30 25 14 Congho Ressource – The Lake that Probably Won't Kill You (anytime soon)

Looks safe from up here

 I remembered that episode when I read that the Congolese government had temporarily banned fishing and bathing on
Lake Kivu in February out of concern that carbon dioxide eruptions
along the shoreline had caused a number of recent drownings. Kivu is one
of three lakes in Africa known to experience periodic lake overturns,
in which gas that has been dissolved and compressed in the water
suddenly erupts from deep inside the lake, with potentially devastating
consequences. Two small lakes in the Cameroons famously overturned in
the mid-1980s, killing 1,500 people.

Lake Kivu is
not only 2,000 times larger than those lakes—it is located in a far
more densely populated area, with over three million people living along
its shores. When I lived in Bukavu, I was always told the chances of an
overturn were virtually nil, but a quick google search led me to an NBC article suggesting
that overturns occur with reasonable frequency–on the order of once a
millenium or so. Given the number of potential casualties, this seemed
often enough to be a matter of concern.

So I wrote a half dozen
scientists who have studied the lake to try to find out more about our
state of knowledge regarding the lake's dangers.[1] On the whole, they seemed fairly sanguine. Here's what I learned:

1)
The lake is currently stable, chemically speaking; the methane is sunk
at the bottom of the lake and there’s virtually no chance of it
spontaneously welling up However, there is some evidence that methane
concentrations in parts of the lake are increasing, and on current
trends this could lead to an unstable situation in about a century or
so.  

2) The amounts of methane and carbon dioxide bubbling up
around the surface of the lake are entirely normal, occur in many lakes,
and present zero danger. There was almost certainly no good reason for
the government to ban fishing and swimming.

3) Some monitoring of
the lake composition and volatility is being done but more could and
should be done. For one thing, we don't know whether the methane
concentrations are increasing in a steady and predictable fashion. And
we’re still a long way from really understanding what might trigger an
overturn.

4) The geologic evidence suggests overturns occur on
the order of once every few hundred to once every few thousand years
(there's a difference of opinion about this). These would have
devastated the lake’s biota, but it’s not clear how catastrophic they
were beyond the lake's shoreline. What matters is how explosive these
overturns were, and the evidence on that question is very hard to read. 

5)
There’s a real but tiny risk of catastrophe. Given the current chemical
stability of the lake, an overturn wouldn’t happen spontaneously, as it
did in the Cameroons, but would have to be triggered by a major
volcanic or seismic event, such as an eruption from Nyiragongo, near
Goma—which would of course be a catastrophe in its own right—or an
underwater landslide associated with a major earthquake. Scientists have
recently uncovered evidence of volcanic activity at the bottom of the
lake in the north basin; this is a matter of an as-yet unquantified
concern. That said, the lake experienced both an earthquake and an
eruption in the past decade without triggering an overturn, so the
dangers should not be exaggerated.

6) On the whole, methane
extraction is not only a good investment (the methane in the lake could
be worth $20 billion), but probably wise ecologically, in that
de-gassing the lake under controlled conditions reduces the already
minimal risk of an overturn. One concern: that the de-gassed waters be
re-infused into the lake so as not to disturb its delicate surface
biochemistry in a way that that harms Kivu’s small fishing industry.

7)
Bottom line: Given current conditions, the risks of an overturn are
minimal. That said, should a massive volcanic event occur all bets would
be off. The problem is that there would be no way to predict whether
the eruption would trigger an overturn. Nor, given the short warning
time volcanoes provide, would there be any realistic way to get the
millions of Kivu-proximate residents to safety, even if the decision
were made to evacuate.

Oh, and those rumors about the gas
bubbling up and silently asphyxiating unfortunate fisherman out on their
canoes? Old sailors’ tales. 

[1] In
particular, I'd like to thank Anthony Vodacek at the Rochester
Institute of Technology;  Thomas C. Johnson, at the University of
Minnesota Duluth; Martin Schmid at Eawag Aquatic Research; Alberto
Vierra Borges, at  University of Liège Allée; and Jean-Pierre Descy, at
the University of Namur, Belgium, who all gave generously of their time.
Needless to say, all errors are my own.

5/6: I just came upon this video, which provides an interesting overview of the 
technical and political challenges of extracting the methane from Kivu.

 

http://www.congoresources.org/2013/04/the-lake-that-probably-wont-kill-you.html