Tom Sharpe is a geologist originally from Glasgow, Scotland, who has spent the last 35 years as a geology curator in the National Museum of Wales. He is a Chartered Geologist, a Fellow of the Geological Society, and a Fellow of the Royal Geographical Society, as well as a member of a dozen other geological and polar societies. Here, Tom shares his excitement about one of his favorite places on the planet.
It’s always exciting to catch that first glimpse of Torres del Paine National Park on the drive north from Punta Arenas, Chile. The mountains are so distinctive, they’re immediately identifiable rising above the low terrain around them. And, late in the day, if the weather is fine, the mountains take on a golden hue as they catch the light from the setting sun; there are few more spectacular places to watch the ever-changing light on the mountains as the sun sets.
Few places, too, tell their geological story more clearly than the bare, vertical cliffs of these mountains, with a layer of pale gray granite sandwiched between dark rocks above and below. Erosion by glaciers during the last ice age has opened up cracks and weaknesses in the rocks to cut deep, steep, narrow valleys and create the isolated mountain pinnacles for which Torres del Paine is so famous. The Torres del Paine massif is a discrete mountain block lying to the east of the main Andes chain, measuring about 11 miles east to west and six miles north to south. The highest point, Cerro Paine Grande in the western part of the massif, is about 9,500 feet high and a spectacular mountain in its own right—but you can’t help but have your eye drawn to its neighbors, Cuernos del Paine, or the Horns of Paine, and peeking out from behind, the Towers of Paine, or Torres del Paine.
The Towers, which give Torres del Paine its name, are three narrow, bare, vertical granite spires about 8,000 feet high—their exact heights aren’t known—in the eastern part of the massif, and only really visible from that side; but the Cuernos dominate the view from the south and display the geology for all to see. Like the Towers, the sheer rock faces of the Cuernos are made up of a pale gray granite; though here the granite is capped by a black sedimentary rock. The same black or dark gray sedimentary rock forms the low ground around the base of the mountains. It’s mainly shale or mudstone, a rock unit that geologists call the Cerro Toro Formation. It was deposited as slurries of mud and sand swept down into the deep water of a sea that covered this area 86 million years ago. You can see these rocks along the roadside and along the edges of the lakes at the foot of the mountains.
About 12.5 million years ago, molten rock pushed its way up a crack in the earth’s crust just to the west of Paine Grande. It never reached the surface, but instead spread out sideways to the east, prising apart layers of the black shales of the Cerro Toro Formation. As the molten rock cooled, it solidified as a sheet of granite. This happened not just once, but three times, with each successive granite sheet pushing in below the one before it. This took place over a period of just (to a geologist!) 90,000 years and at a depth of about 2.5 miles below the earth’s surface. Together, the three granite sheets are about 6,500 feet thick, and their full thickness is exposed in the cliffs of the Cuernos. So, the black rocks you see at the top of the Cuernos were once continuous with the black rocks at the base of the cliffs. Although the rocks at the top are sedimentary rocks, they are sometimes described as metamorphic because they have been affected by the heat from the cooling granite.
Since then, this part of the crust has been lifted up and erosion has worn away the many thousands of meters of rock that once lay on top of the granite to expose these rocks at the surface.
We have the ice age to thank for the wonderful rock exposures we see today, and that make this place a geologist’s dream. Ice has exploited lines of weakness such as natural cracks (joints) or faults in the rocks to cut deep U-shaped glacial valleys like the Valle del Francés which separates Paine Grande and the Cuernos, or the narrow defiles that isolate each of the Towers. Glacial erosion along two sets of faults is also responsible for the deep valleys now occupied by the azure-blue lakes in the lower ground around the mountains. It’s a truly spectacular landscape, and without doubt, one of my favorite places on the planet.