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!

Glimpses of the Antarctic Peninsula

From sweltering Rio de Janeiro and its 92°days to a frosty 34° in Antarctic days and "nights", this voyage has had its variety! We have been lucky with the weather and seeing exceptional views. The crossing from the Falklands to the Peninsula was rather smooth and Seven Seas Splendor takes any motion quite well. Suddenly, the frozen landscape began to appear.

We approached Antarctica by way of the South Shetland Islands, transiting the Nelson Strait and motoring southward toward Greenwich and Livingston islands. These "outer bands" of rocky islands are composed of volcaniclastic material (sediments derived from volcanic terrain). The cause is subduction of the Phoenix plate beneath the Antarctic plate, beginning in the Middle Jurassic (∼160 Ma) and continuing through to the Neogene (23 Ma).

A Google Earth image our route upon entering the Peninsula area. The Captain brought us into Half Moon Bay on Livingston Island and then further south to Deception Island.

The clouds parted to reveal Livingston Island, second largest in the South Shelands after King George Island. In view are the Tangra Mountains with Helmet Peak visible. The peak is 1254 m (4114 ft.) in elevation. Many fossil plants and trees come from the sedimentary rocks on Livingston Island. A paper about the paleobotany of Livingston Island can be accessed here.

This is Baily Head on the southeast corner of Deception Island. It is a tuff cone (also called scoria or cinder cones) that was emplaced in a sub-glacial setting. During the Pleistocene Epoch (2.58 Ma to about 10,000 years) ice covered the entire edifice of Deception Island. However, ice cover cannot stop volcanic eruptions and as they say, "The show must go on!" Note the yellowish-colored tuff beds on the top right of the cone, eruptive material called palagonite, that is quenched in the presence of melted glacial ice.

Deception Island was first sighted by sealers in January 1820 and visited later that year by famed American sealer Nathaniel Palmer, who named the island for its narrow and thus, deceptive entrance, now called Neptunes Bellows. The British built a station inside the bay in the 1940s but it was destroyed by the volcanic eruptions that rocked the island between December 1967 and February 1970. I have highlighted the location of Baily Head with a green circle, the feature shown in the previous photo.

Many details about the geologic history of Deception Island are still forthcoming but not for a lack of study. Classified as a large shield volcano, its diameter on the seafloor is 30 kilometers (or about 20 miles)! The island gradually grew from a water depth of more than 4000 ft. (1300 m) before it broke to the surface as either a subaerial or sub-glacial edifice. Its original elevation is unknown, as sometime between 10,000 and 6,000 BP (years Before Present) much of the volcano was catastrophically destroyed in a massive phreatic steam blast, much like the eruption of Krakatoa in 1883 or the Thera volcano that created Santorini Island in Greece about 3,600 years ago. At Deception Island, hot magma likely encountered seawater or melted glacial ice to create the steam explosion that created this large caldera. Soon after, water from the Bransfield Strait entered the depression to form Port Foster, 6 miles (or 10 kilometers) in diameter. Most of the exposed rocks today are post-caldera rocks. Historical documentation of eruptions are from 1839 to 1842 and those of the 1960s.

See previous posts from me here and here with views of the interior of the caldera and Port Foster.  

A lone iceberg at sunset (9:20 PM local time) on February 1, 2025 - sailing south from Deception Island.

December 2, 7:40 AM. Shrouded in fog is not an unusual occurrence in the Antarctic Peninsula but no one signed up to see this. Our goal was Wilhelmina Bay and we tried two different entrances on each side of Nansen Island. Still thick fog. So, quick thinking had us retrace our wake, back out into the Gerlache Strait, where clearer skies were hoped for.

And it worked! This is a view to the south from outside Wilhelmina Bay. We spent our 2nd day here cruising toward Niemeyer Channel and Fournier Bay. However, on Day 3...

We found ourselves at the north entrance of the Errera Channel (background). The channel was full of ice but we eventually pulled up adjacent to Cueverville Island (right).

It may be difficult to see but note the pinkish areas on Cueverville Island where gentoo penguins are nesting.

The Peace Boat moves toward the Ererra Channel under increasingly ideal conditions.

Passengers on Deck 12 of Splendor enjoying a glorious sunny day!

Over on the Arctowski Peninsula the clouds were dancing around the peaks.

While on Anvers Islands, rocks of the Trinity Peninsula Group were visible from beneath huge thicknesses of ice. For a more in-depth description of these rocks, see today's Facebook post from the Arizona Geological Survey. I am a contributor to posts on that site, accessed here on Facebook. To access the post moving forward, scroll to a date of February 7, 2025 on their FB site.

Humpback whales also made an appearance for us. There were at least five pairs as we headed toward Dallmann Bay.

And then, the sky opened! Streaming cirrus clouds above an icy world.

This completed our three day stay in the Antarctic Peninsula. I will be posting about Terra del Fuego and the Chilean fjords in future posts. As Captain Marco likes to say on Splendor, "Ciao for now!"