Week 4 - Volcanoes - Travis Suggitt

San José volcano: A 19,000 foot consequence of subduction

On a trip to visit my good friend in Santiago, Chile, we decided to take a day trip east into the Andes to see the majestic landscape that was shielded by the smog of the city. After about 60 km on a bus ride and a couple hours of hiking, we found ourselves at the foot of the San José stratovolcano. From our vantage point, it’s easy to see the two summits and consider how they formed. They both have generally conical shapes and smooth, gradually sloping sides, likely formed from explosive events. There are 2 less noticeable summits on the mountain that have more of an amphitheater form, leading me to believe that 3 of the 4 summits were created by secondary vents of the main volcano.

The northern summit of San José volcano (pictured on the left) has a visible crater and a lower secondary vent is seen in the depression directly below the main summit on the right (SummitPost, 2007).

The San José volcano is one of many similar volcanoes that parallel the convergent plate boundary off the western coast of South America. As the denser oceanic crust sinks below the continental crust, it eventually reaches depths where heat and pressure melt it into molten rock. The molten rock ascends toward the surface leading to volcanic eruptions. More than 100 km east of the plate boundaries, we see the results of this process in San José and throughout the Andes. Regardless of the tourism and mining industries in the area, the subduction process that formed this volcano has not stopped and the volcano has potential to erupt again. One fumarole releases gas continuously and light pyroclastic columns have occurred during earthquake events. 

Crater at the summit of San José (SummitPost, 2009).

The ease of visiting this volcano as a day trip initially seemed like it would only benefit the ~6 million people living in Santiago’s metropolitan area, but now I realize that their proximity increases the risk of receiving large amounts of pyroclastic material if and when San José erupts again. The Argentinians on the downwind side of the mountain would likely see more windswept pyroclastic material and ash, but their major population centers are further away. With no major explosions witnessed since the founding of Santiago, potential dangers are easy to shrug off. So we did by hiking back to our bus to take us back to the city

Picture References:

SummitPost. (2007, November 29). San José Chile. Image ID 361189. https://www.summitpost.org/san-jose-chile/361189/c-154361 

SummitPost. (2009, August 17). San José: Summit. Image ID 541774. https://www.summitpost.org/san-jose-summit/541774/c-154361