The Silverpit crater

Crack patterns in ice and rock

First a little warning to all volcanoholics: The only direct connection this post has to volcanoes, is the crack pattern of Katla’s cauldrons!

In July 2011 geothermal heating caused local melting of Katla’s icecap. Internet soon brought aerial footage of the formation of circular depressions on the ice surface, the cauldrons – or in Icelandic, “sigkatlar”.

Katla cauldron on 10 July 2011, picture by the crew of TF Life. From:

The remaining ice “roofs” above the molten areas were not longer strong enough to carry their own weight, and not plastic enough to bend. So they had no choice, cracked / broke and dropped until a new state of equilibrium was reached. Each cauldron shows a circulair pattern of cracks around a center.

Ever since this images appeared I have wondered if rock would fracture in the same way under similar circumstances. A sudden subsidience or uplift of rock layers because of magma movements might be a comparable situation.

Then one day I ran into this seismic picture of the Silverpit crater. In the first place it fascinates me because its pattern very much resembles the pattern of the cracked ice of the Katla cauldrons.

Silverpit crater seismic map. Credit and copyright: Phil Allen (Production Geoscience Ltd) and Simon Stewart (BP). From:

The Silver Pit is known as a submarine valley in the North Sea, about 45 km east of Spurn Head of East Yorkshire, England. It is thought to be a tunnel valley formed by subglacial erosion and once, when the sea level was much lower than now, being a part of the Wash river. The Silver Pit is currently covered by sediments up to 1500m thick. Fishermen are familiar with the Silver pit fishing ground.

Search for natural gas deposits in the North Sea led to the discovery of a crater-like structure in the Silver Pit. Geoscientists studied three-dimensional seismic reflection data and discovered unusual concentric rings with a diameter up to 20km.

The scientists think the structure is the result of a 60–65 million years old meteor impact. In 2002 the discovery and the impact theory were published in the Nature journal. Abstract here.
If the crater actually is a meteor impact and the age is correct, the impact could be part of the Cretaceous–Paleogene extinction event which led to mass extinction about 65.5 million years ago.

silverpit section

Cross section of the Silverpit crater. From: Journal of the Geological Society; 2008; v. 165; issue 4;

A fact that speaks for the impact theory is the presence of an uplift, a central peak in the middle of the crater.

The impact theory is however disputed. Salt withdrawal in the underground has also been suggested as a possible reason for the crater-like subsidience. A proof for the impact theory might be the finding of molten host rock at the crater bottom, caused by the extreme heat of a meteor.

But whatever the final conclusions about the structure will be, its crack pattern has at least been visualized and scientifically documented.


More information:


Just to compare: A picture of a well preserved impact structure on Jupiter’s moon Europa:

Europa impact crater

Image from NASA / JPC Planetary Photojournal


168 thoughts on “The Silverpit crater

  1. PETROPAVLOVSK-KAMCHATSKY, December 11 (RIA Novosti) – The erupting Plosky Tolbachik volcano in Russia’s Far Eastern Kamchatka Peninsula is spilling a record 1,200 metric tons of lava every second, local seismologists reported on Tuesday.

    The 3,085-meter Plosky Tolbachik, which is part of a volcanic complex located 343 kilometers from the region’s capital of Petropavlovsk-Kamchatsky, erupted on November 27 for the first time in 36 years.

    “This year’s eruption is very powerful. During the Great Tolbachik Fissure Eruption in 1975, the volcano spilled on average 40 cubic meters of magma per second while at present its ‘productivity’ is about 400 cubic meters or 1,200 tons per second,” said Gennady Karpov, a deputy director of the Institute of Volcanology and Seismology under the Russian Academy of Sciences.

  2. Here is an example of rock subsidence caused by sub-level caving,+Western+Australia,+Australia&hl=en&ll=-27.819066,120.705285&spn=0.009109,0.016512&sll=37.0625,-95.677068&sspn=65.390746,135.263672&oq=leinster+w&hnear=Leinster+Western+Australia,+Australia&t=h&z=17

    Sublevel caving is the process of extracting “ore” and letting the roof collapse overhead. In the mine below, the open pit is ~180 meters deep and, I think there was some underground mining done below the pit to some depth before they started the caving operation @~500m

    You can see in the picture the surface expression of the subsidence. The subsidence cracks follow a roughly north-south trend on the left hand side. This co-incides with the angle of the strata which dips approx 60-70 degrees from horizontal. To the south end of the pit, it start cracking across the strata and is more like the ice subsidence.

    If i recall, the mine shaft and office buildings to the north west will need to be relocated or be sucked into the cave.

      • Yes it is a Nickel Mine…how did you guess?

        Caving a few years before i worked there, and teh surface expression started when i was there, so maybe it took 3 years or so to break though to the surface. I worked there 3 1/2 years and it it was half way to how it looks in the photo.

        The orebody is full of ultramafic type rock, I do recall the geologists described it as serpentinised, it did have a slippery texture about it. The rock was almost plastic in behavior. We used to tunnel 6mx6m wide and when retreating the cave, the adjustment of rock pressure woudl squeeze the tunnel sometimes down to 3m wide. It was protected by lots of fibre-create (spray on contrete with small metal slpiters and mesh to hold together the crushing concrete wall.

        • I googled it! It must have been a strange experience to be inside that plastic rock. To me it looks like it sinks down like a big jelly instead of cracking / collapsing like solid rock or concrete.

  3. I do have issue with the impact idea.

    How is it, that the surface deposit are so undistrubed? An impactor of this size… the size needed to remove that much underlying material, would decimate the surface structure.

    Have any drill holes been made to look for things like shocked quartz or cone fracture features?

    • Yep,
      Never seen that kind of concentric / circular structures and sagging even in complex craters. If you show me that and ask what it is, and me not having been led to the trail of impact, my first idea would be to think that thing in terms of some kind of sagging. And I’d be buffled by the buckle in the middle. But an impact? No crater rim, no typical deposits inside or around the crater…
      Very interesting. Really needs some additional info. As you say, PDF’s in shocked quartz and that stuff.

      • A description of “the buckle in the middle”:

        “The exact mechanism of the forma-tion of central peaks and central uplifts in impact structures is still not clear. On Earth, most craters are either deeply eroded or covered, and thus not accessible or not in pristine condition. A high resolution study of lunar craters woulkd be highly desirable to provide data on structural elements of central uplifts of iimpact craters of various sizes.
        Complex craters: Impact craters (before post-impact modification by erosion and other processes) occur on Earth in two distinctly different morphologi-cal forms – simple and complex craters (the exact change-over diameter between simple and complex crater depends on the composition of the target). On the Moon the changeover diameter is at about 15-20 km crater diameter, and very large craters are multi-ring basins, which are rare on Earth.
        Complex craters are characterized by a central up-lift. Craters of both types have an outer rim and are filled by a mixture of fallback ejecta and material slumped in from the walls and crater rim during the early phases of formation. Such crater infill may in-clude brecciated and/or fractured rocks, and impact melt rocks.”

        The article also describes research that has been done on the central uplift of the Bosumtwi impact structure, “a moderately sized (10.5-km-diameter) and well preserved complex impact structure that was recently the target of a multidisciplinary and international drilling project.”

      • Sissel said: “First a little warning to all volcanoholics: The only direct connection this post has to volcanoes, is the crack pattern of Katla’s cauldrons!”
        But from the paper (p. 213) Shérine France cited the connection is rather direct:
        “What becomes clear from the
        well-calibrated seismic stratigraphy is that the SC was created
        during the Palaeogene in the axis of a growth syncline that had
        its origins in Zechstein Supergroup halokinetic flow and salt
        withdrawal at depth initiated by heat flow consequent upon
        dyke intrusion.”

        • Several drilling has been carried which allowed the dating of the structure. Unfortunately, these drillings did found no definitive evidence to confirm the exact origin of the structure. This crater will keep long time her mystery.

  4. Katla cauldrons: actually Icelandic scientists said that in July 2011 what most likely happened was a subglacial eruption of Katla. Geothermal heat cannot melt such a large part of the glacier!

    In Iceland, a VEI2 eruption CANNOT erupt through the ice of Vatnajokull or Myrdalsjokull, since it is too weak to do that; it only melts part of the ice. Only an eruption of intensity VEI4 or stronger can create such a ash cloud powerful enough to cut through the 800 meter thick ice caps.

    • And in July 2011, there was most likely not only one subglacial eruption of Katla, but also one of Hamarinn volcano, beneath the ice cap. Both eruptions were probably in the range VEI0-VEI2, as often occurs in Iceland, which cannot create a ash cloud through the thick ice cap.

      After that summer, I had a flight above both ice caps, and I saw many cauldrons at both of these volcanoes, which were not there before the July 2011 events.

      • Very true. I’d just like to add the geographical separation of the craters into three distinct groups of which only one coincides with the inferred area of the small subglacial eruption would suggest that the in the other two areas, the processes responible for their formation is other than a subglacial eruption.

    • Irpsit, I’m quite sure you are right about the subglacial eruption. Just did not want to call the event that, as it does not seem to be commonly accepted. Please correct me if I’m wrong.

  5. Reply to last post (to Inge): yes, the earthquake pattern you posted does reflect the two tectonic faults of the Tjornes transform zone. Both faults seem to be releasing a lot of stress recently.

    This does not seem to stop. There has been enough time since the last major earthquake, especially in the Husavík-Flatey fault, for a new major quake to occur.

    Its not going to be with small earthquakes – even if they are by thousands – that the strain is going to e sufficiently released. Because one thousand M2 earthquakes is only equivalent to one single M5 earthquake. We have probably at least 10x more of this energy to be released (to give approx a M6 earthquake).

  6. Just came home, and after shoveling away the snow from the walkway like every houseowner has to, here in my homecountry, i found this very nice post. Thank you Sissel!!!

  7. New magma intrusion?

    11.12.2012 16:56:22 65.026 -16.462 24.8 km 0.2 99.0 6.9 km ESE of Dreki
    11.12.2012 16:56:06 65.062 -16.456 23.3 km 0.3 99.0 4.3 km SW of Herðubreiðartögl
    11.12.2012 16:55:59 65.032 -16.454 15.9 km 0.5 99.0 6.9 km SSW of Herðubreiðartögl
    11.12.2012 16:55:50 65.050 -16.440 22.4 km 0.7 99.0 4.9 km SSW of Herðubreiðartögl
    11.12.2012 16:55:33 65.051 -16.436 22.2 km 0.6 99.0 4.7 km SSW of Herðubreiðartögl

    • Could well be. Very small ones, but at an interesting depth, and Askja is “under the microscope” (as Icelanders say: “undir smásjá”) since last summer, or even longer, I’d say. All of them confirmed.

      There has been a remarkable uplift at Askja lately:

      There was also this (possible) intrusion at the high temperature or low temperature areas at Öxarfjördur , and I saw somewhere that this also could be connected to Askja’s system. Which then would be longer still than Bárdarbunga’s and the longest in Iceland. (over 200 km)

        • Carl tried to get access for me to that set, but there are a cartload of vectors that have to be backed out in order to get meaningful data. As such, they tend to be protective of the raw data since its the core of a lot of research, and unless you know what your doing, its meaningless anyway.

          Some of the stuff that has to be accounted for: Continental Drift, Lithostatic Rebound, Noise, Path loss and delay, what particular Geiod you are using for the shape of the Earth, etc. Mess up on any of that and you are out in left field.

        • In essence, the data we want is not availible.

          On occasion, I’ve tried digitizing the graphics that they do release, but it’s a pain in the arse and tends to add its own errors in the process.

    • @ KarenZ, Thanks for that link – I had never even heard of Doggerland before, although I knew that at sometime in the past GB was joined to mainland Europe! I found it quite fascinating – I just love this place as you learn something new everyday –
      @IngeB @13.29 is that where you got your inspiration to send us the link for the dog story? Which I have to say, I found very personally moving (I lost my golden lab/retriever six years ago and still miss him now)…even though we have a new dog now,who has her own personality, my old boy will never be replaced….
      @Sissel, that you so much for the post, I know that I am probably the least scientifically minded person that comments on VC, but this post was very interesting to me and one that I found easy to follow.

  8. The recent earthquake swarm at Coso Volcanic Field in California seems to be over. The swarm which began in late November included hundreds of events ranging from less than magnitude 0.0 to M3.7, at depths of >10 km at the beginning to shallow 2 km near the end of the swarm. A small magmatic intrusion could have been the cause.

    • The “fog” visible between the village houses and the volcano, would be what Icelanders call “öskumistur” (and Americans from Hawaii “vog”), a mixture of H2O vapour, different gases, esp. H2S and ash.

      • H2S?

        Is there some type of low temp sulphur release going on? Maybe water and a sulphur deposit being heated or a slowly cooking peat deposit? SO2 release is usually a high temperature transaction.

          • I don’t have any numbers here, just thought about it because of the fog. This does not look like a dry fog. More like a mixture between water (perhaps ground water or the snow … ) and sulfur as well as other gases.

            When Eyja erupted there was a distinct rotten egg smell around it, eg.

            I can’t indicate a clear scientific source at the moment, this is just from looking at the webcam and my own experience with eruptions.

            I found a cited text with this title, but can’t find it on the net: Doubik, P. and Hill, B. E.: Magmatic and hydrothermal conduit development during the 1975
            Tolbachik eruption, Kamchatka, with implications for hazards assessmnet at Yucca mountain, N V, J. Volcanol. Geoth. Res., 91, 43–64, 1999. Perhaps someone else here has access to it.

            But if there where hydromagmatic activity involved, eg. by a high ground water reservoir nearby, that would explain a) an existent hightened level of H2SO4 and b) the higher explosivity of this eruption eg. compared to Fimmvörduháls (Eyjafjallajökull 1 in Iceland).

  9. The cold, for the most part, has broken. But I can’t really lay down or I get congested again. Managed to get about 3 hors of sleep… much better than the staccato 30 minute “naps” of the last two days. I was a total zombie by the time I got home today. So far, I’ve driven this cold about 500 miles, so its well spread. Not my intention, but thats the way it works out. Ya got to eat. In defense of society, I’ve been keeping my hands rinsed down with Isopropyl before and after each site.

    • Bear in mind it could be flu; its looks like its going to be a doozy of a season in the US, and secondary pneumonia infection is common. Zinc supplementation is good to reduce this risk, so you may want to think about that Lurking… Vaccines this year are a good idea.

        • do a google scholar search for terms zinc and pneumonia and risk factors and flu and immune system in a variety of combinations and you will find there are an awful lot of studies – and many studies are large, double blind and placebo controlled, although mechanistic ones are smaller by their nature. Simply put zinc is critical for immune system function at many levels and modulation of Th1 and Th2 responses & balance in particular (modulation of the cytokine cascades). Even a moderate deficiency results in immune system compromise (deficiency is a direct consequence of an influenza infection, aside and apart from that caused by poor diet when feeling ill – also probably tied to increased demand through involvement in ZIP transporters and zinc finger domains during the infective process.) There are also zinc dependent innate and cellular barrier mechanisms at play here too (inflammation as part of the immune response), and a few other things. Its too off topic but I could put up a full clinical summary if wished, but here is not the place for it! I think that a suitablu accurate statement is that maintinining zinc sufficiency during flu and flu like viral infections may reduce the risk of secondary infections such as pneumonia. Just trust me on this one:)

      • It only tastes weird when you are deficient. Try a soluble format as part of 1000mg vitamin C soluble tablets or you can add to orange juice if you get a liquid format, but dont take too much in one day (its as harmful as too little)- more than 24mg/ day intake is definitely counter productive, and this is best taken in 2 divided doses 12 hours apart.

  10. Great post Sissel!! I love people who search and find patterns between disparate things. All part of the journey of exploration. Great stuff.

    Makes me think, given that most calderas are actually collapse structures, why do they have such clean edges and not exhibit this kind of staggered slumping? Thought for the day.

    • Because it’s a collaps into a properly defined, already existing (at the very moment of the collapse) void, nearly “at once”, while as the kind of structure you refer to as “staggered slumping” appears when the collapsing or sagging process is kind of “progressive” or “successive” (doens’t mean that it can even tough be pretty fast). Think of sinkholes where you have a progressive evacuation of the material underneath and you successively collapse into the void in parallel to it’s formation, somehow…

        • I love polenta. As much for looking at it when it cooks as for eating it afterwards. I tend to make volcanoes out of it and fill the crater with sauce. Then I always come into a conflict: eat inside the craterlake to make it larger and add sauce, or eat like if I was erosion that alters the outer structure until the lake empties flowing down the sides of the edifice, the whole event causing severe flooding that threatens the carots…

          • Carrots??? what do carrots have to do with Polenta???
            Anyway, i think ill try Bruce recipe and experiment with throwing things into Polenta.

          • Following what my grandpa did, I often make Polenta with Ragout (too lazy to leo or google around today). The sauce I’m talking about comes from the ragout. And next to it I make carrots, cooked in butter, as it’s a vegetable I can eat and the way I spice it I think it interestigly fits together somehow.
            Fully aware that many might not imagine polenta in this culinary context. But as much as it’s important to know your basics in the kitches, as important it seems to me to try things and explore potentials. I mean, the first time I heard of caramelized onions I just had to run an try it out, even if at first glance it was not what we’re used to. And I didn’t regret it… Ever tried mashed apples on pasta-gratin? Saffron-bread with pear-mustard-jam?
            Eating and cooking is survival/health, passion/love and freedom. And when it even becomes volcanoholism, I mean, isn’t that the greatest thing on earth? 😉

  11. Volcanic Alert Bulletin RUA-2012/05 – Ruapehu Volcano
    Skip to end of metadataGo to start of metadata
    12 December 2012, 11:15 am – Ruapehu heightened unrest continues; Volcanic Alert remains at Level 1; Aviation Colour Code remains Yellow
    Following a thorough review of recent monitoring data GNS Science has confirmed that it believes Ruapehu remains at a heightened level of unrest and that an eruption is more likely than normal….

  12. Wednesday 12th December 2012
    White Island Volcano, New Zealand
    On 12th December 2012 the alert at White Island volcano, New Zealand was raised to level 2 after a 20-30 m wide spiny lava dome was observed in a small crater. Tour operators on the island had noticed the lava dome for about 2 weeks. The dome possibly started forming after the August 2012 ash eruption. This is the first time a lava dome has been observed at White Island volcano.

  13. Thanks Bruce and everybody who have shared their thoghts and put in links to more information on this subject! In the first place I was a little afraid you would not find it interesting so I kept the post rather short. But you convinced me that you did find it intersesting, so I will start preparing a part 2 (for next year).

  14. Hi

    Iceland earthquake animation for TF Zone since december 1st to 12th.
    Dot size is proportional to earthquake magnitude
    Moho and elevation are shown. I have supressed the Moho for the later stages to get a better view.
    Earthquake data come courtesy of IMO
    In the second part of the video, the age of the earthquake is according to colorbar. Red is youngest, blue oldest.

  15. Hi All, excuse me for going OT but regarding El Hierro, I just saw this from Armand on Earthquake Report, after all the quakes on the 10th, I was wondering if things were going to start “hotting” up again…..

    2012-11-12 19:28 UTC

    – Only 2 earthquakes so far the last 2 days, but the location of the epicenters is showing that something is really going on. We would not be surprised at all if a new activity period would start. Both epicenters are located in the direct Sabinosa area, exactly the same area where the last swarm started.

    • One at 0.8 mbLg at 9.3km depth and the other 1.10 mbLg at 9.6km.

      Too early to tell so I am afraid that it is still watch this space ….. 😦

    • You make an “OT apology” for actually talking about a volcano (I know, it’s not related to that very post). That’s so nice, respectful and cute.
      Now I feel like I’m a very, very bad boy… 🙂 And as such I right away have to make a bad joke. For those who know TopGear and the Stig (sorry Diana). It’s said that those who have seen the Stig in the dark believe he has 3 legs…

      • 🙄 aww gee…… thanks GeoLoco I feel like a little perfect princess now – Don´t know much about Top Gear and the Stig but think I get the drift – bad boy indeed 🙂 I shall wait for Diana to catch up with you!!

        • For very good reasons Diana doesn’t appreciate TopGear and Jeremy Clarkson. That’s why I apologized. Being a little bit fuel blooded, TopGear of course is pure entertainment to me. And I share a deep disrespect for the Toyota Prius with Mr. Clarkson… 🙂
          I think the princess job in here is still free. So my suggestion is that we officially give it to DebbieZ. Those who disagree could possibly have to deal with my fury… 😉

    • Must say I have a strange feeling about the shallower quakes the last days – eight small quakes from 7 to 10 kms deep from 10 december until now. Tanganasoga and Sabinosa. Bob never stops surprising.

    • Georgiade, is there anywhere that you’ve found further information about Nisyros? I see that it had a 2.9 at 10km depth today. Where have you found information about the people on Nisyros?

      This is one volcano that scares me right now. It’s been quiet for quite a long time, and while that doesn’t necessarily indicate it will erupt, I would fear for a very violent eruption if it did decide to erupt.

      You don’t see many caldera volcanoes reawaken after a longer-than normal dormancy with effusive eruptive activity. There has been too much time for that magma to evolve & pressurize down there.

      • Hello, cbus20122 🙂

        my English is not so good and I let myself translate my comments by German English translator,

        there a little bit funny things sometimes come out,
        I have no information of the people 😦 is sorry me
        I pursue Euro-Med earthquakes, and there has struck me that this area is very actively 3.9-in 10-km depth,
        I am no expert, mad only a little volcano

        • Herzlich willkommen georgiade! There are loads of German-speakers here. Carl did set a rule about all posts being in English for everyone’s benefit which makes sense but don’t let that you stop you from posting. I am sure Spica, me, Inge or any of the other German-speakers would be happy to help you out if have any language questions.

          • Hi Bruce, georgiade is not a newbie. She has been around for a while and gave very valuable hints and images when Shiveluch burbed some month ago. But i am going to help her naturally when she needs help with trasnlations. 😉 And of course she is very welcome!

      • I can tell you that there is likely more there than meets the eye.

        I can’t say what, but I suspect that there are more geological connections and inferences than we have unearthed (pun intended).

        I guess that seals the deal. Ruminarian III now has a topic. I just have to go write it.

        (I already had a proto-topic, but not the wherewithal to do the draft… been a bit pekid)

        • Looking forward to it! I am still taking the current activity with a grain of salt. The swarm is 60 km away from Nisyros. The noise we saw on Nisyros was only seen on one of the seismograms and not the other, which makes me think they had just dialed it up really high and it is totally unrelated to the swarm going on between Simi and the coast of Turkey.

  16. Hi

    Update on Tolbachik Area since Dec 1 to Dec 10.

    Main activity seems still to be with the magma reservoir deep down. Some earthquakes under Tolbachik around the 6th

  17. offtopic: nothing going on in Iceland earthquake and northern light wise. but there is a nice meteor shower tonight, from Geminids. I saw about 5 bright shooting stars tonight, and I was only about 5-10min outside, not paying much attention. peak of that meteor shower is probably tonight the weather has been also very mild for a winter here, so nice to be outside

    • Hey cool! It looks like you’ve just discovered a new seismic pattern, now we just need a descriptor for them, one we can add to tornillos – let’s call these ones fish bones! They really look like a pile of fish after the cats have been at them. Very strange signal.
      I have no idea what it could be.

      • Your looking at anywhere from 10 to 15 seconds in the spacing of those bursts.

        I’ve seen steam whistles choked down by condensate water that chug until they blow the vent clear. Really wild and really messy if you are on the Flying Bridge. Usually they only have a period of a second or two…. but it depends on how much steam and how much water it has to deal with.

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