“Mountains are an archive of Earth’s history”

an interview with Gillian Foulger

Above (Issue I/2019)

Starting with the basics: What is a mountain?

Well, in geology we usually talk about a mountain when we see a hill that is higher than 1000 feet, which is 305 meters. And apart from that? Nothing but a pile of stones, which can form in many different ways.

How exactly?

There are about three main ways in which mountains form: volcanism, glacial processes and plate tectonics. An example for mountains that originate in volcanic activity are Mount Hekla in Iceland and Mount St. Helens in the US. When lava streams upwards to the Earth’s surface for millions of years, you can get massive mountains, the biggest of which are located in Hawaii nowadays. The second way they form is via glacial processes. Glaciers don't really form mountains, but they erode the valleys, as you can see in the Yosemite Valley in California, for example. There, the flanks of the glaciers have cut a deep valley into the landscape, createding mountain ranges at their flanks. Most mountains form via a third mechanism: plate tectonics. The Alps and the Himalaya are good examples of that.

So the highest mountains form when tectonic plates collide?

Exactly. When they do so, the material in between the plates arches and is pushed up above sea level. Mount Everest for example is almost 9,000 meters high was solely built by plate tectonics. But in real time it is hardly an exciting process: Mountains only grow a couple of centimeters a year at the most, so they take millions of years to form. That means that if you are standing on top of a mountain today it is a bit like standing in a natural elevator that moves you upwards ever so slowly.

Still, there are no mountains higher than 10,000 meters on Earth. Is there a scientific explanation for that?

That’s not exactly right. Technically, Mount Kea on Hawaii is higher if it’s measured from the bottom of the Pacific Ocean. From sea level it is only 4,200 meters though. That also somehow answers your question: If Mount Kea wasn’t submerged in the ocean it would probably never have grown to more than 10,000 meters.

Why not?

Because gravity and erosion would have prevented it. Most mountains are constantly pushed up, but also crumbling at the same time. Erosion processes like rainfalls and landslides tear them down. And the higher a mountain grows, the more it crumbles under its own weight. Mount Kea is as high as it is only because its base is supported by seawater. It is the same reason why Olympus Mons, the highest mountain on Mars and the highest mountain we know of in our solar system, is 26,000 meters high. Mars’ gravity is only 40 percent of earth’s gravity and it has much thinner atmosphere, which means less erosion. For Earth to produce a mountain as high as that it would need an extraordinary tectonic event, not to mention millions of years. 

That's more than enough time to discuss what makes mountains so interesting from a geological point of view …

To answer that it is enough to compare the Alps to the Sahara desert. In the Sahara desert you are generally standing on top of one layer of soil. You can dig into the ground but you won’t find much there at all. In the Alps, however, you find kilometers and kilometers of rock sequences that have been pushed to the earth’s surface for millions of years spread out right before you. In this sense, mountains are the biggest archive of Earth’s history that’s available to mankind.


The rock sediments lie right before our naked eye like the pages of an open book. They allow us to make very exact statements about the history of this planet. In some sense, they offer a complete record of the past 4 billion years. By examining rock layers we have traced how climate has changed over time and we found out that supercontinents once existed and which animal species populated Earth. One could potentially argue even that without mountains humankind would not have made it into the modern age.

In the sense that they catalyzed scientific progress, you mean?

And also the resulting societal change! The study of rocks and mountains has really separated the modern days from the pre-geological days. It’s not that long ago that our predecessors found fossils high up in the Alps and took them as proof for Noah’s flood. Or that the Polynesians believed that the goddess Pele was driven from island to island by her enraged sister, whose husband Pele had seduced, thus explaining the sequence of volcanic eruptions. Before people gathered the first geological facts, the world was a much more mysterious place. After the inception of geology it was only a matter of time that religious beliefs faded and scientific breakthroughs occurred. In so far, the importance of mountains to our social and also cultural life cannot be overestimated. And you don’t need to be a geologist to appreciate that.

You don’t?

No, it is enough to ask yourself the question, what the world would look like today if there were no mountains? You’ll find that it is actually very difficult to find any part of human life that is not affected by mountains. If the world was pancake flat there wouldn’t be rivers for example, and where there are no rivers there is no irrigation and without irrigation there is no farming. Or take politics: There wouldn’t be any natural borders without mountains and without those the entire history of military conflicts would have changed and also the political landscape. This thought experiment can be applied to any part of life: from the weather report all the way to linguistics. It is a fact that the world as we know it is almost unimaginable without mountains. 

an interview by Kai Schnier.

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