Kerguelen, Amsterdam/St Paul, and Iceland

How Australia became an island

rossmer2
(https://elowyn.wordpress.com/2010/06/04/kerguelen-islands/)

By Albert

The oceans were once less known than the Moon. Perhaps this is true no longer. Gravity maps released last year show remarkable details of the ocean floor. Chains of (ex-)volcanoes are everywhere. Spreading ridges and transform faults are visible. Under water plateaus around islands are revealed. A new world has opened up.

A large, deep underwater plateau in the far southern Indian Ocean shows up, with an island on top that looks like an inverted version of Iceland. A quick search shows that the island is already discovered (by Kerguelen – twice), named (by Cook – twice), owned (by France), and occupied (by a colony of scientists). The main island is surrounded by an archipelago of perhaps 300 much smaller islands (I am not sure whether anyone has actually counted them). The archipelago is called Kerguelen Islands (Cook’s second name was Desolation Island). Kerguelen is supposed to be the most isolated piece of occupied real estate in the world. It is reachable only by boat across a storm-swept ocean. Questions arise – why is it there? Why the underwater plateau? And why does it look like an Iceland of the South?

gravity

As so often, the first stop for more information leads to Volcanocafe. A post by Alan gives fascinating detail on Kerguelen. The plateau is a ‘micro continent’, rather larger than shown above, traces a hot spot/mantle plume — and it was responsible for breaking up Gondwana. The kind of post that makes you want to know more!

The full underwater plateau is shown below (image credit: Australian government). It is over 2000 km long, covers an area of about 1.3 million square kilometres (four times the size of the British Isles, one sixth of Australia), and was created by volcanic eruptions. The southern end of the plateau formed 120 million years ago. The northern end, with Kerguelen itself, is younger, at 40 million years. But the age structure is complex, and in fact the central part, with Heard Island and McDonald island, has the youngest, and active, volcanoes (the only active volcanoes owned by Australia). Drilling has found evidence for charcoal: at times part of the plateau, now 2 km deep, was above water and covered in forests.

KerguelenPlateauKP

The large area qualifies it as a large igneous province (LIP). By definition, this is an eruption area covering more than 100,000 square kilometres. Kerguelen is larger than the Deccan Trapps. Eruptions this size, even if spread over as long as 50 million years, are often attributed to hot plumes melting the lithosphere below the eruption site. The head of such a plume can extend over 1000 km. This has lead to the hypothesis of the ‘Kerguelen mantle plume’. One problem with this hypothesis is that ocean floors move, and one place would not be expected to stay over a mantle plume for that long. It is hard to think of another explanation, though.

The map below shows the location of Kerguelen in the Indian Ocean (click to see full detail). Faintly visible is the SouthEast Indian Ridge, the ocean spreading centre between Kerguelen and Australia (the transform faults are better visible than the spreading ridge). Much clearer is the spreading ridge toward Africa. A straight line extending almost due south from the Andaman Islands is called the Ninety East Ridge and may be a hotspot trail. Just to the right of where it ends is the Broken Ridge. This is now best known as the area where the search for the missing MH370 flight is taking place, but Broken Ridge was actually part of the Kerguelen Plateau, separated by ocean floor spreading. Go back more than 100 million years, and the Indian Ocean didn’t exist. All of this was at the heart of East Gondwana, the last supercontinent.

IndianOcean indianocean_formation

Reeves and DeWit have calculated how the various spreading centres, active at different times, would have acted to form the Indian Ocean, starting from ancient Gondwana (click on the image above to see more detail). The ‘K’ indicates Kerguelen. ‘RT’ is the Rajmahal Trapps in India, near the border with Bangladesh, dated to 118 million years ago: in the simulations the Rajmahal Trapps, Broken Ridge, and Kerguelen belong to the same LIP, separated near birth. When the SouthEast Indian Ridge formed, 43 million years ago, it disected the Kerguelen Plateau; Broken Ridge broke off and became stranded on the India-Australia plate. (‘DT’ stands for the Deccan Trapps which formed, almost as an afterthought, 65 million years ago.)

Once separated, India moved very rapidly across its namesake ocean, leaving a trail of debris behind. One of those bits of debris is the Ninety East Ridge. In the picture below, it is shown beautifully as the line roughly north-south just above the centre. The top end is about 80 million years old, the bottom (where it connects to Broken Ridge) 43 million years. Re-connecting it to Kerguelen (following the transform faults, roughly southeast-northwest) shows that it came from the northernmost end of Kerguelen plateau — where the Kerguelen Islands are. It seems a typical hotspot trail. However, note how the SouthEast Indian ridge is offset towards Kerguelen in this position, with the hotspot located at the top end of this offset. This suggests an overactive transform fault rather than a hotspot trail. Perhaps it is a combination of both?

Kerguelen_Plateau_Location

How did Gondwana break up? Africa/South America split off from the rest 180 million years ago. India separated from Australia between 150 and 130 million years ago. Next, India separated from Antartica. A sliver of the continent became the Kerguelen micro-continent. Finally, perhaps 100 million years ago, Australia separated from Antartica. India migrated to form a new partnership with Asia, leaving Australia isolated — the island ark it is now.

In the traditional picture, continental break-up is caused by mantle plumes, affecting large regions. India could have required several plumes. One is associated with the Comei-Bunbury LIP (connecting southwest Australia to current Tibet) which was probably erupted within 5 million years, around 132 million years ago. 15 million years later, the Kerguelen plume continued the division. Was this an accidental coincidence, was it the same plume, or was it in some other way caused by the earlier plume? It also coincided approximately with the Ojong Java Nui, the largest LIP in the past 300 million years (it may have covered as much as 1.2% of the Earth), emplaced below the sea 125 million years ago. Was the Earth a tad active at this time, or are we too quick to ascribe all LIPs to mantle plumes?

Although mantle plumes are the more likely, there are other models. In one of these, the thermal insulation by the thick supercontinent causes the mantle underneath it to warm up. The heat lowers the viscosity and can cause sideways convection. Once it reaches the edge of the continental plates it can melt through. This would explain why the breakup starts at the edge, and appears at multiple places in close succession. A warmer upper mantle can also suppress mantle convection underneath the continent, reducing the heat flow. To compensate, the heat flow and convection around the edges of the continent would increase.

In the case of Gondwana, a possibility is that as the Comei-Bunbury plume forced India and Antartica apart, the spreading caused the lithosphere to thin. The reduced pressure, together with heat from the distant mantle plume, allowed de-compression melt, and it was this melt which caused the Kerguelen-Rajmahal LIP, pretending to be a mantle plume.

What happened afterwards is also interesting. Kerguelen remained ‘hot’ and subject to eruptions. A spreading centre developed across it, probably not by accident but due to the fact that the lithosphere was weaker here. Most of Kerguelen ended up on the Antarctic plate, pulling the spreading ridge with it. The resulting transform fault lead to Ninety East Ridge. Whether Kerguelen stayed hot because of residual heat and melt, or that it accidently managed to stay exactly above a remnant hotspot, is a good question. A shallow hotspot (residual heat) could move with the oceanic crust, fixing the relative location. For a deep hotspot this is much harder.

Amsterdam_StPaul
( Figure from Janin et al.)

The Kerguelen spreading centre finally let Kerguelen go and moved north east. A new plateau developed on the SouthEast Indian Ridge. It currently breaks the surface in two places, Amsterdam Island and St Paul Island, both volcanic — one of a few places in the world where mid-ocean spreading ridges come above the surface. Under water, a chain of extinct volcanoes points towards the Ninety East Ridge, with the unlikely name of the Chain of Dead Poets. The gravity map shows that this chain continues all the way to the end point of the Ninety East Ridge. Thus, if there is a hotspot, it is not even clear whether it is now underneath Kerguelen or underneath Amsterdam/St Paul!

Is Kerguelen like Iceland? Both sit where continents once split, and both are in fact the last phase of this split (in the case of Iceland, about 50 million years ago, when further south Europe and America had long separated). Both captured a nearby spreading ridge, causing transform faults, and both stayed ‘hot’, not letting the hotspot move away. They even have the same climate. Iceland and Kerguelen are not identical: they differ in age, level of activity, and presence of a continental crust. The Indian Ocean is not the Atlantic. But the similarities are fascinating.

Albert

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55 thoughts on “Kerguelen, Amsterdam/St Paul, and Iceland

  1. I particularly like that last bit. Isotope measurements have hinted at a non super deep source of the hotspot in Iceland. More of a mid mantle feature.

    That it’s there is evidenced by the North Atlantic LIP, and seismic tomography have shown the presence of a slow speed region that looks quite a bit like a large dollop of something upwelling there. But how deep it goes is a point for research.

    If anyone interprets this as me saying that it’s not there, you are flat out wrong. It is definitely there, and some IMO comments are that it’s in an incipient state, (meaning it’s growing).

    BTW, a fantastic article Albert, many thanks!

  2. Reunite Gondwanaland!-my old Geology professor had that on a bumpersticker.
    Great post… I had no idea..
    Been at Redmond, Oregon for training for Air Attack and Fire Patrol. Was out over the Newberry and Lava Butte area dodging thunderstorms…

    • Some reminder. An entire culture was wiped out in very short order, never to be seen again except through the prism of archaeologists. And this was not some long past ancient culture, this was a thriving culture just 200+ years ago, done in by it’s unfortunate placement fully within the pyroclastic flow region of their volcano.

    • There is a book available about Tambora. De schaduw van Tambora, by Philip Dröge, 352 pp, € 19,99, Unieboek/Het Spectrum. Just published. Dutch language.

      Haven’t seen it yet; there was an article in the paper about it.
      “Dröge is research journalist and has a passion for natural disasters”…, ” did three years research on the subject in several libraries, as the Hernhutters library in Germany.” Interesting.
      “In Boston birds fell dead from the sky, in many European countries harvesting failed causing famine. Paintings of Williams Turner contain sunsets with remarkable colors. Climate worldwide has been influenced badly for a period of at least 2 years. The number of victims is hard to estimate, also because of the fact that many casualties has been caused by the famines 1 1/2 year after the eruption. The eruption itself and the following tsunami would have caused 40.000 – 90.000 victims. (Translated from Newspaper Trouw, 9 april 2015)”.

  3. Had one of those “I wish I had a camera.” Moments. flew out of Redmond going
    over to Prineville. Did landing practice in the Cessna 206 then back to Redmond.
    On return the clouds opened up, revealing the Three Sisters, Broken Top and
    Bachelor in all their volcanic glory…
    Been having a great time with this it is good to be back in the saddle…

    Riders in the Sky
    I love Western Swing, BTW

    • I always carry a camera with me. Generally as a talisman to ward off anything worthy of being photographed from actually happening. (Auto accidents, UFOs, unexplained phenomena, etc) It’s a way of playing Murphy’s law to my advantage. The idea is that if I am always ready with a camera, it’s less likely to happen. The one time that I had a vehicle incident and a camera, it turned out to my benefit anyway. He got listed as “Driver #1” on the report, which is a clear sign to the insurance company that he was at fault. I had no damage worth noting. I took photo’s of his vehicle from a distance, telephoto is great for that. The images proved that he had no damage worth noting either should it have come to that. He had tried to force me off the road when his illegal pass didn’t work and we made contact. Pissed, he pulled off to call the highway patrol and report me as a hit and run. I pulled off a half mile down the road and called directly to their trouble desk and let them know what was going on, and that I suspected that I was being set-up for such a claim. I then walked up into the trees and sat down with my bottle of water and waited for the trooper to show up. My dad had always said to keep a camera with you if you are out on the road. As “Driver #1” he would have had a really hard time selling that he was not at fault to the insurance company.

      This logic is faulty: Ever since I have carried a camera, I have seen not one UFO or unexplained critter out on the roads. That’s bona-fide proof that it works! (can you identify the logic fault?)

      • The logic implied is that there ARE UFO’s and unexplained critters to be seen, if only you had a camera. At least I think that’s the faulty logic.

        I think it’s very strange that UFOs and weird beasts are only captured on blurry shots, if at all. To me that implies faulty identification. A couple of years ago, in an area where Big Cats are supposed to lurk (but never caught on camera) a viewer to the local TV station reported seeing a pure white deer. Within two days a local photographer had gone out and got perfect close up shots of this very rare, but not in any way unexplained, creature. Deer in this country are shy and reclusive, like any self-respecting big cat would be, but it was soon found and caught on camera. To me this points to the deer being very real and the cats being imaginary, or mis-diagnosed feral/domestic cats.

        • Took me a while to realise you meant Big Cats, Talla! 🙂 Here I was wondering why large motor vehicles were lurking… For white deer they can come to my workplace in West Sussex. Loads of them around here. Proper white ones including stags.

        • Yeah, “Big Cars” got me too. Here I was thinking of Large bore Hemi’s and Big Block Fords… or even the line of Rat Motors from Chevy.

          I have corrected it to “Cat”

          As for cars and deer, it usually doesn’t turn out well. But it’s not as bad as hitting a hog. I’ve done the deer thing, but never a hog, (Thank God!).

      • Actually wouldn’t have had time- another factor added into my own “I wish I had”
        moments in aviation is as soon as you key , say “Redmond Tower” on the radio, the whole Airplane world descends on the airport- and in the interest of safety
        you forget about the camera…

      • I think the issue is more that all the stuff that are easily seen are more or less explained and what is left are incredible rare phenomenon or those occurring in hard to reach places.

        The problem is that currently science has developed an aversion to various subjects. Resulting in phenomenon like Ghost and UFOs being ignored. While serious investigation in them could result in valuable information in fields like psychology and atmospheric phenomena. Or at least show that people are taken serious so they don’t fall prey to superstition and such.

        After al it is not that long ago that we laughed about people coming back with stories of big apes living in the Jungle. Or weird lights shooting in the sky on top of lightning storms.

        • I agree that there are phenomena that should be looked at, such as ghosts and UFOs, but all too often the people who say they know what causes these things are just as zealous in their beliefs as the people who say they cannot exist. I’ve seen several Flying Objects which could not be Identified, I’ve even seen a classic UFO at a UFO hotspot! But, although it happened nearly 50 years ago I am still waiting for an explanation that fits in and explains what I saw. I like to keep an open mind on most things and am quite happy to have my ideas and beliefs changed radically – in fact I find it quite refreshing! 🙂

        • The only “UFO” that I have “seen” wasn’t visually seen by me at all. I picked up a radar that had characteristics of being on an aircraft, but nothing was within range of our air search radars. The rate that it tracked meant that if it were actually an aircraft, it had to be doing an abnormally high rate of speed in order to fit the physical constraints from the available measurements. Only one aircraft that I know of could have physically done that, but the parameters of it’s equipment were beyond my level of access, so I will never really know. Technically, that’s a UFO. It was flying, and it’s unidentified, though I have a pretty good idea of what it was.

  4. Thought I’d say – extremely interesting article! Definitely makes you wonder whether Iceland is or isn’t related to that same hotspot that caused the Siberian Traps. I know Carl used to be in favor of this thought, but it wasn’t universally accepted, and there are definitely some issues with the idea.

    One thing that struck me as odd with the thought that Iceland was one continuous hotspot tracking around the north atlantic is that there isn’t a consistent line of magmatic output that forms a neat “line” as you see in other hotspot tracks like Hawaii. If we were assuming it is a deep hotspot that is tracking around the continent like Hawaii, it is odd, because it seems to have massive output, but that output hasn’t been consistent. Even with the assumption that it’s previous spot was over by Greenland, it seems to have jumped from Greenland to the current Iceland spot without much output as it traveled between the two areas. The same is true in other areas of the North Atlantic, where there are quite a few LIP’s which are attributed to the Icelandic plume, but they all pop up in “spots”, instead of one more continuous line.

    If this IS a continuous hotspot, why does it seem to shut off for a while then turn back on? And when it turns back on, why does it do so with much greater vigor than other more consistent hotspots like Hawaii? And of course, the final question remains, Is this a deep hot spot at all, or is Iceland another type of hotspot altogether?

    One thing I’ve noticed with the initial studies and research done on hotspots, is it seems there was a rush to generalize them, and many assumed all hotspots were essentially the same. At this point, this is clearly not the case, but I still see a lot of assumptions thinking all hotspots are very similar. I can’t help but think that many hotspots are formed from entirely different dynamics in the mantle and lithosphere, and I’m sure I’m not the only one who sees this. Comparing the East African rift hotspot (or rather, hot “area”) to a hotspot like Hawaii simply doesn’t work, and I’m 98% sure their dynamics are very different from one another.

    • You are raising good points. A possibly related question is why supercontinents can fracture along the line where they first stitched together? In the case of Europe/America, they collided to form Pangea along the Caledonia/Apalachian chain. When it broke apart again, the break happened along almost the same line – not identical (parts of the mountain chain are now on either side of the Atlantic) but pretty close. But the crust thickens a lot along the line of collision spot this should have been the place where Pangea was strongest. If the splitting is due to the Icelandic mantle plume, why did this pick exactly this location to appear?

      It has been suggested that the preceding subduction zone is at fault, and that Iceland’s activity is because it sits above a bit of subducted material.

      • Carl has noted that issue before in some of Hekla’s magma samples. A few of them more closely resemble subducted material chemistry than they should. Some people’s take on it was that the Hreppar microplate was starting to subduct and was the source. Personally, I think this is erroneous. There was enough chaos going on during the formation and demolishing of Avalonia to provide embeded subduction zone fragments all through the region.

        My pet theory, and just as likely wrong, is that Icelandic crust is so thick that it is due to a section of continental crust being laid on top of an old section of oceanic crust… like a pancake.

        No evidence, just an idea.

  5. Sakurajima update: I’ve just been speaking to a friend in Japan, who has relatives in Kagoshima. They state that even locals, who live with the volcano and are usually very blasé about it, are becoming distinctly concerned. Inflation is continuing quite strongly, I’m told, and I’m trying to get more details – where exactly, how much, maybe an interferogram. Volcanologists are being fairly restrained and tight-lipped, in public at least, so far.

    Visual observations at the webcam have been difficult due to the weather over the last few days, but during those times when visibility has existed, the volcano has been in virtually continuous eruption.

        • Thanks!

          And just as a reference to other readers, Sakurajima has been nearing the level of inflation it had before the early 1900’s VEI-4 eruption, and that was prior to this current level of inflation (which we’re still awaiting details). Many volcanologists are expecting a decent sized explosive eruption of Sakurajima within the next 50 or so years as a result of the ongoing inflation as well as the overall history of the volcano.

          And while the frequent explosions are fun to watch on the webcam, they are not particularly large or productive. I believe the cumulative ejecta from the explosions over the past 4-5 years it not even equivalent to a VEI-2 eruption in total, so while it is degassing slightly, there isn’t as much pressure being relieved as you would perhaps think.

          Before the VEI-4 eruption in the early 1900’s, there was a lot of rapid inflation that occurred, as well as some significant earthquakes. If Sakurajima decides it wants to do more than the daily puff, it will likely become readily obvious without needing to be a volcanologist that something is “up” at the volcano.

  6. Albert thank you so much. I find the scatter of remote Islands in the South Atlantic and eastwards absolutely fascinating. You have given me so much info there to add to my knowledge. How anyone manages to eke out a living on some of those Islands is amazing.
    There is just so much to learn still. Discovery is never ending it seems…and just when a nice theory fits all it all goes T*ts -up 😀
    A good scientist should have an open mind. A bad one gets left behind.
    Ghosts and UFO? I think most people have had an unexplained happening. I have seen a “ghost” One night, driving from Kingston to Spanish Town (Jamaica) in our beat up VW beetle . Ex-husband slammed on brakes as we nearly collided with an elderly man dressed in light coloured 3/4 length pants and a grubby white top. He had a small jack Russell terrier type dog running besides him. It was a fraction of a second from the jolt of stopping suddenly to looking out to cuss the stupidity of the man we had nearly killed. There was nothing. Nowhere for anyone to hide in the open savannah type countryside. We had both seen the man. I had shouted something like “Look out” as the driver also reacted by braking.
    On telling the tale to Mamma Dee ,who lived next door and having no previous knowledge of the area ( We had only been in Jamaica a couple of months ) we were informed that the huge Cottonwood tree that grew next to the road at the site of our experience was a “Hanging Tree”. Where runaway slaves were hung in cages as a warning to others slaves who may be contemplating escape.
    Evidently others had also seen similar “Duppies/ghosts” on the road there.
    I can’t explain what we both saw. I cannot also just accept it was a “Ghost”. It was an unexplained happening like an Unidentified flying object.
    Out of curiosity I have just googled Cotton Wood tree Spanish Town Road Jamaica and I found this! So no hangings recorded there. What did we see or think we saw? We had absolutely no knowledge of these stories. It was an unpleasant experience but I’d love know why why it happened.
    https://books.google.co.uk/books?id=71MEAAAAMBAJ&pg=PA78-IA6&lpg=PA78-IA6&dq=Cottonwood+hanging+tree+slaves+jamaica&source=bl&ots=Ug8E9RJ6Uy&sig=3nCFy7SFGbeUTmbAZ3z6cfGkd7Y&hl=en&sa=X&ei=CJQnVaWCLoHTaPjzgYAM&ved=0CCoQ6AEwAg#v=onepage&q=Cottonwood%20hanging%20tree%20slaves%20jamaica&f=false

    • The problem is that the oceans are not becoming acidic. They are becoming less alkaline. The amount of buffering there is pretty phenomenal. Sure, it just denotes a direction in pH movement, but the phrasing is being specifically selected in order to hype the phenomena.

      Now, if you want acidic, the waters around the vent south of La Restinga (Bob) reportedly approached that of battery acid for a while, killing fish. This was during the period that one of the bureaucrats was calling for an amateur underwater photo contest while trying to downplay the eruption. Carl inadvertently mistook his name as “Perfido,” In my reckoning it was a more descriptive moniker, through it was a mistake. And that was due to teh SO2 being emitted from the vent. Scale that up to cover all the eruptions along the MAR that happen all the time, and you begin to wonder why the whole of the oceans are not already the pH of battery acid. Simple. Buffering from all the dissolved carbonates.

  7. Another thought – isn’t Grimsvotn normally aseismic? There have been quite a few quakes near the primary caldera recently. Nothing huge, but I don’t believe Grimsvotn ever does any particularly large quakes anyway.

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