Skeptophilia (skep-to-fil-i-a) (n.) - the love of logical thought, skepticism, and thinking critically. Being an exploration of the applications of skeptical thinking to the world at large, with periodic excursions into linguistics, music, politics, cryptozoology, and why people keep seeing the face of Jesus on grilled cheese sandwiches.

Monday, June 7, 2021

Reconsidering Storegga

Ever heard of the Storegga Slide?

It sounds like some bizarre crossover between Scandinavian folk music and a country line dance, but it isn't.  It's an event that took place 8,150 years ago (plus or minus thirty years or so) and is entirely unlike anything we've seen since.

The simplest description is that it was an underwater landslide.  But this thing was bigger than any landslide you've ever heard of.  It took place in the North Atlantic between Iceland and Norway.  For uncertain reasons -- but probably linked to seismic activity along the Mid-Atlantic Ridge -- a 290-kilometer-long piece of continental shelf collapsed, sending an estimated 3,500 cubic kilometers of debris sliding down the continental slope, where it ultimately piled up on the floor of the deep ocean.

What happened next is kind of mind-blowing, but to get how it worked, we have to take a brief digression into biochemistry.

It's thought that the most numerous organisms on Earth are methanogens, a group of bacteria that are kind of everywhere in anaerobic mud (including the sediments of the oceanic abyss).  As you might guess from the name, these bacteria produce methane as a waste product of their metabolism.  If they're living at the bottom of a shallow lake, the methane is in gaseous form and bubbles up when the mud is disturbed, giving it the name "marsh gas." 

But something more interesting happens in the deep ocean.  At the enormous pressures and low temperatures found in the abyss, the methane forms a weird substance called methane clathrate (also known as frozen methane hydrate).  It's a crystalline slush made of a latticework of water and methane.  If you bring it up to the surface -- which, as you'll see, has to be done carefully -- it looks like snow.

But it's flammable.

[Image of methane clathrate is in the Public Domain, courtesy of the United States Geological Service]

So back to the Storegga Slide, wherein an enormous clump of debris went tumbling down the continental slope... and landed in the clathrate-rich mud of the abyssal plain.

Methane clathrate isn't just flammable; it's unstable.  If anything wallops it hard enough, it breaks up the lattice, and the two compounds separate.  The methane turns back into a gas, the water to a liquid. 

Some of you probably have gone scuba diving, and noticed what happens to the air bubbles when you breathe out.  The bubbles rise (duh) but more interestingly, they expand.  The higher you go in the water column, the lower the pressure, and the more the air in the bubble is free to balloon outward.

A lot.  One liter of methane clathrate produces 169 liters of methane gas (at zero degrees Celsius and one atmosphere of pressure).  So when the Storegga Slide crashed into the methane clathrate on the ocean floor, it caused an unknown (but huge) quantity of methane clathrate to fall apart, making it suddenly increase in volume by a factor of 169 -- triggering an explosion that displaced enough water to generate a megatsunami.

This comes up because of a paper last week in the journal Boreas that looked at the effect of the Storegga Slide on nearby land, and found that the tsunami this generated was on the order of thirty meters high.  For comparison purposes, the devastating tsunami generated by the 2011 Japanese earthquake maxed out at a little under ten meters.

The Storegga Slide tsunami was three times higher than that.  It completely inundated what is now northern Scotland.  It's also likely this is what destroyed Doggerland, a broad, marshy land that once connected Great Britain to northern continental Europe.  Doggerland was already in trouble -- at this point, the climate was warming and the seas were rising -- but the Storegga Slide tsunami would have been catastrophic.  Unlike the rugged terrain of Scotland, Doggerland was a featureless flat plain, and the tsunami rolled across it like a bulldozer.  This severed Great Britain from the rest of Europe -- isolating the Mesolithic people there permanently.

[Image licensed under the Creative Commons Francis Lima, Doggerland3er en, CC BY-SA 4.0]

All this isn't speculation, by the way.  The fact that Doggerland was once dry land (well, dry-ish) was established when a trawler out in the North Sea east of the Wash brought up a barbed antler point that was dated to about ten thousand years ago.  Since that time, lots of other artifacts have been discovered out there on the ocean floor, including prehistoric tools and the bones of mammoths, lions, and other extinct fauna.

And of course, what this makes me think about is how much more methane clathrate there is out there.  "Methane burps" like this one -- although the word "burp" kind of underplays how enormous these are -- release enough methane into the atmosphere to raise the temperature significantly.  In fact, a massive methane clathrate release is thought to be the cause of the Paleocene-Eocene Thermal Maximum of 55 million years ago, during which the average temperature climbed by between five and eight degrees Celsius, causing widespread extinction and ecosystem disruption.  That "methane burp" at the PETM is thought to have been a hundred times bigger than the Storegga Event.

Ready for the punchline?  The estimates are that the rate we're pumping carbon into the atmosphere from fossil fuel burning is right around the same as the rate that led to the PETM.

So by all means, governmental leaders, continue to ignore the scientists who have been warning you about this for decades.  Business as usual, damn the torpedoes, full speed ahead.

The universe is a dangerous place.  The Storegga Slide and the resultant tsunami happened suddenly and without warning.  Much more commonly, earthquakes and volcanoes can cause tremendous loss of life and property.

But it's a little terrifying to see that what we're doing to our home right now is equivalent to some of the most violent ecological shifts in the geologic record.


I'm in awe of people who are true masters of their craft.  My son is a professional glassblower, making precision scientific equipment, and watching him do what he does has always seemed to me to be a little like watching a magic show.  On a (much) lower level of skill, I'm an amateur potter, and have a great time exploring different kinds of clays, pigments, stains, and glazes used in making functional pottery.

What amazes me, though, is that crafts like these aren't new.  Glassblowing, pottery-making, blacksmithing, and other such endeavors date back to long before we knew anything about the underlying chemistry and physics; the techniques were developed by a long history of trial and error.

This is the subject of Anna Ploszajski's new book Handmade: A Scientist's Search for Meaning Through Making, in which she visits some of the finest craftspeople in the world -- and looks at what each is doing through the lenses of history and science.  It's a fascinating inquiry into the drive to create, and how we've learned to manipulate the materials around us into tools, technology, and fine art.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

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