Nimrod103 wrote:dspp wrote:Nimrod103 wrote:
Periodic devastation from catastrophic glacial lake drainage is not a new phenomenon. Friends of mine were very nearly swept away in Greenland by such a flood caused by the build-up of summer meltwaters, which, when reaching a certain size, lift the ice dam, so that the lake drains away in hours. Something that happened about every 10 years. They had moved camp the day before. That was 50 years ago.
People should not live in such dangerous places.
Nimrod,
I happen to know these Peruvian places very well and am very aware of the dangers of being beneath either the lakes or the glaciers, as indeed are the locals. Very few of them in this area exhibit the mechanism your friends observed. There are many reasons for the 'alluvions' as the locals term them, but amongst them climate change would appear to be one factor. I will be interested to see how the courts rule, it seems to be climbing the legal ladder.
regards,
dspp
You are right, it is a different mechanism. So in 1941 the glacier ended in the lake, calved an iceberg, which caused a wave which damaged the lip of the lake and resulted in a fatal mud slide.
But now, the glacier has retreated and terminates on land, so there is no risk of a wave. Meltwater just goes into the lake, and flows out. All peacefully. Surely this new situation is safer, not more dangerous?
Of the top of my head, and noting that it has been 40-years since I last paid serious attention, there are several mechanisms on most of these Andean glacier end lakes, including most of the Blanca ones and many can contribute to any one event:
1) earthquake directly triggering morainic dam collapse;
2a) earthquake triggering glacier serac which then results in wave overtopping morainic dam and/or morainic dam collapse;
2b) earthquake triggering rockslide which then results in wave overtopping morainic dam and/or morainic dam collapse;
3) glacier serac calving due to glacier movement which then results in wave overtopping morainic dam and/or morainic dam collapse;
4) stranded ice core of morainic dam melting out leading to dam collapse;
5) semipermeable morainic dam 'leaking' meltwater more slowly than glacial melt, leading to overtopping & dam collapse through erosion at crest (or sidewall junction);
6) under-ice lubrication from increased meltwater leading to widespread glacier collapse thence down over the rockslab glacis into the lake and various of the above, can have earthquake trigger events;
7) weakening and undermining and slumping of downhill dam face, not very often in these areas.
In all these cases what was observed was that the fuller the lakes are the lower the strength reserve of the end dams is, and that with warming these lakes are spending more of the season at higher states, increasing downstream risk. Back in the 80s/90s which was when I was most active in the region they were cutting artificial spillways with concrete and etc linings to reduce the lake levels artificially so as to increase the strength reserve. If you look at the picture in the article you will see the upper (intake) end of one of those spillways in the foreground. That was Hidrandina doing it back then often funded by German foreign aid money, there is a long history of Germans in these zones. Then I think it got called something else.
Note that retreating glaciers can increase serac fall risk and general glacier collapse risk as well as decrease it. In both cases it all depends.
Most of the locals don't understand the precise mechanisms but they are very well aware of the generalities and the consequent dangers. I happen to have known a lot of these ranges extremely well and I have observed the before and after of these events, and I have thought
"I camped there last year and now it is under 30' of alluvial boulder debris from that event, yikes".
It is very difficult to look around one and
not think that climate is a significant influence, and thence to
not make the link to at least a partial contribution by mankind. Personally I am sure that there are many other factors as well, and so allocating % human blame is tricky. Which is why the courts are playing football with all these sorts of cases.
I don't think there are any absolutes with this. But I do think we are all to an extent guilty. How big an extent I am very unsure of.
regards, dspp