This here is a map of the Brooks Range in northern Alaska:

enter image description here

As you can see, it is an inland range shaped in a downward curve. Why is that? What is the history of the uplift of the Brooks Range? How and when did a piece of sea or lowland rise up into a downward-curving mountain range far from the coast?


1 Answer 1


If you extend your map out a little bit further, you will see that the Brooks Range is just a continuation of the Rocky Mountains into Alaska.

North America mountains

Source: freeworldmaps.net, ©Daniel Feher (explicitly permitted use here)

The Brooks Range was formed at the same time as the front ranges of the Rockies in Canada and the Lower 48, during the Laramide Orogeny which lasted from abut 80 million years ago to about 35 million years ago. This was caused by the subduction of oceanic plates (mainly the Farallon Plate but also the Kula Plate, and to a lesser extent, the Pacific Plate) beneath the west coast of North America.

The Farallon plate went under North America at a shallow angle; because of this, a large part of Western North America was uplifted, deep into the continent, with faults pushing ancient basement rocks up where the Front Ranges and the Brooks Range are today.

Plates 55 Ma

Pacific Ocean plates, 55 Ma. Source: Wikimedia Commons

The Kula plate is "all gone", and the Farallon Plate is mostly gone, except for a few remnants like the Juan de Fuca Plate. Because of the different direction that the Pacific Plate moves, subduction ialong the West Coast is mostly gone as the Pacific Plate slides past North America. The shallow subduction that created mountains deep in the interior is done. A subduction zone further west has created the Aleutian volcanic arc, but this is a much steeper subduction.

  • $\begingroup$ I wonder what’s the cause for the valley that separates the Brooks range from the rest of the mountains $\endgroup$
    – Gimelist
    Commented Aug 4, 2019 at 6:36
  • $\begingroup$ @Gimelist If you look further south, you'll see other outliers such as the Bighorns Mountains and the Front Range. $\endgroup$
    – Spencer
    Commented Aug 4, 2019 at 12:40
  • $\begingroup$ @Gimelist: By "rest of the mountains", do you mean the Alaska Range or the Mackenzie Mountains? $\endgroup$
    – jamesqf
    Commented Aug 5, 2019 at 6:01

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.