Issued: Thu, 30 Nov 2017 15:00:00 GMT
Malcolm Kennedy, Professor of Natural History, writes:
This summer I completed a traverse of the Cordillera Real in Bolivia. This was partly to see the mountains but also to see the environment that gave rise to the great South American civilisations. The Incas were the last, their empire being relatively brief before it was weakened by internecine conflict and measles before Pizarro’s soldiers destroyed it.
Before the Incas were the Tiwanaka and the Wari civilisations, from whom the Incas had learned how to construct earthquake-proof buildings, and how to cultivate crops at high altitudes. The Tiwanaka occupied a huge region covering all the land west of the Cordillera to the Pacific Ocean. Their civilisation is thought to have collapsed due to climate drying that made their agriculture unable to sustain their population, and that this had been exacerbated by deforestation. The foothills of the Cordillera falling away to the altiplano are vast, and now completely devoid of native trees. This state is maintained by grazing animals, much as happens widely in Scotland. Two rather similar-looking ecological disaster areas that were once productive and could be again if allowed to recover.
We came to a place illustrating how our modern activities may prove to be, globally, more disastrous than experienced by the Tiwanaku. This was a large glacier lake (pictured) at above 4,000 metres in the Cordillera. We were standing on a rock sill that dammed it. This is one of those places where a glacier cuts down under the weight of the ice bearing down on its back wall, lifts as the glacier moves forward and the weight is taken off it, then tips over a sill and into the valley below, leaving behind it a huge hollow now filled by a lake. The lake is coloured green-blue with suspended fine rock particles, and the grey headwall beyond is itself topped by a rock sill.
The headwall is grey and clear of plants. But pioneer plants are abundant around it, evidence that the headwall has only recently been exposed. Our mountain guide had been there twenty-five years ago. The glacier had then been high where we were standing. It is now far away across the lake, its snout well up towards the peaks behind. Using a rope for security, we climbed the flank of the valley and on to a high pass. Twenty-five years ago those flanks were completely blocked by the glacier. As we climbed higher I noticed rock faces deeply scratched by stones pressed along by the glacier, and now covered in lichens. I do not remember seeing any lichens down on the rock sill, which is another testament to how recently the glacier had withdrawn.
From the top of the mountain pass at about 5,000 metres we looked down and saw a smaller lake just behind the glacier’s headwall sill. This lake was white with rafts of floating ice. It will soon be larger and free of ice, the glacier even further withdrawn.
Almost all of the glacier lakes in the lower valleys of the Cordillera are being dammed. The villagers fear that the climate may be again warming and drying, such that the glacier melt water will soon be unable to supply water to their crops through a growing season.
When I looked back from above the rope-assisted climb I could see that the rock strata that the glacier had broken though were vertically aligned. They would once have been horizontal, then tipped skyward by the enormous forces that created these mountains, and then sliced through by the force of a once giant glacier. A place of reminders of the powers of plate tectonics, and water. A place to be both inspired, and worried.