Watching continents flow

Going northwards from Almora to Munsiyari, we crossed at some point from the Siwaliks to the lower Himalayas. We halted at the Birthi waterfall for a cup of tea. Thick smoke enveloped the area, and I was glad to have my N95 mask on. The sunlight that filtered through was a strange yellow. I clambered up a small slope next to the road to look at the 80 meters high waterfall. The Ramganga river fell from the upper plateau down before me, pooled briefly, and then flowed on to my left. Goats grazed on the cliff opposite me, their tinkling bells the loudest sound around me.

The Himalayas are still growing upwards as the Indian and Asian continental plates push towards each other at a speed of about 50 to 60 mm every year. The lower Himalayas are created by the buckling and twisting of the Indian plate, and the upper Himalyas by the Asian plate being pushed up as the Indian plate plunges north. East and west of the Kumaon region there have been many huge earthquakes in the last century and a half, but the Kumaon region seems to be miraculously stable. Still, that high wall of rock just across the stream from me seemed like the result of an ancient earthquake. Was it? A little search led to me to a paper which related it to the flow of the rocks in this region. What I’d seen here was continental movement, the driver of earthquakes and landforms. I’m amazed in retrospect.

Unbalanced worlds

Sometimes I look at the map of the world etched on to a paperweight on my table. It is designed to sit with the southern hemisphere on top. The shift in perspective forces me to think in different ways. One odd thought popped into my mind in the morning. Why does the world look unbalanced, with most of the continents clustered around the north pole? Mars, on the other hand has its biggest concentration of mass, the Tharsis plateau and the solar system’s highest mountain, near its equator.

Both planets have a liquid core over which the crust can move (see a good explainer here). A spinning globe of this kind should spin the heavy parts off towards the equator (although this is called polar wandering, the true pole remains fixed; it is the magnetic pole which moves). Mars makes sense, but the earth does not seem to. But some searching assured me that others have looked deeply into this problem before me. The mobile elements of the earth are not just the features we see on the crust, but the crust and the deeper mantle together. When you take everything into account, the earth seems to be in balance. The past positions of the continents show that the same principle held. When supercontinents form, they tend to be at the equator. Present day Africa is just such a remnant of the ancient supercontinent of Gondwanaland. (The video above plays out four possible futures of the earth’s continental movement; notice that most of them result in landmasses close to the equator.) It is a balanced world, but there is a lot going on below the surface.