Energy and the Earth

Energy and the Earth

Raising Tibet

It’s more than a little disconcerting to wake every hour or so, gasping for air, suffocating.

It happened to me during a field season in southern Tibet camped at about 5400 metres above sea level. With my normal sleep breathing patterns, I just couldn’t get enough oxygen. In terms of my metabolism, Tibet is clearly unreasonably high, and the question why it is so high is something I’ve been working on, on and off, for over 20 years.

Incredibly, the story of how it got to be so high shines a light on the immense geophysical scale of human energy use.

The Kampa dome

This time our field work was in an area known as the Kampa dome, some 50 kilometres north of the border with India and about 150 kilometres east of Mount Everest [see footnote 1].

Crossing a pass into the Kampa dome, southern Tibet, elevation 5500 metres.

The Kampa dome is a sort of giant geological “blister”. The dome, which is about 25 kilometres across, comprises a core of rocks originating deep within the Tibetan crust now exposed beneath a carapace of much shallower rocks.

Google Earth image of the Kampa dome in southern Tibet, viewed from the south-east. The dome rises to almost 6000 metres above sea level at its highest point. The lighter coloured rocks in the valleys in the core of the dome are granites and metamorphic rocks that have been forced up through a carapace of darker coloured and shallower sedimentary rocks, now exposed around the rim of the dome and along the ridge crests in its core. Image obtained from Google Earth - 29/04/2016

Kampa is just one of a number of domes distributed in a belt along the southern boundary of Tibet, not far north of the Himalaya. These domes attract the attention of geologists interested in what’s going on deep under Tibet and in the sequence of events that raised the plateau over the last 50 million years or so.

And that is not just of geological interest. The Tibetan plateau is so large, and so high, that it influences the global pattern of atmospheric circulation. So the raising of Tibet has had a profound impact on the evolution of the modern climate system. It is one of the elements in the transition from the green-house world of the dinosaur era to the ice-house world in which our own species has evolved.

Our work in Kampa was part of a broader program investigating the magnitude of the forces that drive tectonic plate motion. Amongst other things, getting a handle on those forces is important for understanding what limits the heights of our great mountain ranges such as the Himalaya.

The particular issue that motivated our interest in Kampa was the idea that weak rocks heated beneath Tibet were being, or had been, squeezed outwards to the south in a giant pincer movement by the ongoing convergence between the Indian and Asian plates. The idea that the rocks exposed in Kampa, as well as in the high Himalaya, are a kind of geological “toothpaste” is quite a departure from the conventional view that the mountain system has been created by stacking of thrust sheets one on top of the other.

One of the master faults lying above this purported channel of extruded rock is exposed high up in the face of Everest beneath a limestone that was deposited immediately prior to the raising of Tibet. The southern Tibetan domes make for rather easier and less dangerous field work than the face of Everest.

More than any other, mountain landscapes manifest the awesome power of our restless planet. In the rarefied atmosphere high up in the Kampa, the sense of awe was greatly magnified, especially with the Himalaya towering above the horizon.

Comparing human and planetary energetics

The amount of energy involved in building these mountains, in lifting those 50 million year old limestones out of the sea to now sit high up the slopes of Everest, is simply mind boggling, or so you would think.

To give you a sense, let’s calculate it. Even though it involves some big numbers, the calculation is really quite trivial.

From the way the Earth’s gravity field varies over mountains such as the Himalaya that we know it takes about 4 trillion joules to push a one square metre column of the Earth’s crust up by 4.5 kilometres - the average elevation of Tibet [see footnote 2]. To get the work done against gravity in raising Tibet we just need to multiply that number by the 2.5 million square kilometre area of the plateau.

The total is 10 yottajoules - or 10 followed by 24 zeros.

The trouble with big numbers such as these, and one reason they feel so daunting, is we have no natural reference frame to make comparisons.

So let’s compare it to the energy we humans consume to run our daily lives. We could ask, how many years would it take to raise Tibet if we put all human energy consumption to that effort?

In its Statistical review of world energy BP estimated the human primary energy consumption in 2015 at 550 exajoules (think 550 followed by 18 zeros). At that rate, and neglecting inefficiencies, it would take about 20,000 years to raise Tibet.

While that’s a long time, it’s far less than than the 50 million years that nature took to raise Tibet.

In fact, the rate we consume energy is more than 2000 times greater than the 10 gigawatt rate nature has been storing it in the raising of Tibet.

Here in Victoria, with a population at about 6 million, we consume electrical power at a rate of about 5 gigawatts. Making that electricity is only about 30% efficient, and so the burning of the coal to make it releases heat at a rate of about 15 gigawatts.

We use energy at a rate, quite literally, that could make mountains move.

Now that is something I think really is mind boggling.


Footnotes

[1] We were guided in our work in the Kampa in 2004 by local Tibetan herders. Hardier folk it’s difficult to imagine. While communication from Tibetan to Chinese to English and back again meant many nuances were missed, it was a special experience. It seemed our guides hadn’t much to do with westerners before, and we were quite the source of amusement for them. Indeed, it seemed to me there was a very real sense of fun in the way they went about their daily life on the roof of the world.

Our Tibetan guides in one of the glacial valleys high in the Kampa dome, southern Tibet.

A particular highlight was an offer, on our arrival, of some yak butter tea in their yurt at the edge of the dome. At these heights with little oxygen, not much fuel and with everything just a little damp, cooking is challenging. Burning damp goat dung in the close environment of a yurt produces an awful lot of foul smelling, acrid smoke, but not much heat. I didn’t much enjoy the taste of the rancid butter either. While the invitation to join with our Tibetan hosts in their rudimentary “summer house” remains one of my most treasured experiences, it was with necessity that I declined a second “cuppa”. There was little doubt, I was not going to hold another one down.

‘Enjoying’ yak butter tea inside our host’s yurt at over 5000 metres above sea level in Southern Tibet.

Despite it’s remoteness, this is a region in transition, for many reasons. One of my enduring memories of the Kampa is captured in the photo below, showing the alarming degradation of the thin soils that mantle these recently de-glaciated landscapes.

Like so many parts of the world, soil loss in the Tibetan plateau is an issue of critical importance. As this photograph dramatically illustrates, the thin soils that mantle the rocky, recently de-glaciated landscape in the Kampa appear to be degrading at a frightening pace .

The story of what we are doing to soils on this planet is an issue of immense importance, for all people.

[2] Strictly, the gravity pattern over large mountain systems such as the Himalaya shows the surface topography is isosatically supported by a greatly thickened crustal root. The work done against gravity in the building the mountains needs to account for this crustal root as well as the excess topography.

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