Is there anything more peaceful than the timeless panorama of a mountain landscape? Well, appearances can be misleading. The mountains and cloud-filled valleys of Plate 1.1 hide a sinister story. Far from being a scene of ageless serenity, they are evidence of a ferocious, ongoing collision.

We are not immediately aware of the landscape's dynamism because the calamitous clash that it represents is played out in very, very slow motion. It began some 50 million years ago, but its impact on everyday life continues to this day.

It is the story of a large land mass (the Indian tectonic plate) moving north through what is now the Indian Ocean and crashing into the Eurasian plate. This gigantic collision never stopped. The Indian plate continues to push north, sliding underneath the Eurasian plate. The violence of the crash is clearly visible in how the earth's crust formed huge creases, wrinkles and folds, and it is noticeable in how the contact zone is shaken by frequent earthquakes. The most spectacular crease is the Himalayas, the highest (and youngest) mountain range on earth, which is still being pushed up by the movement of the Indian plate. Connected to the eastern Himalayas is another crumple zone with folded mountain ranges that run from north to south for some 1,200 kilometres. Geologists call it ‘the Indo-Burma Arc’. This term is not used locally: various sections of this ‘rugged knot of hills and mountain ranges’ – or the extended eastern Himalayas – are known by other names (Map 1.1). The mountains of the Indo-Burma Arc are lower than the Himalayas, but they are steep, with some reaching over 3,000 metres above sea level.

An experimental space: The Triangle

This book is about the effects of this calamitous collision on climate, ecosystems and human histories in a roughly triangular region formed by the mountain knot of the eastern Himalayas and the Indo-Burma Arc, and the rivers flowing from these mountains. It is a region without sharp boundaries or administrative unity, it often drops off conventional maps and it has no ready-made name. For lack of a better designation, we call it ‘the Eastern Himalayan Triangle’ or simply ‘the Triangle’. Today it is divided between five countries: India, Myanmar/Burma, Bangladesh, Bhutan and China. It also crosses the boundaries between uplands (also theorised as ‘Highland Asia’5) and lowlands.