Where Geologists Go to Heaven!

By: La Geologa Reyna (Emily;-)

What does the number five-hundred million mean to you? Probably something you can’t even imagine right? 500 million M&Ms would fill about 35 average-sized bedrooms. 500 million dollars would buy you 500 thousand 2012 Porsche 911s. And the rocks you observe in the Peruvian Andes are more than 500 million years old.

Mountain building, rock ages, and the geologic history of the Earth are hard concepts to wrap our minds around. When I think of human history and ancient cultures like the Egyptians, Polynesians, or Incas, it is hard for me to imagine what life was like so long ago. It is hard for me to even fathom these peoples’ existence, and they lived a mere 5,000-600 years ago. So how is it possible that I can understand, like a video playing in my mind, the entire geologic history of the Andes mountains that have been building for 500,000,000 years?! I don’t know.

All I can say is that I am obsessed with rocks! Since we arrived in Ecuador, I have been completely taken by the igneous intrusions, structural geology, stratigraphy, and volcanoes of the Andes. So to let you all in on some little facts about what I am seeing, here goes:

1) Background: 500-240 million years ago the supercontinent of Gondwana began to break apart, and the Nazca and Antarctic Plates (crust of the Earth that float, essentially, in separate pieces called plates, on the surface of the planet) began subducting under the South American Plate.

a. Supercontinent:

b. Subduction:

2) The rocks we see in the Andes today were once sand at the bottom of an ocean. I know this because I see rocks here that look like they were once sand or mud.

a. In this picture below you see fine-grained, dark-colored rock layers that would come from deep-ocean. You also see layers of lighter rocks that are larger-grained, which would have come from shallower oceans. This means you see layers from an ocean that receded and regressed over and over again:

3) The mountains came about when the plates (described above) ran into one another and began to squish and fold the sand and mudstones you see in the picture above. The Andes were formed in three different orogenic (mountain building) events.

a. 360 million years ago: Eo-Hercynian Orogeny- rifting and river conglomerates. Also random igneous intrusions like this:

b. 300 million years ago: Jurua Orogeny- folds and faulting like this:

c. 200 million years ago: Nevadan Orogeny- high planes uplifted to 14,500ft like this-

4) And through all of this some of the worlds largest, most impressive, and most visited volcanoes were formed.

a. How? When one plate subducts under another, it melts and magma rises to the surface. Then, exploding like a zit, lava and ash flow over the surface of the Earth:

b. Now we see peaks like these:

c) c. And beautiful layers of white ash that cover the uplifted valleys that surround the volcanoes:

5) The final result of these extraordinary geologic events is the incredible landscape we have been biking through for the last four and a half months. However, we were all particularly taken by the scenery we rode through from Juliaca to Arequipa—the beautiful mountains, high altitude deserts, massive volcanic peaks, and strange sand formations.

I knew there was something particularly special about our surroundings when I saw my friends, friends who constantly laugh at my enthusiasm for a boulder, finally appreciate the geology lessons I often voluntarily provide. This must be where I will go to heaven!