Back to Chile, a geologic wonderland

Chile is an amazing country. The most obvious feature is its unique pencil-like shape. North–south, Chile extends 4,270 km (2,653 mi), yet east–west it extends only 64 km–356 km (40–221 miles). Another striking feature is the Andes Mountains that extend along the length of Chile. The Andean crest forms the border with Argentina to the east.

The highest mountain in the Western Hemisphere, at 6,967 m (22,858 feet), is Aconcagua on the Andean crest east of Santiago, Chile’s capital city. Geologically, the Andes exist because of a subduction zone that extends along the entire west coast of South America.

In this post I describe my past associations with Chile and the places I will visit during the upcoming six weeks. I also provide a little geologic background.

The latitudinal extent of Chile

Chile can be viewed as a mirror of western North America—that is, the same latitudinal position in each hemisphere will have similar climates and appearances. To understand Chile’s latitudinal extent and its range of climates we can flip the country to align its latitudes with the same latitudes in the Northern Hemisphere.

Living in Chile in 2006

Twenty years ago Jay and I lived in Chile for six months (January–July). As a Fulbright Scholar, I worked at the Universidad de Chile in Santiago for four months, from March–June. Before my position started, we traveled for a month in Chilean Patagonia and after my position ended, we traveled for a few weeks in the Atacama region of northern Chile. While in Santiago, we took trips to the Andean foothills, the lake/volcano district and many other nearby locations.

While at the university, I taught a course in sedimentology, my specialty. It was the same course I taught at San Francisco State University, but I had to translate it all into Spanish! I also helped with some graduate student research and participated in departmental activities. It was a great experience that certainly fulfilled the Fulbright organization’s goal of promoting cultural understanding. I’ve keep in touch with some of my former students and plan to get together with them next week.

Other travels to Chile and Patagonia

Two years later, in January 2008, I organized a three-week-long trip to Chile and Argentina for my San Francisco State University (SFSU) students. We started in Santiago and completed a loop east across the Andes, south along the east side of the Andes in Argentina, back across the Andes and then returning north to Santiago along the west side of the Andes.

After traveling through much of Chilean Patagonia in 2006, during a sabbatical in 2012, I spent two months traveling through Argentinian Patagonia. This was when I started this blog—see my initial posts in 2012.

A brief introduction to South American geology

Unique among our planet’s continents, South America has a subduction zone extending along its entire length. Along most of South America’s western edge, the Nazca plate is moving eastward relative to the continent and subjecting (that is, descending) beneath the continent. This is a convergent plate boundary where two plates (in this case, Nazca and South American) are moving toward each other.

At the south end of the continent, there is a divergent plate boundary between the Nazca and Antarctica plate that is also being subducted beneath South America. South of this boundary, the Antarctica plate is descending beneath South America but at a much slower rate than the Nazca plate.

At subduction zones, the oceanic plate descends to great depths, which causes rock to melt. Some of the melted rock (called magma) ascends all of the way to the surface to create a line of volcanoes. For example, the Cascade Range of volcanoes in the U.S. Pacific NW is part of the Cascadia Subduction zone. Similarly, much of the Andes Mountains consists of active and recently active volcanoes that are there because of the Andean subduction zone.

Because of the great pressures produced where plates converge, the largest earthquakes on Earth are produced at subduction zone plate boundaries. Because the cold oceanic plates descend to great depths, the deepest earthquakes also occur here.

As you can see in the map at the top of this page, Chile extends from the south end of South America all of the way to the major bend in the coastline. Subduction zone dynamics dominate the geologic makeup of Chile and produce much of its scenic beauty. Lines of stratovolcanoes with their classic cone shapes and snowy caps are a major scenic element.

Chile also has many earthquakes. In fact, the largest earthquake ever measured (magnitude 9.5) occurred in coastal Chile in 1960. Residents throughout the country are rarely surprised when their life is interrupted by yet another temblor. But this natural hazard is also what causes the mountains to get uplifted to such magnificent heights.

Upcoming travel

From February 9 to March 24 we will be traveling in Chile, other parts of South America, and Antarctica. Our first week will be in Santiago, where we’ll get together with some of my former geology students and a fellow graduate student who has been married to a Chilean geologist and living in Santiago for 35 years.

After that, we will fly to Punta Arenas and after a few days fly to Antarctica with the Chilean company Antarctica21. Once there we will board a boat and spend six days exploring the Antarctica Peninsula. We’ll also be trying to do some science—drilling ice cores and exploring snow/ice layers at depth with a Ground Penetrating Radar (GPR) device. I’ll return to the earthquake map above to explain a little of what is happening to the plates in southernmost Chile and in Antarctica. Glaciers are another important scenic and climate element in these southerly latitudes.

After returning to Punta Arenas, we’ll hike in Patagonia for 1.5 weeks. Finally, we’ll fly to Buenos Aires and take a ferry across the river to Montevideo, where we’ll spend two weeks exploring that country.

I hope you’ll choose to follow these adventures. In addition to rocks, I promise photos of penguins!