The tallest peaks in the famous Rocky Mountains of Colorado are half the height of most of the those in the Himalayas and are dwarfed by many mountains in the South American Andes. Why is that? And, where do mountains come from? What makes some mountains grow taller and others grow faster? If mountains affect the weather and thus the climate, is it possible that climate and weather could affect the growth of mountains?

I don’t know about you, but such questions have been with me ever since I realized that the mountains I drove through or flew over were not just rocks and dirt that had somehow been there forever. Living in Marin County, California in the eastern shadow of Mt. Tamalpais helps keep such questions alive. The chert beds so clearly visible, folded back and forth in enormous vertical S’s, on the road to the peak just beg as I drive by: exssssplain this! The green serpentine taunts: how did I get here from miles below the ocean floor? In my daily life of making a living and living with family those questions pop up and recede during the length of a Sunday drive. But they swarm out again, bothering and bewitching me when in the company of many mountains, as I was recently in the Peruvian Andes. Along the way I found the perfect book to consult and bring me a little closer to understanding the mysteries.

Devil in the Mountain: A Search for the Origin of the Andes (2004, Princeton) by Simon Lamb, a British geologist of wide experience in both mountains and in explaining mountains, is a very good book. It will draw in anyone with the stirrings of curiosity of how did these mountains come to be?

It turns out the Andes are young, only 40 million years or so, with many sections of it much younger, rising up as the lower layers skidded up the wedge shaped, and much more solid, Brazilian Shield. The youngest portions of the Canadian-US Rockies by contrast, are 100 to 65 million years old.

Simon’s approach is not pure geology. He takes us on some of his trips, driving over the rugged and often freezing cordillera, in a beat-up old Land Cruiser, with friends. He writes of what they saw, and how it tied into previous sightings, or remained a mystery until later ones. There is enough adventure here for those who might give up on the sometimes intimidating words of geology [the Moho, an unconformity, synclines and anticlines,] and the unfamiliar three dimensional imaging the brain is called upon to produce. Led by an exuberant guide, and unprepared for their own misestimation of the distance to some intriguing fumaroles (cavities belching steam, helium and other chemicals from deep in the earth,) the party is caught far from base camp and separated as darkness and extreme cold descend. They all survive and have their precious helium samples and we have experienced science in action.

But the real reward of the book is the way Simon carefully builds his own discoveries into the increasing knowledge he gives us of advances in modern geology, and a sense that many of these mountain formation, and mountain destruction questions can be answered. While many of us might casually know that coastal mountains are created by the oceanic crust diving and pushing up and under the continental crust we cannot say why the Andes, and why nothing similar say, in southern California; why there is a mountain range in New Zealand and not something similar in Australia. He gives us detail and simple analogies to begin to understand. Just as a man pushing a flat board against a pile of sand cannot push it very high if he is standing on slick ground so, if the intersection between ocean crust and continental crust is well lubricated there is not enough friction to push very high. On the other hand, if the intersection is “rough” the friction will increase and the push will be stronger.

And what creates lubrication, or not? It turns out that sediment settled onto ocean floors over long periods of time, or in shallow tropical seas are very “slippery.” Where the ocean crust runs into volcanic terrain of relatively recent origin, it is very “rough.” And so it is at the bend on the west coast of South America. As the plate pushed below the continent, it slid relatively easily to the north and south, and pushed very hard right at the bend, giving rise to the alti-plano of Peru, Bolivia and northern Argentina.

Furthermore, the cold Humboldt current which sweeps north along the continent and creates the weather conditions which keep the coasts of Peru and northern Chile a desert has an effect. The rain filled air along the Andes comes from the east, across the Amazon and releases itself on the eastern slopes of the mountains, draining the sediment down into the Amazon basin. Only tiny amounts of rain hit the mountains from the west. Thus they are dry, releasing almost no runoff or sediment into the ocean, and ensuring that the contact zone between ocean and continental crusts remains rough, and the mountains maintain their heights.

One of the most surprising ideas Simon advances is that the rise of the Andes, and near simultaneous rise of the Tibetan plateau, were what changed the earth’s climate enough to create conditions for the evolution of man. It turns out that the rise of the two mountain cordilleras were likely caused by the same million year event: the smashing of India into the Eurasian land mass. 40 million years ago, two-thirds of the way through the Eocene era, earth’s atmosphere was heavy with CO2; plant life was tropical, broad leaved and dense.

As the Tibetan plateau rose rock was exposed to falling rain carrying CO2 and other molecules of air. Rock and rain reacted chemically, forming carbonates. Carbonates, when washed down the rivers into the ocean were [and still are] used for shell formation by marine organisms. When they die they sink to the ocean floor, keeping their CO2 with them and forming limestone. As the CO2 diminished in the atmosphere the climate grew colder, allowing the formation of grasslands — replacing jungles– and the evolution of grazing animals. Eventually our early ancestors were tempted out of the trees and set off across the grasslands themselves, evolving over the millions of years into homo sapiens.

It’s a fascinating speculation, backed up by much research, which Lamb uses enough of to make it both plausible and readable. There are sketches of mountain uplift, and the layers of earth which make them up, often the remnants of mountains before them. A good story is told, and even if at the end you couldn’t retell it with anything like the same detail and clarity you will feel as if you’ve advanced your own understanding of the great rock we stand on. You might want to go on, as I do, to his earlier book, Earth Story: The Shaping of Our World.