Tierra del Fuego - The Land of Fire (and Mountains, Ice and Strike Slip Faults)!

With the Antarctic Peninsula 600 miles to our stern, the Seven Seas Splendor approached and docked in Ushuaia Argentina on February 5, 2025. This former penal colony (which now houses a fantastic museum), is commonly known as our globe's southernmost city. It is located along the shores of the Beagle Channel on the island of Tierra del Fuego. I've walked the streets and hills of Ushuaia many times, so instead of doing that  again I signed up for a trek into the heart of its rugged mountains.

Part 1 - An Inland Trek on Terra del Fuego

The approach to Ushuaia with Tierra del Fuego's mountains as a backdrop.

Through the years, I have watched this dock become 3 times longer and 100% wider - all to accommodate the ever increasing traffic to Antarctica. All the ships here are part of the Antarctic trade. The hills in the background are part of Argentina's Tierra del Fuego National Park. To see a previous post about the park click here.**And remember, you can search for any location on this blog using the search function in the upper left!

First, some locations. This is a map of Isla Grande de Tierra del Fuego outlined rather simply in yellow. Ushuaia and Punta Arenas shown for reference and the track of the Splendor is also shown. Note the mountainous southern side of the island and the north being a subdued coastal plain. Isostatic loading, glacial erosion and (in some instances) faulting, are responsible for the large eastward-projecting bays into the islands' western (left) side.

Zooming in a little more, the active Magallanes-Fagnano Fault system is shown (yellow line). This is a left-lateral strike slip fault that separates the South American plate (top) from the Scotia plate (below). The highest elevations shown (south of the fault) are part of the Darwin Range (glaciers emanating from this range are shown at the end of this post). The white line fills another linear valley, where our trek took place and is curiously parallel to the major transform valley. For a recent discussion about slip rates on this fault see this paper.

About 20 miles north of Ushuaia on National Route 3 (the Pan American Highway in Argentina), we reached the valley where our trek would begin. This valley runs parallel to and is south of the Fagnano Lake and valley where the Magallanes-Fagnano Fault is located (the fault is behind the saw-tooth peaks appearing on the skyline). Note that there is also a thrust fault just below the saw-tooth peaks, where metamorphosed Upper Jurassic volcanic and sedimentary sequences (dark rocks and called the Tobífera Fm.) are thrust over and on top of Lower Cretaceous marine rocks (lighter colors and also slightly metamorphosed).

A close-up of the Tobífera volcanic sediments (slightly metamorphosed).

A large beaver dam was encountered at the terminus of our hike. Beavers were brought to Tierra del Fuego in the 1940s with the hopes of creating a demand for pelts. This area however is much warmer than northern North America where they are native and the fur was of poor quality. The beavers remain and have wrought ecological disaster to the local ecosystem. Some efforts have been made to eradicate them but so far have only been locally successful.

U-shaped valley formed by Pleistocene glaciations. The entire southern side of Tierra del Fuego was overrun by ice.

Part 2 - An Evening Cruise on the Beagle Channel and the Cordillera Darwin

Splendor set off at 8 PM from Ushuaia. This view to the south is toward Isla Navarino, located in Chile. The Beagle Channel serves as the international boundary here.

This is a view back to the east toward Ushuaia along the trace of the Beagle Channel.

But up ahead, the clouds parted as the higher peaks in the Cordillera Darwin came into view. Glaciers spill from the heights onto the Southern Patagonia batholith. This is a series of granite intrusions that were emplaced in the Late Jurassic, between about 157 to 145 Ma (there are also much younger intrusions). These granite bodies are the likely source of the Tobífera volcanic sediments seen on the trek in the previous Part above.

This photo was taken at 8 PM local time.

It is somewhat uncommon to have no wind or clouds on the peaks in this area but once again we had a great experience.

The mountains here go from sea level to nearly 9,000 feet in elevation.

Ice spills from the mountains well into non-glaciated terrain.

Note the moraine in the center of the photo.

Many of the glacier names in this stretch are after countries - Italy, Romania, Germany, etc. This is the Italian Glacier (Glacier Italia). The names honor countries that participated in surveys taken in the area during a transit of Venus in 1874.

An image of the Italian Glacier taken in 2008 showing some recession. The photo is from a paper dealing with the extent of these glaciers during the Little Ice Age, which can be accessed here.

The Alemania (German) Glaciar.

The Romanche (Romania) Glacier. I love Tierra del Fuego!