On Wednesday I was asked to look into the possibility that there had been an eruption on the West Coast of Sweden. It was one of those phone calls that are really confusing and making you wonder if it is you, or the rest of the Universe, that has gone utterly bonkers.
Since it was an official request I had to go and take a look at things. But, let us begin from the beginning.
On Monday 16/4 2018 a lot of coastal residents in the islands around Gothenburg started to call the Swedish Coast Guard about a suspected oil spill. A distance of 150 kilometres was inundated by grey globs and water with light grey suspended goop.
The Coast Guard quickly came to the conclusion that it was not an oil spill, and sent samples for laboratory testing since they suspected that it was some sort of algae bloom of unknown origin. Simple microscope studies gave at hand that there was no algae to be found in the samples. In fact, there was no organic structures at all in it.
And this is consistent with deeper sediment layers. Yes, they started out as organic sediments (mostly), but over time all organic structures will be removed and only the organic base products will remain.
It was about that moment I was called in to take a look at it, and I must admit that I was rather amused as I went. The idea of a volcanic eruption in the waters outside of the Swedish West Coast is pretty hilarious, if you know your geology.
As I came to the coast and started to look at the goopy lumps and the greyish water I had a feeling that I had seen this before in other parts of the world. The lumps were like modelling clay, and the suspended grey material had a distinctly muddy look to it. The surprising part was that the lumps floated in water.
In the call they had said that it was like ash covered in fat. But, as I looked closer it was just very finely ground clay, and that can feel quite fatty as you handle it. And as I stood there I understood what it probably is, and that I had indeed seen it around the world.
The most famous example of a mudcano is of course the Sidoarjo mud flow that created the Lusi mudcano. Another famous example is the Fiumicino Mudcano near an airport outside of Rome.
The point central of mud volcanism is Azerbaijan, it holds about 40 percent of all the 1000 known mud volcanoes around the world. Normally mud volcanoes are small and never reach the size of their magmatic namesakes. That being said, a couple of the Azerbaijani versions are ten kilometres across and 700 metres tall.
They are caused as methane is heated, or ignited, and as the methane expands there will be an explosion that hurls clay and mud into the air or pushes it out in a slower fashion as a mudflow. Sometimes these eruptions are accompanied by large flames of burning methane.
The good part of this is that you most likely have a deposit with hydrocarbons in the vicinity, either as natural gas, or as coal or oil.
Even though the hyperbolic press found it all to be unknown, unheard of, and a new thing, it turned out that this has happened before along the same stretch of the coast. Last time it happened was on the 27th of November 2017, but earlier finds are also known.
This also strengthened my belief that we are dealing with a mudcano out in the waters. There are also known deposits of hydrocarbons out there, but they have been deemed to be commercially unviable.
I also checked seismological data for any signals that might point towards this being volcanic in origin just to rule out any black swans. And as I suspected there was nothing to be found in that regard.
A couple of weeks ago I wrote about magma residing under Norway, so I thought I should put the probable mudcano into perspective to that. Most likely these two phenomena are unrelated since there is just too much bedrock for the magma to go through to come near a deposit of methane.
Any methane deposit would reside at a fairly shallow depth with a maximum of 4 kilometres. And the magma under Norway is residing at a depth of more than 44 kilometres. It is though possible, even if it is farfetched, that there has been a dyke formation quite some time ago, and that this has warmed the deposit of methane.
Is this dangerous? Yes and no, mudcanoes are in general rather benign and slow features impacting local life only. But, in this case it is in the ocean, so if the methane outlet is big enough it can lower the buoyancy of the water directly above it, and that can be a hazard for smaller ships.
The second thing is fairly obvious, it is not good with a lot of goopy mud in the gills of fish. This may take out a season of fish spawning. Otherwise we should be good.