The Khumbu Glacier Meltdown
For many tourists trekking to Mount Everest Base Camp this autumn, the trip will be an adventure of a lifetime. The thin clear air, stark landscape, and ice-tipped peaks pierce the inky sky providing great Instagram backdrops.
However, what is stunning scenery to tourists is for climate scientists an apocalyptic sight. They see dramatic evidence all around of a rapidly warming atmosphere.
Visitors returning to the Everest region after 20 years also notice changes: large lakes where there were none, glacial ice replaced by ponds, boulders and sand, the snowline moving up the mountains, and glaciers that have receded and shrunk.
All these features are visible from ground level right from the start of the trek in Lukla. The banks of the Bhote Kosi still bear the scars of the deadly flash flood in 1985 which washed off a long section of the Everest Trail and the hydropower plant in Thame. It was caused by an avalanche falling into the Dig Tso glacial lake, causing it to top over.
Further up near Tengboche, the Imja Khola also bears signs of a huge glacial lake outburst flood that thundered down the western flank of Ama Dablam in 1977. And below the formidable south face of Lhotse is Imja Tso, a lake 2km long that has formed and grown in the last 30 years. It does not exist on trekking maps from the 1980s. All these lakes were formed and enlarged as a result of global warming melting the ice.
The Khumbu Glacier is the highest in the world and receding at 30m/y. It is also shrinking: Base Camp is now 50m lower than when Hillary and Tenzing climbed Mt Everest in 1955. Photo (C) Kunda Dixit
The terminal moraine of the Khumbu Glacier looms 400m above Dughla. This is the debris bulldozed down from Mt Everest and surrounding peaks over millions of years, and represents the extent of the glacier’s advance in the last Ice Age. Today, the surface ice on the world’s highest glacier is all but gone due to natural and anthropogenic warming.
For an even more dramatic glimpse of how global warming is changing the Himalayan landscape, there is nothing like an aerial perspective. Nepali Times got a chance last week to take these striking images of the terrain below Mt Everest. The barren beauty foretells of a time when this terrain will be stripped of much of what remains of its ice cover.
The Khumbu Icefall funnels ice from the Western Cwm below Everest, Lhotse and Nuptse, through the Icefall to the glacier below. The ice here has receded at an average of 30m/y in the past 20 years, but it has also shrunk vertically, losing up to 50m in thickness.
Everest Base Camp was at 5,330m when Hillary and Tenzing climbed Mt Everest in 1953, today it is at 5,270m.
The glacier is also getting flatter: the darker debris makes the ice beneath melt faster near Base Camp, but the thicker layers of boulders and sand further down insulate the ice.
Glaciologists say this flatter profile means the ice moves slower, leading to more ponding, and more rapid melting of the ice underneath.
The velocity of the glacier is 70m/y at Base Camp, and it slows down to 10m/y further below, but is zero at the terminus situated at 4,900m. This means the ice is decelerating as it is squeezed, and the pressure is being released by the melting of the ice mass.
Researchers monitoring the supraglacial ponds say their area has grown by 70% in the past ten years alone. The ponds are fringed by ice cliffs and caves which accelerate the melting. The melted ice has carved an outflow channel through the left lateral moraine, so there is no large glacial lake on the Khumbu like as elsewhere in Nepal.
Scientists conclude that the Khumbu Glacier is not about to vanish, and the Icefall is not going to turn into a water fall any time soon. However, the permanent ice catchment of the glacier above 6,000 could start to deplete under the worst-case ‘beyond catastrophic’ scenario of +5oC warming.
Source: Nepali Times