Most of the “Sunday sand” posts so far have come from beaches around the world (with the exception of last week’s desert location); there’s an obvious reason for this – beaches are specific destinations (sand being a key characteristic), they provide the opportunity for intimately communing with sand, and they are thus obvious places for collection of the stuff – by me or my circle of arenokleptomaniacal friends. But, moving upstream, river sands are equally fascinating and diverse, representing the material as it travels along these highways from its source to the ocean. Close to the source, these are dramatically dynamic, high-speed highways, and nowhere is this more apparent than in the Himalayas.
The sand above comes from Bhutan and shows the distinctive character of young river grains: sharp and angular, not yet smoothed by the buffeting of the journey, and an exotic mix of ingredients, rock fragments, mineral grains not yet rotted into clay. Plus a wide range of grain sizes, not yet sorted and winnowed as currents wax and wane. These are sand grains flushed along by rapid mountain torrents, left, briefly, along the banks as flood waters subside. These particular grains, newly born in the Himalayas, come from the River Torsa (also spelt Torsha and also known as Machu, or Mochu, and Amo Chu - the word "Chhu" means "river" or "water" in Dzongkha, the official national language in Bhutan). The Torsa rises from the Chumbi Valley in Tibet, China, and flows through Bhutan and into India before joining the massive system of the Brahmaputra and onwards to the Indian Ocean.
In Bhutan, the youth and dynamics of the Torsa are also illustrated by its large-scale morphology – its flood plain is wide, covered by multiple channels winding sinuously around bare, elongate oval islands of sand and gravel. The appearance is one of a rough braid, and indeed this is referred to as a braided river, typical of youth and dynamism, water and huge cargoes of sediment continuously sculpting an ever shape-shifting landscape. This photo shows a typical braided river pouring out the Brooks Range in Alaska:
But these images (thanks to the wonders of Google Earth’s historic imagery feature) also show the dramatic and rapid changes that occur in this kind of river system: the two images are but fifteen months apart, but look at the way in which all the channels have shifted, new channels formed, old ones disappeared, sand banks changed. Every year, with the monsoon rains, Himalayan rivers such as this create catastrophic floods, changing the landscape and causing devastation. Look at the two images below – in December 2004 there was a village on the bank of the Torsa, but little more than a year later there’s virtually no sign of it, swept away in the floods.
These are destructive events that happen every year, but periodically they occur on such a devastating scale that they receive worldwide attention. On the other great Himalayan river system, the Indus, last year’s appalling floods in Pakistan were such an event. One understandable reaction is to build dams in an attempt to control the floods (and generate hydroelectric power) – but, as I wrote last year, the complexities of these giant river systems is so great that, more often than not, more problems are caused by these solutions than are resolved. Water supplies, flood control, and power generation in the Himalayas are fundamental issues being addressed by major projects in India, Pakistan, China, Tibet, Nepal, and Bhutan (a dam on the Torsa is currently being planned); each country’s needs and resources are often in conflict and the challenge is a truly geopolitical one.
My original intention with these Sunday Sand posts was simply to catalogue some of the dazzling variety of our planet’s sand grains – but every sand grain has a story to tell and so I find myself rambling off into these tales. Oh well….
[These Bhutan sands were among the many collected on their world travels by two very cherished family friends. Sadly (the word hardly seems adequate), Laurie passed away suddenly last year – while travelling. Libby continues her travels and I shall always be grateful for the enthusiasm and devotion shown by two of my favourite arenokleptomaniacs.]