In above photograph, geologic layers that were originally created as horizontal layers are now tilted, folded, and thrusted by tectonic collisions. Parallel mountain ridges lie like a fallen stair case. The left ridge contains layers of bedrock (strata) that are now nearly vertical(!) which helps create the conditions for the creation of flatirons. Below is a zoomed in view of the left ridge to reveal the side view of numerous triangular, nearly-vertical slabs of rock termed flatirons. There are more examples below.
From ocean bottom to mountain tops
What caused all this geologic drama? The Rockies are partly made of limestone geology, and yet limestone forms at the bottom of the sea. So the mountain tops are old ocean bottom! The highest point on Earth, Mt Everest, is also made of limestone! Such a geologic journey makes for a lot of geologic drama! How did this occur?
The Rockies are thrusted up from the compressional forces of many ancient islands crashing into the ancient North American shoreline. In fact, most of British Columbia, and parts of Yukon and Alaska, are composed of many geologic terrains from multiple and violent collisions, which have given us a huge diversity of geology and natural beauty.
Below is an incredible photo of flatirons from Argentina. Stunning! Again, the steeply dipping sedimentary rock creates the context for the formation of triangular erosional remnants (flatirons). This is yet another magical way (via differential erosion) in which geomorphology (flatirons) can be used to infer geologic structure (steeply dipping sedimentary rock).
The Serranía de Hornocal mountain range province of Jujuy, Argentina. A limestone geologic formation with various minerals producing wonderful multicoloured flatirons. Photo by Lahi, CC BY-SA 3.0, Link
Here’s another dramatic example of flatirons that form the backdrop of Boulder, Colorado. The softer rock behind the flatirons has been eroded to leave them pointing like arrows into the heavens.
Flatiron formation process
Flatirons are created by the following geologic process: 1) creation of flat lying geology to form sedimentary layers, 2) tectonic forces compressing the rock to tilt, fold, and thrust it, 3) erosional processes that differentially erode the rock, and 4) steeply dipping mountain faces eroding to leave behind triangular remnants.
Geoscientists work in reverse from the geomorphology to infer the geology. Put another way, by simply looking at the form of a mountain, from say an aerial photo, the geologic structure and history can be figured out! This is powerful!, and is just one example of many ways in which geoscientists work and add meaning to our environment.
The name “flatiron” is an antiquated term for what we now call a clothes iron, or simply an iron, that we use to “iron” our clothes. No doubt, the triangular shape of these landforms reminded early scientists of the triangular base of a “flatiron” they had in their homes.
QUESTION OF THE DAY: What do you see in the photos? Please comment below, including attaching photos of flatirons.
Dr. Tim Johnsen is the founder and president of ProGeoscience Consulting. He is a senior geologist specialized in Quaternary, surficial and overburden geology. He integrates a suite of specialized skills to create high quality geologic reconstructions that are tuned to solve the particular problems of his clients – on budget and on time. He turns the complex and often intimidating world of Quaternary, surficial and overburden geology into the predictable and