more opaque than medicine in its language. The terminology of geology has turned the Earth into a veritable tower of Babel. (More on that in part II.)

The Babel fish (the guide says “the poor Babel fish, by effectively removing all barriers to communication between different races and cultures, has caused more and bloodier wars than anything else in the history of creation“) will tell you that ringwoodite (found in the deeper part of the upper mantle) is a spinel. If that doesn’t help much, spinels are minerals with a (rather complex) pyramid-like structure of their atoms. Spinels are named after one particular mineral which is also called spinel. There is a gem with the same name. The gem spinel is a variant from the mineral spinel which belongs to group of the spinel. What’s in a name? In geology, confusion. I actually like spinels because one of these minerals is called (rather inaccurately) galaxite – a name that promises much more than it delivers.

We now need to make a small step (for humankind) from geology to geometry. The picture below shows the structure of a spinel. The large orange dots are magnesium or silicon atoms, encased by four red dots (oxygen atoms) arranged as a four-sided pyramid, also known as a tetrahedral structure (tetra meaning four). (You can do the translation without even a babel fish: ‘tetrahedal’ just means four-sided. You just earned yourself a geology Babel fish diploma.) These pyramids are linked by blue dots (calcium or aluminium atoms) which are arranged in an eight-sided structure called an octahedral structure. (You can do the translation.) The two structures are shown separately in the second frame (right, with different colours – sorry). The oxygen atoms are shared in a complex way. There are some variations but this is the basic structure of a spinel. It requires four oxygen atoms for each magnesium or silicon atom.

Olivine (the upper part of the upper mantle, before it becomes pressurised into a spinel in the lower part of the upper mantle) (still with me?) is quite similar but the octahedes (I am not sure that that is an existing word) are linked to each other at only one corner rather than two. You can create it by taking the image of spinel and shifting one of the two blue octahedes (and the attached orange pyramids) one step towards the top right. This leaves one connecting point between the blue shapes, and the blue octapy (a word that should exist) instead now share one edge with an orange pyramid.

Bridgmanite (found in the lower mantle) is a perovskite. Instead of the tetrahedral (pyramid) structure, it has only 3 oxygen atoms for each silicon or magnesium atom. A quick try with the lego box shows that this should form flat structures. But by linking these, you can make a linear chain of pyramids attached at one corner, with the silicon or magnesium atom slightly above the triangle of oxygen atoms. This is more compact overall than the structure of a spinel, and therefore pyroxenes take up less volume and consequently have a slightly higher density. This form is called pyroxene. But it is not quite bridgmanite.

At the pressure of the lower mantle, the pyroxene structure changes to that of a perovskite, compressed even further. Now the big atoms (green in the depiction, for instance silicon) line up in a cube, surrounded by smaller atoms at the corners of the cube (blue, for instance magnesium or calcium) and oxygen atoms at the centre of each edge line. This is repeated in each direction. Some math shows that there are three oxygens for each silicon, the same as for pyroxenes. It is a bit more dense than that. This is the structure of bridgmanite, which is found throughout the lower mantle.

That is enough for geometrics. Play time is over, and we need to get back to work.

Circulation

After this excursion to Legoland, let’s return to the mantle. The division between the upper and lower mantle is where ringwoodite (a spinel) compresses into pyroxene and subsequently a perovskite. This change happens at a depth of around 660 km. It requires energy and therefore the change occurs a bit deeper for colder material, and a bit less deep for hotter material. We now have the funny situation that at this depth, there is a mix between cold, lower density material and hot, higher density material. The colder material is more buoyant. This makes it harder for warmer material from the lower mantle to mix into the cooler upper mantle and vice versa. The two layers have a degree of separation: they are kept apart by a buoyancy barrier.

The mantle rock circulates in large convection currents, powered by the heat below: heated rock moves up, cools, and comes down again. It is different from the convection in the core: core convection happens in liquid matter, whilst the mantle is solid. Mantle convection is therefore very slow, typically less than 1 meter per year. (Our garden snails would be embarrassed.) Rock is a reluctant mover! But this convection runs into the 660 km transition zone and has difficulty crossing this. In effect there are two separate convection zones, one in the upper mantle which circulates oceanic crust, and one in the lower mantle which circulates material from near to the core-mantle boundary up through the lower mantle. Only the hottest rocks manage to break through the barrier on the way up, and only the coldest (oldest) subducting plates manage to pass it downward. Otherwise, rarely the two do meet.

The subduction of oceanic rock is a bit like the Earth breathing (taking breaths of rock), while the circulation of the lower mantle is like the blood being pumped around.

Dissection

Figure taken from McNamara, 2019, Tectonophysics 70, 199-220: A review of large low shear velocity provinces and ultra low velocity zones

The picture shows a cross section of the Earth. This particular cut runs through both poles, Africa and the Pacific and is chosen to highlight the life of the mantle. Note that this is a cartoon, and may deviate from reality.

At the top left the cut cuts through the Aleutian subduction zone. Here oceanic crust is descending into the upper mantle as the Earth takes a breath. The subducting crust is shown in dark blue, reflecting its lower temperature. (It has spend the last 100 million years being cooled by the ocean.) The subducted ex-crust has collected near the transition zone between the upper and lower mantle. As mentioned above, it is held up by the denser and warmer material around it, which has phase shifted to bridgmanite while the subducting crust is still the lighter ringwoodite. However, the cartoon depicts that the subducting material has managed to break the barrier and enter the lower mantle. Once that happens, it will descend rapidly (rapid for a rock moving through rock – our well-fed snails would still have rocket speed in comparison), sinking all the way to the bottom of the mantle.

South Sandwich Islands. Source: https://doi.pangaea.de/10.1594/PANGAEA.937574

At the bottom of the picture (the far south), the cross section cuts though another subduction zone. This is most likely meant to be the subduction zone at the South Sandwich Islands (although in that case the cross section does not go through the south pole itself). That region with its 7-km deep deep trench is shown here: click on the image for higher resolution. The cartoon shows this subduction zone to also have broken the barrier and sunk to the bottom of the mantle.

The red colours in the cartoon represent warmer matter that is rising from the deep mantle. There are two big warm plumes in the lower mantle, one underneath the tropical Pacific, and the other underneath Africa. Both are shown to have reached the transition region, but have pooled there as the plumes are unable to break through this barrier. But thin plumes are shown to reach the surface, some coming from those plume heads and some starting much deeper. These rise up underneath Afar, Reunion, Louisville and Hawai’i. The secret lies in the temperature: to break through the barrier, the rising matter needs to be some 100C warmer than the surrounding mantle. Such hotter plumes form thinner, faster rising columns.

However, this is just a cartoon! It shows the general idea but it is not meant to be accurate in details of the internal structure. There will be a deeper discussion (pun intended) in part II.

The dashed white lines show the movement in the lower mantle, downward around the subductions and upward at the large plumes. The blue dashed lines (rather harder to see) show a similar movement in the upper mantle. In the upper mantle, this comes up at the spreading ridges, flows outward below the oceanic crust and goes down and bends back where the oceanic crust subducts. The general movement in the upper and lower mantle do not connect to each other. They are separate circulations.

Body work

How does it work in practice? Subduction is a bit more complex than depicted above. Ocean floor is almost mantle material but it is slightly altered. The densest mantle minerals have more difficulty surfacing: the other materials melt a bit and trickle up, leaving the densest minerals behind. That is the reason why the ocean floor floats and doesn’t immediately sink back. But as the ocean ages, it slowly loses its mantle heat to the cold water. The slab that makes up the oceanic crust, perhaps 10 km thick, cools. As it cools it contracts a bit and becomes a bit more dense. Initially this is fine, but at some point it becomes as dense as the mantle below. The upper mantle thinks ‘gotcha’ and the oceanic crust sinks back down. Subduction begins.

(There are variations on this theme. Different parts of the crust can have different temperatures and densities, and when they collide the lowest density wins and ends up on top. The other one is caught between the upper crust and the mantle but is too young and warm to sink. This is called ‘flat slab subduction’ and it happens underneath part of North America and in the west Pacific. Eventually the slab will still begin to sink – you can’t avoid old age by hiding.)

As it sinks, the slab remains colder than the surrounding mantle. It takes a very long time to heat a 10-km thick stone slab. So it keeps sinking, until it hits the boundary with the lower mantle. The lower mantle is denser, so the slab stops in its tracks. The slabs may spend time hanging around this boundary, at the so-called slab graveyard. But many do manage to eventually cross into the Hades of the lower mantle and once they do, they will sink all the way to the bottom of the mantle, finally hitting the D″ boundary. This part is reasonably well understood.

The reverse process, where parts of the mantle rise into plumes and hot spots, is much less well understood. In fact, there is no particular reason why plumes should exist. If you drop a stone in a bucket of water the water level will rise in response, but it does so everywhere: it doesn’t form a plume in one location which channels the rising water. The fact that we see rising plumes in the mantle means that the mantle is not uniform. It is thought that the plumes begin when a part of the lower mantle heats up, expands a bit and becomes less dense. It is now buoyant and begins to rise. The rise again has difficulty crossing the boundary between the lower and the upper mantle, so it typically gets stuck there. Only some hot and narrow plumes overcome this barrier and make their way to the surface.

Ultrasound scans

An ultrasound can show surprises

How do we know this? Even the upper mantle is tens of kilometers below the surface. We have never been able to drill that deep. The rock in the bottom half of the continental crust is too soft for a drill to gain purchase. The Mars lander ran into this very problem (‘running’ might be a bit overstating for a completely stationary robot), when it failed to get its probe into the unexpectedly sticky ground. The robot arm tried to push the probe into the ground, but in vain. It makes you realize what a human on Mars could have achieved: they could have forced it in, with the age-old motto that a good kick solves many mechanical (and electrical) problems. The Mars lander should have brought a human for the essential kick. And in fact, a kick is just what is needed to create a viewing window into the Earth.

The medical world has already solved the problem how to look inside a body without having to open it up. Ultrasound echoes have become an essential part of any pregnancy. The same technique can be used to map the inside of the Earth. Of course the Earth is rather bigger than a typical human body, so we need infrasound rather the ultrasound: infrasound consists much larger waves, needed for a larger body. The infrasound is kindly provided by the Earth itself, by giving itself a good kick. This causes an earthquake, and the earthquake produces the infrasound waves.

After a shake, the waves pass through the Earth and reach the surface somewhere elsewhere. From the arrival time of the wave and the distance, you know the speed of the wave inside the Earth. And it turns out, this speed is not always the same. Especially the shear waves often arrive late. These waves are late anyway, as they move slower, but sometimes they are even slower than normal. If you know what determines the speed of this wave (we are talking physics), you can have an idea of the conditions deep below your feet.

What is a shear wave? It is one of the types of sound waves created by an earthquake that travels through the body of the Earth. There are two: the P wave and the S wave, where ‘P’ stands for ‘primary’ (it travels faster and is the first to arrive) and ‘S’ is the ‘secondary’ wave. Still with me? The P wave is a compression wave: material moves forward, pushes the material ahead. This pushes the matter behind back, and itself in turn moves forward and pushes the material ahead of it. This is in essence a sound wave and it is a fast way to travel. The ‘S’ wave, in contrast, moves sideways, pulls the matter ahead to the side while being itself pulled back to starting point, etcetera. This is a shear wave (‘shear’ for sideways movement) and it is slower because it tries to go forward by moving in the wrong direction.

P waves travel through any type of material. But S waves can only travel through solids. In liquids or gasses, they don’t do anything. So if somewhere on Earth an earthquake is detected, and the P wave arrives but the S wave does not, it means there is a liquid somewhere along the line of travel. That is how we discovered that the core of the Earth is liquid but that the mantle is solid. It is also one way to detect a magma chamber.

Got it? You can easily do this experiment yourself. All you need is some cooperative students (ask the local school for some) and the instructions as in this video:

Waves which arrive in different locations have taken different paths through the Earth. The further from the source, the deeper the wave has traveled. Based on the arrival times close to the source it is easy to calculate when they should arrive at more distant locations. As so often, this gives the wrong answer. They arrive earlier than they should. This shows that deeper waves travel faster.

The figure below gives the velocity versus depth for the crust and upper mantle. The velocities increase with depth in the crust. The asthenosphere shows lower velocity, and at 400 km depth there is a jump in the speed of primary waves which comes from the formation of ringwoodite. Go deeper, and the velocities continue to increase. The secondary waves go about 40% slower, but this factor varies a bit.

For those used to equations, the two velocities are given by two fairly simple relations:

compression versus shear. Source: tec-science

Here ρ is the local density of the rock, G is the shear modulus of the rock (the amount of pressure needed to deform the rock) and K is the bulk modulus (the amount of pressure needed to compress the rock into a smaller volume). A liquid offers no resistance to deformation, so G = 0 and the vs becomes zero: the secondary wave comes to a screeching halt when entering a liquid. A solid is more easily deformed at higher temperature, so G reduces when the temperature increases: both wave velocities decrease in hotter material. But the compressibility, K, is much harder to change. Cold rock, hot rock and liquid rock are all highly resistant to compression. The primary wave can keep a high velocity even where the secondary wave slows down, because K remains high and this term contributes to the primary wave (which is a compression wave) but not to the secondary wave (which is a shear or deformation wave). But don’t evaporate the rock: unlike a solid or liquid, a gas is compressible, and it has a much lower K. So the primary wave is much slower in the atmosphere than it is in water or rock.

The deformability of different mineral structures. Most ductile on the right, least ductile on the right

A material that is easily deformable is also known as ‘ductile’. Making a material hotter makes it more ductile, and melting it makes it completely ductile: the force needed to deform it becomes smaller (and for a liquid goes to zero): this is what the G above is. But is also depends on the structure of mineral. Some minerals (for example graphite) are much easier to deform than others (say diamond). It depends how the atoms are organised. A cubic lattice bends more easily than a less symmetric arrangement. This changes the shear wave velocity, and it gives us a way to study the inside Earth. It is not always possible to say exactly which mineral fits the data (and we don’t always know how each mineral behaves under very high pressure) but the shear waves can be used to show that the minerals are changing at a certain depth. In practice, olivine has the lowest G (easiest to deform), ringwoodite is about 50% stronger (higher G), and perovskite is again 50% stronger than ringwoodite. (The precise values depend on the exact compositions: adding iron makes it weaker.) Bridgmanite (and related minerals) are similar to ringwoodite, and therefore the 660-km transition is not easy to see in seismology.

Still with me? You reached the end of the physics lesson. Now we know enough to dive into the mantle, in search of the heart of the Earth. But that is for another day, in part II.

Albert, June 2022

90 thoughts on “The living Earth: Rocks, plumes and hot spots. Part I

  1. https://phys.org/news/2022-06-earth-feet-core-oscillates.html
    More information: Wei Wang et al, Seismological observation of Earth’s oscillating inner core, Science Advances (2022). DOI: 10.1126/sciadv.abm9916. http://www.science.org/doi/10.1126/sciadv.abm9916
    JUNE 10, 2022

    The Earth moves far under our feet: A new study shows that the inner core oscillates
    by University of Southern California

    USC researchers identified a six-year cycle of super- and sub-rotation in the Earth’s inner core, contradicting previously accepted models that suggested it consistently rotates at a faster rate than the planet’s surface.

  2. Looking at the plume figure led me to wonder if the centrifugal forces of the earths rotation could play any role in mantle circulation? Wouldn’t this also interact with different mantle densities?

    • Good question. It does in the outer liquid core where the movement is much faster. The mantle is solid, and plumes rise very slow (and the viscosity is very high), so the plume juts follows whatever the mantle around it is doing. That includes the rotation.

    • Along the same lines, I envision the Earth as being a giant centrifuge which helps drive the downward motion of denser material deeper into the mantle than from mere thermal/buoyancy forces emanating from the core (mantle convection).

      • That would mean that deep subduction only happens near the equator. It is the case for the Mariana trench but the Aleutian and South Sandwich subduction zones are at high latitudes. Centrifugal forces go as velocity-squared over radius. velocity for the earth is large (several hundred meters per second) but the radius is very large. So the centrifugal force is not large, as you can see by the fact that you have pretty much the same weight on the pole and on the equator. But if the Earth were spinning ten times faster, you would start seeing things beginning to float away

    • Good point Albert. The centrifugal force is small, especially relative to gravity. If not, we would all live near the poles!

      My questions can be reframed. Does the difference in effective gravity between the poles and the equator have any impact on mantle circulation? Centrifugal force is not a true force. It is a perceived force resulting from the push-pull of inertia from the earths rotation (which wants to send us out into space) and centripetal force (i.e. gravity) which pulls us towards the earth’s core. This clearly affects the earth on a large scale – the earth is a flattened sphere and wider at the poles. This results from the balancing of forces; however, there is a small gradient in effective gravity as one moves from the poles to the equator.

      If this does affect mantle circulation, the forces must be small, and part of a complex, dynamic process. As Alfred notes, the location of mantle plumes and subduction zones does not seem to be correlated with latitude, and viscosity of the mantle is high Moreover, plumes, subduction zones, and crust characteristics (density, thickness) also change effective gravity and the shape of the geoid, but would that affect the mantle?

      I did find this interesting discussion on stack exchange as to whether centrifugal forces might have affected the initial location of Pangea: https://physics.stackexchange.com/questions/630859/had-the-centrifugal-force-of-the-rotation-of-earth-in-the-past-forced-liquid-ho

      Anyway, this is making my head spin, and I wonder if that will affect the shape of my head and the flow of my thoughts?

  3. Alarming coincidence: I was just thinking how I needed to email one of the directors of that very ‘Star Trekkin’ video about an entirely un-volcanic arty thing, whilst chilling out/procrastinating by reading Volcano Cafe. :O

    The Film Garage made it (in a week!) and a few years later, when I left college, they gave me my first job.

    • I find it fascinating to hear these stories. We live in a small world which is doing big things

  4. I will have to find the video, but a while back I remember seeing something that plumes are formed from ocean crust reacting with the core, then rising. Basalt reacts rapidly with iron under core boundary conditions. Maybe that is what the D” layer is, plume starter material.

    This was in specific application to Hawaii, but with broader implications that many large plumes that go to the core are the same. Iceland, Hawaii, Galapagos and Yellowstone all erupt basically the same magma and go to the core, I think Reunion and a number of other Pacific islands are the same, though volumetrically less productive.

    • It is a bit more complex than that. I’ll try to go into that in part II. It got too long so I decided to split the background from the rest. Part I is the hard bit, part II is for real. Should be later this week, unless we get another pina-tonga

      • Thanks for this detailed insight into the inner workings. Not wanting to lower the tone of scientific discourse here, but have you factored in impacts? The variety of gravitational density, plate tectonics, and rift zones always make me consider comets which bring water, and large rocks from space, which dig deep through the crust, and must surely affect orbit, spin, and climate.
        I have been remembering Comet Lovejoy’ passage through the sun in December 2011.

        https://www.nasa.gov/mission_pages/sunearth/news/comet-lovejoy.html

        I have been remembering the slingshot of hot rocks which passed over Brazil in April 2012. Newspaper reports were in Portuguese. And the slingshot traverse of the same hot rocks across the northern hemisphere in September 2012. Our friend in NASA advised that there had been a 3 second bright as day flash over Finland when it started. People uploaded sightings across Northern Europe, the U.K., Ireland, and North America, until daylight.. I estimated they were about 2 miles above the Earth as they passed overhead.

        I predicted that the risk of it impacting was high, on its next arrival, and that we had a timescale and direction, if my hypothesis was correct.
        We were fortunate that it went into a deep lake near Chelyabinsk, and that only minor injuries and structural damage to buildings was reported.

        But there is detailed analysis of the impact pieces, which would seem on a brief reading to support my hypothesis, if anyone would like to write a paper……

        https://www.nature.com/articles/s43247-022-00373-1

        • Luckily large impacts are very rare. They were important at the very beginning of the Earth when we were hit by impacts so large that they created the moon. That era ended very quickly. This was also the time when one or more impacts added some elements that were absent or rare beforehand, such as water and something called the late veneer. Later there was (probably) an impact storm called the late heavy bombardment which would have destroyed much of the crust. But since, we have not had much joy with impacts. Otherwise we wouldn’t be here. Let’s look at the Chicxulub impact, an asteroid perhaps 15 km across. If something like that would have hit us once very 1000 years, over the life time of the Earth it would have added 2% to the Earth’s mass. In reality they hit 50,000 times less frequent. That is why major impacts are considered important for climate and for the local crust when they hit, but don’t affect the Earth overall. Our orbit, the core and mantle, are not affected. But locally they can cause havoc. We discussed some of that in the Hiawatha impact post.

          • Lovejoy or Chelyabinsk was quite small, and if it was the same think it burned off each time it grazed Earth’s atmosphere. Some of the sightings across North America included thumps in the night, when the smaller pieces at the ends of its forked tail probably dropped off in open landscape. It ould have slowed too, on its slingshot orbit, I am guessing.

            The article I linked to above observes repeated hearings and coolings in the fractured make up of the rocks which were gathered at Chelyabinsk. The hottest of these would be its journey through the sun, but also the friction heat which made it glow like coals as it passed overhead on its trajectory.

            The timescale was right, and it landed in the best possible place, where dash cams could record it from many angles, and avoiding centres of population.

            I have a book which supports the hypothesis that Yellowstone was a massive impact which plunged the Farallon Plate vertical, and this theory matches the mountain ranges to the smaller scale impact crater at the South Pole of the moon.

            What split India off from Africa? It travelled fast towards its collision with Asia and the African Rift Zone remains hot. Could it be the consequence of an impact on the opposite side of the planet?

            Or the eye of Africa, in Mali, with uranium of both spent and unspent varieties nearby? To me it seems like an exit wound of something relatively small…..

            Idle speculation, but somebody has to do it……

        • I held a semi moon-bat idea a while back that large impostors had an effect on the locations of plumes, but that was erroneous.

          If you want to get a mental grasp on it, go to the impact effects program and put through a few impact scenarios and keep an eye on the depth of the temporary and final crater.

          https://impact.ese.ic.ac.uk/ImpactEarth/ImpactEffects/

          Additionally, you can check to see if you arbitrarily burst into flame if you are within sight of the fireball.

          Events of this level are beyond inconvenient.

          • It was not such a bad idea. It followed basic rules of physics, sadly though it was impossible to line up any impacts antipodaly. When I looked the suspected traps was at a different location than antipodal.
            I do though not still rule out that it could work and that somewhere out there such an antipodal trap exists, but that it was so far back in time that we can’t track it to a specific large impactor.

      • Exactly! Earths formation scale Impacts are stuff beyond human level of imagination.. tens of thousands of degrees C and Earth enveloped in a rock vapour atmosphere cloud .. Earth shined like star of kinetic energy during really large protoplanetary mergers

        During really energetic mergers Earth coud have been totaly vaporized forming a hot ”magma nebula” which cooling droplets condense and falls back on a remelted magma Earth as the nebula condense back into a liquid magma ocean

        The violent days of Early Hadean

      • Large impacts does not cause flood basalts, They are caused by powerful Mantle Plumes.

        Large impacts are indeed tremedously powerful But most of that energy is lost to space .. and very little goes into the Earth, that have very low heat conductivity.

        Chicxulub vaporized a 180 km wide and 35 km deep cavity in the Crust .. But that only resulted in an 7 km thick and 170 km wide melt sheet .. very little of the impacts energy penetrate deep into the planet.

        But large impacts can form a LIP impact melt Province Of Non Volcanic origin in the impact crater itself

  5. The low altitude vent on Etna is still going, at the same time as the SEC and more vigorous effusive vents higher up. The 1900 m vent is effusive and slow as expected for a lateral vent but then it should have drained all the magma above it if it was really connected to the other eruptions. Maybe it is a lateral vent of one of the other summit conduits, they are all erupting and relatively independant. If this is coming from the NEC then the magma will have cooled a bit and degassed, where the SEC is much more active so the lava is more fluid.

  6. Quite a bit of movement occuring around the plate boundry close to Ascension island. Been about 3 M5+ and quite a few of M4+ earthquakes in the last 2 days.

  7. low-level background tremor has returned to Taal with very high steam plumes, more magma is reaching the surface, and more interesting still is the lack of volcanic quakes as the magma is rising so there must be a pretty open conduit

    • GeologyHub mentioned a bit about this and what how it’s comparing to other recent swarms there…

      May 2022 – present >3,000 earthquakes.
      Sep 2018-Nov 2019 147,000 earthquakes.
      Nov 2013-Nov 2014 132,000 earthquakes.

      They tend to be around 4 – 6 km deep and the and uplift is extensive.

      • It is probably an early sign of a future major eruption, but then these systems can take a very long time to recharge without doing anything. This is basically a resurgent dome caldera except the caldera hasnt happened yet, so it is just the dome.

        Chances are really that this will not do anything for centuries, and that it has been doing what it is doing now for just as long or longer.

        • Chiles-cerro negro has produced 3 major swarms and this looks to be it’s fourth and this one has started with a bang. Looking at the deformation, the uplift is slowing and actually looks like it’s reversing. Deformation plus swarm sounds nasty.

  8. (still with me?)

    Very funny. Concerning some basics I’m always with you when water is involved. If my physics teacher had come along with examples with water (or ice) I would have been a better student.
    The Lego doesn’t catch me that much, that is why I also failed (more or less) in Chemistry.
    Water is life.

    So, Carl beat you with the caldera lakes. Water is beautiful. Fire and water or ice can be dangerous, but is still fascinating.

    There were lots of basics with the article of the Pacific Ocean, and I was drawn into it because of the extremely beautiful map of that large blue beauty that makes you forget that nations fight about it. I studied the magnetic lines on the ocean floor and had no trouble at all.

    Your lego models and also petrology are not as far as fascinating for me as the dancing earth around the Pacific Ocean.

    • The problem with the Earth is that below the surface it is all desert. The only water we have is at or near the surface. So if you like blue, the mantle may not be for you! Part of the core is liquid iron – it has its own beauty. Eye candy

      There is a part II. But that will also be rather dry, I’m afraid

      • No, Albert, these articles are brilliant. Extremely informative and helps me wrap my mind around the inner workings of the planet.

        This is a great series, dry or otherwise. Thank you.

  9. You can very much predict where the next subduction zones on earth will form from eventual sinking of old crust.
    East coast of America. West coast of Africa. North-west Canada/Alaska. North Atlantic Antarctica.
    West coast of Australia. East of Japan.

    Notable that much of these are already adjacent to ongoing subduction zones – in the case of the Mediterranean, Sandwich/Scotia and Carribbean – starting to spread.

    If slab graveyards exist then they could only push hotter material aside and power plumes millions of years in advance, by the time the mantle recirculates, but we also know that rock saturated with water in the downgoing slab lowers the melting point of the rock above as it goes down – case in point the volcanism around Mount Baekdu.

    If that’s the case then mantle plumes nowhere near recent subduction could only really be explained by a non-uniform mantle, very accomodating lithosphere, or impacts.

    • Also Western Europe. There’s a suggestion of a subduction zone under the Iberian Plate.

  10. No official word from NASA yet but Ingenuity Flight 29 navcam landing images have arrived on the raw image server!

    https://twitter.com/martiandennis/status/1536379576015720448

    Dennis @martiandennis
    Sol 465: WOOHOO! The last 5 landing images from #MarsHelicopter Flight 29 have been posted! Genie is still healthy and executed its latest flight to move closer to Percy.

    And for the first time we don’t see Ingenuity’s shadow in the navcam as the flight took place late in the day to allow the batteries to charge. Presumably this flight would be followed by the longest period so far without heating until the next morning so again fingers crossed no further issues arose.

    • And the official confirmation

      https://twitter.com/NASAJPL/status/1536738980766445568

      NASA JPL @NASAJPL
      The #MarsHelicopter successfully completed Flight 29 over the weekend, its first since the start of winter operations at the end of April. On this 66.6-second flight, Ingenuity traveled at 5.5 m/s for 179 m.

      How the team has adapted to recent challenges: http://go.nasa.gov/3tCpCrl

      So obviously the patch to substitute the failed inclinometer with IMU accelerometers worked. Another 3 months or so to go before they’ll have enough solar power to keep the heaters on overnight again.

          • Obviously NASA in cover-up mode as the current best guess is literally a cover – a thermal blanket cover story 🙂

            https://twitter.com/dejasu/status/1536672618497155075

            DejaSu@dejasu
            Replying to @thomas_appere and @GCC_Mars

            Check out the image showing thermal blankets at this @Nasa
            page, I think it shows a comparable match

          • It is from a patisserie oven, I blame the Space French Alien Mars Invaders! 🙂

          • Nah. Just alien teenagers dropping empty crisp packets everywhere

          • Yep the French are also in full cover mode. They give it away by posting analysis in French 🙂

            https://twitter.com/thomas_appere/status/1536780784316588032

            Thomas Appéré @thomas_appere

            Ce matin, en scrollant les dernières images de Perseverance, je suis tombé sur un objet inhabituel. Après enquête par @L3G33K @Corentin_Buti @GCC_Mars et @dejasu
            , il s’avère qu’il s’agit très probablement d’un bout d’isolant thermique. Le vent a-t-il pu l’amener ici ? Thread 1/..
            Translated from French by Giggle Translate
            This morning, while scrolling through the latest Perseverance images, I came across an unusual object. After investigation by @L3G33K @Corentin_Buti @GCC_Mars and @dejasu
            , it turns out that it is most likely a piece of thermal insulation. Could the wind have brought it here? Thread 1/..

  11. Looks like the start of another little burst of activity in the Reykjanes peninsula. A 3.9 mag at 2.1kms depth just north of Grindavik.

    • About 500 meter west of Thorbjorn, and very shallow for such a large(ish) quake, at 2.6 km. The magma intrusion ended two weeks ago, so this is release of pent-up stress.

  12. Thank you Albert!

    This is an article that I wanted to write for a decade, but never felt that I could write in the correct manner.
    I well and truly loved it, far better than I could have done.

    It is also tying back quite nicely to mantleplumes.
    This is how we know how deep the plumes are. We just look for Perovskite, Ringwoodite, Bridgmanite or Peridotite… that gives us a good ballpark of how deep in the mantle it comes from.
    This is how we know that Iceland is a young shallow plume burrowing from top down as it transitioned from Peridotite to more Ringwoodite over time.
    And Hawai’i is all Perovskite in it’s plumey heart, so it is deep indeed.

    Then we have what I call Oddskite. It is not a mineral in the ordinary sense, but it works well as a mineral process at least.
    It is what happens when the D-doubleprime pokes up (at least some believe it, me included).
    We find this when really deep mantleplumes get moving, we can call those coreplumes or coreboundary plumes.
    There are 3 known in geological history, so a lack of nomenclature is perhaps something that can be forgiven.
    You have one in Northwest Africe that did not bother with truly poking through, it just left a very large magnetogravitic anomaly.
    And then there are Norilsk-Talnakh that poked up at the center of the Siberian Traps, and the Kirunavaara monstrosity.
    These all contain extreme iron and nickel deposits suggesting extreme depths. These should not be confused with the hydrothermally altered iron deposits.
    Anyhoo, that is something for another day.

    Just wanted to say nice article.

    And while I am at it… who stole my summer? I blame Hunga-Tonga Hunga-Haapai delivering oodles of water and dust 50km up in the atmosphere. Yesterday I woke up and had morning frost. This time of year we should have every day above 20C, now we have had a single day (in May) with above 20C.
    Instead we have leadgrey skies, dry air, and rain. WTF weather…

    • Thanks! We are having an entirely normal Manchester summer. Meaning, same weather as you, minus the frost. Welcome to the north atlantic treaty weather

      • I am a polite Swede, so I will just state that I have “opinions” about your north atlantic treaty weather…

        • Ah, but now you are nearly new members so will have to toe the Treaty line😄😄😄

    • The US, and Canadian Pacific Northwest are still having mountain snows, and we just had a 4 inch rainfall. Like you, we have only had one 20 so far this year. I think you are right… Hunga-Tonga Hunga-Haapai is probably the culprit.

      • The drumplots show no sign of magma, and the sequence of shocks is typical for tectonic aftershocks. But if there is magma waiting below, it may take a bit of time before it responds to the change above

    • As Albert said, no magma is moving.

      But, what moved a lot apart is an area above 4km. You can see the dilation clearly on the LF drumplot.

      The magma is stuck below 5km, and there is still an area between 5 and 4km that is keaping things below that is “uncracked”. If and that happens the cavity upwards is done and ready waiting for the upwards moving magma.
      But, for now there is a very tight slab in the way, I expect that to break at any day now. And then it is interesting times again.

      • It is an unusual set of signals, it is a very clear tectonic signal, but the LF shows separation. Normally you get fluid movement almost directly afterwards, but there was nothing. So, basically a predrilled dilating dyke that is bonedry waiting for some fluids to come flowing.

        • There is some more quakes happening right as we speak, might be that final push.

          Hopefully this will be fairly small, but history suggests an eruption here will not be slow, a small eruption might only last a few days but still with great intensity, so will be much more hazardous than it sounds. A big eruption might be like Krafla in 1984, a fissure that becomes a single vent,

        • So are we still waiting for a >4.5 – 5.0 magnitude earthquake to let the magma breakthrough? Or can it rise quietly?

          • An M3+ plus a little swarm should do.
            After that it would most likely be a fairly quiet last stage.

          • Svartsengi is also a very hot area, the ground is very plastic and still steaming even at the surface. Same at Krysuvik or Hengill. If there was obvious sign of any of these erupting the final push might be fairly quiet.

        • You look at the length of the long wave amplitude.
          If you have a waveform that has a frequency that is several minutes long it is movement of crust, not earthquake amplitude as such. If you put the LF and HF images next to each other you can see that the VLF is lasting far longer than the earthquake signal itself, and that put together is pretty much a dead giveaway.

          One day I should probably explain this in an article.

          • Are you sure it’s not an artefact from the lowpass filter combined with the ridiculously large impulse the seismometer gets from being directly on top of the quake? I’ve seen similar waveforms resulting from the transients coming from instrument glitches.

          • Are there any other instances of similar magnitude where seismometers are directly over the quakes that you can compare this to?

          • Without having seen what you have seen, not in this case at least.

            If it is a digital cutoff artifact you still have the same total wavelength on both, or just a short spike on the LF.
            Here you have a sVLF signal with a considerably longer duration than the earthquake signal. Also note that the LF component is minute compared to the VLF, it is almost completely masked out.

            Depending on the type of seismometer you can at times see such a signal as the vent is opening up right before the start of an eruption. It all depend on the instrument obviously, most seismos can’t show this.

          • And the first GPS-datapoint is now in.
            Thorbjörn station was kicked 10mm to the West.
            Early days, I want 5 datapoints before we can say anything for sure though.
            But, the kick to the west is likely to be the result of the signal dilation.

            It will be interesting to see if the crack closes in the next few days, or if it remains like that.

            http://brunnur.vedur.is/gps/thorbjorn.html

          • THOB is not the only station with movement. SENG and SKSH also moved a lot to the west, the others moved to a lesser extent. SKSH and MOHA showed upward motion too.

          • I would really appreciate an article explaining how to interpret drum and tremor plots, the different frequency bands of the latter, plus integrating all of that with GPS data to obtain a picture of events down below.

  13. Very nice article! Thanks!

    A question that came to my mind already a while ago: I read somewhere that the total amount of water om Mars is actually quite high if you count chemically bound water in the crust; and, as you write here, the earth is actually quite dry, except on the surface.
    Is it known what is the reason for this? (is it even true?) Is it the fact that Earth is hotter inside, so volcanism and the general heat gradient “boils” the water out of the crust and makes sure it stays on the surface?

    (And so that would mean that once the earth cools, it will also lose surface water into the crust?)

    • I’d expect it to be predominantly because Mars formed closer to the “snow line” than Earth did.

    • Both …. Earth is hotter on the inside and that makes the water rise To the surface.. a hotter mantle holds less water. Earth is also closer to the sun and formed inside the snow – free line as you say. But Venus too had its oceans before they evaporated

      In Earliest Archean When the upper mantle was much hotter and the continents still not fully formed, Earth was probaly a blue sphere dotted with numerous subduction arcs and hotspot chains in a global ocean
      Early Archean Earth was probaly almost competely oceanic .. a true Sea World

  14. Oh, and while I am here, a second question, maybe someone here is in the know about the logistics of seismometers and such:

    Iceland is generally regarded as very well instrumented in terms of seismometers and such.
    However, with the expectation of a new, long-term volcanic cycle starting in Reykjanes, one could imagine they’d be interested in maximizing data and precision to make predictions for that area. The Reykjanes peninsula has stations every 20-30km or so. But with the vast majority of the action located in a 20 x 15 sq km area around Grindavik, it would seem to be efficient to put more sensors closer together in that are to get higher resolution info.
    In olden time the data integration/processing would have been the issue, but most of that is automated, and the data connections should be trivial with the amount of cell phone network that is there…
    Are such stations so expensive? Or expensive to operate for some reason? Or is there simply nothing to be gained, for example because even the depth resolution would not improve significantly with a tighter network?

    • A denser network does improve things, that is what HVO is doing at Pahala, although that is a way bigger and deeper thing than anything going on at Reykjanes.

      I remember also a HVO video or article that said the seismometers cost several tens of thousands a piece for permanent stations… and if there is an eruption having them clustered in the area… 🙂

    • I do have a “tad” of knowledge.

      First of all, IMO always dense things up as needed, and have extra seismometers on hand to put up on short notice.

      Installing a seismometer is not an easy task, you need to find a spot that is less prone to be “noisy” from human and other non-related signals. So, a survey needs to be done.
      After that you have to build the station, normally a concrete structure. This requires a bit of digging to get good result.
      The seismometer can be anything from 5000USD to 500 000USD depending upon type, number of axis, technology used, how exact it is…
      That does not include the rest like power units, batteries, solar panels, transmitters, etcetera.
      And using 5G mobile networks is not always a good idea, especially around a volcano where you can expect several thousand people wearing funny hats while livestreaming things.

      With installation and everything even a sacrificial “simple” unit expected to be blown up can be expected to be close to 100K when all is tallied up.
      And then you have monitoring costs, these also go up in “interesting times” since workload tend to be extreme then.

      In other words, even a fairly simple network with 5 Seismos and 5 GPS stations you easily run into the 1 million dollar range.
      This is your typical local network for volcanoes in Reykjanes, and if warranted this will easily double, and there will also be gas-monitors, webcams, mobile ash-radars… the list is extensive.

      IMOs network is truly a thing of beauty. We tend to forget that since we always want more equipment, but even the base-level is incredible in Iceland.

    • Interesting! The size of the eruption was a bit small for this, but perhaps the sheer height of the plume may have put more in the stratosphere than normal. It will fall out over the the next weeks. There wasn’t much sulphur so I expect little effect on temperatures. (Perhaps not zero though.) The long-lasting La Nina will have more of an impact.

      • Nah, it is 2022, it will cause imminent glaciation as the new iceage decends upon me. After that there will be a large impactor and the Atomic Fruitbats will invade us.
        Still farkin’ cold.

        And no, I am not looking forward to 2023.
        That is when the Space Nazis from Antarctica will enslave us and serve us as dinner to the Lizzard Men of Uranus.
        Japan will though be saved by a Godzilla/King Kong-tagteam, the rest of us are doomed.

        • You are forgetting the new covid variant, hunga-tau-5.9vei and of course the vei-8 eruption of the mud volcanoes of the Crimea.

          And Hekla. How could I forget Hekla. A world-leading M0.9 immediately below the surface spells doom for us all. d-o-o-m

          • Interestingly lots of people I know seem to have had covid in the last 2 months, generally saying it was ‘quite nasty’. All well vaccinated and never had it before.

          • We are not out of the woods. This will be the new variant (Ba 5). There is an increase of cases again and there are some reports of an increase in hospitalizations. Vaccine immunity will be significantly down by now, although protection against severe covid lasts better than against ‘just’ catching it. The UK has not picked the best time to end all monitoring. (And it seems to us that the test kits with ‘best before’ date of 2023 have become pretty insensitive – they age faster than expected.) But in the long term, it is better to have this wave in our summer (25 today) (I just mention it, Carl) rather than in winter when it spreads much more easily. I wouldn’t be too worried but might avoid very crowded places like festivals. Not a big sacrifice in my case.

          • On that topic, how big do mud volcanoes actually get in terms of eruption volume? I know that sometimes they can last a long time, like the Lusi volcano in Indonesia. But then that one probably wouldnt have happened naturally, so hard to say.

            I guess it would be hard to tell a big eruption of a mud volcano from a landslide or debris flow of other origin.

          • They can get to 0.2km3, perhaps larger. The Indonesian one may be 0.02km3 – it is hard to find an accurate number, and of course a mud eruption causes significant deflation of the ground which makes it hard to measure the volume. They can grow to 100 or 200 meters but that is exceptional.

  15. Still writing on my Nyiragongo Article.. refining it
    Making it better and more readable

    • We are looking forward to it! And we can help you with the editing. We do this more often for guest posts

    • The Photos must be included and I noted the source and photographers in every one and provided links

      Without the Photos .. this text will die

      Im still working on it .. will be about Nyiragongo and a look at its magma and some general information and a little discussion: all in my own words: Im also collecting links

      Its in my computer .. its been a little slow recently since my mental health is tired

      The lenght of the Article is long since completed: now Im refining the text and that takes some time. But finaly its up To you to make it really good

      I will try To work on it .. a little this evening

    • HVO is starting to think it isnt rootless anymore, the lake responds closely to tilt, not quite so much as the lake before 2018 but then that was literally the exposed magma conduit, where a conduit today would be submerged and buffered somewhat.

      My guess is there are probably several open conduits, the shallowest one being the known vent area but there were obviously other vents open when it all began last September, the deeper ones might be more like drains, the net input to the lake is about 3-4 m3/s but the flow in that whirlpool looks significantly higher flow rate. There was a vent within the lake that stayed open for about a week at the start, that might be the main drain, all vents from the start are deeply submerged, the west vent began above the lake and is now over 100 meters deep under it.

      • I’ve seen a few swarms around that size in the past few years, I read a few times that it tends to be hydrothermal activity.

        Though if I had to put money on the next Canaries eruption it would probably be on Teide or if it takes too long (50 years or so) another Cumbre Veija one.

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