Travels in Geology: Exploring an icon of Patagonia: Chile's Torres del Paine National Park

by Terri Cook and Lon Abbott
Tuesday, November 29, 2016

Mount Almirante Nieto and the Torres del Paine reflect in the still waters of Lake Amarga. Credit: Lon Abbott & Terri Cook.

While planning a family trip to Chile last year, Torres del Paine (pronounced “PIE nay”), a group of impossibly steep granite spires, was number one on our Chilean travel list. Despite their reputation for some of the foulest weather on earth, the peaks are magnets for tourists and rock climbers from around the world. But considering that reputation, the park’s location at 51 degrees south latitude and the fact that we were going during the Southern Hemisphere winter, we reluctantly crossed it off our list and concentrated on destinations in the country’s comparatively balmy north. That was until our teenage son Logan, an amateur mountain meteorologist, excitedly shared with us the results of his Patagonian climate research. “Dad, Dad!” he exclaimed. “High-pressure systems with clear weather are more common in the Patagonian winter than in summer, and winter temperatures seldom drop far below zero Celsius!” That report got Dad on board. Mom, who is not fond of the cold, was a harder sell, but sister Kailas' enthusiasm sealed the deal. We’d soon purchased inexpensive off-season air tickets from Santiago to Punta Arenas and booked a room at Hosteria Pehoé, a lodge on Lake Pehoé, the location for the iconic photos of spectacular peaks that made the park famous. We were hoping that the investment would pay off with at least one fleeting glimpse of the mighty peaks through the notorious mist.

Torres del Paine may be off the beaten path, but if you're already in Patagonia, you only need a couple of days to see these sites. Credit: both: K. Cantner, AGI.

“The sky was overcast and light snow was falling when we landed at Punta Arenas airport. The four-hour drive north to the park was scenic, but mist shrouded the peaks we’d come to see. We had just arrived, but we couldn’t help but wonder if a winter trip was a good idea after all.

A Classic Laccolith

Although the national park is named for the tallest granite spires, the iconic Lake Pehoé vista isn’t actually of the Torres del Paine themselves, but rather of the equally majestic Cuernos del Paine — the “Horns of Paine.” “Horns” is an apt description of the two peaks because each is a sheer wall of light gray granite crowned by a jagged horn of dark brown metamorphic rocks.

The Grey Glacier (seen in the distance) calves icebergs into glacial Lake Grey. During the Pleistocene ice ages, the glacier polished and striated the rock knobs on the banks of Lake Grey. Credit: Lon Abbott & Terri Cook.

“Seen from Lake Pehoé, the sharp contact between the two rock types angles upward from right to left. This is because the metamorphic rocks arch over the top of a mushroom-shaped granite body known as a laccolith. The laccolith began to form 12.6 million years ago when an 18-cubic-kilometer pod of granite injected parallel to two sedimentary layers of the Cerro Toro Formation, forming a sill. Heat from the granite “cooked” that formation’s adjacent mudstone and sandstone, converting them into the dark brown metamorphic rock that crowns the Cuernos — a metamorphic contact aureole. A smaller (8-cubic-kilometer) pod of granite was injected below the first one soon thereafter, and finally a third, much larger one (54 cubic kilometers) completed the laccolith 100,000 years later, resulting in the pronounced mushroom shape.

Dark metamorphic rock overlies the light-colored granitic spires of the Torres del Paine, which glaciers carved from a laccolith. More of the metamorphic rock is visible in front of Torre Central, the highest spire. Credit: Lon Abbott & Terri Cook.

“The laccolith is adjacent to the modern Patagonian Ice Cap, and the mushroom’s top stands just above 3,000 meters elevation, high enough to spawn massive glaciers during the Pleistocene ice ages. Those glaciers quarried the modern peaks out of the laccolith. The glaciers stripped the contact aureole’s relatively less resistant metamorphic rock off the top of the laccolith but left a few scraps atop the Cuernos. Geologists call such isolated bits of metamorphic rock atop a granite intrusion “roof pendants,” and the Cuernos are among the world’s most majestic examples.

Lake Grey and the Patagonian Fold-and-Thrust Belt

On our first night in Torres del Paine National Park, the temperature dipped to minus 5 degrees Celsius and light snow fell, but we were snug in our lodge at Lake Pehoé. Despite a forecast for clear skies and a high of 2 degrees Celsius, however, cloud and mist wreathed the peaks all the next day. But our disappointment was soon forgotten as we reveled in a 1-kilometer stroll through snow-dusted beech trees to a scenic overlook of glacial Lake Grey. Icebergs discharged by Grey Glacier, visible at the far end of the lake, floated in the blue-green water, and colorful tundra vegetation, interspersed with orange knobs of glacially polished sandstone, blanketed the lakeshore.

The sandstone is part of the 92-million-year-old Punta Barossa Formation, whose sediments were produced by erosion of the mountains being built along the active Andean subduction zone to the west. Then, as now, the subduction zone trench lay west of the Chilean coast, but a period of very active mountain-building at that time loaded the edge of the South American Plate on the opposite (east) side of the Andes from the trench creating a deep marine basin in the Torres del Paine region. Submarine landslides delivered sand and mud to the basin, gradually depositing a series of repeating layers collectively called turbidites. The sand settled out of the turbid water first, followed by the mud. The resulting orange (sandstone) and gray (mudstone) stripes in the Punta Barossa Formation outcrops at Lake Grey provide a textbook example of turbidites, recording deposition by one such submarine slide after another.

Lake Pehoé provides the iconic view of Paine Grande (left) and the Cuernos del Paine. Credit: Lon Abbott & Terri Cook.

“Another spasm of plate compression began about 75 million years ago, causing the Andean thrust front to migrate eastward, creating a new thrust fault near Lake Grey. This fault has squashed the local Punta Barossa Formation turbidites into tight folds. These contorted turbidites are on display next to the Lake Grey parking lot at the start of the strenuous, two-hour hike up to the Ferrier Lookout point. On a clear day it would provide a grand vista of the area, but not when the clouds hug the peaks like they did when we were there.

Unusual Microbial Communities in the Eastern Lakes

After a mistier than predicted first day, to our great excitement, the next day dawned still and cloudless. We threw on down jackets, grabbed our cameras and reveled in sunrise on the majestic Cuernos del Paine reflected in Lake Pehoé.

The main park road winds through Cretaceous turbidites belonging to the Cerro Toro Formation. Credit: Lon Abbott & Terri Cook.

“We were eager to see the Torres themselves. We needed to get to the Nordenskjöld vista point, about 10 kilometers northeast down a dirt road. We dared not squander this fine weather window, knowing it could close at any moment, so we inhaled breakfast and hit the road. Mist began to build, heightening our sense of urgency, but it soon dissipated, and we enjoyed a glorious winter day. An obliging herd of guanaco, a type of South American camelid, lounged about the Nordenskjöld vista, providing a perfect foreground for the peaks. The view of the Torres and the Cuernos to the northwest was riveting indeed, but an unexpected geologic treat also lay in store for us here in the park’s eastern sector.

Glacial Lake Sarmiento is surrounded by hills of more turbidites belonging to the 80-million-year-old Cerro Toro Formation. A white bathtub ring surrounds the lake consisting of nodular limestone secreted by lake-dwelling microbial communities called thrombolites. Nearby Lake Amarga harbors similar microbial communities, but there they secrete the more famous banded stromatolites. Thrombolites and stromatolites both formed extensively early in Earth’s history. The cyanobacteria that contribute to the formation of thrombolites and stromatolites injected the first oxygen into Earth’s atmosphere billions of years ago. But the presence of that oxygen allowed animals to evolve, and the animals paid back the cyanobacteria by eating them. Because the exacting conditions necessary for thrombolite formation are rare today, they are found in only a handful of places worldwide.

From a vista overlooking Lake Nordenskjöld, the Torres del Paine are visible behind and to the right of the Cuernos del Paine. Credit: Lon Abbott & Terri Cook.

“The first ingredient necessary for thrombolite formation is an abundance of calcium and carbonate ions in the water. Weathering of the surrounding marine turbidites fulfills that requirement. But the lake must also be hydrologically isolated to prevent ion dilution. A series of glacial moraines conspired to cut Lake Sarmiento and six smaller lakes off from the regional drainage network, thus accomplishing this second requirement. Even then, the rate of evaporation must exceed precipitation into the lake in order to concentrate the ions enough to trigger microbially mediated limestone precipitation. That requirement is met at Lake Sarmiento because it lies east of the Andes, in their rain shadow. So despite the cool climate, evaporation still exceeds precipitation. Finally, animals that graze on bacterial mats must be absent; the harsh Patagonian climate excludes them here.

Mist often cloaks the Torres del Paine, obscuring them from the ground, but making the vista even grander from the air. Credit: Lon Abbott & Terri Cook.

“Scientists have used the oxygen isotope ratios from Lake Sarmiento’s thrombolites to deduce changes in lake temperature since retreat of the last glaciers 20,000 years ago. They discovered that the average lake temperature 1,200 years ago was 9.3 degrees Celsius and that it cooled to 7.7 degrees Celsius during the “Little Ice Age” 183 years ago — data that contributed to the recognition that the Little Ice Age wasn’t just a European and North American phenomenon.

It’s a short and scenic drive from Lake Sarmiento to Lake Amarga, in whose still waters a perfect reflection of the Torres del Paine is visible. Colorful flamingos wade in its shallow water. Another worthwhile excursion is the one-hour hike to the Cuernos overlook, passing the Salto Grande waterfalls en route.

Mylodon Cave

Mylodon Cave Natural Monument, 24 kilometers northwest of Puerto Natales, is an unexpected bonus on the drive north from Puerto Natales to Torres del Paine. The monument protects several caves eroded from the Cerro Toro Formation that have yielded artifacts and bones that document human habitation of the area since at least 6000 B.C. The caves first gained scientific notoriety in 1895 when German explorer Hermann Eberhard discovered the remains of a Mylodon, a giant ground sloth that has been extinct for more than 10,000 years, with skin attached. The remains of other Pleistocene cave inhabitants, including dwarf horses and saber-toothed cats, have also been discovered here. All of these artifacts have been removed from the caves, but there is a life-sized replica of a Mylodon at the cave entrance. The monument’s 8.7 kilometers of trails offer close-up views of Cerro Toro Formation conglomerate that was deposited in a submarine canyon when this part of Patagonia lay submerged deep beneath the sea. The trails also provide access to the caves and several scenic viewpoints, including a panoramic vista of the nearby Eberhard Fjord.

Treks With Views

The Torres del Paine are among the premier mountaineering challenges in South America. Credit: Lon Abbott & Terri Cook.

A walk through snow-dusted beech forest is a wonderful outing even if clouds obscure the peaks. Credit: Lon Abbott & Terri Cook.

“It turns out that winter is indeed a fine time to visit Torres del Paine, even if, like us, you only have a couple of days. We were treated to excellent weather, magnificent views and minimal crowds. Although temperatures were cold, a down jacket, hat and gloves were all we needed to stay comfortable. If there were a drawback to a winter excursion, it’s that the seasonal closure of facilities limits access to the backcountry. We enjoyed jaw-dropping views despite not venturing farther than 8 kilometers off the road network, but our visit merely whet our appetites to get closer to these spectacular peaks. The crown jewel of Torres del Paine treks is the 10-day, 84-kilometer Torres del Paine Circuit, which circumambulates the massif. Snow closes the 1,200-meter-high John Gardner Pass in winter, but during the summer you can camp or stay in a well-spaced series of huts. Less committing, but still mighty spectacular, is the W-Circuit. This trek does remain open in the winter, but becomes a more committing endeavor because the huts are closed and the ferries that transport you from trek end points across lakes Pehoé or Grey don’t operate that time of year.

Thus, despite having already been to Torres del Paine once, the national park still tops our Chilean travel list now that we know how magnificent and geologically varied the landscape is. We only need to figure out how to find vacation time during the Northern Hemisphere winter! Winter or summer, Torres del Paine should be on every geologist’s travel list, whether you have a couple of days or a couple of weeks to spend there.

Hosteria Pehoé, which occupies a small island in Lake Pehoé, provides one of the best vistas of Paine Grande and the Cuernos del Paine. Credit: Lon Abbott & Terri Cook.

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