Volcano or Not? – October 9, 2019

Volcano or Not? October 9, 2019

We’ve just recently returned from hiking Maine’s highpoint (Katahdin) for the Summits, Songs and Science project. What’s next on the horizon? With enough participants, an expedition to the highest mountain in the Southern and Western hemispheres: Aconcagua (6961 meters/22,837 ft.) in Argentina, January 2020!

Aconcagua was formed by the subduction (or, pushing of one tectonic plate beneath another) of the Nazca plate beneath the South American plate. Aconcagua used to be an active stratovolcano from the Late Cretaceous (100 – 66 million years ago) through the Miocene, 10 million years ago. Sometime 8 to 10 million years ago, though, the angle of pushing of the Nazca plate started to change, becoming more horizontal, thus resulting in a stop of melting of rock or, fodder for active volcanism. The stresses changed so much that it caused Aconcagua to be lifted up off its volcanic root – stopping all eruptive activity. The rocks found on Aconcagua’s flanks are all volcanic and consist of lavas, breccias and pyroclastics. But there’s lots of other rocks of different color and origin in the area, too, speaking to a more complex geologic history. What gives?