Day 8 - Pancakes for Breakfast!

The sun arose, we packed our things, and hit the road, ready for our second roadside outcrop adventure. Sitting aside the road, with cars speeding past (or inching forward, I'm looking at you, log trucks), we discussed the truth behind the outcrop in front of us. After establishing our location, which was a few kilometers northwest of Jaquirana, we started sketching, and resketching and RESKETCHING the outcrop before us. Getting just a little hammer crazy, we began discussing our observations. It appeared that the outcrop could be generalized into three different sections, separated diagonally, like a rhombus. The rocks above and to the left were different from those below and to the right—the latter rocks appeared to have a striped or laminated pattern. Finally, we had reached a point of conversation: breakfast.

That's right, the rocks had pancakes in them! Don’t get too excited though, these stripes, which thinned significantly as you moved down the outcrop, were simply deposits of explosive volcanic material that deposited progressively to create a thicker deposit. As more pancakes deposited, pressure increased, flattening the older deposits and creating these different effects. Confused? So were we, but it’s simple! The deposit just squished itself! A unique phenomena yet to be formally labeled, we referred to the pancakes as “Barbosas”. This outcrop was our first example of not only an explosive eruption, and one currently believed to be the result of continued and sustained explosive eruptions piling on top of one another.

The fun didn’t stop there—one outcrop down, two to go! After noticing an interesting curvature in the flow banding of certain rocks (shout out to XJ for his brilliant work), Guil and Lydia (miming and sound effects included) guided us about 200 meters up the road to a second outcrop, one that would be the most curious yet. Immediately we noticed that almost all of these stripes and pancake formations were curved, twisted, and scrunched up! How you ask? Let me explain. As the flow continued, the magma melt began to collapse under its own weight (don’t we all?) causing the twists and turns in the flow banding we were observing. These were some of the most mysterious and interesting rock formations we had yet to observe, but we weren’t done yet.

Our stomachs full with, yep, you guessed it, more bread and cheese (and strawberry wafers), we headed back to the cars with one more outcrop to go. After slight distractions from the farm animals (there were piglets, y’all!) we actually hit the road. 20 kilometers east of Bom Jesus, our final outcrop contained larger Barbosas with fewer twists and turns. An always-excited Guil eagerly informed us that the presence of larger blobs (recap: these are the result of juvenile blobs of explosive magma,) indicates that this outcrop was probably closer to the source than the first two, OR it was from a bigger eruption. 

Essentially our day had involved us progressively moving chronologically backwards, constructing a timeline of this massive 135 million year old deposit. Somebody call Dr. Who—we had effectively traveled through time!

Until next time,

Volcanic Virginia and Silicic

Scott

P.S. We stayed at a gas station last night, so that was fun, too…